View source for Earth:Sea level rise

{{Short description|Rise in sea levels due to climate change}}
<noinclude>[[File:1880- Global average sea level rise (SLR) - annually.svg |thumb|upright=1.35 |The global average sea level has risen about {{convert|250|mm|in}} since 1880.<ref name=EPA_SLR_202207>{{cite web |title=Climate Change Indicators: Sea Level / Figure 1. Absolute Sea Level Change |url=https://www.epa.gov/climate-indicators/climate-change-indicators-sea-level |website=EPA.gov |publisher=U.S. Environmental Protection Agency (EPA) |archive-url=https://web.archive.org/web/20230904035800/https://www.epa.gov/climate-indicators/climate-change-indicators-sea-level |archive-date=4 September 2023 |date=July 2022 |quote=Data sources: CSIRO, 2017. NOAA, 2022. |url-status=live }}</ref>]]</noinclude>

Between 1901 and 2018, the average global [[Sea level|sea level]] rose by {{cvt|15|–|25|cm|in|frac=2}}, or an average of 1–2&nbsp;mm per year.<ref name="SROCC_SPM_20190925">IPCC, 2019: [https://www.ipcc.ch/site/assets/uploads/sites/3/2022/03/01_SROCC_SPM_FINAL.pdf Summary for Policymakers]. In: [https://www.ipcc.ch/srocc/ IPCC Special Report on the Ocean and Cryosphere in a Changing Climate] [H.-O. Pörtner, D. C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M.&nbsp;Nicolai, A. Okem, J. Petzold, B. Rama, N. M. Weyer (eds.)]. Cambridge University Press, Cambridge, UK and New York, New York, US. https://doi.org/10.1017/9781009157964.001.</ref> This rate accelerated to 4.62&nbsp;mm/yr for the decade 2013–2022.<ref name=WMO_20230421/> [[Earth:Climate change|Climate change]] due to human activities is the main cause.<ref name="IPCC_2021_WGI_SPM" />{{rp|5,8}} Between 1993 and 2018, [[Physics:Thermal expansion|thermal expansion]] of water accounted for 42% of sea level rise. Melting temperate glaciers accounted for 21%, with [[Place:Greenland|Greenland]] accounting for 15% and [[Earth:Antarctica|Antarctica]] 8%.<ref name="WCRP2018">{{cite journal |author=WCRP Global Sea Level Budget Group |year=2018 |title=Global sea-level budget 1993–present |journal=Earth System Science Data |volume=10 |issue=3 |pages=1551–1590 |bibcode=2018ESSD...10.1551W |doi=10.5194/essd-10-1551-2018 |quote=This corresponds to a mean sea-level rise of about 7.5 cm over the whole altimetry period. More importantly, the GMSL curve shows a net acceleration, estimated to be at 0.08mm/yr<sup>2</sup>. |doi-access=free}}</ref>{{Rp|1576}} Sea level rise lags changes in the [[Astronomy:Earth|Earth]]'s temperature. So sea level rise will continue to accelerate between now and 2050 in response to warming that is already happening.<ref name="us nrc 2011 long term slr">{{cite book |author=((National Academies of Sciences, Engineering, and Medicine)) |year=2011 |quote=Box SYN-1: Sustained warming could lead to severe impacts |chapter-url=https://nap.nationalacademies.org/read/12877/chapter/3 |page=[https://nap.nationalacademies.org/read/12877/chapter/3#5 5] |chapter=Synopsis |title=Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia |location=Washington, DC |publisher=The National Academies Press |doi=10.17226/12877|isbn=978-0-309-15176-4 }}</ref> What happens after that depends on human [[Earth:Greenhouse gas emissions|greenhouse gas emissions]]. Sea level rise may slow down between 2050 and 2100 if there are deep cuts in emissions. It could then reach a little over {{cvt|30|cm|ft|frac=2}} from now by 2100. With high emissions it may accelerate. It could rise by {{cvt|1|m|ft|frac=2}} or even {{cvt|2|m|ft|frac=2}} by then.<ref name="IPCC_2021_WGI_SPM" /><ref name="IPCC AR6 WG1 Ch.9" /> In the long run, sea level rise would amount to {{convert|2-3|m|ft|0|abbr=on}} over the next 2000 years if warming amounts to {{convert|1.5|C-change|F-change}}. It would be {{convert|19-22|m|ft}} if warming peaks at {{convert|5|C-change|F-change}}.<ref name="IPCC_2021_WGI_SPM">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf Summary for Policymakers]. In: [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, New York, US, pp. 3−32, doi:10.1017/9781009157896.001.</ref>{{rp|21}}

Rising seas ultimately impact every coastal and island population on Earth.<ref>{{Cite journal|last1=McMichael|first1=Celia|last2=Dasgupta|first2=Shouro|last3=Ayeb-Karlsson|first3=Sonja|last4=Kelman|first4=Ilan|date=2020-11-27 |title=A review of estimating population exposure to sea-level rise and the relevance for migration|journal=Environmental Research Letters|volume=15|issue=12|page=123005|doi=10.1088/1748-9326/abb398|pmid=34149864|pmc=8208600|bibcode=2020ERL....15l3005M|issn=1748-9326}}</ref><ref name="wg1-5-5-1">{{cite book |author=Bindoff |first1=N. L. |title=Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change |last2=Willebrand |first2=J. |last3=Artale |first3=V. |last4=Cazenave |first4=A. |last5=Gregory |first5=J. |last6=Gulev |first6=S. |last7=Hanawa |first7=K. |last8=Le Quéré |first8=C. |last9=Levitus |first9=S. |date=2007 |isbn=978-0-521-88009-1 |editor=Solomon |editor-first=S. |language=en |chapter=Observations: Ocean Climate Change and Sea Level: §5.5.1: Introductory Remarks |author4-link=Anny Cazenave |access-date=25 January 2017 |editor2=Qin |editor-first2=D. |editor3=Manning |editor-first3=M. |editor4=Chen |editor-first4=Z. |editor5=Marquis |editor-first5=M. |editor6=Averyt |editor-first6=K. B. |editor7=Tignor |editor-first7=M. |editor8=Miller |editor-first8=H. L. |chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch5s5-5.html#5-5-1 |archive-url=https://web.archive.org/web/20170620210108/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch5.html |archive-date=20 June 2017 |author10=Nojiri, Y. |author11=Shum, C. K. |author12=Talley, L. D. |author13=Unnikrishnan, A.}}</ref> This can be through flooding, higher [[Physics:Storm surge|storm surge]]s, king tides, and [[Tsunami|tsunami]]s. These have many follow-on effects. They lead to loss of coastal [[Earth:Ecosystem|ecosystem]]s like mangroves. Crop production falls because of [[Earth:Freshwater salinization|salinization]] of [[Earth:Irrigation|irrigation]] water and damage to ports disrupts sea trade.<ref name="IPCC-2001" /><ref name="UPI-2018">{{cite web |year=2018 |title=Sea level to increase risk of deadly tsunamis |url=https://www.upi.com/Science_News/2018/08/15/Sea-level-to-increase-risk-of-deadly-tsunamis/2361534362716/ |website=United Press International}}</ref><ref name="Holder-2017" /> The sea level rise projected by 2050 will expose places currently inhabited by tens of millions of people to annual flooding. Without a sharp reduction in greenhouse gas emissions, this may increase to hundreds of millions in the latter decades of the century.<ref name="Kulp2019" /> Areas not directly exposed to rising sea levels could be affected by large scale migrations and economic disruption.

At the same time, local factors like [[Earth:Tidal range|tidal range]] or land [[Subsidence|subsidence]], as well as the varying resilience and adaptive capacity of individual ecosystems, sectors, and countries will greatly affect the severity of impacts.<ref>{{Cite journal|last=Mimura|first=Nobuo|date=2013|title=Sea-level rise caused by climate change and its implications for society|journal=Proceedings of the Japan Academy. Series B, Physical and Biological Sciences|volume=89|issue=7|pages=281–301|doi=10.2183/pjab.89.281|issn=0386-2208|pmc=3758961|pmid=23883609|bibcode=2013PJAB...89..281M}}</ref> For instance, sea level rise in the United States (particularly along the US East Coast) is already higher than the global average, and is expected to be 2 to 3 times greater than the global average by the end of the century.<ref>{{cite web |last1=Choi |first1=Charles Q. |date=27 June 2012|title=Sea Levels Rising Fast on U.S. East Coast |url=https://www.nationalgeographic.com/science/article/120625-sea-level-rise-east-coast-us-science-nature-climate-change |archive-url=https://web.archive.org/web/20210504002931/https://www.nationalgeographic.com/science/article/120625-sea-level-rise-east-coast-us-science-nature-climate-change |archive-date=May 4, 2021 |access-date=October 22, 2022 |website=National Oceanic and Atmospheric Administration}}</ref><ref name="NOAA-2022">{{Cite web |title=2022 Sea Level Rise Technical Report |url=https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html |access-date=2022-07-04 |website=oceanservice.noaa.gov |language=EN-US}}</ref> Yet, of the 20 countries with the greatest exposure to sea level rise, 12 are in [[Earth:Asia|Asia]]. Bangladesh, {{wipe|China}}, {{wipe|India}}, Indonesia, {{wipe|Japan}}, the {{wipe|Philippines}}, Thailand and Vietnam collectively account for 70% of the global population exposed to sea level rise and land subsidence.<ref name="AR6_WGII_Chapter10" /> Finally, the greatest near-term impact on human populations will occur in the low-lying Caribbean and Pacific islands—many of those would be rendered uninhabitable by sea level rise later this century.<ref name="AR6_WGII_Chapter15">Mycoo, M., M. Wairiu, D. Campbell, V. Duvat, Y. Golbuu, S. Maharaj, J. Nalau, P. Nunn, J. Pinnegar, and O. Warrick, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter15.pdf Chapter 15: Small islands]. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] [H.-O. Pörtner, D. C. Roberts, M. Tignor, E. S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, New York, US, pp. 2043–2121 |doi=10.1017/9781009325844.017.</ref>

Societies can adapt to sea level rise in three ways: by [[Earth:Managed retreat|managed retreat]], by [[Earth:Coastal management|accommodating coastal change]], or by protecting against sea level rise through hard-construction practices like [[Earth:Seawall|seawall]]s<ref>{{cite web |year=2013 |title=IPCC's New Estimates for Increased Sea-Level Rise |url=http://www.yaleclimateconnections.org/2013/10/ipccs-new-estimates-for-increased-sea-level-rise/ |publisher=Yale University Press}}</ref> or soft approaches such as [[Earth:Sand dune stabilization|dune rehabilitation]] and [[Earth:Beach nourishment|beach nourishment]]. Sometimes these adaptation strategies go hand in hand; at other times choices must be made among different strategies.<ref name="Thomsen-2012">{{Cite journal |last1=Thomsen |first1=Dana C. |last2=Smith |first2=Timothy F. |last3=Keys |first3=Noni |date=2012 |title=Adaptation or Manipulation? Unpacking Climate Change Response Strategies |journal=Ecology and Society |volume=17 |issue=3 |doi=10.5751/es-04953-170320 |jstor=26269087 |doi-access=free}}</ref> A managed retreat strategy is difficult if an area's population is quickly increasing: this is a particularly acute problem for [[Earth:Africa|Africa]], where the population of low-lying coastal areas is projected to increase by around 100 million people within the next 40 years.<ref name="AR6_WGII_Chapter9">Trisos, C. H., I. O. Adelekan, E. Totin, A. Ayanlade, J. Efitre, A. Gemeda, K. Kalaba, C. Lennard, C. Masao, Y. Mgaya, G. Ngaruiya, D. Olago, N. P. Simpson, and S. Zakieldeen 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter09.pdf Chapter 9: Africa]. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] [H.-O. Pörtner, D.C. Roberts, M. Tignor, E. S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, New York, US, pp. 2043–2121 |doi=10.1017/9781009325844.011.</ref> Poorer nations may also struggle to implement the same approaches to adapt to sea level rise as richer states, and sea level rise at some locations may be compounded by other environmental issues, such as [[Subsidence|subsidence]] in so-called [[Earth:Sinking cities|sinking cities]].<ref>{{Cite journal|last1=Nicholls|first1=Robert J.|last2=Marinova|first2=Natasha|last3=Lowe|first3=Jason A.|last4=Brown|first4=Sally|last5=Vellinga|first5=Pier|last6=Gusmão|first6=Diogo de|last7=Hinkel|first7=Jochen|last8=Tol|first8=Richard S. J.|date=2011|title=Sea-level rise and its possible impacts given a 'beyond 4°C (39.2°F)world' in the twenty-first century|journal=Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences|volume=369|issue=1934|pages=161–181|doi=10.1098/rsta.2010.0291|issn=1364-503X|pmid=21115518|bibcode=2011RSPTA.369..161N|s2cid=8238425|doi-access=free}}</ref> [[Earth:Marine coastal ecosystem|Coastal ecosystems]] typically adapt to rising sea levels by moving inland; but may not always be able to do so, due to natural or artificial barriers.<ref name="birdlife-2015" />
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== Observations ==
[[File:Sea surface height change from 1992 to 2019.webm|thumb|upright=1.35| {{center|Sea surface height change from 1992 to 2019 – NASA}} The visualization is based on data collected from the TOPEX/Poseidon, Jason-1, Jason-2, and Jason-3 satellites. Blue regions are where sea level has gone down, and orange/red regions are where sea level has risen.<ref name="NASA2020">[https://svs.gsfc.nasa.gov/4853 27-year Sea Level Rise – TOPEX/JASON] ''NASA Visualization Studio'', 5 November 2020. {{PD-notice}}</ref>]]
Between 1901 and 2018, the global mean sea level rose by about 20&nbsp;cm (or 8 inches).<ref name="IPCC_2021_WGI_SPM" /> More precise data gathered from satellite [[Engineering:Radar|radar]] measurements found a rise of {{cvt|7.5|cm|in|frac=4}} from 1993 to 2017 (average of 2.9&nbsp;mm/yr).<ref name="WCRP2018" /> This accelerated to 4.62&nbsp;mm/yr for 2013–2022.<ref name=WMO_20230421>{{cite web |title=WMO annual report highlights continuous advance of climate change |url=https://wmo.int/news/media-centre/wmo-annual-report-highlights-continuous-advance-of-climate-change |publisher=World Meteorological Organization |date=21 April 2023 |quote=Press Release Number: 21042023 }}</ref>

=== Regional variations ===
{{Further|Earth:Relative sea level|Earth:Sinking cities}}
Sea level rise is not uniform around the globe. Some land masses are moving up or down as a consequence of [[Subsidence|subsidence]] (land sinking or settling) or [[Earth:Post-glacial rebound|post-glacial rebound]] (land rising as melting ice reduces weight). Therefore, local relative sea level rise may be higher or lower than the global average. Changing ice masses also affect the distribution of sea water around the globe through gravity.<ref>{{Cite journal |last1=Katsman |first1=Caroline A. |last2=Sterl |first2=A. |last3=Beersma |first3=J. J. |last4=van den Brink |first4=H. W. |last5=Church |first5=J. A. |last6=Hazeleger |first6=W. |last7=Kopp |first7=R. E. |last8=Kroon |first8=D. |last9=Kwadijk |first9=J. |date=2011 |title=Exploring high-end scenarios for local sea level rise to develop flood protection strategies for a low-lying delta—the Netherlands as an example |journal=Climatic Change |volume=109 |issue=3–4 |pages=617–645 |doi=10.1007/s10584-011-0037-5 |issn=0165-0009 |doi-access=free |s2cid=2242594}}</ref><ref name="ipcc13">{{cite book |last1=Church |first1=J. A. |title=Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change |last2=Clark |first2=P. U. |publisher=Cambridge University Press |year=2013 |editor-last=Stocker |editor-first=T. F. |location=Cambridge, United Kingdom and New York, New York, US |chapter=Sea Level Change |display-editors=etal |chapter-url=https://ipcc.ch/report/ar5/wg1/}}</ref>

When a glacier or ice sheet melts, it loses mass. This reduces its gravitational pull. In some places near current and former glaciers and ice sheets, this has caused water levels to drop. At the same time water levels will increase more than average further away from the ice sheet. Thus ice loss in [[Place:Greenland|Greenland]] affects regional sea level differently than the equivalent loss in [[Earth:Antarctica|Antarctica]].<ref name="Rovere-2016">{{cite journal |last1=Rovere |first1=Alessio |last2=Stocchi |first2=Paolo |last3=Vacchi |first3=Matteo |date=2 August 2016 |title=Eustatic and Relative Sea Level Changes |journal=Current Climate Change Reports |volume=2 |issue=4 |pages=221–231 |doi=10.1007/s40641-016-0045-7 |bibcode=2016CCCR....2..221R |doi-access=free |s2cid=131866367}}</ref> On the other hand, the Atlantic is warming at a faster pace than the Pacific. This has consequences for Europe and the U.S. East Coast. The East Coast sea level is rising at 3–4 times the global average.<ref>{{cite news |year=2016 |title=Why the U.S. East Coast could be a major 'hotspot' for rising seas |newspaper=The Washington Post |url=https://www.washingtonpost.com/news/energy-environment/wp/2016/02/01/why-the-u-s-east-coast-could-be-a-major-hotspot-for-sea-level-rise/}}</ref> Scientists have linked extreme regional sea level rise on the US Northeast Coast to the downturn of the [[Earth:Atlantic meridional overturning circulation|Atlantic meridional overturning circulation]] (AMOC).<ref>{{cite news |author1=Jianjun Yin |author2=Stephen Griffies |name-list-style=amp |date=March 25, 2015 |title=Extreme sea level rise event linked to AMOC downturn |publisher=CLIVAR |url=https://usclivar.org/research-highlights/extreme-sea-level-rise-event-linked-amoc-downturn}}</ref>

Many [[Engineering:Port|port]]s, urban conglomerations, and agricultural regions stand on river deltas. Here land subsidence contributes to much higher [[Earth:Relative sea level|''relative'' sea level]] rise. Unsustainable extraction of [[Earth:Groundwater|groundwater]] and oil and gas is one cause. [[Earth:Levee|Levee]]s and other flood management practices are another. They prevent sediments from accumulating. These would otherwise compensate for the natural settling of deltaic soils.<ref>{{Cite journal |last1=Tessler |first1=Z. D. |last2=Vörösmarty |first2=C. J. |last3=Grossberg |first3=M. |last4=Gladkova |first4=I. |last5=Aizenman |first5=H. |last6=Syvitski |first6=J. P. M. |last7=Foufoula-Georgiou |first7=E. |date=2015-08-07 |title=Profiling risk and sustainability in coastal deltas of the world |url=https://cloudfront.escholarship.org/dist/prd/content/qt46n8t5mp/qt46n8t5mp.pdf |journal=Science |volume=349 |issue=6248 |pages=638–643 |doi=10.1126/science.aab3574 |issn=0036-8075 |pmid=26250684|bibcode=2015Sci...349..638T |s2cid=12295500 }}</ref>{{rp|638}}<ref name="Bucx 2010">{{cite book |last=Bucx |first=Tom |title=Comparative assessment of the vulnerability and resilience of 10 deltas: synthesis report |date=2010 |publisher=Deltares |isbn=978-94-90070-39-7 |publication-place=Delft, Netherlands |oclc=768078077}}</ref>{{rp|88}} Estimates for total human-caused subsidence in the Rhine-Meuse-Scheldt delta (Netherlands) are {{Cvt|3-4|m|ft|0}}, over {{Cvt|3|m|ft|0}} in urban areas of the Mississippi River Delta (New Orleans), and over {{Cvt|9|m|ft|0}} in the Sacramento–San Joaquin River Delta.<ref name="Bucx 2010" />{{rp|81–90}} On the other hand, relative sea level around the Hudson Bay in {{wipe|Canada}} and the northern [[Place:Baltic Sea|Baltic]] is falling due to post-glacial isostatic rebound.<ref>{{Cite journal |last1=Cazenave |first1=Anny |last2=Nicholls |first2=Robert J. |date=2010 |title=Sea-Level Rise and Its Impact on Coastal Zones |journal=Science |volume=328 |issue=5985 |pages=1517–1520 |bibcode=2010Sci...328.1517N |doi=10.1126/science.1185782 |issn=0036-8075 |pmid=20558707 |s2cid=199393735}}</ref>

== Projections ==
[[File:2050 Projected sea level rise - United States coasts - NOAA.svg|thumb|upright=1.35|NOAA predicts different levels of sea level rise through 2050 for several US coastlines.<ref name=NOAA-2022 />|alt=A comparison of SLR in six parts of the US. The Gulf Coast and East Coast see the most SLR, whereas the West Coast the least]]
There are two complementary ways to model sea level rise (SLR) and [[Earth:General circulation model#Projections|project]] the future. The first  uses process-based modeling. This combines all relevant and well-understood physical processes in a global physical model. This approach calculates the contributions of ice sheets with an [[Earth:Ice-sheet model|ice-sheet model]] and computes rising sea temperature and expansion with a [[Earth:General circulation model|general circulation model]]. The processes are not fully understood. But this approach can predict non-linearities and long delays in the response, which studies of the recent past will miss.

The other approach employs semi-empirical techniques. These use historical geological data to determine likely sea level responses to a warming world, and some basic physical modeling.<ref name="Mengel2016" /> These semi-empirical sea level models rely on statistical techniques. They use relationships between observed past contributions to global mean sea level and temperature.<ref>{{Cite book |last1=Hoegh-Guldberg |first1=O. |title=Special Report: Global Warming of 1.5 °C |last2=Jacob |first2=Daniela |last3=Taylor |first3=Michael |publisher=In Press |year=2018 |chapter=Impacts of 1.5&nbsp;°C of Global Warming on Natural and Human Systems |access-date=2019-01-18 |chapter-url=https://www.ipcc.ch/site/assets/uploads/sites/2/2018/12/SR15_Chapter3_Low_Res.pdf |archive-url=https://web.archive.org/web/20190119120846/https://www.ipcc.ch/site/assets/uploads/sites/2/2018/12/SR15_Chapter3_Low_Res.pdf |archive-date=2019-01-19 }}</ref> Scientists developed this type of modeling because most physical models in previous [[Organization:Intergovernmental Panel on Climate Change|Intergovernmental Panel on Climate Change]] (IPCC) literature assessments had underestimated the amount of sea level rise compared to 20th century observations.<ref name="ipcc13" />

=== Projections for the 21st century ===
[[File:Sea level history and projections.svg|thumb|right|upright=1.35|Historical sea level reconstruction and projections up to 2100 published in 2017 by the [[Organization:U.S. Global Change Research Program|U.S. Global Change Research Program]].<ref name="NOAA-2017">{{Cite web|url=https://tidesandcurrents.noaa.gov/publications/techrpt83_Global_and_Regional_SLR_Scenarios_for_the_US_final.pdf|title=January 2017 analysis from NOAA: Global and Regional Sea Level Rise Scenarios for the United States}}</ref> RCPs are different scenarios for future concentrations of greenhouse gases.]]
[[Organization:Intergovernmental Panel on Climate Change|Intergovernmental Panel on Climate Change]] is the largest and most influential scientific organization on climate change, and since 1990, it provides several plausible scenarios of 21st century sea level rise in each of its major reports. The differences between scenarios are mainly due to uncertainty about future [[Chemistry:Greenhouse gas|greenhouse gas]] emissions. These depend on future economic developments, and  also future political action which is hard to predict. Each scenario  provides an estimate for sea level rise as a range with a lower and upper limit to reflect the unknowns. The scenarios in the 2013-2014 Fifth Assessment Report (AR5) were called [[Earth:Representative Concentration Pathway|Representative Concentration Pathway]]s, or RCPs and the scenarios in the [[Earth:IPCC Sixth Assessment Report|IPCC Sixth Assessment Report]] (AR6) are known as [[Earth:Shared Socioeconomic Pathways|Shared Socioeconomic Pathways]], or SSPs. A large difference between the two was the addition of SSP1-1.9 to AR6, which represents meeting the best Paris climate agreement goal of {{convert|1.5|C-change|F-change}}. In that case, the likely range of sea level rise by 2100 is {{cvt|28–55|cm|in|frac=2}}.<ref name="IPCC AR6 WG1 Ch.9" />

The lowest scenario in AR5, RCP2.6, would see greenhouse gas emissions low enough to meet the goal of limiting warming by 2100 to 2&nbsp;°C. It shows sea level rise in 2100 of about 44&nbsp;cm with a range of 28–61&nbsp;cm. The "moderate" scenario, where {{CO2}} ''emissions'' take a decade or two to peak and its atmospheric ''concentration'' does not plateau until 2070s is called RCP 4.5. Its likely range of sea level rise is {{cvt|36–71|cm|in|frac=2}}. The highest scenario in RCP8.5 pathway sea level would rise between {{cvt|52 and 98|cm|in|frac=2}}.<ref name="ipcc13" /><ref name="CAT" >{{cite web |url=https://climateactiontracker.org/global/cat-thermometer/ |title=The CAT Thermometer |access-date=8 January 2023}}</ref> AR6 had equivalents for both scenarios, but it estimated larger sea level rise under both. In AR6, the SSP1-2.6 pathway results in a range of {{cvt|32–62|cm|in|frac=2}} by 2100. The "moderate" SSP2-4.5 results in a {{cvt|44–76|cm|in|frac=2}} range by 2100 and SSP5-8.5 led to {{cvt|65–101|cm|in|frac=2}}.<ref name="IPCC AR6 WG1 Ch.9" />
[[File:Sea level rise projections for the 21st century.png|thumb|left|upright=1.5|Sea level rise projections for the years 2030, 2050 and 2100 from 2007 to 2012|alt=A set of older (2007-2012) projections of sea level rise. There was a wide range of estimates.]]
Further, AR5 was criticized by multiple researchers for excluding detailed estimates the impact of "low-confidence" processes like marine ice sheet and marine ice cliff instability,<ref name="pmid30013142" /><ref name="Pollard2015" /><ref name="Hansen2016">{{cite journal |last1=Hansen |first1=James |last2=Sato |first2=Makiko |last3=Hearty |first3=Paul |last4=Ruedy |first4=Reto |last5=Kelley |first5=Maxwell |last6=Masson-Delmotte |first6=Valerie |last7=Russell |first7=Gary |last8=Tselioudis |first8=George |last9=Cao |first9=Junji |last10=Rignot |first10=Eric |last11=Velicogna |first11=Isabella |date=22 March 2016 |title=Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous |journal=Atmospheric Chemistry and Physics |volume=16 |issue=6 |pages=3761–3812 |arxiv=1602.01393 |bibcode=2016ACP....16.3761H |doi=10.5194/acp-16-3761-2016 |first18=Michael |first19=Kwok-Wai |last19=Lo |first12=Blair |last18=Bauer |first17=Allegra N. |last17=Legrande |first16=Pushker |last16=Kharecha |first15=Karina |last15=von Schuckmann |first14=Evgeniya |last14=Kandiano |first13=Bailey |last13=Donovan |last12=Tormey |s2cid=9410444 |doi-access=free }}</ref>  which can substantially accelerate ice loss to potentially add "tens of centimeters" to sea level rise within this century.<ref name="ipcc13" /> AR6 includes a version of SSP5-8.5 where these processes take place, and in that case, sea level rise of over {{cvt|2|m|ft|frac=2}} by 2100 could not be ruled out.<ref name="IPCC AR6 WG1 Ch.9">{{Cite journal |last1=Fox-Kemper |first1=B. |last2=Hewitt |first2=Helene T. |last3=Xiao |first3=C. |last4=Aðalgeirsdóttir |first4=G. |last5=Drijfhout |first5=S. S. |last6=Edwards |first6=T. L. |last7=Golledge |first7=N. R. |last8=Hemer |first8=M. |last9=Kopp |first9=R. E. |last10=Krinner |first10=G. |last11=Mix |first11=A. |date=2021 |editor-last=Masson-Delmotte |editor-first=V. |editor2-last=Zhai |editor2-first=P. |editor3-last=Pirani |editor3-first=A. |editor4-last=Connors |editor4-first=S. L. |editor5-last=Péan |editor5-first=C. |editor6-last=Berger |editor6-first=S. |editor7-last=Caud |editor7-first=N. |editor8-last=Chen |editor8-first=Y. |editor9-last=Goldfarb |editor9-first=L. |title=Chapter 9: Ocean, Cryosphere and Sea Level Change |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf |journal=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press, Cambridge, UK and New York, NY, US |page=1302}}</ref> The general increase of projections in AR6 was caused by the observed ice-sheet erosion [[Earth:Climate change in the Arctic|in Greenland]] and Antarctica matching the upper-end range of the AR5 projections by 2020,<ref>{{cite news |title=Ice sheet melt on track with 'worst-case climate scenario' |language=en |work=www.esa.int |url=https://www.esa.int/Applications/Observing_the_Earth/Space_for_our_climate/Ice_sheet_melt_on_track_with_worst-case_climate_scenario |access-date=8 September 2020}}</ref><ref name="Slater-2020">{{cite journal |last1=Slater |first1=Thomas |last2=Hogg |first2=Anna E. |last3=Mottram |first3=Ruth |author-link3=Ruth Mottram |date=31 August 2020 |title=Ice-sheet losses track high-end sea-level rise projections |url=https://www.nature.com/articles/s41558-020-0893-y |journal=Nature Climate Change |language=en |volume=10 |issue=10 |pages=879–881 |bibcode=2020NatCC..10..879S |doi=10.1038/s41558-020-0893-y |issn=1758-6798 |archive-url=https://web.archive.org/web/20200902132539/https://www.nature.com/articles/s41558-020-0893-y |archive-date=2 September 2020 |access-date=8 September 2020 |s2cid=221381924}}</ref> and the finding that AR5 projections were likely too slow next to an extrapolation of observed sea level rise trends, while the subsequent reports had improved in this regard.<ref name="Grinsted-2021">{{Cite journal |last1=Grinsted |first1=Aslak |last2=Christensen |first2=Jens Hesselbjerg |date=2 February 2021 |title=The transient sensitivity of sea level rise |url=https://os.copernicus.org/articles/17/181/2021/ |journal=Ocean Science |volume=17 |issue=1 |pages=181–186 |bibcode=2021OcSci..17..181G |doi=10.5194/os-17-181-2021 |issn=1812-0784 |s2cid=234353584 |doi-access=free }}</ref>

Notably, some scientists believe that ice sheet processes may accelerate sea level rise even at temperatures below the highest possible scenario, though not as much. For instance, a 2017 study from the University of Melbourne researchers suggested that these processes increase RCP2.6 sea level rise by about one quarter, RCP4.5 sea level rise by one half and practically double RCP8.5 sea level rise.<ref>{{cite news |author=Chris Mooney |date=October 26, 2017 |title=New science suggests the ocean could rise more – and faster – than we thought |language=en-us |work=The Chicago Tribune |publication-place=Chicago, Illinois |url=http://www.chicagotribune.com/news/nationworld/science/ct-climate-change-sea-level-rise-20171026-story.html}}</ref><ref>{{cite journal |last1=Nauels |first1=Alexander|last2=Rogelj |first2=Joeri |last3=Schleussner |first3=Carl-Friedrich |last4=Meinshausen |first4=Malte |last5=Mengel |first5=Matthias |date=1 November 2017 |title=Linking sea level rise and socioeconomic indicators under the Shared Socioeconomic Pathways |journal=Environmental Research Letters |volume=12 |issue=11 |page=114002 |bibcode=2017ERL....12k4002N |doi=10.1088/1748-9326/aa92b6 |doi-access=free}}</ref> A 2016 study led by Jim Hansen hypothesized that vulnerable ice sheet section collapse can lead to near-term exponential sea level rise acceleration, with a doubling time of 10, 20 or 40 years. Such acceleration would lead to multi-meter sea level rise in 50, 100 or 200 years, respectively,<ref name="Hansen2016" /> but it remains a minority view amongst the scientific community.<ref>{{cite news |year=2015 |title=James Hansen's controversial sea level rise paper has now been published online |newspaper=The Washington Post |url=https://www.washingtonpost.com/news/energy-environment/wp/2015/07/23/controversial-sea-level-rise-paper-is-now-published-online/ |quote="There is no doubt that the sea level rise, within the IPCC, is a very conservative number," says Greg Holland, a climate and hurricane researcher at the [[Organization:National Center for Atmospheric Research|National Center for Atmospheric Research]], who has also reviewed the Hansen study. "So the truth lies somewhere between IPCC and Jim."}}</ref>

For comparison, a major scientific survey of 106 experts in 2020 found that even when accounting for instability processes they had estimated a median sea level rise of {{cvt|45|cm|in|frac=2}} by 2100 for RCP2.6, with a 5%-95% range of {{cvt|21–82|cm|in|frac=2}}. For RCP8.5, the experts estimated a median of {{cvt|93|cm|in|frac=2}} by 2100  and a 5%-95% range of {{cvt|45–165|cm|in|frac=2}}.<ref name="npj106"/> Similarly, NOAA in 2022 had suggested that there is a 50% probability of {{cvt|0.5|m|in|frac=2}} sea level rise by 2100 under {{convert|2|C-change|F-change}}, which increases to >80% to >99% under {{convert|3-5|C-change|F-change}}.<ref name="NOAA-2022"/> Year 2019 elicitation of 22 ice sheet experts suggested a median SLR of {{cvt|30|cm|in|frac=2}} by 2050 and {{cvt|70|cm|in|frac=2}} by 2100 in the low emission scenario and the median of {{cvt|34|cm|in|frac=2}} by 2050 and {{cvt|110|cm|in|frac=2}} by 2100 in a high emission scenario. They also estimated a small chance of sea levels exceeding 1 meter by 2100 even in the low emission scenario and of going beyond 2 metres in the high emission scenario, with the latter causing the displacement of 187&nbsp;million people.<ref name="PNAS22">{{cite journal |last1=L. Bamber |first1=Jonathan |last2=Oppenheimer |first2=Michael |last3=E. Kopp |first3=Robert |last4=P. Aspinall |first4=Willy |last5=M. Cooke |first5=Roger |date=May 2019 |title=Ice sheet contributions to future sea-level rise from structured expert judgment |journal=Proceedings of the National Academy of Sciences |volume=116 |issue=23 |pages=11195–11200 |bibcode=2019PNAS..11611195B |doi=10.1073/pnas.1817205116 |pmc=6561295 |pmid=31110015 |doi-access=free}}</ref> 

=== Post-2100 sea level rise ===
[[File:1900-2300 Long-term projections of sea level rise.svg|thumb|upright=1.35|If countries cut greenhouse gas emissions significantly (lowest trace), the IPCC expects sea level rise by 2100 to be limited to 0.3 to 0.6 meters (1–2 feet).<ref name=NASA_SLR_2021/> However, in a worst-case scenario (top trace), sea levels could rise 5 meters (16 feet) by the year 2300.<ref name=NASA_SLR_2021>{{cite web |title=Anticipating Future Sea Levels |url=https://earthobservatory.nasa.gov/images/148494/anticipating-future-sea-levels |website=EarthObservatory.NASA.gov |publisher=National Aeronautics and Space Administration (NASA) |archive-url=https://web.archive.org/web/20210707220354/https://earthobservatory.nasa.gov/images/148494/anticipating-future-sea-levels |archive-date=7 July 2021 |date=2021 |url-status=live }}</ref>]]
[[File:6m Sea Level Rise.jpg|thumb|upright=1.5|Map of the Earth with a long-term {{Convert|6|m|ft|adj=on}} sea level rise represented in red (uniform distribution, actual sea level rise will vary regionally and local adaptation measures will also have an effect on local sea levels).|alt=A map showing major SLR impact in south-east Asia, Northern Europe and the East Coast of the US]]
Even if the temperature stabilizes, significant sea-level rise (SLR) will continue for centuries.<ref name="nrccon">{{cite book |author=National Research Council |title=Advancing the Science of Climate Change |publisher=The National Academies Press |year=2010 |isbn=978-0-309-14588-6 |location=Washington, DC |page=245 |chapter=7 Sea Level Rise and the Coastal Environment |doi=10.17226/12782 |access-date=2011-06-17 |chapter-url=http://books.nap.edu/openbook.php?record_id=12782&page=245}}</ref> This is what models consistent with [[Earth:Proxy (climate)|paleo records]] of sea level rise.<ref name="ipcc13" />{{rp|1189}}  After 500 years, sea level rise from thermal expansion alone may have reached only half of its eventual level. Models suggest this may lie within ranges of {{cvt|0.5-2|m|ft|frac=2}}.<ref name="solomon">{{cite journal |last1=Solomon |first1=Susan |last2=Plattner |first2=Gian-Kasper |last3=Knutti |first3=Reto |last4=Friedlingstein |first4=Pierre |date=10 February 2009 |title=Irreversible climate change due to carbon dioxide emissions |journal=Proceedings of the National Academy of Sciences |volume=106 |issue=6 |pages=1704–1709 |bibcode=2009PNAS..106.1704S |doi=10.1073/pnas.0812721106 |pmc=2632717 |pmid=19179281 |doi-access=free}}</ref> Additionally, [[Earth:Tipping points in the climate system|tipping points]] of Greenland and Antarctica ice sheets are likely to play a larger role over such timescales.<ref name="Pattyn-2018">{{cite journal |last1=Pattyn |first1=Frank |last2=Ritz |first2=Catherine |last3=Hanna |first3=Edward |last4=Asay-Davis |first4=Xylar |last5=DeConto |first5=Rob |last6=Durand |first6=Gaël |last7=Favier |first7=Lionel |last8=Fettweis |first8=Xavier |last9=Goelzer |first9=Heiko |last10=Golledge |first10=Nicholas R. |last11=Kuipers Munneke |first11=Peter |date=12 November 2018 |title=The Greenland and Antarctic ice sheets under 1.5 °C global warming |url=https://dipot.ulb.ac.be/dspace/bitstream/2013/278021/3/ReviewOnePointFive_v7.pdf |journal=Nature Climate Change |volume=8 |issue=12 |pages=1053–1061 |bibcode=2018NatCC...8.1053P |doi=10.1038/s41558-018-0305-8 |first13=Sophie |last13=Nowicki |s2cid=91886763 |last12=Lenaerts |first18=Michiel |last14=Payne |last18=van den Broeke |first17=Luke D. |last17=Trusel |first16=Hélène |last16=Seroussi |first15=Alexander |last15=Robinson |first14=Antony J. |first12=Jan T. M.}}</ref>  Ice loss from [[Earth:Antarctica|Antarctica]] is likely to dominate very long-term SLR, especially if the warming exceeds {{convert|2|C-change|F-change}}. Continued carbon dioxide emissions from fossil fuel sources could cause additional tens of metres of sea level rise, over the next millennia. The available fossil fuel on Earth is enough to melt the entire Antarctic ice sheet, causing about {{Cvt|58|m|ft}} of sea level rise.<ref>{{cite journal |last1=Winkelmann |first1=Ricarda |last2=Levermann |first2=Anders |last3=Ridgwell |first3=Andy |last4=Caldeira |first4=Ken |date=11 September 2015 |title=Combustion of available fossil fuel resources sufficient to eliminate the Antarctic Ice Sheet |journal=Science Advances |volume=1 |issue=8 |pages=e1500589 |bibcode=2015SciA....1E0589W |doi=10.1126/sciadv.1500589 |pmc=4643791 |pmid=26601273}}</ref>

In the next 2,000 years, sea level is predicted to rise by {{cvt|2-3|m|ft|frac=2}} if the temperature increase peaks at its current {{convert|1.5|C-change|F-change}}, It would rise by {{cvt|2-6|m|ft|frac=2}} if it peaks at {{convert|2|C-change|F-change}} and by {{cvt|19-22|m|ft|frac=2}} if it peaks at {{convert|5|C-change|F-change}}.<ref name="IPCC_2021_WGI_SPM" />{{rp|SPM-28}} If the temperature rise stops at {{convert|2|C-change|F-change}} or at {{convert|5|C-change|F-change}}, the sea level would still continue to rise for about 10,000 years. In the first case it will reach {{cvt|8-13|m|ft|frac=2}} above pre-industrial level, and in the second {{cvt|28-37|m|ft|frac=2}}.<ref>{{cite book |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf |title=Technical Summary. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |date=August 2021 |publisher=IPCC |page=TS14 |access-date=12 November 2021}}</ref>

With better models and observational records, several studies have attempted to project SLR for the centuries immediately after 2100. This remains largely speculative. An April 2019 expert elicitation asked 22 experts about total sea level rise projections for the years 2200 and 2300 under its high, 5{{Nbsp}}°C warming scenario. It ended up with 90% confidence intervals of −{{cvt|10|cm|in|frac=2}} to {{cvt|740|cm|ft|frac=2}} and −{{cvt|9|cm|in|frac=2}} to {{cvt|970|cm|ft|frac=2}}, respectively. Negative values represent the extremely low probability of very large increases in the ice sheet surface mass balance due to climate change-induced increase in [[Earth:Precipitation|precipitation]].<ref name="PNAS22">{{cite journal |last1=L. Bamber |first1=Jonathan |last2=Oppenheimer |first2=Michael |last3=E. Kopp |first3=Robert |last4=P. Aspinall |first4=Willy |last5=M. Cooke |first5=Roger |date=May 2019 |title=Ice sheet contributions to future sea-level rise from structured expert judgment |journal=Proceedings of the National Academy of Sciences |volume=116 |issue=23 |pages=11195–11200 |bibcode=2019PNAS..11611195B |doi=10.1073/pnas.1817205116 |pmc=6561295 |pmid=31110015 |doi-access=free}}</ref> An elicitation of 106 experts led by Stefan Rahmstorf also included 2300 for RCP2.6 and RCP8.5. The former had the median of {{cvt|118|cm|in|frac=2}}, and a 5%-95% range of {{cvt|24–311|cm|in|frac=2}}. The latter had the median of {{cvt|329|cm|in|frac=2}},  and a 5%-95% range of {{cvt|88–783|cm|in|frac=2}}.<ref name="npj106">{{Cite journal |last1=Horton |first1=Benjamin P. |last2=Khan |first2=Nicole S. |last3=Cahill |first3=Niamh |last4=Lee |first4=Janice S. H. |last5=Shaw |first5=Timothy A. |last6=Garner |first6=Andra J. |last7=Kemp |first7=Andrew C. |last8=Engelhart |first8=Simon E. |last9=Rahmstorf |first9=Stefan |date=2020-05-08 |title=Estimating global mean sea-level rise and its uncertainties by 2100 and 2300 from an expert survey |url=https://www.nature.com/articles/s41612-020-0121-5 |journal=npj Climate and Atmospheric Science |volume=3 |issue=1 |page=18 |bibcode=2020npjCA...3...18H |doi=10.1038/s41612-020-0121-5 |s2cid=218541055}}</ref>

By 2021, AR6 was also able to provide estimates for sea level rise in 2150 alongside the 2100 estimates for the first time. This showed that keeping warming at 1.5{{Nbsp}}°C under the SSP1-1.9 scenario would result in sea level rise in the 17-83% range of {{cvt|37–86|cm|in|frac=2}}. In the SSP1-2.6 pathway the range would be {{cvt|46–99|cm|in|frac=2}}, for SSP2-4.5 a {{cvt|66–133|cm|in|frac=2}} range by 2100 and for SSP5-8.5 a rise of {{cvt|98–188|cm|in|frac=2}}. It stated that a "low-confidence" projection of over {{cvt|2|m|ft|frac=2}} by 2100, would accelerate further to potentially {{cvt|5|m|ft|frac=2}} by 2150. AR6 also provided lower-confidence estimates for year 2300 sea level rise under SSP1-2.6 and SSP5-8.5. The former had a range between {{cvt|0.5|m|ft|frac=2}} and {{cvt|3.2|m|ft|frac=2}}, while the latter ranged from just under {{cvt|2|m|ft|frac=2}} to just under {{cvt|7|m|ft|frac=2}}. The low-confidence projections of SSP5-8.5 project sea level rise exceeding {{cvt|15|m|ft|frac=2}} by then.<ref name="IPCC AR6 WG1 Ch.9" />

A 2018 paper estimated that sea level rise in 2300 would increase by a median of 20&nbsp;cm (8&nbsp;in) for every five years {{CO2}} emissions increase before peaking. It shows a 5% likelihood of a {{cvt|1|m|ft|frac=2}} increase due to the same. The same estimate found that if the temperature stabilized below {{convert|2|C-change|F-change}}, 2300 sea level rise would still exceed {{cvt|1.5|m|ft|frac=2}}. Early net zero and slowly falling temperatures could limit it to {{cvt|70–120|cm|in|frac=2}}.<ref>{{Cite journal |last1=Mengel |first1=Matthias |last2=Nauels |first2=Alexander |last3=Rogelj |first3=Joeri |last4=Schleussner |first4=Carl-Friedrich |date=20 February 2018 |title=Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action |journal=Nature Communications |volume=9 |issue=1 |page=601 |doi=10.1038/s41467-018-02985-8 |pmid=29463787 |pmc=5820313 |bibcode=2018NatCo...9..601M }}</ref>

== Measurements ==
Variations in the amount of water in the oceans, changes in its volume, or varying land elevation compared to the sea surface can drive sea level changes. Over a consistent time period, assessments can attribute contributions to sea level rise and provide early indications of change in trajectory. This helps to inform adaptation plans.<ref>{{Cite web |title=2022 Sea Level Rise Technical Report |url=https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html#step4 |access-date=2022-02-22 |website=oceanservice.noaa.gov |language=EN-US}}</ref> The different techniques used to measure changes in sea level do not measure exactly the same level. Tide gauges can only measure relative sea level. [[Astronomy:Satellite|Satellite]]s can also measure absolute sea level changes.<ref name="Rovere-2016-2">{{cite journal |last1=Rovere |first1=Alessio |last2=Stocchi |first2=Paolo |last3=Vacchi |first3=Matteo |date=2 August 2016 |title=Eustatic and Relative Sea Level Changes |journal=Current Climate Change Reports |volume=2 |issue=4 |pages=221–231 |doi=10.1007/s40641-016-0045-7 |bibcode=2016CCCR....2..221R |s2cid=131866367 |doi-access=free}}</ref> To get precise measurements for sea level, researchers studying the ice and oceans factor in ongoing [[Physics:Geomorphology|deformations of the solid Earth]]. They look in particular at landmasses still rising from past ice masses retreating, and the [[Physics:Gravity of Earth|Earth's gravity]] and [[Earth's rotation|rotation]].<ref name="WCRP2018" />

===Satellites===
[[File:TOPEX-JasonSeries2008.jpg|left|thumb|[[Earth:Jason-1|Jason-1]] continued the sea surface measurements started by TOPEX/Poseidon. It was followed by the Ocean Surface Topography Mission on Jason-2, and by Jason-3.]]
Since the launch of TOPEX/Poseidon in 1992, an overlapping series of [[Earth:Satellite geodesy#Altimetry|altimetric satellites]] has been continuously recording the sea level and its changes.<ref>{{cite web |title=Ocean Surface Topography from Space |url=http://sealevel.jpl.nasa.gov/missions/topex/ |archive-url=https://web.archive.org/web/20110722010847/http://sealevel.jpl.nasa.gov/missions/topex/ |archive-date=2011-07-22 |publisher=NASA/JPL}}</ref> These satellites can measure the hills and valleys in the sea caused by currents and detect trends in their height. To measure the distance to the sea surface, the satellites send a microwave pulse towards Earth and record the time it takes to return after reflecting off the ocean's surface. [[Physics:Microwave radiometer|Microwave radiometer]]s correct the additional delay caused by [[Physics:Water vapor|water vapor]] in the [[Astronomy:Atmosphere|atmosphere]]. Combining these data with the location of the spacecraft determines the sea-surface height to within a few centimetres.<ref>{{Cite web |title=Jason-3 Satellite – Mission |url=https://www.nesdis.noaa.gov/jason-3/mission.html |access-date=2018-08-22 |website=www.nesdis.noaa.gov}}</ref> These satellite measurements have estimated rates of sea level rise for 1993–2017 at {{convert|3.0|±|0.4|mm|frac=64|in}} per year.<ref name="Nerem-2018">{{cite journal |last1=Nerem |first1=R. S. |last2=Beckley |first2=B. D. |last3=Fasullo |first3=J. T. |last4=Hamlington |first4=B. D. |last5=Masters |first5=D. |last6=Mitchum |first6=G. T. |date=27 February 2018 |title=Climate-change–driven accelerated sea-level rise detected in the altimeter era |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=115 |issue=9 |pages=2022–2025 |bibcode=2018PNAS..115.2022N |doi=10.1073/pnas.1717312115 |pmc=5834701 |pmid=29440401 |doi-access=free}}</ref>

Satellites are useful for measuring regional variations in sea level. An example is the substantial rise between 1993 and 2012 in the western tropical Pacific. This sharp rise has been linked to increasing [[Earth:Trade winds|trade winds]]. These occur when the Pacific Decadal Oscillation (PDO) and the [[Earth:El Niño–Southern Oscillation|El Niño–Southern Oscillation]] (ENSO) change from one state to the other.<ref>{{cite journal |last1=Merrifield |first1=Mark A. |last2=Thompson |first2=Philip R. |last3=Lander |first3=Mark |date=July 2012 |title=Multidecadal sea level anomalies and trends in the western tropical Pacific |journal=Geophysical Research Letters |volume=39 |issue=13 |pages=n/a |bibcode=2012GeoRL..3913602M |doi=10.1029/2012gl052032 |s2cid=128907116}}</ref> The PDO is a basin-wide climate pattern consisting of two phases, each commonly lasting 10 to 30 years. The ENSO has a shorter period of 2 to 7 years.<ref>{{cite journal |last1=Mantua |first1=Nathan J. |last2=Hare |first2=Steven R. |last3=Zhang |first3=Yuan |last4=Wallace |first4=John M. |last5=Francis |first5=Robert C. |date=June 1997 |title=A Pacific Interdecadal Climate Oscillation with Impacts on Salmon Production |journal=Bulletin of the American Meteorological Society |volume=78 |issue=6 |pages=1069–1079 |bibcode=1997BAMS...78.1069M |doi=10.1175/1520-0477(1997)078<1069:APICOW>2.0.CO;2 |doi-access=free}}</ref>

=== Tide gauges ===
[[File:Sea_level_change_1993_to_2018.jpg|thumb|upright=1.2|Between 1993 and 2018, the mean sea level has risen across most of the world ocean (blue colors).<ref>Lindsey, Rebecca (2019) [https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level Climate Change: Global Sea Level] ''NOAA Climate'', 19 November 2019.</ref>]]
The global network of [[Earth:Tide gauge|tide gauge]]s is the other important source of sea-level observations. Compared to the satellite record, this record has major spatial gaps but covers a much longer period.<ref name="Rhein-2013">{{Cite book |last1=Rhein |first1=Monika |title=IPCC AR5 WGI |last2=Rintoul |first2=Stephan |publisher=Cambridge University Press |year=2013 |location=New York |page=285 |chapter=Observations: Ocean |access-date=2018-08-26 |chapter-url=https://ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter03_FINAL.pdf |archive-url=https://web.archive.org/web/20180613012554/https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter03_FINAL.pdf |archive-date=2018-06-13 }}</ref> Coverage of tide gauges started mainly in the [[Earth:Northern Hemisphere|Northern Hemisphere]]. Data for the [[Earth:Southern Hemisphere|Southern Hemisphere]] remained scarce up to the 1970s.<ref name="Rhein-2013" /> The longest running sea-level measurements, NAP or [[Amsterdam Ordnance Datum]] were established in 1675, in [[Place:Amsterdam|Amsterdam]].<ref>{{cite web |title=Other Long Records not in the PSMSL Data Set |url=http://www.psmsl.org/data/longrecords/ |access-date=11 May 2015 |publisher=PSMSL}}</ref> Record collection is also extensive in {{wipe|Australia}}. They including measurements by an amateur meteorologist beginning in 1837. They also include measurements taken from a sea-level benchmark struck on a small cliff on the [[Earth:Isle of the Dead (Tasmania)|Isle of the Dead]] near the Port Arthur convict settlement in 1841.<ref>{{cite journal |last=Hunter |first=John |author2=R. Coleman |author3=D. Pugh |date=2003 |title=The Sea Level at Port Arthur, Tasmania, from 1841 to the Present |url=https://figshare.com/articles/journal_contribution/22846694 |journal=Geophysical Research Letters |volume=30 |issue=7 |page=1401 |bibcode=2003GeoRL..30.1401H |doi=10.1029/2002GL016813 |s2cid=55384210}}</ref>

Together with satellite data for the period after 1992, this network established that global mean sea level rose {{Convert|19.5|cm|in|abbr=on}} between 1870 and 2004 at an average rate of about 1.44&nbsp;mm/yr. (For the 20th century the average is 1.7&nbsp;mm/yr.)<ref name="church2">{{cite journal |author=Church, J.A. |author2=White, N.J. |date=2006 |title=20th century acceleration in global sea-level rise |journal=Geophysical Research Letters |volume=33 |issue=1 |pages=L01602 |bibcode=2006GeoRL..33.1602C |citeseerx=10.1.1.192.1792 |doi=10.1029/2005GL024826 |s2cid=129887186}}</ref> By 2018, data collected by Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) had shown that the global mean sea level was rising by {{Convert|3.2|mm|in|abbr=on|frac=32}} per year. This was double the average 20th century rate.<ref>{{Cite web |title=Historical sea level changes: Last decades |url=http://www.cmar.csiro.au/sealevel/sl_hist_last_decades.html |access-date=2018-08-26 |website=www.cmar.csiro.au}}</ref><ref>{{cite web |last=Neil |first=White |title=Historical Sea Level Changes |url=http://www.cmar.csiro.au/sealevel/sl_hist_few_hundred.html |access-date=25 April 2013 |publisher=CSIRO}}</ref> The 2023 [[Organization:World Meteorological Organization|World Meteorological Organization]] report found further acceleration to 4.62&nbsp;mm/yr over the 2013–2022 period.<ref name=WMO_20230421/> These observations help to check and verify predictions from climate change simulations.

Regional differences are also visible in the tide gauge data. Some are caused by local sea level differences. Others are due to vertical land movements. In [[Earth:Europe|Europe]], only some land areas are rising while the others are sinking. Since 1970, most tidal stations have measured higher seas. However sea levels along the northern [[Place:Baltic Sea|Baltic Sea]] have dropped due to [[Earth:Post-glacial rebound|post-glacial rebound]].<ref>{{cite web |date=18 November 2021 |title=Global and European sea level rise |url=https://www.eea.europa.eu/ims/global-and-european-sea-level-rise |website=European Environment Agency}}</ref>

===Past sea level rise===

[[File:Post-Glacial Sea Level.png|thumb|upright=1.5| Changes in sea levels since the end of the [[Earth:Last glacial period|last glacial episode]]]]An understanding of past sea level is an important guide to where current changes in sea level will end up. In the recent geological past, thermal expansion from increased temperatures and changes in land ice are the dominant reasons of sea level rise. The last time that the Earth was {{convert|2|C-change|F-change}} warmer than pre-industrial temperatures was 120,000 years ago. This was when warming due to Milankovitch cycles (changes in the amount of sunlight due to slow changes in the Earth's orbit) caused the Eemian interglacial. Sea levels during that warmer interglacial were at least {{Convert|5|m|ft|abbr=on|}} higher than now.<ref>{{Cite web |date=2019-08-30 |title=Scientists discover evidence for past high-level sea rise |url=https://phys.org/news/2019-08-scientists-evidence-high-level-sea.html |access-date=2019-09-07 |website=phys.org |language=en-us}}</ref> The Eemian warming was sustained over a period of thousands of years. The size of the rise in sea level implies a large contribution from the Antarctic and Greenland ice sheets.<ref name="ipcc13" />{{rp|1139}} Levels of atmospheric carbon dioxide of around 400 [[Parts per million|parts per million]] (similar to 2000s) had increased temperature by over {{convert|2-3|C-change|F-change}} around three million years ago. This temperature increase eventually melted one third of Antarctica's ice sheet, causing sea levels to rise 20 meters above the preindustrial levels.<ref>{{Cite web |title=Present CO2 levels caused 20-metre-sea-level rise in the past |url=https://www.nioz.nl/en/news/present-co2-levels-caused-20-metre-sea-level-rise-in-the-past |publisher=Royal Netherlands Institute for Sea Research }}</ref>

Since the [[Earth:Last Glacial Maximum|Last Glacial Maximum]], about 20,000 years ago, sea level has risen by more than {{Convert|125|m|ft|-1}}. Rates vary from less than 1&nbsp;mm/year during the pre-industrial era to 40+ mm/year when major ice sheets over Canada and Eurasia melted. [[Earth:Meltwater pulse 1A|Meltwater pulses]] are periods of fast sea level rise caused by the rapid disintegration of these ice sheets. The rate of sea level rise started to slow down about 8,200 years before today. Sea level was almost constant for the last 2,500 years. The recent trend of rising sea level started at the end of the 19th or beginning of the 20th century.<ref>{{cite journal |last1=Lambeck |first1=Kurt |last2=Rouby |first2=Hélène |last3=Purcell |first3=Anthony |last4=Sun |first4=Yiying |last5=Sambridge |first5=Malcolm |date=28 October 2014 |title=Sea level and global ice volumes from the Last Glacial Maximum to the Holocene |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=111 |issue=43 |pages=15296–15303 |bibcode=2014PNAS..11115296L |doi=10.1073/pnas.1411762111 |pmc=4217469 |pmid=25313072 |doi-access=free}}</ref>

== Causes ==
[[File:20210125 The Cryosphere - Floating and grounded ice - imbalance - climate change.png|thumb|upright=1.5|Earth lost 28&nbsp;trillion tonnes of ice between 1994 and 2017: ice sheets and glaciers raised the global sea level by 34.6 ± 3.1 mm. The rate of ice loss has risen by 57% since the 1990s−from 0.8 to 1.2&nbsp;trillion tonnes per year.<ref name=Cryosphere20210125>{{cite journal |last1=Slater |first1=Thomas |last2=Lawrence |first2=Isobel R. |last3=Otosaka |first3=Inès N. |last4=Shepherd |first4=Andrew |last5=Gourmelen |first5=Noel |last6=Jakob |first6=Livia |last7=Tepes |first7=Paul |last8=Gilbert |first8=Lin |last9=Nienow |first9=Peter |display-authors=4 |title=Review article: Earth's ice imbalance |journal=The Cryosphere |date=25 January 2021 |volume=15 |issue=1 |pages=233–246 |doi=10.5194/tc-15-233-2021 |bibcode=2021TCry...15..233S |s2cid=234098716 |url=https://tc.copernicus.org/articles/15/233/2021/ |language=English |issn=1994-0416 |doi-access=free }} Fig. 4.</ref>|alt=A graph showing ice loss sea ice, ice shelves and land ice. Land ice loss contributetes to SLR]]
The three main reasons warming causes global sea level to rise are [[Physics:Thermal expansion#Expansion in liquids|the expansion of oceans due to heating]], water inflow from melting ice sheets and water inflow from glaciers. Glacier retreat and ocean expansion have dominated sea level rise since the start of the 20th century.<ref name="Mengel2016" /> Some of the losses from glaciers are offset when [[Earth:Precipitation|precipitation]] falls as snow, accumulates and over time forms glacial ice. If precipitation, surface processes and ice loss at the edge [[Earth:Glacier mass balance|balance]] each other, sea level remains the same. Because of this precipitation began as water vapor evaporated from the ocean surface, effects of climate change on the water cycle can even increase ice build-up. However, this effect is not enough to fully offset ice losses, and sea level rise continues to accelerate.<ref name="AR6_WGII_Chapter9" /><ref name="IMBIE2018" /><ref name="Rignot2019" /><ref name="Zwally2021" />

The contributions of the two large ice sheets, in [[Earth:Greenland ice sheet|Greenland]] and [[Earth:Antarctic ice sheet|Antarctica]], are likely to increase in the 21st century.<ref name="Mengel2016">{{cite journal |last1=Mengel |first1=Matthias |last2=Levermann |first2=Anders |last3=Frieler |first3=Katja |last4=Robinson |first4=Alexander |last5=Marzeion |first5=Ben |last6=Winkelmann |first6=Ricarda |title=Future sea level rise constrained by observations and long-term commitment |journal=Proceedings of the National Academy of Sciences |date=8 March 2016 |volume=113 |issue=10 |pages=2597–2602 |doi=10.1073/pnas.1500515113 |pmc=4791025 |pmid=26903648 |bibcode=2016PNAS..113.2597M |doi-access=free }}</ref> They store most of the land ice (~99.5%) and have a sea-level equivalent (SLE) of {{Convert|7.4|m|ftin|abbr=on}} for Greenland and {{Convert|58.3|m|ftin|abbr=on}} for Antarctica.<ref name="WCRP2018"/> Thus, melting of all the ice on Earth would result in about {{Convert|70|m|ftin|abbr=on}} of sea level rise,<ref>{{cite web |title=How would sea level change if all glaciers melted? |url=https://www.usgs.gov/faqs/how-would-sea-level-change-if-all-glaciers-melted |website=United States Geological Survey |access-date=15 January 2024 }}</ref> although this would require at least 10,000 years and up to of global warming.<ref name="ArmstrongMcKay2022" /><ref name="ArmstrongMcKayExplainer" />

=== Ocean heating ===
{{Main|Earth:Ocean heat content}}
[[File:1955- Ocean heat content - NOAA.svg |thumb|left |There has been an increase in ocean heat content during recent decades as the oceans absorb most of the [[Earth:Earth's energy budget|excess heat]] created by human-induced global warming.<ref name=NOAA_NASA_OHC_1957_>''Top 700 meters:'' {{cite web |last1=Lindsey |first1=Rebecca |last2=Dahlman |first2=Luann |title=Climate Change: Ocean Heat Content |url=https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content |website=climate.gov |publisher=National Oceanic and Atmospheric Administration (NOAA) |archive-url=https://archive.today/20231029171303/https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content |archive-date=29 October 2023 |date=6 September 2023 |url-status=live }} ● ''Top 2000 meters:'' {{cite web |title=Ocean Warming / Latest Measurement: December 2022 / 345 (± 2) zettajoules since 1955 |url=https://climate.nasa.gov/vital-signs/ocean-warming/ |website=NASA.gov |publisher=National Aeronautics and Space Administration |archive-url=https://web.archive.org/web/20231020033606/https://climate.nasa.gov/vital-signs/ocean-warming/ |archive-date=20 October 2023 |url-status=live}}</ref>]]
The oceans store more than 90% of the extra heat added to Earth's climate system by climate change and act as a buffer against [[Biology:Effects of global warming|its effects]]. This means that the same amount of heat that would increase the average world ocean temperature by {{convert|0.01|C-change|F-change}} would increase atmospheric temperature by approximately {{convert|10|C-change|F-change}}.<ref>Levitus, S., Boyer, T., Antonov, J., Garcia, H., and Locarnini, R. (2005) {{cite web|url=http://www.climatescience.gov/workshop2005/default.htm |title=Ocean Warming 1955–2003 |archive-url=https://web.archive.org/web/20090717102249/http://www.climatescience.gov/workshop2005/default.htm|archive-date=17 July 2009}} Poster presented at the U.S. Climate Change Science Program Workshop, 14–16 November 2005, Arlington VA, Climate Science in Support of Decision-Making; Last viewed 22 May 2009.</ref> So a small change in the mean temperature of the ocean represents a very large change in the total heat content of the climate system. Winds and currents move heat into deeper parts of the ocean. Some of it reaches depths of more than {{Convert|2000|m|ft|sigfig=2|abbr=on}}.<ref>{{Cite web|url=https://www.scientificamerican.com/article/deep-ocean-waters-are-trapping-vast-stores-of-heat/|title=Deep Ocean Waters Are Trapping Vast Stores of Heat|last=Upton|first=John|date=2016-01-19|website=Scientific American|access-date=2019-02-01}}</ref>

When the ocean gains heat, [[Physics:Thermal expansion|the water expands]] and sea level rises. Warmer water and water under great pressure (due to depth) expand more than cooler water and water under less pressure.<ref name="ipcc13" />{{rp|1161}} Consequently, cold [[Earth:Arctic Ocean|Arctic Ocean]] water will expand less than warm tropical water. Different climate models present slightly different patterns of ocean heating. So their projections do not agree fully on how much ocean heating contributes to sea level rise.<ref>{{Cite journal|last1=Kuhlbrodt|first1=T|last2=Gregory|first2=J.M.|date=2012|title=Ocean heat uptake and its consequences for the magnitude of sea level rise and climate change|journal=Geophysical Research Letters|volume=39|issue=18|pages=L18608|doi=10.1029/2012GL052952|bibcode=2012GeoRL..3918608K|s2cid=19120823|url=http://centaur.reading.ac.uk/28951/1/Kuhlbrodt_Gregory_GRL_2012.pdf}}</ref> 

=== Antarctic ice loss ===
[[File:Antarctic shelf ice hg.png|thumb|upright=1.35|Processes around an Antarctic ice shelf]]
[[File:Corp2400 - Flickr - NOAA Photo Library.jpg|thumb|The [[Earth:Ross Ice Shelf|Ross Ice Shelf]] is Antarctica's largest. It is about the size of {{wipe|France}} and up to several hundred metres thick.]]
The large volume of ice on the Antarctic continent stores around 60% of the world's fresh water. Excluding [[Earth:Groundwater|groundwater]] this is 90%.<ref>{{cite web |title=Antarctic Factsheet |url=https://www.bas.ac.uk/science/science-and-society/education/antarctic-factsheet-geographical-statistics/ |publisher=British Antarctic Survey |access-date=15 January 2024 }}</ref> Antarctica is experiencing ice loss from coastal glaciers in the [[Place:West Antarctica|West Antarctica]] and some glaciers of [[Earth:East Antarctica|East Antarctica]]. However it is gaining mass from the increased snow build-up inland, particularly in the East. This leads to contradicting trends.<ref name="Zwally2021" /><ref name="NASA2023" /> There are different satellite methods for measuring ice mass and change. Combining them helps to reconcile the differences.<ref name="IMBIE2012">{{Cite journal|last1=Shepherd|first1=Andrew|last2=Ivins|first2=Erik|date=2012|title=A Reconciled Estimate of Ice-Sheet Mass Balance|url=http://www.escholarship.org/uc/item/0vq404h7|journal=Science|volume=338|issue=6111|pages=1183–1189|bibcode=2012Sci...338.1183S|doi=10.1126/science.1228102|pmid=23197528|collaboration=[[Earth:Ice Sheet Mass Balance Inter-comparison Exercise|IMBIE]] team|hdl=2060/20140006608|s2cid=32653236}}</ref> However, there can still be variations between the studies. In 2018, a [[Systematic review|systematic review]] estimated average annual ice loss of 43 billion tons (Gt) across the entire continent between 1992 and 2002. This tripled to an annual average of 220 Gt from 2012 to 2017.<ref name="IMBIE2018">{{cite journal |title=Mass balance of the Antarctic Ice Sheet from 1992 to 2017 |journal=Nature |date=13 June 2018 |volume=558 |issue=7709 |pages=219–222 |doi=10.1038/s41586-018-0179-y |hdl=2268/225208 |pmid=29899482 |bibcode=2018Natur.558..219I |author1=IMBIE team |s2cid=49188002 |hdl-access=free }}</ref><ref>{{cite news |author=Scott K. Johnson |date=2018-06-13 |title=Latest estimate shows how much Antarctic ice has fallen into the sea |work=[[Ars Technica]] |url=https://arstechnica.com/science/2018/06/latest-estimate-shows-how-much-antarctic-ice-has-fallen-into-the-sea }}</ref> However, a 2021 analysis of data from four different research satellite systems ([[Astronomy:Envisat|Envisat]], [[Engineering:European Remote-Sensing Satellite|European Remote-Sensing Satellite]], [[Physics:GRACE and GRACE-FO|GRACE and GRACE-FO]] and [[Engineering:ICESat|ICESat]]) indicated annual mass loss of only about 12 Gt from 2012 to 2016. This was due to greater ice gain in East Antarctica than estimated earlier.<ref name="Zwally2021" />

In the future, it is known that West Antarctica at least will continue to lose mass, and the likely future losses of sea ice and [[Earth:Ice shelf|ice shelves]], which block warmer currents from direct contact with the ice sheet, can accelerate declines even in the East.<ref name="Greene2018" /><ref name="CNN_Jan2019">{{cite web|work=CNN|url=https://edition.cnn.com/2019/01/14/world/climate-change-antarctica-ice-melt-twin-studies/index.html|title=Antarctica ice melt has accelerated by 280% in the last 4 decades|date=14 January 2019 |access-date=January 14, 2019 |quote=Melting is taking place in the most vulnerable parts of Antarctica&nbsp;... parts that hold the potential for multiple metres of sea level rise in the coming century or two}}</ref> Altogether, Antarctica is the source of the largest uncertainty for future sea level projections.<ref name="Nature_20210505A">{{cite journal |last1=Edwards |first1=Tamsin L. |last2=Nowicki |first2=Sophie |last3=Marzeion |first3=Ben |last4=Hock |first4=Regine |last5=Goelzer |first5=Heiko |last6=Seroussi |first6=Hélène |display-authors=4 |date=5 May 2021 |title=Projected land ice contributions to twenty-first-century sea level rise |url=https://www.nature.com/articles/s41586-021-03302-y |journal=Nature |volume=593 |issue=7857 |pages=74–82 |bibcode=2021Natur.593...74E |doi=10.1038/s41586-021-03302-y |issn=0028-0836 |pmid=33953415 |hdl=1874/412157 |archive-url=https://web.archive.org/web/20210511000000/https://www.nature.com/articles/s41586-021-03302-y |archive-date=11 May 2021 |s2cid=233871029}} Alt URL https://eprints.whiterose.ac.uk/173870/</ref> By 2019, several studies attempted to estimate 2300 sea level rise caused by ice loss in Antarctica alone. They suggest a median rise of {{cvt|16|cm|in|frac=2}} and maximum rise of {{cvt|37|cm|in|frac=2}} under the low-emission scenario. The highest emission scenario results in a median rise of {{cvt|1.46|m|ft|frac=2}} metres, with a minimum of {{cvt|60|cm|ft|frac=2}} and a maximum of {{cvt|2.89|m|ft|frac=2}}).<ref name="IPCC AR6 WG1 Ch.9" />

====East Antarctica====
The world's largest potential source of sea level rise is the [[Earth:East Antarctic Shield|East Antarctic]] Ice Sheet (EAIS). It is 2.2&nbsp;km thick on average and holds enough ice to raise global sea levels by 53.3 m (174&nbsp;ft 10 in)<ref>{{cite journal |last1=Fretwell |first1=P. |last2=Pritchard |first2=H. D. |last3=Vaughan |first3=D. G. |last4=Bamber |first4=J. L. |last5=Barrand |first5=N. E. |last6=Bell |first6=R. |last7=Bianchi |first7=C. |last8=Bingham |first8=R. G. |last9=Blankenship |first9=D. D. |last10=Casassa |first10=G. |last11=Catania |first11=G. |last12=Callens |first12=D. |last13=Conway |first13=H. |last14=Cook |first14=A. J. |last15=Corr |first15=H. F. J. |last16=Damaske |first16=D. |last17=Damm |first17=V. |last18=Ferraccioli |first18=F. |last19=Forsberg |first19=R. |last20=Fujita |first20=S. |last21=Gim |first21=Y. |last22=Gogineni |first22=P. |last23=Griggs |first23=J. A. |last24=Hindmarsh |first24=R. C. A. |last25=Holmlund |first25=P. |last26=Holt |first26=J. W. |last27=Jacobel |first27=R. W. |last28=Jenkins |first28=A. |last29=Jokat |first29=W. |last30=Jordan |first30=T. |last31=King |first31=E. C. |last32=Kohler |first32=J. |last33=Krabill |first33=W. |last34=Riger-Kusk |first34=M. |last35=Langley |first35=K. A. |last36=Leitchenkov |first36=G. |last37=Leuschen |first37=C. |last38=Luyendyk |first38=B. P. |last39=Matsuoka |first39=K. |last40=Mouginot |first40=J. |last41=Nitsche |first41=F. O. |last42=Nogi |first42=Y. |last43=Nost |first43=O. A. |last44=Popov |first44=S. V. |last45=Rignot |first45=E. |last46=Rippin |first46=D. M. |last47=Rivera |first47=A. |last48=Roberts |first48=J. |last49=Ross |first49=N. |last50=Siegert |first50=M. J. |last51=Smith |first51=A. M. |last52=Steinhage |first52=D. |last53=Studinger |first53=M. |last54=Sun |first54=B. |last55=Tinto |first55=B. K. |last56=Welch |first56=B. C. |last57=Wilson |first57=D. |last58=Young |first58=D. A. |last59=Xiangbin |first59=C. |last60=Zirizzotti |first60=A. |title=Bedmap2: improved ice bed, surface and thickness datasets for Antarctica |journal=The Cryosphere |date=28 February 2013 |volume=7 |issue=1 |pages=375–393 |doi=10.5194/tc-7-375-2013 |bibcode=2013TCry....7..375F |doi-access=free }}</ref> Its great thickness and high elevation make it more stable than the other ice sheets.<ref name="Singh2020">{{Cite journal |last1=Singh |first1=Hansi A. |last2=Polvani |first2=Lorenzo M. |date=10 January 2020 |title=Low Antarctic continental climate sensitivity due to high ice sheet orography |journal=npj Climate and Atmospheric Science |language=en |volume=3 |doi=10.1038/s41612-020-00143-w |s2cid=222179485 |doi-access=free }}</ref> As of the early 2020s, most studies show that it is still gaining mass.<ref name="King2012">{{Cite journal | last1 = King | first1 = M. A. | last2 = Bingham | first2 = R. J. | last3 = Moore | first3 = P. | last4 = Whitehouse | first4 = P. L. | last5 = Bentley | first5 = M. J. | last6 = Milne | first6 = G. A. | doi = 10.1038/nature11621 | title = Lower satellite-gravimetry estimates of Antarctic sea-level contribution | journal = Nature | volume = 491 | issue = 7425 | pages = 586–589 | year = 2012 | pmid =  23086145|bibcode = 2012Natur.491..586K | s2cid = 4414976 }}</ref><ref name="IMBIE2018">{{cite journal |title=Mass balance of the Antarctic Ice Sheet from 1992 to 2017 |journal=Nature |date=13 June 2018 |volume=558 |issue=7709 |pages=219–222 |doi=10.1038/s41586-018-0179-y |hdl=2268/225208 |pmid=29899482 |bibcode=2018Natur.558..219I |author1=IMBIE team |s2cid=49188002 |hdl-access=free }}</ref><ref name="Zwally2021" /><ref name="NASA2023">{{cite web |title=Antarctic Ice Mass Loss 2002-2023 |url=https://svs.gsfc.nasa.gov/31158 |author=NASA |date=7 July 2023 }}</ref> Some analyses have suggested it began to lose mass in the 2000s.<ref>{{cite journal |last1=Chen |first1=J. L. |last2=Wilson |first2=C. R. |last3=Blankenship |first3=D. |last4=Tapley |first4=B. D. |year=2009 |title=Accelerated Antarctic ice loss from satellite gravity measurements |journal=Nature Geoscience |volume=2 |issue=12 |pages=859 |doi=10.1038/ngeo694 |bibcode=2009NatGe...2..859C |s2cid=130927366 }}</ref><ref name="Rignot2019">{{cite journal |last1=Rignot |first1=Eric |last2=Mouginot |first2=Jérémie |last3=Scheuchl |first3=Bernd |last4=van den Broeke |first4=Michiel |last5=van Wessem |first5=Melchior J. |last6=Morlighem |first6=Mathieu |title=Four decades of Antarctic Ice Sheet mass balance from 1979–2017 |journal=Proceedings of the National Academy of Sciences |date=22 January 2019 |volume=116 |issue=4 |pages=1095–1103 |doi=10.1073/pnas.1812883116 |pmid=30642972 |pmc=6347714 |bibcode=2019PNAS..116.1095R |doi-access=free }}</ref><ref name="CNN_Jan2019"/> However they over-extrapolated some observed losses on to the poorly observed areas. A more complete observational record shows continued mass gain.<ref name="Zwally2021">{{Cite journal |last1=Zwally |first1=H. Jay |last2=Robbins |first2=John W. |last3=Luthcke |first3=Scott B. |last4=Loomis |first4=Bryant D. |last5=Rémy  |first5=Frédérique |date=29 March 2021 |title=Mass balance of the Antarctic ice sheet 1992–2016: reconciling results from GRACE gravimetry with ICESat, ERS1/2 and Envisat altimetry |journal=Journal of Glaciology |language=en |volume=67 |issue=263 |pages=533–559 |doi=10.1017/jog.2021.8 |quote=Although their methods of interpolation or extrapolation for areas with unobserved output velocities have an insufficient description for the evaluation of associated errors, such errors in previous results (Rignot and others, 2008) caused large overestimates of the mass losses as detailed in Zwally and Giovinetto (Zwally and Giovinetto, 2011).}}</ref>
[[File:Denman_oli_2020-057-059_lrg-labeled.svg|thumb|left|Aerial view of ice flows at Denman Glacier, one of the less stable glaciers in the East Antarctica]]
In spite of the net mass gain, some East Antarctica glaciers have lost ice in recent decades due to ocean warming and declining structural support from the local [[Earth:Sea ice|sea ice]],<ref name="Greene2018">{{cite journal |last1=Greene |first1=Chad A. |last2=Young |first2=Duncan A. |last3=Gwyther |first3=David E. |last4=Galton-Fenzi |first4=Benjamin K. |last5=Blankenship |first5=Donald D. |title=Seasonal dynamics of Totten Ice Shelf controlled by sea ice buttressing |journal=The Cryosphere |date=6 September 2018 |volume=12 |issue=9 |pages=2869–2882 |doi=10.5194/tc-12-2869-2018 |bibcode=2018TCry...12.2869G |doi-access=free }}</ref> such as Denman Glacier,<ref name="BrancatoRignot2020">{{cite journal|last1=Brancato |first1=V. |last2=Rignot |first2=E. |last3=Milillo |first3=P. |last4=Morlighem |first4=M. |last5=Mouginot |first5=J. |last6=An |first6=L. |last7=Scheuchl |first7=B. |last8=Jeong |first8=S. |last9=Rizzoli |first9=P. |last10=Bueso Bello |first10=J.L. |last11=Prats-Iraola |first11=P. |title=Grounding line retreat of Denman Glacier, East Antarctica, measured with COSMO-SkyMed radar interferometry data |journal=Geophysical Research Letters |year=2020 |volume=47 |issue=7 |pages=e2019GL086291|issn=0094-8276 |doi=10.1029/2019GL086291 |bibcode=2020GeoRL..4786291B |doi-access=free}}</ref><ref>{{cite news|newspaper=BBC|url=https://www.bbc.com/news/science-environment-52007637|title=Climate change: Earth's deepest ice canyon vulnerable to melting |last=Amos|first=Jonathan|date=2020-03-23}}</ref> and Totten Glacier.<ref>{{cite journal |last1=Greene |first1=Chad A. |last2=Blankenship |first2=Donald D. |last3=Gwyther |first3=David E. |last4=Silvano |first4=Alessandro |last5=van Wijk |first5=Esmee |title=Wind causes Totten Ice Shelf melt and acceleration |journal=Science Advances |date=1 November 2017 |volume=3 |issue=11 |pages=e1701681 |doi=10.1126/sciadv.1701681 |pmid=29109976 |pmc=5665591 |bibcode=2017SciA....3E1681G }}</ref><ref>{{cite journal |last1=Roberts |first1=Jason |last2=Galton-Fenzi |first2=Benjamin K. |last3=Paolo |first3=Fernando S. |last4=Donnelly |first4=Claire |last5=Gwyther |first5=David E. |last6=Padman |first6=Laurie |last7=Young |first7=Duncan |last8=Warner |first8=Roland |last9=Greenbaum |first9=Jamin |last10=Fricker |first10=Helen A. |last11=Payne |first11=Antony J. |last12=Cornford |first12=Stephen |last13=Le Brocq |first13=Anne |last14=van Ommen |first14=Tas |last15=Blankenship |first15=Don |last16=Siegert |first16=Martin J. |title=Ocean forced variability of Totten Glacier mass loss |journal=Geological Society, London, Special Publications |date=2018 |volume=461 |issue=1 |pages=175–186 |doi=10.1144/sp461.6 |bibcode=2018GSLSP.461..175R |s2cid=55567382 |url=https://research-information.bristol.ac.uk/en/publications/ocean-forced-variability-of-totten-glacier-mass-loss(27694a07-b3c7-45fd-bdfb-74eb6b09c3e0).html |doi-access=free }}</ref> Totten Glacier is particularly important because it stabilizes the Aurora Subglacial Basin. Subglacial basins like Aurora and Wilkes Basin are major ice reservoirs together holding as much ice as all of West Antarctica.<ref>{{cite journal |last1=Greenbaum |first1=J. S. |last2=Blankenship |first2=D. D. |last3=Young |first3=D. A. |last4=Richter |first4=T. G. |last5=Roberts |first5=J. L. |last6=Aitken |first6=A. R. A. |last7=Legresy |first7=B. |last8=Schroeder |first8=D. M. |last9=Warner |first9=R. C. |last10=van Ommen |first10=T. D. |last11=Siegert |first11=M. J. |title=Ocean access to a cavity beneath Totten Glacier in East Antarctica |journal=Nature Geoscience |date=16 March 2015 |volume=8 |issue=4 |pages=294–298 |doi=10.1038/ngeo2388 |bibcode=2015NatGe...8..294G }}</ref> They are more vulnerable than the rest of East Antarctica.<ref name="Pollard2015">{{cite journal |last1=Pollard |first1=David |last2=DeConto |first2=Robert M. |last3=Alley |first3=Richard B. |title=Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure |journal=Earth and Planetary Science Letters |date=February 2015 |volume=412 |pages=112–121 |doi=10.1016/j.epsl.2014.12.035 |bibcode=2015E&PSL.412..112P |doi-access=free }}</ref> Their collective [[Earth:Tipping points in the climate system|tipping point]] probably lies at around {{convert|3|C-change|F-change}} of global warming. It may be as high as {{convert|6|C-change|F-change}} or as low as {{convert|2|C-change|F-change}}. Once this tipping point is crossed, the collapse of these subglacial basins could take place over as little as 500 or as much as 10,000 years. The median timeline is 2000 years.<ref name="ArmstrongMcKay2022" /><ref name="ArmstrongMcKayExplainer" /> Depending on how many subglacial basins are vulnerable, this causes sea level rise of between {{convert|1.4|m|ftin|abbr=on}} and {{convert|6.4|m|ftin|abbr=on}}.<ref name="Pan2021">{{Cite journal|last1=Pan |first1=Linda |last2=Powell |first2=Evelyn M. |last3=Latychev |first3=Konstantin |last4=Mitrovica |first4=Jerry X. |last5=Creveling |first5=Jessica R. |last6=Gomez |first6=Natalya |last7=Hoggard |first7=Mark J. |last8=Clark |first8=Peter U. |date=30 April 2021 |title=Rapid postglacial rebound amplifies global sea level rise following West Antarctic Ice Sheet collapse |journal=Science Advances |volume=7 |issue=18 |doi=10.1126/sciadv.abf7787 }}</ref>

On the other hand, the whole EAIS would not definitely collapse until global warming reaches {{convert|7.5|C-change|F-change}}, with a range between {{convert|5|C-change|F-change}} and {{convert|10|C-change|F-change}}. It would take at least 10,000 years to disappear.<ref name="ArmstrongMcKay2022" /><ref name="ArmstrongMcKayExplainer" /> Some scientists have estimated that warming would have to reach at least {{convert|6|C-change|F-change}} to melt two thirds of its volume.<ref name="Garbe2020">{{Cite journal |last1=Garbe |first1=Julius |last2=Albrecht |first2=Torsten |last3=Levermann |first3=Anders |last4=Donges |first4=Jonathan F. |last5=Winkelmann |first5=Ricarda |date=2020 |title=The hysteresis of the Antarctic Ice Sheet |url=https://www.nature.com/articles/s41586-020-2727-5 |journal=Nature |volume=585 |issue=7826 |pages=538–544 |doi=10.1038/s41586-020-2727-5|pmid=32968257 |bibcode=2020Natur.585..538G |s2cid=221885420 }}</ref>

====West Antarctica====
[[File:Thwaites Glacier.jpg|thumb|upright=1.35|Thwaites Glacier, with its vulnerable bedrock topography visible.]]
East Antarctica contains the largest potential source of sea level rise. However the [[Place:West Antarctica|West Antarctica]] ice sheet (WAIS) is substantially more vulnerable. Temperatures on West Antarctica have increased significantly, unlike East Antarctica and the Antarctic Peninsula. The trend is between {{convert|0.08|C-change|F-change}} and {{convert|0.96|C-change|F-change}} per decade between 1976 and 2012.<ref>{{cite journal |last1=Ludescher |first1=Josef |last2=Bunde |first2=Armin |last3=Franzke |first3=Christian L. E. |last4=Schellnhuber |first4=Hans Joachim |title=Long-term persistence enhances uncertainty about anthropogenic warming of Antarctica |journal=Climate Dynamics |date=16 April 2015 |volume=46 |issue=1–2 |pages=263–271 |doi=10.1007/s00382-015-2582-5 |bibcode=2016ClDy...46..263L |s2cid=131723421 }}</ref> Satellite observations recorded a substantial increase in WAIS melting from 1992 to 2017. This resulted in {{Convert|7.6 ± 3.9|mm|in|frac=64|abbr=on}} of Antarctica sea level rise. Outflow glaciers in the Amundsen Sea Embayment played a disproportionate role.<ref name="RignotBamber2008">{{cite journal |last1=Rignot |first1=Eric |last2=Bamber |first2=Jonathan L. |last3=van den Broeke |first3=Michiel R. |last4=Davis |first4=Curt |last5=Li |first5=Yonghong |last6=van de Berg |first6=Willem Jan |last7=van Meijgaard |first7=Erik |title=Recent Antarctic ice mass loss from radar interferometry and regional climate modelling |journal=Nature Geoscience |date=13 January 2008 |volume=1 |issue=2 |pages=106–110 |doi=10.1038/ngeo102 |bibcode=2008NatGe...1..106R |s2cid=784105 |url=http://www.escholarship.org/uc/item/26f4j9vv}}</ref>

The 2021 IPCC Sixth Assessment Report estimated that the ''median'' increase in sea level rise from the West Antarctic ice sheet melt by 2100 is ~{{convert|11|cm|in|round=5|abbr=on}}. There is no difference between scenarios, because the increased warming would intensify the water cycle and increase snowfall accumulation over the ice sheet at about the same rate as it would increase ice loss. However, most of the [[Earth:Bedrock|bedrock]] underlying the WAIS lies well below sea level, and it has to be buttressed by the Thwaites and Pine Island glaciers. If these glaciers collapse, the entire ice sheet would as well.<ref name="Pollard2015"/> They would take at least several centuries to disappear. But scientists consider this almost inevitable, as their bedrock [[Earth:Topography|topography]] deepens inland and becomes more vulnerable to meltwater.<ref name="Pettit2021">{{Cite web |last1=Voosen |first1=Paul |date=13 December 2021 |title=Ice shelf holding back keystone Antarctic glacier within years of failure|url=https://www.science.org/content/article/ice-shelf-holding-back-keystone-antarctic-glacier-within-years-failure|access-date=2022-10-22|website=Science Magazine|language=en|quote=Because Thwaites sits below sea level on ground that dips away from the coast, the warm water is likely to melt its way inland, beneath the glacier itself, freeing its underbelly from bedrock. A collapse of the entire glacier, which some researchers think is only centuries away, would raise global sea level by 65 centimeters.}}</ref><ref name=BBC1 >{{cite news |last=Amos |first=Jonathan |date=December 13, 2021 |title=Thwaites: Antarctic glacier heading for dramatic change |url=https://www.bbc.com/news/science-environment-59644494 |work=BBC News |location=London |access-date=December 14, 2021 }}</ref><ref name=CIRES >{{cite press release |author=<!--Not stated--> |title=The Threat from Thwaites: The Retreat of Antarctica's Riskiest Glacier |url=https://cires.colorado.edu/news/threat-thwaites-retreat-antarctica's-riskiest-glacier |location= |publisher=Cooperative Institute for Research in Environmental Sciences (CIRES) |agency=[[Organization:University of Colorado Boulder|University of Colorado Boulder]] |date=2021-12-13 |access-date=2021-12-14}}</ref>

The contribution of these glaciers to global sea levels has already accelerated since the beginning of the 21st century. The Thwaites Glacier now accounts for 4% of global sea level rise.<ref name="Pettit2021" /><ref>{{cite web|url=https://www.theatlantic.com/science/archive/2018/06/after-decades-of-ice-loss-antarctica-is-now-hemorrhaging-mass/562748/|work=The Atlantic|year=2018|title=After Decades of Losing Ice, Antarctica Is Now Hemorrhaging It}}</ref><ref>{{cite web|url=http://www.antarcticglaciers.org/glaciers-and-climate/ice-ocean-interactions/marine-ice-sheets/|work=AntarcticGlaciers.org|year=2014|title=Marine ice sheet instability}}</ref> It could start to lose even more ice if the [[Earth:Thwaites Ice Shelf|Thwaites Ice Shelf]] fails, potentially in mid-2020s.<ref name=Kaplan1>{{cite news |last=Kaplan |first=Sarah |date=December 13, 2021 |title=Crucial Antarctic ice shelf could fail within five years, scientists say |url=https://www.washingtonpost.com/climate-environment/2021/12/13/thwaites-glacier-melt-antarctica/ |newspaper={{wipe|The Washington Post}} |location=Washington DC |access-date=December 14, 2021}}</ref> This is due to the [[Earth:Marine ice sheet instability|marine ice sheet instability]] hypothesis. This suggests that warm water enters between the seafloor and the base of the ice sheet once it is no longer heavy enough to displace the flow. This causes accelerated melting and collapse.<ref>{{cite journal |last1=Robel |first1=Alexander A. |last2=Seroussi |first2=Hélène |last3=Roe |first3=Gerard H. |title=Marine ice sheet instability amplifies and skews uncertainty in projections of future sea-level rise |journal=Proceedings of the National Academy of Sciences |date=23 July 2019 |volume=116 |issue=30 |pages=14887–14892 |doi=10.1073/pnas.1904822116 |pmid=31285345 |pmc=6660720 |bibcode=2019PNAS..11614887R |doi-access=free }}</ref> Marine ice cliff instability, when ice [[Earth:Cliff|cliff]]s with heights greater than {{convert|100|m|ft|round=5|abbr=on}} collapse under their own weight once they are no longer [[Engineering:Buttress|buttress]]ed by [[Earth:Ice shelf|ice shelves]], may also occur. However it has never been observed. More detailed modelling has ruled it out.<ref>{{cite news|url=https://www.sciencenews.org/article/climate-marine-ice-cliffs-sheets-collapse-not-inevitable-sea-level|title=Collapse may not always be inevitable for marine ice cliffs|last1=Perkins|first1=Sid|date=June 17, 2021|access-date=9 January 2023|agency=ScienceNews}}</ref> 
[[File:West Antarctic Collapse.ogv|thumb|upright=1.35|left|A graphical representation of how warm waters, and the Marine Ice Sheet Instability and Marine Ice Cliff Instability processes are affecting the West Antarctic Ice Sheet]]
Another hard-to-model process is hydrofracturing. Here meltwater collects atop the ice sheet, pools into fractures and forces them open.<ref name="pmid30013142">{{cite journal |last1=Pattyn |first1=Frank |date=16 July 2018 |title=The paradigm shift in Antarctic ice sheet modelling |journal=Nature Communications |volume=9 |issue=1 |page=2728 |bibcode=2018NatCo...9.2728P |doi=10.1038/s41467-018-05003-z |pmc=6048022 |pmid=30013142}}</ref> Another is changes in the ocean circulation at a smaller scale.<ref>{{Cite journal |last1=Golledge |first1=Nicholas R. |last2=Keller |first2=Elizabeth D. |last3=Gomez |first3=Natalya |last4=Naughten |first4=Kaitlin A. |last5=Bernales |first5=Jorge |last6=Trusel |first6=Luke D. |last7=Edwards |first7=Tamsin L. |date=2019 |title=Global environmental consequences of twenty-first-century ice-sheet melt |url=https://www.nature.com/articles/s41586-019-0889-9 |journal=Nature |language=en |volume=566 |issue=7742 |pages=65–72 |doi=10.1038/s41586-019-0889-9 |pmid=30728520 |bibcode=2019Natur.566...65G |s2cid=59606358 |issn=1476-4687}}</ref><ref>{{Cite journal |last1=Moorman |first1=Ruth |last2=Morrison |first2=Adele K. |last3=Hogg |first3=Andrew McC |date=2020-08-01 |title=Thermal Responses to Antarctic Ice Shelf Melt in an Eddy-Rich Global Ocean–Sea Ice Model |url=https://journals.ametsoc.org/view/journals/clim/33/15/jcliD190846.xml |journal=Journal of Climate |language=EN |volume=33 |issue=15 |pages=6599–6620 |doi=10.1175/JCLI-D-19-0846.1 |bibcode=2020JCli...33.6599M |s2cid=219487981 |issn=0894-8755}}</ref><ref name="Naughten2023" /> A combination of these processes could cause the WAIS to contribute as much as {{convert|41|cm|in|0|abbr=on}} by 2100 under the low-emission scenario and {{convert|57|cm|in|0|abbr=on}} under the highest-emission one.<ref name="IPCC AR6 WG1 Ch.9" /> 

The melting of all the [[Earth:Ice|ice]] in West Antarctica would increase the total sea level rise to {{convert|4.3|m|ftin|abbr=on}}.<ref name="BEDMAP2-2013">{{cite journal |last1=Fretwell |first1=P. |display-authors=et al |title=Bedmap2: improved ice bed, surface and thickness datasets for Antarctica |journal=The Cryosphere |volume=7 |issue=1 |page=390 |date=28 February 2013 |url=http://www.the-cryosphere.net/7/375/2013/tc-7-375-2013.pdf |access-date=6 January 2014 |doi=10.5194/tc-7-375-2013 |bibcode=2013TCry....7..375F |s2cid=13129041 |doi-access=free |archive-date=16 February 2020 |archive-url=https://web.archive.org/web/20200216072841/https://www.the-cryosphere.net/7/375/2013/tc-7-375-2013.pdf |url-status=live }}</ref> However, mountain [[Earth:Ice cap|ice cap]]s not in contact with water are less vulnerable than the majority of the ice sheet, which is located below the sea level. Its collapse would cause ~{{convert|3.3|m|ftin|abbr=on}} of sea level rise.<ref name="Bamber2009">{{cite journal |last1=Bamber |first1=J.L. |last2=Riva |first2=R.E.M. |last3=Vermeersen |first3=B.L.A. |last4=LeBrocq |first4=A.M. |title=Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet |journal=Science |date=14 May 2009 |volume=324 |issue=5929 |pages=901–903 |doi=10.1126/science.1169335 |pmid=19443778 |bibcode=2009Sci...324..901B |s2cid=11083712}}</ref> Scientists consider this collapse practically inevitable. It seems to have already occurred during the [[Earth:Eemian|Eemian]] period 125,000 years ago. At that time temperatures were similar to the early 21st century.<ref>{{Cite web|url=https://www.science.org/content/article/discovery-recent-antarctic-ice-sheet-collapse-raises-fears-new-global-flood|title=Discovery of recent Antarctic ice sheet collapse raises fears of a new global flood|last=Voosen|first=Paul|date=2018-12-18|website=Science|language=en|access-date=2018-12-28}}</ref><ref>{{Cite journal|last1=Turney|first1=Chris S. M.|last2=Fogwill|first2=Christopher J.|last3=Golledge|first3=Nicholas R.|last4=McKay |first4=Nicholas P. |last5=Sebille |first5=Erik van |last6=Jones |first6=Richard T. |last7=Etheridge |first7=David|last8=Rubino |first8=Mauro|last9=Thornton|first9=David P. |last10=Davies|first10=Siwan M.|last11=Ramsey|first11=Christopher Bronk|date=2020-02-11|title=Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica|journal=Proceedings of the National Academy of Sciences |volume=117 |issue=8 |pages=3996–4006 |language=en |doi=10.1073/pnas.1902469117|issn=0027-8424 |pmid=32047039 |pmc=7049167 |bibcode=2020PNAS..117.3996T|doi-access=free}}</ref><ref name="Carlson2018">{{Cite conference |last1=Carlson |first1=Anders E |last2=Walczak |first2=Maureen H |last3=Beard |first3=Brian L |last4=Laffin |first4=Matthew K |last5=Stoner |first5=Joseph S |last6=Hatfield |first6=Robert G |date=10 December 2018 |title=Absence of the West Antarctic ice sheet during the last interglaciation |url=https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/421418  |conference=American Geophysical Union Fall Meeting }}</ref><ref name="Lau2023">{{Cite journal |last1=Lau |first1=Sally C. Y. |last2=Wilson |first2=Nerida G. |last3=Golledge |first3=Nicholas R.  |last4=Naish |first4=Tim R. |last5=Watts |first5=Phillip C. |last6=Silva |first6=Catarina N. S. |last7=Cooke |first7=Ira R. |last8=Allcock |first8=A. Louise |last9=Mark |first9=Felix C. |last10=Linse |first10=Katrin |date=21 December 2023 |title=Genomic evidence for West Antarctic Ice Sheet collapse during the Last Interglacial |journal=Science |language=en |volume=382 |issue=6677 |pages=1384–1389 |doi=10.1126/science.ade0664 }}</ref><ref>{{Cite web |last=AHMED |first=Issam |title=Antarctic octopus DNA reveals ice sheet collapse closer than thought |url=https://phys.org/news/2023-12-antarctic-octopus-dna-reveals-ice.html |access-date=2023-12-23 |website=phys.org |language=en}}</ref><ref name="Naughten2023">{{cite journal |last1=A. Naughten |first1=Kaitlin |last2=R. Holland |first2=Paul |last3=De Rydt |first3=Jan|title=Unavoidable future increase in West Antarctic ice-shelf melting over the twenty-first century |journal=Nature Climate Change |date=23 October 2023 |volume=13 |issue=11 |pages=1222–1228 |doi=10.1038/s41558-023-01818-x |s2cid=264476246 |url=https://www.nature.com/articles/s41558-023-01818-x |access-date=26 October 2023|doi-access=free }}</ref><ref>{{cite news |last1=Poynting |first1=Mark |title=Sea-level rise: West Antarctic ice shelf melt 'unavoidable' |url=https://www.bbc.com/news/science-environment-67171231 |access-date=26 October 2023 |agency=BBC |date=24 October 2023}}</ref> This disappearance would take an estimated 2000 years. The absolute minimum for the loss of West Antarctica ice is 500 years, and the potential maximum is 13,000 years.<ref name="ArmstrongMcKay2022">{{Cite journal |last1=Armstrong McKay |first1=David|last2=Abrams |first2=Jesse |last3=Winkelmann |first3=Ricarda |last4=Sakschewski |first4=Boris |last5=Loriani |first5=Sina |last6=Fetzer |first6=Ingo|last7=Cornell|first7=Sarah |last8=Rockström |first8=Johan |last9=Staal |first9=Arie |last10=Lenton |first10=Timothy |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points |url=https://www.science.org/doi/10.1126/science.abn7950 |journal=Science |language=en |volume=377 |issue=6611 |pages=eabn7950 |doi=10.1126/science.abn7950 |pmid=36074831 |hdl=10871/131584 |s2cid=252161375 |issn=0036-8075}}</ref><ref name="ArmstrongMcKayExplainer">{{Cite web |last=Armstrong McKay |first=David |date=9 September 2022 |title=Exceeding 1.5°C global warming could trigger multiple climate tipping points – paper explainer |url=https://climatetippingpoints.info/2022/09/09/climate-tipping-points-reassessment-explainer/ |access-date=2 October 2022 |website=climatetippingpoints.info |language=en}}</ref> 

The only way to stop ice loss from West Antarctica once triggered is by lowering the global temperature to {{convert|1|C-change|F-change}} ''below'' the preindustrial level. This would be {{convert|2|C-change|F-change}} below the temperature of 2020.<ref name="Garbe2020" /> Other researchers suggested that a [[Earth:Climate engineering|climate engineering]] intervention to stabilize the ice sheet's glaciers may delay its loss by centuries and give more time to adapt. However this is an uncertain proposal, and would end up as one of the most expensive projects ever attempted.<ref name="Wolovick2023a">{{Cite journal |last1=Wolovick |first1=Michael |last2=Moore |first2=John |last3=Keefer |first3=Bowie |date=27 March 2023 |title=Feasibility of ice sheet conservation using seabed anchored curtains |url=https://academic.oup.com/pnasnexus/article/2/4/pgad103/7087219 |journal=PNAS Nexus |volume=2 |issue=3 |pages=pgad053 |language=en |doi=10.1093/pnasnexus/pgad053 |pmid=37007716 |pmc=10062297 }}</ref><ref name="Wolovick2023b">{{Cite journal |last1=Wolovick |first1=Michael |last2=Moore |first2=John |last3=Keefer |first3=Bowie |date=27 March 2023 |title=The potential for stabilizing Amundsen Sea glaciers via underwater curtains |url=https://academic.oup.com/pnasnexus/article/2/4/pgad103/7087219 |journal=PNAS Nexus |volume=2 |issue=4 |pages=pgad103 |language=en |doi=10.1093/pnasnexus/pgad103 |pmid=37091546 |pmc=10118300 }}</ref>

====Isostatic rebound====
2021 research indicates that isostatic rebound after the loss of the main portion of the West Antarctic ice sheet would ultimately add another {{convert|1.02|m|ftin|abbr=on}} to global sea levels. This effect would start to increase sea levels before 2100. However it would take 1000 years for it to cause {{convert|83|cm|ftin|abbr=on}} of sea level rise. At this point, West Antarctica itself would be {{convert|610|m|ftin|abbr=on}} higher than now. Estimates of isostatic rebound after the loss of East Antarctica's subglacial basins suggest increases of between {{convert|8|cm|ftin|abbr=on}} and {{convert|57|cm|ftin|abbr=on}}<ref name="Pan2021" />

=== Greenland ice sheet loss ===
[[File:Greenland ssi 2007.jpg|thumb|upright=1.05|Greenland 2007 melt, measured as the difference between the number of days on which melting occurred in 2007 compared to the average annual melting days from 1988 to 2006<ref>{{cite web|url=https://earthobservatory.nasa.gov/newsroom|title=NASA Earth Observatory - Newsroom|date=18 January 2019|website=earthobservatory.nasa.gov}}</ref>]]
Most ice on Greenland is in the [[Earth:Greenland ice sheet|Greenland ice sheet]] which is {{Convert|3|km|ft|abbr=on|sigfig=1}} at its thickest. The rest of Greenland ice forms isolated glaciers and ice caps. The average annual ice loss in Greenland more than doubled in the early 21st century compared to the 20th century.<ref>{{cite journal |last1=Kjeldsen |first1=Kristian K. |last2=Korsgaard |first2=Niels J. |last3=Bjørk |first3=Anders A. |last4=Khan |first4=Shfaqat A. |last5=Box |first5=Jason E. |last6=Funder |first6=Svend |last7=Larsen |first7=Nicolaj K. |last8=Bamber |first8=Jonathan L. |last9=Colgan |first9=William |last10=van den Broeke |first10=Michiel |last11=Siggaard-Andersen |first11=Marie-Louise |last12=Nuth |first12=Christopher |last13=Schomacker |first13=Anders |last14=Andresen |first14=Camilla S. |last15=Willerslev |first15=Eske |last16=Kjær |first16=Kurt H. |title=Spatial and temporal distribution of mass loss from the Greenland Ice Sheet since AD 1900 |journal=Nature |date=16 December 2015 |volume=528 |issue=7582 |pages=396–400 |doi=10.1038/nature16183 |pmid=26672555 |bibcode=2015Natur.528..396K |hdl=10852/50174 |s2cid=4468824 |url=https://research-information.bris.ac.uk/en/publications/spatial-and-temporal-distribution-of-mass-loss-from-the-greenland-ice-sheet-since-ad-1900(29ed76ed-b8f7-4b99-bf59-a275b0a22ce7).html }}</ref> Its  contribution to sea level rise correspondingly increased from 0.07&nbsp;mm per year between 1992 and 1997 to 0.68&nbsp;mm per year between 2012 and 2017. Total ice loss from the Greenland ice sheet between 1992 and 2018 amounted to 3,902 gigatons (Gt) of ice. This is equivalent to a SLR contribution of 10.8&nbsp;mm.<ref>{{Cite journal|last1=Shepherd|first1=Andrew|last2=Ivins|first2=Erik|last3=Rignot|first3=Eric|last4=Smith|first4=Ben|last5=van den Broeke|first5=Michiel|last6=Velicogna|first6=Isabella|last7=Whitehouse|first7=Pippa|last8=Briggs|first8=Kate|last9=Joughin|first9=Ian|last10=Krinner|first10=Gerhard|last11=Nowicki|first11=Sophie|date=2020-03-12|title=Mass balance of the Greenland Ice Sheet from 1992 to 2018|journal=Nature|language=en|volume=579|issue=7798|pages=233–239|doi=10.1038/s41586-019-1855-2|pmid=31822019|hdl=2268/242139|s2cid=219146922|issn=1476-4687|url=https://orbi.uliege.be/handle/2268/242139}}</ref> The contribution for the 2012–2016 period was equivalent to 37% of sea level rise from ''land ice'' sources (excluding thermal expansion).<ref name="Bamber2018">{{cite journal |last1=Bamber |first1=Jonathan L |last2=Westaway |first2=Richard M |last3=Marzeion |first3=Ben |last4=Wouters |first4=Bert |title=The land ice contribution to sea level during the satellite era |journal=Environmental Research Letters |date=1 June 2018 |volume=13 |issue=6 |page=063008 |doi=10.1088/1748-9326/aac2f0 |bibcode=2018ERL....13f3008B |doi-access=free }}</ref> This observed rate of ice sheet melting is at the higher end of predictions from past IPCC assessment reports.<ref>{{Cite web|url=https://news.uci.edu/2019/12/19/greenland-ice-loss-is-at-worse-case-scenario-levels-study-finds/|title=Greenland ice loss is at 'worse-case scenario' levels, study finds|date=2019-12-19|website=UCI News|language=en-US|access-date=2019-12-28}}</ref><ref name="Slater-2020"/> 

In 2021, AR6 estimated that the Greenland ice sheet would continue to melt and add to sea level rise even under the [[Earth:Shared Socioeconomic Pathways|SSP1-2.6]] emission scenario. This largely fulfils the Paris Agreement goals. Under this scenario Greenland ice sheet melt adds around {{cvt|6|cm|in|frac=2}} to global sea level rise by the end of the century. It shows a plausible maximum of {{cvt|15|cm|in|frac=2}}. It also shows a very small chance of the ice sheet reducing sea levels by around {{cvt|2|cm|in|frac=2}} by gaining mass through surface mass balance feedback. The scenario associated with the highest global warming, SSP5-8.5, would see Greenland add at least {{cvt|5|cm|in|frac=2}} to sea level rise. It shows a likely median of {{cvt|13|cm|in|frac=2}} cm and a plausible maximum of {{cvt|23|cm|in|frac=2}}.<ref name="IPCC AR6 WG1 Ch.9" />
[[File:Mass changes of the Greenland Ice Sheet between 2002 and 2019.webp|thumb|left|Trends of Greenland ice loss between 2002 and 2019<ref>{{cite journal |last1=Sasgen |first1=Ingo |last2=Wouters |first2=Bert |last3=Gardner |first3=Alex S. |last4=King |first4=Michalea D. |last5=Tedesco |first5=Marco |last6=Landerer |first6=Felix W. |last7=Dahle |first7=Christoph |last8=Save |first8=Himanshu |last9=Fettweis |first9=Xavier |date=20 August 2020 |title=Return to rapid ice loss in Greenland and record loss in 2019 detected by the GRACE-FO satellites |journal=Communications Earth & Environment  |volume=1 |issue=1 |page=8 |doi=10.1038/s43247-020-0010-1 |bibcode=2020ComEE...1....8S |s2cid=221200001 |language=en |issn=2662-4435|doi-access=free }} 50px Text and images are available under a [https://creativecommons.org/licenses/by/4.0/  Creative Commons Attribution 4.0 International License].</ref>]]
Greenland's peripheral glaciers and ice caps crossed an irreversible tipping point around 1997. So they are already causing unstoppable sea level rise.<ref>{{cite journal |last1=Noël |first1=B. |last2=van de Berg |first2=W. J |last3=Lhermitte |first3=S. |last4=Wouters |first4=B. |last5=Machguth |first5=H. |last6=Howat |first6=I. |last7=Citterio |first7=M. |last8=Moholdt |first8=G. |last9=Lenaerts |first9=J. T. M. |last10=van den Broeke |first10=M. R. |title=A tipping point in refreezing accelerates mass loss of Greenland's glaciers and ice caps |journal=Nature Communications |date=31 March 2017 |volume=8 |issue=1 |page=14730 |doi=10.1038/ncomms14730 |pmid=28361871 |pmc=5380968 |bibcode=2017NatCo...814730N }}</ref><ref>{{cite news |title=Warming Greenland ice sheet passes point of no return|url=https://news.osu.edu/warming-greenland-ice-sheet-passes-point-of-no-return/|date=13 August 2020|access-date=15 August 2020 |work=Ohio State University}}</ref><ref>{{cite journal|last1=King|first1=Michalea D.|last2=Howat|first2=Ian M.|last3=Candela|first3=Salvatore G.|last4=Noh|first4=Myoung J.|last5=Jeong|first5=Seongsu|last6=Noël|first6=Brice P. Y.|last7=van den Broeke|first7=Michiel R.|last8=Wouters|first8=Bert|last9=Negrete|first9=Adelaide|date=13 August 2020|title=Dynamic ice loss from the Greenland Ice Sheet driven by sustained glacier retreat|journal=Communications Earth & Environment|language=en|volume=1|issue=1|pages=1–7|doi=10.1038/s43247-020-0001-2|bibcode=2020ComEE...1....1K |issn=2662-4435|doi-access=free}} [[File:CC-BY icon.svg|50x50px]] Text and images are available under a Creative Commons Attribution 4.0 International License.</ref> However the temperature changes in future, the warming of 2000–2019 had already damaged the ice sheet enough for it to eventually lose ~3.3% of its volume. This is leading to {{cvt|27|cm|in|frac=2}} of future sea level rise.<ref>{{cite journal |last1=Box |first1=Jason E. |last2=Hubbard |first2=Alun |last3=Bahr |first3=David B. |last4=Colgan |first4=William T. |last5=Fettweis |first5=Xavier |last6=Mankoff |first6=Kenneth D. |last7=Wehrlé |first7=Adrien |last8=Noël |first8=Brice |last9=van den Broeke |first9=Michiel R. |last10=Wouters |first10=Bert |last11=Bjørk |first11=Anders A. |last12=Fausto |first12=Robert S. |title=Greenland ice sheet climate disequilibrium and committed sea-level rise |url=https://www.nature.com/articles/s41558-022-01441-2 |journal=Nature Climate Change |date=29 August 2022 |volume=12 |issue=9 |pages=808–813 |doi=10.1038/s41558-022-01441-2 |bibcode=2022NatCC..12..808B |s2cid=251912711 }}</ref> At a certain level of global warming, the Greenland ice sheet will almost completely melt. Ice cores show this happened at least once during the last million years, even though temperatures have not been higher than {{convert|2.5|C-change|F-change}} above preindustrial levels.<ref>{{Cite journal|last1=Irvalı|first1=Nil|last2=Galaasen|first2=Eirik V.|last3=Ninnemann|first3=Ulysses S.|last4=Rosenthal|first4=Yair|last5=Born|first5=Andreas|last6=Kleiven|first6=Helga (Kikki) F.|date=2019-12-18|title=A low climate threshold for south Greenland Ice Sheet demise during the Late Pleistocene|journal=Proceedings of the National Academy of Sciences|volume=117|issue=1|pages=190–195|language=en|doi=10.1073/pnas.1911902116|issn=0027-8424|pmid=31871153|pmc=6955352|doi-access=free}}</ref><ref name="Christ2021">{{cite journal |last1=Christ |first1=Andrew J. |last2=Bierman |first2=Paul R. |last3=Schaefer |first3=Joerg M.|last4=Dahl-Jensen |first4=Dorthe |last5=Steffensen |first5=Jørgen P. |last6=Corbett |first6=Lee B. |last7=Peteet |first7=Dorothy M. |last8=Thomas |first8=Elizabeth K. |last9=Steig |first9=Eric J. |last10=Rittenour |first10=Tammy M. |last11=Tison |first11=Jean-Louis |last12=Blard |first12=Pierre-Henri |last13=Perdrial |first13=Nicolas |last14=Dethier |first14=David P. |last15=Lini |first15=Andrea |last16=Hidy |first16=Alan J. |last17=Caffee |first17=Marc W. |last18=Southon |first18=John |title=A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century |journal=Proceedings of the National Academy of Sciences of the United States|date=30 March 2021 |volume=118 |issue=13 |pages=e2021442118 |doi=10.1073/pnas.2021442118 |pmid=33723012 |pmc=8020747 |bibcode=2021PNAS..11821442C |doi-access=free }}</ref> 

2012 research suggested that the tipping point of the ice sheet was between {{convert|0.8|C-change|F-change}} and {{convert|3.2|C-change|F-change}}.<ref>{{cite journal |last1=Robinson |first1=Alexander |last2=Calov |first2=Reinhard |last3=Ganopolski |first3=Andrey |title=Multistability and critical thresholds of the Greenland ice sheet |journal=Nature Climate Change |date=11 March 2012 |volume=2 |issue=6 |pages=429–432 |doi=10.1038/nclimate1449 |bibcode=2012NatCC...2..429R }}</ref> 2023 modelling has narrowed the tipping threshold to a {{convert|1.7|C-change|F-change}}-{{convert|2.3|C-change|F-change}} range. If temperatures reach or exceed that level, reducing the global temperature to {{convert|1.5|C-change|F-change}} above pre-industrial levels or lower would prevent the loss of the entire ice sheet. One way to do this in theory would be large-scale [[Earth:Carbon dioxide removal|carbon dioxide removal]]. But it would also cause greater losses and sea level rise from Greenland than if the threshold was not breached in the first place.<ref name="Bochow2023">{{cite journal |last1=Bochow |first1=Nils |last2=Poltronieri |first2=Anna |last3=Robinson |first3=Alexander |last4=Montoya |first4=Marisa |last5=Rypdal |first5=Martin |last6=Boers |first6=Niklas |date=18 October 2023 |title=Overshooting the critical threshold for the Greenland ice sheet |journal=Nature |volume=622 |issue=7983 |pages=528–536 |bibcode=2023Natur.622..528B |doi=10.1038/s41586-023-06503-9 |pmc=10584691 |pmid=37853149}}</ref> Otherwise, the ice sheet would take between 10,000 and 15,000 years to disintegrate entirely once the tipping point had been crossed. The most likely estimate is 10,000 years.<ref name="ArmstrongMcKay2022" /><ref name="ArmstrongMcKayExplainer" /> If climate change continues along its worst trajectory and temperatures continue to rise fast for a long time, it would only take 1,000 years.<ref name="Aschwanden2019">{{Cite journal |last1=Aschwanden |first1=Andy |last2=Fahnestock |first2=Mark A. |last3=Truffer |first3=Martin |last4=Brinkerhoff |first4=Douglas J. |last5=Hock |first5=Regine |last6=Khroulev |first6=Constantine |last7=Mottram |first7=Ruth |last8=Khan |first8=S. Abbas |date=19 June 2019 |title=Contribution of the Greenland Ice Sheet to sea level over the next millennium |journal=Science Advances |volume=5 |issue=6 |pages=218–222 |language=EN |doi=10.1126/sciadv.aav9396 |pmid=31223652 |pmc=6584365 |bibcode=2019SciA....5.9396A }}</ref>

===Mountain glacier loss===
[[File:2015-2100 Impacts of global warming on glaciers and sea level rise.svg|thumb|Based on national pledges to reduce greenhouse gas emissions, global mean temperature is projected to increase by {{convert|2.7|C-change|F-change}}, which would cause loss of about half of Earth's glaciers by 2100—causing a sea level rise of 115±40 millimeters.<ref name=Science_20230105>{{cite journal |last1=Rounce |first1=David R. |last2=Hock |first2=Regine |last3=Maussion |first3=Fabien |last4=Hugonnet |first4=Romain |last5=Kochtitzky |first5=William |last6=Huss |first6=Matthias |last7=Berthier |first7=Etienne |last8=Brinkerhoff |first8=Douglas |last9=Compagno |first9=Loris |last10=Copland |first10=Luke |last11=Farinotti |first11=Daniel |last12=Menounos |first12=Brian |last13=McNabb |first13=Robert W. |display-authors=4 |title=Global glacier change in the 21st century: Every increase in temperature matters |journal=Science |date=5 January 2023 |volume=379 |issue=6627 |pages=78–83 |doi=10.1126/science.abo1324 |pmid=36603094 |bibcode=2023Sci...379...78R |s2cid=255441012 |url=https://www.science.org/doi/10.1126/science.abo1324}}</ref>]]

There are roughly 200,000 glaciers on Earth, which are spread out across all continents.<ref name="Huss-2015">{{cite journal |last1=Huss |first1=Matthias |last2=Hock |first2=Regine |title=A new model for global glacier change and sea-level rise |journal=Frontiers in Earth Science |date=30 September 2015 |volume=3 |page=54 |doi=10.3389/feart.2015.00054 |bibcode=2015FrEaS...3...54H |s2cid=3256381 |doi-access=free }}</ref> Less than 1% of glacier ice is in mountain glaciers, compared to 99% in Greenland and [[Earth:Antarctica|Antarctica]]. However, this small size also makes mountain glaciers more vulnerable to melting than the larger ice sheets. This means they have had a disproportionate contribution to historical sea level rise and are set to contribute a smaller, but still significant fraction of sea level rise in the 21st century.<ref>{{cite journal |last1=Radić |first1=Valentina |last2=Hock |first2=Regine |title=Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise |journal=Nature Geoscience |date=9 January 2011 |volume=4 |issue=2 |pages=91–94 |doi=10.1038/ngeo1052 |bibcode=2011NatGe...4...91R }}</ref> Observational and modelling studies of [[Earth:Retreat of glaciers since 1850|mass loss from glaciers and ice caps]] show they contribute 0.2-0.4&nbsp;mm per year to sea level rise, averaged over the 20th century.<ref>{{cite report |doi=10.7265/N52N506F |year=2002 |last1=Dyurgerov |first1=Mark |title=Glacier Mass Balance and Regime Measurements and Analysis, 1945-2003 }}</ref> The contribution for the 2012–2016 period was nearly as large as that of Greenland. It was 0.63&nbsp;mm of sea level rise per year, equivalent to 34% of sea level rise from ''land ice'' sources.<ref name="Bamber2018" /> Glaciers contributed around 40% to sea level rise during the 20th century, with estimates for the 21st century of around 30%.<ref name="WCRP2018"/> 

In 2023, a ''Science'' paper estimated that at {{convert|1.5|C-change|F-change}}, one quarter of mountain glacier mass would be lost by 2100 and nearly half would be lost at {{convert|4|C-change|F-change}}, contributing ~{{cvt|9|cm|in|frac=2}} and ~{{cvt|15|cm|in|frac=2}} to sea level rise, respectively. Glacier mass is disproportionately concentrated in the most resilient glaciers. So in practice this would remove 49-83% of glacier formations. It further estimated that the current likely trajectory of {{convert|2.7|C-change|F-change}} would result in the SLR contribution of ~{{cvt|11|cm|in|frac=2}} by 2100.<ref>{{Cite journal |last1=Rounce |first1=David R. |last2=Hock |first2=Regine |last3=Maussion |first3=Fabien |last4=Hugonnet |first4=Romain |last5=Kochtitzky |first5=William |last6=Huss |first6=Matthias |last7=Berthier|first7=Etienne |last8=Brinkerhoff |first8=Douglas |last9=Compagno |first9=Loris |last10=Copland |first10=Luke |last11=Farinotti |first11=Daniel |last12=Menounos |first12=Brian |last13=McNabb |first13=Robert W. |date=5 January 2023 |title=Global glacier change in the 21st century: Every increase in temperature matters |url=https://www.science.org/doi/10.1126/science.abo1324 |journal=Science |language=en |volume=79 |issue=6627 |pages=78–83 |doi=10.1126/science.abo1324 |pmid=36603094 |bibcode=2023Sci...379...78R |s2cid=255441012 }}</ref> Mountain glaciers are even more vulnerable over the longer term. In 2022, another ''Science'' paper estimated that almost no mountain glaciers could survive once warming crosses {{convert|2|C-change|F-change}}. Their complete loss is largely inevitable around {{convert|3|C-change|F-change}}. There is even a possibility of complete loss after 2100 at just {{convert|1.5|C-change|F-change}}. This could happen as early as 50 years after the tipping point is crossed, although 200 years is the most likely value, and the maximum is around 1000 years.<ref name="ArmstrongMcKay2022" /><ref name="ArmstrongMcKayExplainer" />

=== Sea ice loss ===
Sea ice loss contributes very slightly to global sea level rise. If the melt water from ice floating in the sea was exactly the same as sea water then, according to [[Physics:Archimedes' principle|Archimedes' principle]], no rise would occur. However melted sea ice contains less [[Earth:Salinity|dissolved salt]] than sea water and is therefore less [[Physics:Density|dense]], with a slightly greater volume per unit of mass. If all floating [[Earth:Ice shelf|ice shelves]] and icebergs were to melt sea level would only rise by about {{convert|4|cm|in|frac=2|abbr=on}}.<ref>{{cite journal |last1=Noerdlinger |first1=Peter D. |last2=Brower |first2=Kay R. |title=The melting of floating ice raises the ocean level |journal=Geophysical Journal International |date=July 2007 |volume=170 |issue=1 |pages=145–150 |doi=10.1111/j.1365-246X.2007.03472.x |bibcode=2007GeoJI.170..145N |doi-access=free }}</ref>
[[File:Trends-in-land-water-storage-from-GRACE-observations,-April-2002-to-November-2014.jpg|thumb|upright=1.35|right|Trends in land water storage from [[Physics:Gravity Recovery and Climate Experiment|GRACE]] observations in gigatons per year, April 2002 to November 2014 (glaciers and ice sheets are excluded).]]

=== Changes to land water storage ===
Human activity impacts how much water is stored on land. Dams retain large quantities of water, which is stored on land rather than flowing into the sea, though the total quantity stored will vary from time to time. On the other hand, humans extract water from lakes, [[Earth:Wetland|wetland]]s and [[Earth:Aquifer|underground reservoirs]] for food production. This often causes [[Subsidence|subsidence]]. Furthermore, the [[Physics:Water cycle|hydrological cycle]] is influenced by climate change and deforestation. This can increase or reduce contributions to sea level rise. In the 20th century, these processes roughly balanced, but dam building has slowed down and is expected to stay low for the 21st century.<ref>{{cite journal |last1=Wada |first1=Yoshihide |last2=Reager |first2=John T. |last3=Chao |first3=Benjamin F. |last4=Wang |first4=Jida |last5=Lo |first5=Min-Hui |last6=Song |first6=Chunqiao |last7=Li |first7=Yuwen |last8=Gardner |first8=Alex S. |title=Recent Changes in Land Water Storage and its Contribution to Sea Level Variations |journal=Surveys in Geophysics |date=15 November 2016 |volume=38 |issue=1 |pages=131–152 |doi=10.1007/s10712-016-9399-6 |pmid=32269399 |pmc=7115037 }}</ref><ref name="ipcc13" />{{rp|1155}}

Water redistribution caused by irrigation from 1993 to 2010 caused a drift of Earth's [[Earth:Geographical pole|rotational pole]] by {{convert|78.48|cm|in}}. This caused groundwater depletion equivalent to a global sea level rise of {{convert|6.24|mm|inches}}.<ref name=GeophysRschLtrs_20230615>{{cite journal |last1=Seo |first1=Ki-Weon |last2=Ryu |first2=Dongryeol |last3=Eom |first3=Jooyoung |last4=Jeon |first4=Taewhan |last5=Kim |first5=Jae-Seung |last6=Youm |first6=Kookhyoun |last7=Chen |first7=Jianli |last8=Wilson |first8=Clark R. |title=Drift of Earth's Pole Confirms Groundwater Depletion as a Significant Contributor to Global Sea Level Rise 1993–2010 |journal=Geophysical Research Letters |date=15 June 2023 |volume=50 |issue=12 |page=e2023GL103509 |doi=10.1029/2023GL103509 |bibcode=2023GeoRL..5003509S |s2cid=259275991 |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023GL103509}}</ref>

{{clear}}

== Impacts ==
[[File:1950- High tide flooding, by year - NOAA tide gauges (U.S.).svg|thumb|left|High tide flooding, also called tidal flooding, has become much more common in the past seven decades.<ref name="N0AAHighTideFlooding201802">{{cite web |last1=Sweet |first1=William V. |last2=Dusek |first2=Greg |last3=Obeysekera |first3=Jayantha |last4=Marra |first4=John J. |title=Patterns and Projections of High Tide Flooding Along the U.S. Coastline Using a Common Impact Threshold |url=https://tidesandcurrents.noaa.gov/publications/techrpt86_PaP_of_HTFlooding.pdf |website=tidesandcurrents.NOAA.gov |publisher=National Oceanic and Atmospheric Administration (NOAA) |archive-url=https://web.archive.org/web/20221015221519/https://tidesandcurrents.noaa.gov/publications/techrpt86_PaP_of_HTFlooding.pdf |archive-date=15 October 2022 |page=4 |date=February 2018 |quote=Fig. 2b |url-status=live }}</ref>]]
The impacts of sea level rise include higher and more frequent high-tide and [[Physics:Storm surge|storm-surge]] flooding, increased [[Earth:Coastal erosion|coastal erosion]], inhibition of [[Earth:Primary production|primary production]] processes, more extensive coastal inundation, along with changes in surface [[Earth:Water quality|water quality]] and [[Earth:Groundwater|groundwater]]. These can lead to a greater loss of property and coastal habitats, loss of life during floods and loss of cultural resources. Agriculture and aquaculture can also be impacted. There can also be loss of tourism, recreation, and transport related functions.<ref name="IPCC-2001">{{Cite report|url=https://www.ipcc.ch/site/assets/uploads/2018/03/WGI_TAR_full_report.pdf|title=TAR Climate Change 2001: The Scientific Basis|date=2001|publisher=International Panel on Climate Change, Cambridge University Press|isbn=0521-80767-0|access-date=23 July 2021}}</ref>{{rp|356}} Coastal flooding impacts are exacerbated by land use changes such as urbanisation or deforestation of low-lying coastal zones. Regions that are already vulnerable to the rising sea level also struggle with coastal flooding washing away land and altering the landscape.<ref>{{Cite journal|last=Wu|first=Tao|date=October 2021|title=Quantifying coastal flood vulnerability for climate adaptation policy using principal component analysis|url=https://linkinghub.elsevier.com/retrieve/pii/S1470160X21006713|journal=Ecological Indicators|language=en|volume=129|page=108006|doi=10.1016/j.ecolind.2021.108006}}</ref>

Because the projected extent of sea level rise by 2050 will be only slightly affected by any changes in emissions,<ref name="us nrc 2011 long term slr" /> there is confidence that 2050 levels of SLR combined with the 2010 population distribution (i.e. absent the effects of population growth and [[Biology:Human migration|human migration]]) would result in ~150&nbsp;million people under the water line during high tide and ~300&nbsp;million in places which are flooded every year—an increase of 40 and 50 million people relative to 2010 values for the same.<ref name="Kulp2019">{{cite journal |last1=Kulp |first1=Scott A. |last2=Strauss |first2=Benjamin H. |title=New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding |journal=Nature Communications |date=29 October 2019 |volume=10 |issue=1 |page=4844 |doi=10.1038/s41467-019-12808-z |pmid=31664024 |pmc=6820795 |bibcode=2019NatCo..10.4844K }}</ref><ref>{{cite news|url=https://www.ecowatch.com/sea-level-rise-predictions-2641159739.html|title=300 Million People Worldwide Could Suffer Yearly Flooding by 2050|last1=Rosane|first1=Olivia|date=October 30, 2019|access-date=31 October 2019|agency=Ecowatch}}</ref> By 2100, there would be another 40 million people under the water line during high tide if sea level rise remains low, and 80 million for a high estimate of the median sea level rise.<ref name="Kulp2019" /> If ice sheet processes under the highest [[Software:Climate change scenario|emission scenario]] result in sea level rise of well over {{convert|1|m|ft|frac=4|spell=in}} by 2100, with a chance of levels over {{convert|2|m|ft|frac=2|spell=in}},<ref name="NOAA-2022" /><ref name="IPCC_2021_WGI_SPM" />{{rp|TS-45}} then as many as 520 million additional people would end up under the water line during high tide and 640&nbsp;million in places which are flooded every year, when compared to the 2010 population distribution.<ref name="Kulp2019" />
[[File:Major cities threatened by sea level rise.png|thumb|upright=1.35|Major cities threatened by sea level rise. The cities indicated are under threat of even a small sea level rise (of 1.6 feet/49&nbsp;cm) compared to the level in 2010. Even moderate projections indicate that such a rise will have occurred by 2060.<ref>:File:Projections of global mean sea level rise by Parris et al. (2012).png</ref><ref>{{Cite web|url=https://skepticalscience.com/sea-level-rise-predictions.htm|title=How much will sea levels rise in the 21st Century?|website=Skeptical Science}}</ref>]]
Over the longer term, coastal areas are particularly vulnerable to rising sea levels, changes in the frequency and intensity of storms, increased precipitation, and rising [[Earth:Ocean temperature|ocean temperature]]s. Ten percent of the world's population live in coastal areas that are less than {{Convert|10|m|ft}} above sea level. Furthermore, two-thirds of the world's cities with over five million people are located in these low-lying coastal areas.<ref>{{cite journal |last1=McGranahan |first1=Gordon |last2=Balk |first2=Deborah |last3=Anderson |first3=Bridget |title=The rising tide: assessing the risks of climate change and human settlements in low elevation coastal zones |journal=Environment and Urbanization |date=29 June 2016 |volume=19 |issue=1 |pages=17–37 |doi=10.1177/0956247807076960 |s2cid=154588933 }}</ref> In total, approximately 600 million people live directly on the coast around the world.<ref>{{cite news |last1=Sengupta |first1=Somini |others=Photographer: Chang W. Lee|title=A Crisis Right Now: San Francisco and Manila Face Rising Seas |url=https://www.nytimes.com/interactive/2020/02/13/climate/manila-san-francisco-sea-level-rise.html |access-date=4 March 2020 |work=The New York Times |date=13 February 2020}}</ref> Cities such as Miami, Rio de Janeiro, {{wipe|Osaka}} and [[Place:Shanghai|Shanghai]] will be especially vulnerable later in the century under the warming of 3&nbsp;°C (5.4&nbsp;°F), which is close to the current trajectory.<ref name="Holder-2017">{{Cite news|last1=Holder|first1=Josh|last2=Kommenda|first2=Niko|last3=Watts|first3=Jonathan|date=3 November 2017|title=The three-degree world: cities that will be drowned by global warming|work=The Guardian|url=https://www.theguardian.com/cities/ng-interactive/2017/nov/03/three-degree-world-cities-drowned-global-warming|access-date=2018-12-28}}</ref><ref name="CAT" /> Altogether, [[Engineering:Lidar|LiDAR]]-based research had established in 2021 that 267 million people worldwide lived on land less than {{cvt|2|m|ft|frac=2}} above sea level and that with a {{cvt|1|m|ft|frac=2}} sea level rise and zero population growth, that number could increase to 410 million people.<ref>{{Cite web|last=Storer|first=Rhi|date=2021-06-29|title=Up to 410 million people at risk from sea level rises – study|url=http://www.theguardian.com/environment/2021/jun/29/risk-from-sea-level-rises-unless-emissions-reduced|access-date=2021-07-01|website=The Guardian|language=en}}</ref><ref>{{Cite journal|last1=Hooijer|first1=A.|last2=Vernimmen|first2=R.|date=2021-06-29|title=Global LiDAR land elevation data reveal greatest sea-level rise vulnerability in the tropics|journal=Nature Communications|language=en|volume=12|issue=1|page=3592|doi=10.1038/s41467-021-23810-9|pmid=34188026|pmc=8242013|bibcode=2021NatCo..12.3592H|issn=2041-1723}}</ref>

Even populations who live further inland may be impacted by a potential disruption of sea trade, and by migrations. In 2023, United Nations secretary general António Guterres warned that sea level rises risk causing human migrations on a "biblical scale".<ref>{{Cite news|last1=Carrington|first1=Damian|date=14 February 2023|title=Rising seas threaten 'mass exodus on a biblical scale', UN chief warns|work=The Guardian|url=https://www.theguardian.com/environment/2023/feb/14/rising-seas-threaten-mass-exodus-on-a-biblical-scale-un-chief-warns|access-date=2023-02-25}}</ref> Sea level rise will inevitably affect [[Engineering:Port|port]]s, but the current research into this subject is limited. Not enough is known about the investments required to protect the ports currently in use, and for how they may be protected before it becomes more reasonable to build new port facilities elsewhere.<ref>{{Cite journal|last1=Xia|first1=Wenyi|last2=Lindsey|first2=Robin|date=October 2021|title=Port adaptation to climate change and capacity investments under uncertainty|url=https://linkinghub.elsevier.com/retrieve/pii/S0191261521001600|journal=Transportation Research Part B: Methodological|language=en|volume=152|pages=180–204|doi=10.1016/j.trb.2021.08.009|s2cid=239647501}}</ref><ref>{{Cite web|title=Chapter 4: Sea Level Rise and Implications for Low-Lying Islands, Coasts and Communities — Special Report on the Ocean and Cryosphere in a Changing Climate|url=https://www.ipcc.ch/srocc/chapter/chapter-4-sea-level-rise-and-implications-for-low-lying-islands-coasts-and-communities/|access-date=2021-12-17}}</ref> Moreover, some coastal regions are rich agricultural lands, whose loss to the sea can result in food shortages elsewhere. This is a particularly acute issue for river deltas such as [[Place:Nile Delta|Nile Delta]] in [[Place:Egypt|Egypt]] and Red River and Mekong Deltas in Vietnam, which are disproportionately affected by saltwater intrusion into the soil and [[Earth:Irrigation|irrigation]] water.<ref name="Michaelson-2018" /><ref name="Nagothu-2017">{{Cite web |last=Nagothu |first=Udaya Sekhar |date=2017-01-18 |title=Food security threatened by sea-level rise |url=https://www.nibio.no/nyheter/food-security-threatened-by-sea-level-rise |access-date=2018-10-21 |publisher=Nibio}}</ref>

===Ecosystems===
[[File:Bramble-cay-melomys.jpg|thumb|left|Bramble Cay melomys, the first known mammal species to go extinct due to sea level rise.]]
When seawater reaches inland, [[Earth:Coast|coast]]al plants, birds, and freshwater/estuarine fish are threatened with habitat loss due to flooding and soil/water salinization.<ref name="National Geographic-2017">{{Cite web|url=https://www.nationalgeographic.com/environment/global-warming/sea-level-rise/|archive-url=https://web.archive.org/web/20170117004107/http://www.nationalgeographic.com/environment/global-warming/sea-level-rise/|archive-date=January 17, 2017|title=Sea Level Rise|date=January 13, 2017|website=National Geographic}}</ref> So-called ghost forests emerge when coastal [[Earth:Forest|forest]] areas become inundated with saltwater to the point no trees can survive.<ref>{{cite web|url=http://grist.org/article/ghost-forests-are-eerie-evidence-of-rising-seas/|title=Ghost forests are eerie evidence of rising seas|date=18 September 2016|website=Grist.org|access-date=2017-05-17}}</ref><ref>{{cite web|url=http://e360.yale.edu/features/ghost_forest_rising_sea_levels_killing_coastal_woodlands|title=How Rising Seas Are Killing Southern U.S. Woodlands - Yale E360|website=e360.yale.edu|access-date=2017-05-17}}</ref> Starting around 2050, some nesting sites in Florida, Cuba, Ecuador and the island of Sint Eustatius for leatherback, loggerhead, hawksbill, green and olive ridley turtles are expected to be flooded, and the proportion would only increase over time.<ref>{{Cite journal |last1=Rivas |first1=Marga L. |last2=Rodríguez-Caballero |first2=Emilio |last3=Esteban |first3=Nicole |last4=Carpio |first4=Antonio J. |last5=Barrera-Vilarmau |first5=Barbara |last6=Fuentes |first6=Mariana M. P. B. |last7=Robertson |first7=Katharine |last8=Azanza |first8=Julia |last9=León |first9=Yolanda |last10=Ortega |first10=Zaida |date=2023-04-20 |title=Uncertain future for global sea turtle populations in face of sea level rise |journal=Scientific Reports |language=en |volume=13 |issue=1 |page=5277 |doi=10.1038/s41598-023-31467-1 |pmid=37081050 |pmc=10119306 |bibcode=2023NatSR..13.5277R |issn=2045-2322}}</ref> And in 2016, Bramble Cay islet in the Great Barrier Reef was inundated, flooding the habitat of a rodent named [[Biology:Bramble Cay melomys|Bramble Cay melomys]].<ref>{{cite web|url=http://www.australiangeographic.com.au/news/2016/06/extinct-bramble-cay-melomys|title=Extinct: Bramble Cay melomys|last=Smith|first=Lauren|date=2016-06-15|website=Australian Geographic|access-date=2016-06-17}}</ref> In 2019, it was officially declared extinct.<ref>{{Cite web|url=https://www.smh.com.au/environment/climate-change/our-little-brown-rat-first-climate-change-caused-mammal-extinction-20190219-p50yry.html|title='Our little brown rat': first climate change-caused mammal extinction|last=Hannam|first=Peter|date=2019-02-19|website=The Sydney Morning Herald|language=en|access-date=2019-06-25}}</ref>
[[File:Mangroves.jpg|thumb|An example of mangrove pneumatophores.]]
While some ecosystems can move land inward with the high-water mark, many are prevented from migrating due to natural or artificial barriers. This coastal narrowing, sometimes called 'coastal squeeze' when considering human-made barriers, could result in the loss of habitats such as [[Earth:Mudflat|mudflat]]s and [[Earth:Tidal marsh|tidal marsh]]es.<ref name="birdlife-2015">{{Cite web|url=http://datazone.birdlife.org/sea-level-rise-poses-a-major-threat-to-coastal-ecosystems-and-the-biota-they-support|title=Sea level rise poses a major threat to coastal ecosystems and the biota they support|date=2015|website=birdlife.org|publisher=Birdlife International}}</ref><ref>{{cite journal |last1=Pontee |first1=Nigel |title=Defining coastal squeeze: A discussion |journal=Ocean & Coastal Management |date=November 2013 |volume=84 |pages=204–207 |doi=10.1016/j.ocecoaman.2013.07.010 |bibcode=2013OCM....84..204P }}</ref> [[Earth:Mangrove|Mangrove]] ecosystems on the mudflats of tropical coasts nurture high [[Biology:Biodiversity|biodiversity]], yet they are particularly vulnerable due to mangrove plants' reliance on breathing roots or pneumatophores, which will be submerged if the rate is too rapid for them to migrate upward, resulting in the loss of an ecosystem.<ref>{{Cite web|url=https://www.nrc.govt.nz/for-schools/school-information-packs/mangroves/|title=Mangroves - Northland Regional Council|website=www.nrc.govt.nz}}</ref><ref name="High mangrove density enhances surf">{{cite journal |last1=Kumara |first1=M. P. |last2=Jayatissa |first2=L. P. |last3=Krauss |first3=K. W. |last4=Phillips |first4=D. H. |last5=Huxham |first5=M. |title=High mangrove density enhances surface accretion, surface elevation change, and tree survival in coastal areas susceptible to sea-level rise |journal=Oecologia |pages=545–553 |date=2010|volume=164 |issue=2 |doi=10.1007/s00442-010-1705-2 |jstor=40864709 |pmid=20593198 |bibcode=2010Oecol.164..545K |s2cid=6929383 }}</ref><ref>{{cite journal |last1=Krauss |first1=Ken W. |last2=McKee |first2=Karen L. |last3=Lovelock |first3=Catherine E. |last4=Cahoon |first4=Donald R. |last5=Saintilan |first5=Neil |last6=Reef |first6=Ruth |last7=Chen |first7=Luzhen |title=How mangrove forests adjust to rising sea level |journal=New Phytologist |date=April 2014 |volume=202 |issue=1 |pages=19–34 |doi=10.1111/nph.12605 |pmid=24251960 |url=https://digitalcommons.unl.edu/usgsstaffpub/986 }}</ref><ref name="A Conceptual Model for the Response">{{cite journal|last1=Soares|first1=M.L.G.|date=2009|title=A Conceptual Model for the Responses of Mangrove Forests to Sea Level Rise|journal=Journal of Coastal Research|pages=267–271|jstor=25737579}}</ref> Both mangroves and [[Earth:Tidal marsh|tidal marsh]]es protect against storm surges, waves and tsunamis, so their loss makes the effects of sea level rise worse.<ref>{{cite journal |last1=Crosby |first1=Sarah C. |last2=Sax |first2=Dov F. |last3=Palmer |first3=Megan E. |last4=Booth |first4=Harriet S. |last5=Deegan |first5=Linda A. |last6=Bertness |first6=Mark D. |last7=Leslie |first7=Heather M. |title=Salt marsh persistence is threatened by predicted sea-level rise |journal=Estuarine, Coastal and Shelf Science |date=November 2016 |volume=181 |pages=93–99 |doi=10.1016/j.ecss.2016.08.018 |bibcode=2016ECSS..181...93C |doi-access=free }}</ref><ref>{{cite web|url=https://www.nature.org/media/oceansandcoasts/mangroves-for-coastal-defence.pdf|title=Mangroves for coastal defence. Guidelines for coastal managers & policy makers|author1=Spalding, M.|author2=McIvor, A.|date=2014|publisher=[[Organization:Wetlands International|Wetlands International]] and The Nature Conservancy|author3=Tonneijck, F.H.|author4=Tol, S.|author5=van Eijk, P.}}</ref> Human activities, such as dam building, may restrict sediment supplies to wetlands, and thereby prevent natural adaptation processes. The loss of some tidal marshes is unavoidable as a consequence.<ref>{{cite journal |last1=Weston |first1=Nathaniel B. |title=Declining Sediments and Rising Seas: an Unfortunate Convergence for Tidal Wetlands |journal=Estuaries and Coasts |date=16 July 2013 |volume=37 |issue=1 |pages=1–23 |doi=10.1007/s12237-013-9654-8 |s2cid=128615335 }}</ref>

Likewise, [[Biology:Coral|coral]]s, important for bird and fish life, need to grow vertically to remain close to the sea surface in order to get enough energy from sunlight. The corals have so far been able to keep up the vertical growth with the rising seas, but might not be able to do so in the future.<ref>{{Cite book|title=Climate Change 2014: Impacts, Adaptation, and Vulnerability.|last1=Wong|first1=Poh Poh|last2=Losado|first2=I.J.|last3=Gattuso|first3=J.-P.|last4=Hinkel|first4=Jochen|publisher=Cambridge University Press|year=2014|location=New York|chapter=Coastal Systems and Low-Lying Areas|chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar5/wg2/WGIIAR5-Chap5_FINAL.pdf|access-date=2018-10-07|archive-date=2018-11-23|archive-url=https://web.archive.org/web/20181123125554/http://www.ipcc.ch/pdf/assessment-report/ar5/wg2/WGIIAR5-Chap5_FINAL.pdf}}</ref>

=== Regional impacts ===

==== Africa ====
[[File:Dar es Salaam (Aerial).jpg|thumb|Aerial view of the Tanzanian capital Dar es Salaam]]
In [[Earth:Africa|Africa]], risk from sea level rise is amplified by the future population growth. It is believed that 54.2&nbsp;million people lived in the highly exposed low elevation coastal zones (LECZ) around 2000, but this number will effectively double to around 110 million people by 2030, and by 2060 it will be around 185 to 230&nbsp;million people, depending on the extent of population growth. While the average regional sea level rise by 2060 will be around 21&nbsp;cm (with climate change scenarios making little difference at that point), local geography and population trends interact to increase the exposure to hazards like [[100-year flood|100-year flood]]s in a complex way.<ref name="AR6_WGII_Chapter9" />

{{Multiple image
| total_width       = 500
| align             = right
| direction         = horizontal
| image1            = Abidjan des Lagune.jpg
| width1            = 200
| caption1          = Abidjan, the economic powerhouse of Ivory Coast
| image2            = Maputo_seen_from_Katembe_2014.png
| width2            = 300
| caption2          = Maputo, the capital of Mozambique
}}

{| class="wikitable"
|+Populations within 100-year floodplains.<ref name="AR6_WGII_Chapter9" /><ref group="T1">In millions of people. The second and third columns include both the effects of population growth and the increased extent of floodplains by that point.</ref>
!|Country
!|2000
!|2030
!|2060
!|Growth 2000–2060<ref group="T1">The increase in area's population and the highest plausible scenario of population growth.</ref>
|-
|[[Place:Egypt|Egypt]] || 7.4 || 13.8 || 20.7 || 0.28
|-
|Nigeria || 0.1 || 0.3 || 0.9 || 0.84
|-
|Senegal || 0.4 || 1.1 || 2.7 || 0.76
|-
|Benin || 0.1 || 0.6 || 1.6 || 1.12
|-
|Tanzania || 0.2 || 0.9 || 4.3 || 2.3
|-
|Somalia || 0.2 || 0.6 || 2.7 || 1.7
|-
|Cote d'Ivoire || 0.1 || 0.3 || 0.7 || 0.65
|-
|Mozambique || 0.7 || 1.4 || 2.5 || 0.36
|}
{{reflist|group=T1}}
[[File:ANKOMAH 20221122-009.jpg|thumb|346x346px|A man looking out over the beach from a building destroyed by high tides in Chorkor, a suburb of Accra. Sunny day flooding caused by sea level rise, increases coastal erosion that destroys housing, infrastructure and natural ecosystems. A number of communities in Coastal Ghana are already experiencing the changing tides.]]
In the near term, some of the largest displacement is projected to occur in the [[Place:East Africa|East Africa]] region, where at least 750,000 people are likely to be displaced from the coasts between 2020 and 2050. It was also estimated that by 2050, 12 major African cities ([[Place:Abidjan|Abidjan]], [[Place:Alexandria|Alexandria]], [[Place:Algiers|Algiers]], [[Place:Cape Town|Cape Town]], [[Place:Casablanca|Casablanca]], [[Place:Dakar|Dakar]], [[Place:Dar es Salaam|Dar es Salaam]], Durban, [[Place:Lagos|Lagos]], [[Place:Lomé|Lomé]], [[Place:Luanda|Luanda]] and [[Place:Maputo|Maputo]]) would collectively sustain cumulative damages of US$65&nbsp;billion for the "moderate" climate change scenario [[Earth:Representative Concentration Pathway|RCP4.5]] and US$86.5&nbsp;billion for the high-emission scenario RCP8.5: the version of the high-emission scenario with additional impacts from high ice sheet instability would involve up to US$137.5&nbsp;billion in damages. Additional accounting for the "low-probability, high-damage events" may increase aggregate risks to US$187&nbsp;billion for the "moderate" RCP4.5, US$206&nbsp;billion for RCP8.5 and US$397&nbsp;billion under the high-end instability scenario.<ref name="AR6_WGII_Chapter9" /> In all of these estimates, the Egyptian city of Alexandria alone amounts for around half of this figure:<ref name="AR6_WGII_Chapter9" /> hundreds of thousands of people in its low-lying areas may already have to be relocated in the coming decade.<ref name="Michaelson-2018">{{cite news |url=https://www.theguardian.com/global-development/2018/aug/29/alexandria-little-venice-egypt-climate-change-frontline|title=Houses claimed by the canal: life on Egypt's climate change frontline| last=Michaelson| first=Ruth|date=25 August 2018|work={{wipe|The Guardian}}|access-date=30 August 2018}}</ref> Across [[Place:Sub-Saharan Africa|sub-Saharan Africa]] as a whole, damages from sea level rise could reach 2–4% of [[Finance:GDP|GDP]] by 2050, although this is strongly affected by the extent of future [[Finance:Economic growth|economic growth]] and [[Biology:Adaptation|adaptation]].<ref name="AR6_WGII_Chapter9" />
[[File:Leptis Magna amphitheatre - panoramio.jpg|thumb|left|The remains of Leptis Magna amphitheater, with the sea visible in the background]]
In the longer term, [[Place:Egypt|Egypt]], Mozambique and Tanzania are also projected to have the largest number of people affected by annual flooding amongst all African countries if global warming reaches 4&nbsp;°C by the end of the century (a level associated with the RCP8.5 scenario). Under RCP8.5, 10 important cultural sites (Casbah of Algiers, Carthage Archaeological site, Kerkouane, Leptis Magna Archaeological site, Medina of Sousse, Medina of Tunis, Sabratha Archaeological site, Robben Island, Island of Saint-Louis and Tipasa) would be at risk of flooding and erosion by the end of the century, along with a total of 15 [[Earth:Ramsar site|Ramsar site]]s and other natural heritage sites (Bao Bolong Wetland Reserve, Delta du Saloum National Park, Diawling National Park, Golfe de Boughrara, Kalissaye, Lagune de Ghar el Melh et Delta de la Mejerda, Marromeu Game Reserve, Parc Naturel des Mangroves du Fleuve Cacheu, Seal Ledges Provincial Nature Reserve, Sebkhet Halk Elmanzel et Oued Essed, Sebkhet Soliman, Réserve Naturelle d'Intérêt Communautaire de la Somone, Songor Biosphere Reserve, Tanbi Wetland Complex and Watamu Marine National Park).<ref name="AR6_WGII_Chapter9" />

==== Asia ====
[[File:20091011松川浦.jpg|thumb|Matsukawaura [[Earth:Lagoon|Lagoon]], located in Fukushima Prefecture of Honshu Island]]
As of 2022, it is estimated that 63 million people in the [[Place:East Asia|East]] and [[Place:South Asia|South Asia]] are already at risk from a [[100-year flood|100-year flood]], in large part due to inadequate coastal protection in many countries. This will be greatly exacerbated in the future: Asia has the largest population at risk from sea level and Bangladesh, China, {{wipe|India}}, Indonesia, {{wipe|Japan}}, Pakistan, the {{wipe|Philippines}}, Thailand and Vietnam alone account for 70% number of people exposed to sea level rise during the 21st century.<ref name="AR6_WGII_Chapter10" /><ref>{{Cite journal|last=McLeman|first=Robert|date=2018|title=Migration and displacement risks due to mean sea-level rise|journal=Bulletin of the Atomic Scientists|volume=74|issue=3|pages=148–154|doi=10.1080/00963402.2018.1461951|issn=0096-3402|bibcode=2018BuAtS..74c.148M|s2cid=150179939}}</ref> This is entirely due to the region's densely populated coasts, as the rate of sea level rise in Asia is generally similar to the global average. Exceptions include the [[Earth:Indo-Pacific|Indo-Pacific]] region, where it had been around 10% faster since the 1990s, and the coast of {{wipe|China}}, where globally "extreme" sea level rise had been detected since the 1980s, and it is believed that the difference between and of global warming would have a disproportionate impact on flood frequency. It is also estimated that future sea level rise along the {{wipe|Japan}}ese Honshu Island would be up to 25&nbsp;cm faster than the global average under RCP8.5, the intense climate change scenario. RCP8.5 is additionally associated with the loss of at least a third of the Japanese [[Earth:Beach|beach]]es and 57–72% of Thai beaches.<ref name="AR6_WGII_Chapter10">Shaw, R., Y. Luo, T. S. Cheong, S. Abdul Halim, S. Chaturvedi, M. Hashizume, G. E. Insarov, Y. Ishikawa, M. Jafari, A. Kitoh, J. Pulhin, C. Singh, K. Vasant, and Z. Zhang, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter10.pdf Chapter 10: Asia]. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] [H.-O. Pörtner, D. C. Roberts, M. Tignor, E. S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, New York, US, pp. 1457–1579 |doi=10.1017/9781009325844.012.</ref>

One estimate finds that Asia will suffer direct economic damages of US$167.6&nbsp;billion at 0.47 meters of sea level rise, US$272.3&nbsp;billion at 1.12 meters and US$338.1&nbsp;billion at 1.75 meters (along with the indirect impact of 8.5, 24 or US$15&nbsp;billion from population displacement at those levels), with {{wipe|China}}, {{wipe|India}}, the Republic of Korea, {{wipe|Japan}}, Indonesia and {{wipe|Russia}} experiencing the largest economic losses. Out of the 20 coastal cities expected to see the highest flood losses by 2050, 13 are in Asia. For nine of those ([[Place:Bangkok|Bangkok]], Guangzhou, Ho Chi Minh City, [[Place:Jakarta|Jakarta]], [[Place:Kolkata|Kolkata]], Nagoya, [[Place:Tianjin|Tianjin]], Xiamen and Zhanjiang) sea level rise would be compounded by subsidence. By 2050, Guangzhou would see 0.2 meters of sea level rise and the estimated ''annual'' economic losses of US$254 million – the highest in the world. One estimate calculates that in the absence of adaptation, cumulative economic losses caused by sea level rise in Guangzhou under RCP8.5 would reach ~US$331&nbsp;billion by 2050, ~US$660&nbsp;billion by 2070 and US$1.4&nbsp;trillion by 2100, while the impact of high-end ice sheet instability would increase these figures to ~US$420&nbsp;billion, ~US$840&nbsp;billion and ~US$1.8&nbsp;trillion, respectively. In [[Place:Shanghai|Shanghai]], coastal inundation amounts to ~0.03% of local [[Finance:GDP|GDP]]; but would increase to 0.8% ([[Confidence interval|confidence interval]] of 0.4–1.4%) by 2100 even under the "moderate" [[Earth:Representative Concentration Pathway|RCP4.5]] scenario in the absence of adaptation. Likewise, failing to adapt to sea level rise in {{wipe|Mumbai}} would result in the damages of 112–162&nbsp;billion USD by 2050, which would nearly triple by 2070. As the result, efforts like the Mumbai Coastal Road are being implemented, although they are likely to affect coastal ecosystems and fishing livelihoods.<ref name="AR6_WGII_Chapter10" /> Nations with extensive rice production along the coasts like Bangladesh, Vietnam and China are already seeing adverse impacts from saltwater intrusion.<ref>{{Cite web|url=http://www.fao.org/nr/climpag/pub/EIre0047_en.asp|title=Potential Impacts of Sea-Level Rise on Populations and Agriculture|website=www.fao.org|access-date=2018-10-21|archive-date=2020-04-18|archive-url=https://web.archive.org/web/20200418035608/http://www.fao.org/nr/climpag/pub/eire0047_en.asp}}</ref>

It is estimated that [[Biology:Climate change in Bangladesh|sea level rise in Bangladesh]] may force the relocation of up to one-third of power plants as early as 2030, while a similar proportion would have to deal with the increased salinity of their cooling water by then. Research from 2010s indicates that by 2050, between 0.9 and 2.1&nbsp;million people would be displaced by sea level rise alone: this would likely necessitate the creation of ~594,000 additional jobs and ~197,000 housing units in the areas receiving the displaced persons, as well as to secure the supply of additional ~783&nbsp;billion [[Calorie|calorie]]s worth of food.<ref name="AR6_WGII_Chapter10" /> In 2021, another paper estimated that 816,000 would be directly displaced by sea level rise by 2050, but this would be increased to 1,3&nbsp;million when the indirect effects are taken into account.<ref name="DeLellis2021">{{cite journal |last1=De Lellis |first1=Pietro |last2=Marín |first2=Manuel Ruiz |last3=Porfiri |first3=Maurizio |date=29 March 2021 |title=Modeling Human Migration Under Environmental Change: A Case Study of the Effect of Sea Level Rise in Bangladesh |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020EF001931 |journal=Earth's Future |volume=9 |issue=4 |pages=e2020EF001931 |doi=10.1029/2020EF001931 |bibcode=2021EaFut...901931D |s2cid=233626963 }}</ref> Both studies assume that the majority of the displaced people would travel to the other areas of Bangladesh, and attempt to estimate population changes in different localities.
[[File:Urban-Rural Population and Land Area Estimates, v2, 2010 Bangladesh (13873798283).jpg|thumb|upright=2|2010 estimates of population exposure to sea level rise in Bangladesh]]
{| class="wikitable"
|+Net Variations in the Population Due to Sea Level Rise in 2050 in Selected Districts.<ref name="DeLellis2021" />
!|District
!|Net flux (Davis et al., 2018)
!|Net flux (De Lellis et al., 2021)
!|Rank (Davis et al., 2018)<ref group="T2">Refers to the magnitude of population change relative to the other districts.</ref>
!|Rank (De Lellis et al., 2021)
|-
|[[Place:Dhaka|Dhaka]] || 207,373 || −34, 060 || 1 || 11
|-
|Narayanganj || −95,003 || −126,694 || 2 || 1
|-
|Shariatpur || −80,916 || −124,444 || 3 || 3
|-
|Barisal || −80,669 || −64,252 || 4 || 6
|-
|Munshiganj || −77,916 || −124,598 || 5 || 2
|-
|Madaripur || 61,791 || −937 || 6 || 60
|-
|Chandpur || −37,711 || −70,998 || 7 || 4 
|-
|Jhalakati || 35,546 || 9,198 || 8 || 36
|-
|Satkhira || −32,287 || −19,603 || 9 || 23
|-
|Khulna || −28,148 || −9,982 || 10 || 33
|-
|Cox's Bazar || −25,680 || −16,366 || 11 || 24
|-
|Bagherat || 24,860 || 12,263 || 12 || 28
|}
{{reflist|group=T2}}

In an attempt to address these challenges, the Bangladesh Delta Plan 2100 has been launched in 2018.<ref name="BanglaDelta">{{Cite web|title=Bangladesh Delta Plan 2100 {{!}} Dutch Water Sector|url=https://www.dutchwatersector.com/news/bangladesh-delta-plan-2100|access-date=2020-12-11|website=www.dutchwatersector.com|language=nl}}</ref><ref name="BDP 2100">{{Cite web|url=https://www.gwp.org/globalassets/global/gwp-sas_images/gwp-sas-in-action/ldai/bdp-2100-ppt.pdf|title=Bangladesh Delta Plan (BDP) 2100}}</ref> As of 2020, it was seen falling short of most of its initial targets.<ref>{{Cite web|url=http://www.tbsnews.net/bangladesh/delta-plan-falls-behind-targets-onset-128500|title=Delta Plan falls behind targets at the onset|date=September 5, 2020|website=The Business Standard}}</ref> The progress is being monitored.<ref>{{Cite web|url=http://edepot.wur.nl/381660|title=Bangladesh Delta Plan 2100 Formulation project}}</ref>

In 2019, the president of Indonesia, Joko Widodo, declared that the city of [[Place:Jakarta|Jakarta]] is sinking to a degree that requires him to move [[Place:Capital of Indonesia|the capital]] to another city.<ref>{{Cite news|url=https://www.washingtonpost.com/opinions/2019/05/03/seas-rise-indonesia-is-moving-its-capital-city-other-cities-should-take-note/|title=As seas rise, Indonesia is moving its capital city. Other cities should take note.|last=Englander|first=John|date=3 May 2019|newspaper={{wipe|The Washington Post}}|access-date=31 August 2019}}</ref> A study conducted between 1982 and 2010 found that some areas of Jakarta have been sinking by as much as 28&nbsp;cm (11 inches) per year<ref>{{cite journal |last1=Abidin |first1=Hasanuddin Z. |last2=Andreas |first2=Heri |last3=Gumilar |first3=Irwan |last4=Fukuda |first4=Yoichi |last5=Pohan |first5=Yusuf E. |last6=Deguchi |first6=T. |title=Land subsidence of Jakarta (Indonesia) and its relation with urban development |journal=Natural Hazards |date=11 June 2011 |volume=59 |issue=3 |pages=1753–1771 |doi=10.1007/s11069-011-9866-9 |bibcode=2011NatHa..59.1753A |s2cid=129557182 }}</ref> due to ground water drilling and the weight of its buildings, and the problem is now exacerbated by sea level rise. However, there are concerns that building in a new location will increase tropical deforestation.<ref>{{cite news |last1=Englander |first1=John |title=As seas rise, Indonesia is moving its capital city. Other cities should take note. |url=https://www.washingtonpost.com/opinions/2019/05/03/seas-rise-indonesia-is-moving-its-capital-city-other-cities-should-take-note/ |access-date=5 May 2019 |newspaper=The Washington Post |date=May 3, 2019}}</ref><ref>{{cite news |last1=Rosane |first1=Olivia |title=Indonesia Will Move its Capital from Fast-Sinking Jakarta |url=https://www.ecowatch.com/indonesia-to-move-capital-jakarta-2636197365.html |access-date=5 May 2019 |agency=Ecowatch |date=May 3, 2019}}</ref> Other so called [[Earth:Sinking cities|sinking cities]], such as [[Place:Bangkok|Bangkok]] or [[Place:Tokyo|Tokyo]], are vulnerable to these compounding subsidence with sea level rise.<ref>{{Cite journal|last1=Erkens|first1=G.|last2=Bucx|first2=T.|last3=Dam|first3=R.|last4=de Lange|first4=G.|last5=Lambert|first5=J.|date=2015-11-12|title=Sinking coastal cities|url=https://piahs.copernicus.org/articles/372/189/2015/|journal=Proceedings of the International Association of Hydrological Sciences|language=en|volume=372|pages=189–198|doi=10.5194/piahs-372-189-2015|bibcode=2015PIAHS.372..189E|issn=2199-899X |doi-access=free }}</ref>

==== Australasia ====
[[File:King's Beach since Friday 14th April, 2006 - panoramio.jpg|thumb|left|King's Beach at Caloundra]]
In {{wipe|Australia}}, erosion and flooding of Queensland's Sunshine Coast beaches is projected to intensify by 60% by 2030, with severe impacts on tourism in the absence of adaptation. Adaptation costs to sea level rise under the high-emission [[Earth:Representative Concentration Pathway|RCP]]8.5 scenario are projected to be three times greater than the adaptation costs to low-emission RCP2.6 scenario. For 0.2- to 0.3-m sea level rise (set to occur by 2050), what is currently a [[100-year flood|100-year flood]] would occur every year in [[Earth:New Zealand|New Zealand]] cities of [[Place:Wellington|Wellington]] and [[Place:Christchurch|Christchurch]]. Under 0.5 m sea level rise, the current 100-year flood in Australia would be likely to occur several times a year, while in New Zealand, buildings with a collective worth of NZ$12.75&nbsp;billion would become exposed to new 100-year floods. A metre or so of sea level rise would threaten assets in New Zealand with a worth of NZD$25.5&nbsp;billion (with a disproportionate impact on Maori-owned holdings and cultural heritage objects), and Australian assets with a worth of AUD$164–226&nbsp;billion (including many unsealed roads and railway lines). The latter represents a 111% rise in Australia's inundation costs between 2020 and 2100.<ref name="AR6_WGII_Chapter11">Lawrence, J., B. Mackey, F. Chiew, M.J. Costello, K. Hennessy, N. Lansbury, U.B. Nidumolu, G. Pecl, L. Rickards, N. Tapper,
A. Woodward, and A. Wreford, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter11.pdf Chapter 11: Australasia]. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, US, pp. 1581–1688,
|doi=10.1017/9781009325844.013</ref>

==== Central and South America ====
[[File:Santos Aérea (cropped).jpg|thumb|An aerial view of São Paulo's Port of Santos]]
By 2100, a minimum of 3-4&nbsp;million people in [[Earth:South America|South America]] would be directly affected by coastal flooding and erosion. 6% of the population of Venezuela, 56% of the population of Guyana (including in the capital, [[Place:Georgetown, Guyana|Georgetown]], much of which is already below the sea level) and 68% of the population of Suriname are already living in low-lying areas exposed to sea level rise. In {{wipe|Brazil}}, the coastal ecoregion of Caatinga is responsible for 99% of its shrimp production, yet its unique conditions are threatened by a combination of sea level rise, ocean warming and [[Biology:Ocean acidification|ocean acidification]]. The port complex of Santa Catarina had been interrupted by extreme wave or wind behavior 76 times in one 6-year period in 2010s, with a 25,000-50,000 USD loss for each idle day. In Port of Santos, [[Physics:Storm surge|storm surge]]s were three times more frequent between 2000 and 2016 than between 1928 and 1999.<ref name="AR6_WGII_Chapter12">Castellanos, E., M.F. Lemos, L. Astigarraga, N. Chacón, N. Cuvi, C. Huggel, L. Miranda, M. Moncassim Vale, J.P. Ometto,
P.L. Peri, J.C. Postigo, L. Ramajo, L. Roco, and M. Rusticucci, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter12.pdf Chapter 12: Central and South America]. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, US, pp. 1689–1816 |doi=10.1017/9781009325844.014</ref>

==== Europe ====
[[File:Beach restoration device.jpg|thumb|left|[[Earth:Beach nourishment|Beach nourishment]] in progress in Barcelona.]]
Many sandy coastlines in [[Earth:Europe|Europe]] are vulnerable to erosion caused by sea level rise. In {{wipe|Spain}}, Costa del Maresme is anticipated to retreat by 16 meters by 2050 relative to 2010, and potentially by 52 meters by 2100 under RCP8.5<ref>{{cite journal |last1=Ballesteros |first1=Caridad |last2=Jiménez |first2=José A. |last3=Valdemoro |first3=Herminia I. |last4=Bosom |first4=Eva |date=7 September 2017 |title=Erosion consequences on beach functions along the Maresme coast (NW Mediterranean, Spain) |url=https://link.springer.com/article/10.1007/s11069-017-3038-5 |journal=Natural Hazards |language=en |volume=90 |pages=173–195 |doi=10.1007/s11069-017-3038-5 |s2cid=135328414 }}</ref> Other vulnerable coastlines include Tyrrhenian Sea coast of Italy's Calabria region,<ref>{{cite journal |last1=Ietto |first1=Fabio |last2=Cantasano |first2=Nicola |last3=Pellicone  |first3=Gaetano |date=11 April 2018 |title=A New Coastal Erosion Risk Assessment Indicator: Application to the Calabria Tyrrhenian Littoral (Southern Italy) |url=https://link.springer.com/article/10.1007/s40710-018-0295-6 |journal=Environmental Processes |language=en |volume=5 |issue=2 |pages=201–223 |doi=10.1007/s40710-018-0295-6 |bibcode=2018EProc...5..201I |s2cid=134889581 }}</ref> Barra-Vagueira coast in Portugal<ref>{{cite journal |last1=Ferreira |first1=A. M. |last2=Coelho |first2=C. |last3=Narra |first3=P. |date=13 October 2020 |title=Coastal erosion risk assessment to discuss mitigation strategies: Barra-Vagueira, Portugal |url=https://link.springer.com/article/10.1007/s11069-020-04349-2 |journal=Natural Hazards |language=en |volume=105 |pages=1069–1107 |doi=10.1007/s11069-020-04349-2 |s2cid=222318289 }}</ref> and Nørlev Strand in {{wipe|Denmark}}.<ref>{{cite journal |last1=Rivero |first1=Ofelia Yocasta |last2=Margheritini |first2=Lucia |last3=Frigaard |first3=Peter |date=4 February 2021 |title=Accumulated effects of chronic, acute and man-induced erosion in Nørlev strand on the Danish west coast |url=https://link.springer.com/article/10.1007/s11852-021-00812-9 |journal=Journal of Coastal Conservation |language=en |volume=25 |issue=1 |page=24 |doi=10.1007/s11852-021-00812-9 |bibcode=2021JCC....25...24R |s2cid=231794192 }}</ref>

In France, it was estimated that 8,000-10,000 people would be forced to migrate away from the coasts by 2080.<ref>{{Cite journal|last1=Tierolf|first1=Lars|last2=Haer|first2=Toon Haer|last3=Wouter Botzen|first3=W. J.|last4=de Bruijn|first4=Jens A. |last5=Ton |first5=Marijn J. |last6=Reimann|first6=Lena|last7=Aerts |first7=Jeroen C. J. H. |date=13 March 2023|title=A coupled agent-based model for France for simulating adaptation and migration decisions under future coastal flood risk|journal=Scientific Reports|volume=13 |issue=1 |page=4176 |doi=10.1038/s41598-023-31351-y |pmid=36914726 |pmc=10011601 |bibcode=2023NatSR..13.4176T }}</ref> The Italian city of Venice is located on islands. It is highly vulnerable to flooding and has already spent $6&nbsp;billion on a barrier system.<ref>{{cite news |last1=Calma |first1=Justine |title=Venice's historic flooding blamed on human failure and climate change |url=https://www.theverge.com/2019/11/14/20963878/venice-high-tide-climate-change-flood-barrier-sea-levels |access-date=17 November 2019 |agency=The Verge |date=November 14, 2019}}</ref><ref>{{cite news |last1=Shepherd |first1=Marshall |title=Venice Flooding Reveals A Real Hoax About Climate Change - Framing It As "Either/Or" |url=https://www.forbes.com/sites/marshallshepherd/2019/11/16/venice-flooding-reveals-a-real-hoax-about-climate-changeframing-it-as-eitheror/ |access-date=17 November 2019 |agency=Forbes |date=16 November 2019}}</ref> A quarter of the German state of Schleswig-Holstein, inhabited by over 350,000 people, is at low elevation and has been vulnerable to flooding since the preindustrial times. Many [[Earth:Levee|levee]]s already exist, but to its complex geography, a flexible mix of hard and soft measures was chosen, which is intended to support a safety margin of >1 meter rise per century.<ref name="Hurk2022">{{Cite journal|last1=van der Hurk|first1=Bart|last2=Bisaro|first2=Alexander|last3=Haasnoot|first3=Marjolijn|last4=Nicholls|first4=Robert J. |last5=Rehdanz |first5=Katrin |last6=Stuparu|first6=Dana|date=28 January 2022|title=Living with sea-level rise in North-West Europe: Science-policy challenges across scales|journal=Climate Risk Management|volume=35|page=100403 |doi=10.1016/j.crm.2022.100403 |bibcode=2022CliRM..3500403V |s2cid=246354121 }}</ref> In the {{wipe|United Kingdom}}, sea level at the end of the century would increase by 53 to 115 centimetres at the mouth of river Thames and 30 to 90 centimetres at [[Place:Edinburgh|Edinburgh]].<ref>{{cite journal |last1=Howard |first1=Tom |last2=Palmer |first2=Matthew D |last3=Bricheno |first3=Lucy M |date=18 September 2019 |title=Contributions to 21st century projections of extreme sea-level change around the UK |url=https://iopscience.iop.org/article/10.1088/2515-7620/ab42d7 |journal=Environmental Research Communications |language=en |volume=1 |issue=9 |page=095002 |doi=10.1088/2515-7620/ab42d7 |bibcode=2019ERCom...1i5002H |s2cid=203120550 }}</ref> To address this reality, it has divided its coast into 22 areas, each covered by a Shoreline Management Plan. Those are further sub-divided into 2000 management units in total, spanning across three "epochs" (0–20 years, 20-50 and 50–100 years).<ref name="Hurk2022" />

The Netherlands is a country that sits partially below sea level and is subsiding. It has responded by extending its Delta Works program.<ref>{{Cite news|url=https://www.nytimes.com/interactive/2017/06/15/world/europe/climate-change-rotterdam.html,%20https://www.nytimes.com/interactive/2017/06/15/world/europe/climate-change-rotterdam.html|title=The Dutch Have Solutions to Rising Seas. The World Is Watching.|last1=Kimmelman|first1=Michael|date=2017-06-15|work=The New York Times|access-date=2019-02-02|last2=Haner|first2=Josh|issn=0362-4331}}</ref> Drafted in 2008, the ''Delta Commission'' report said that the country must plan for a rise in the North Sea up to {{convert|1.3|m|ftin|abbr=on}} by 2100 and plan for a {{convert|2 - 4|m|ft|0|sigfig=1|abbr=on}} rise by 2200.<ref>{{Cite news|url=https://www.nytimes.com/2008/09/03/news/03iht-03dutch.15877468.html|title=Dutch draw up drastic measures to defend coast against rising seas|date=3 September 2008|work={{wipe|The New York Times}}}}</ref> It advised annual spending between €1.0 and €1.5&nbsp;billion for measures such as broadening coastal dunes and strengthening sea and river dikes. Worst-case evacuation plans were also drawn up.<ref>{{cite news |title=Rising Sea Levels Threaten Netherlands |url=https://www.newspapers.com/image/514725270/ |access-date=28 October 2022 |work=National Post |agency=Agence France-Presse |date=September 4, 2008 |location=Toronto |page=AL12}}</ref>

==== North America ====
[[File:October 17 2016 sunny day tidal flooding at Brickell Bay Drive and 12 Street downtown Miami, 4.34 MLLW high tide am.jpg|thumb|Tidal flooding in Miami during a king tide (October 17, 2016). The risk of tidal flooding increases with sea level rise.]]
As of 2017, around 95 million Americans lived on the coast: for {{wipe|Canada}} and Mexico, this figure amounts to 6.5 million and 19 million people. Increased chronic nuisance flooding and king tide flooding is already an issue in the highly [[Climate change vulnerability|vulnerable]] state of Florida,<ref>{{Cite web|date=2020-02-10|title=Florida Coastal Flooding Maps: Residents Deny Predicted Risks to Their Property|url=https://www.ecowatch.com/florida-coastal-flooding-maps-2645087745.html|access-date=2021-01-31|website=EcoWatch|language=en}}</ref> as well as alongside the US East Coast.<ref>{{cite journal|last1=Sweet & Park |title=Increased nuisance flooding along the coasts of the United States due to sea level rise: Past and future |journal=Geophysical Research Letters |year=2015 |volume=42 |issue=22 |pages=9846–9852 |doi=10.1002/2015GL066072 |bibcode=2015GeoRL..42.9846M |s2cid=19624347}}</ref> On average, the number of days with tidal flooding in the USA increased 2 times in the years 2000–2020, reaching 3–7 days per year. In some areas the increase was much stronger: 4 times in the Southeast Atlantic and 11 times in the Western Gulf. By the year 2030 the average number is expected to be 7–15 days, reaching 25–75 days by 2050.<ref>{{cite web |title=High Tide Flooding |url=https://coast.noaa.gov/states/fast-facts/recurrent-tidal-flooding.html |website=NOAA |access-date=10 July 2023}}</ref> U.S. coastal cities have responded to that through [[Earth:Beach nourishment|beach nourishment]] or ''beach replenishment'', where mined sand is trucked in and added, in addition to other adaptation measures such as zoning, restrictions on state funding, and building code standards.<ref name="ClimateCentral2012">{{cite web|url=http://www.climatecentral.org/news/its-beach-season-enjoy-it-while-you-can|title=Climate Change, Sea Level Rise Spurring Beach Erosion|year=2012|website=Climate Central}}</ref><ref>{{Cite journal|last=Carpenter|first=Adam T.|date=2020-05-04|title=Public priorities on locally-driven sea level rise planning on the East Coast of the United States|journal=PeerJ|language=en|volume=8|pages=e9044|doi=10.7717/peerj.9044|pmid=32411525|pmc=7204830|issn=2167-8359 |doi-access=free }}</ref> Along an estimated 15% of the US coastline, the majority of local [[Earth:Groundwater|groundwater]] levels are already below the sea level. This places those groundwater reservoirs at risk of sea water intrusion, which renders fresh water unusable once its concentration exceeds 2-3%.<ref>{{cite journal |last1=Jasechko |first1=Scott J.|last2=Perrone |first2=Debra |last3=Seybold |first3=Hansjörg |last4=Fan |first4=Ying |last5=Kirchner |first5=James W. |title=Groundwater level observations in 250,000 coastal US wells reveal scope of potential seawater intrusion |date=26 June 2020 |journal=Nature Communications |volume=11 |issue=1 |page=3229 |doi=10.1038/s41467-020-17038-2 |pmid=32591535 |pmc=7319989 |bibcode=2020NatCo..11.3229J }}</ref> The damages are also widespread in Canada and will affect both major cities like Halifax and the more remote locations like Lennox Island, whose Mi'kmaq community is already considering relocation due to widespread coastal erosion. In Mexico, the damages from SLR to tourism hotspots like Cancun, Isla Mujeres, Playa del Carmen, Puerto Morelos and Cozumel could amount to 1.4–2.3&nbsp;billion USD.<ref name="AR6_WGII_Chapter14" /> The increase in [[Physics:Storm surge|storm surge]] due to sea level rise is also a problem. For example, due to this effect Hurricane Sandy caused additional 8 billion dollars in damage, impacted 36,000 more houses and 71,000 more people.<ref>{{cite journal |title=Economic damages from Hurricane Sandy attributable to sea level rise caused by anthropogenic climate change |journal=Nature Communications |date=18 May 2021 |volume=12 |bibcode=2021NatCo..12.2720S |last1=Strauss |first1=Benjamin H. |last2=Orton |first2=Philip M. |last3=Bittermann |first3=Klaus |last4=Buchanan |first4=Maya K. |last5=Gilford |first5=Daniel M. |last6=Kopp |first6=Robert E. |last7=Kulp |first7=Scott |last8=Massey |first8=Chris |last9=Moel |first9=Hans de |last10=Vinogradov |first10=Sergey |issue=1 |page=2720 |doi=10.1038/s41467-021-22838-1 |pmid=34006886 |pmc=8131618 |s2cid=234783225 }}</ref><ref>{{cite news |last1=Seabrook |first1=Victoria |title=Climate change to blame for $8 billion of Hurricane Sandy losses, study finds |url=https://news.sky.com/story/climate-change-to-blame-for-8-billion-of-hurricane-sandy-losses-study-finds-12309974#:~:text=The%20raised%20water%20levels%20allowed,36%2C000%20homes%20and%2071%2C000%20people. |access-date=9 July 2023 |agency=Sky News |publisher=Nature Communications |date=19 May 2021}}</ref>

In the future, northern Gulf of Mexico, [[Place:Atlantic Canada|Atlantic Canada]] and the Pacific coast of Mexico would experience the greatest sea level rise. By 2030, flooding along the US Gulf Coast could cause economic losses of up to US$176&nbsp;billion: around US$50 billion may be avoided through [[Earth:Nature-based solutions|nature-based solutions]] like wetland restoration and oyster reef restoration.<ref name="AR6_WGII_Chapter14" /> By 2050, the frequency of coastal flooding in the US is expected to rise tenfold to four "moderate" flooding events per year, even without storms or heavy rainfall.<ref>{{cite web |title=U.S Coastline to See Up to a Foot of Sea Level by 2050 |url=https://www.noaa.gov/news-release/us-coastline-to-see-up-to-foot-of-sea-level-rise-by-2050 |access-date=February 16, 2022 |website=National Oceanic and Atmospheric Administration|date=15 February 2022 }}</ref><ref>{{cite web |date=2022 |title=More Damaging Flooding, 2022 Sea Level Rise Technical Report |url=https://oceanservice.noaa.gov/hazards/sealevelrise/sealevelrise-tech-report.html#step2 |access-date=2022-03-18 |website=National Ocean Service, NOAA}}</ref> In the {{wipe|New York City}}, current [[100-year flood|100-year flood]] would occur once in 19–68 years by 2050 and 4–60 years by 2080.<ref>{{cite web| last=Gornitz| first=Vivien|date=2002|title=Impact of Sea Level Rise in the New York City Metropolitan Area| url=https://eportfolios.macaulay.cuny.edu/bird2012/files/2012/07/Impacts-of-SLR-in-the-NYC-Metropolitan-Area.-pdf.pdf|access-date=2020-08-09|website=Global and Planetary Change}}</ref> By 2050, 20&nbsp;million people in the greater {{wipe|New York City}} area would be threatened, as 40% of the existing [[Earth:Water treatment|water treatment]] facilities would be compromised and 60% of power plants will need to be relocated. By 2100, sea level rise of {{cvt|0.9|m|ft|frac=2}} and {{cvt|1.8|m|ft|frac=2}} would threaten 4.2 and 13.1&nbsp;million people in the US, respectively. In {{wipe|California}} alone, {{cvt|2|m|ft|frac=2}} of SLR could affect 600,000 people and threaten over US$150&nbsp;billion in property with inundation, potentially representing over 6% of the state's [[Finance:GDP|GDP]]. In North Carolina, a meter of SLR inundates 42% of the Albemarle-Pamlico Peninsula, costing up to US$14&nbsp;billion (at 2016 value of the currency). In nine southeast US states, the same level of sea level rise would claim up to 13,000 historical and archaeological sites, including over 1000 sites eligible for inclusion in the National Register for Historic Places.<ref name="AR6_WGII_Chapter14">Hicke, J.A., S. Lucatello, L.D., Mortsch, J. Dawson, M. Domínguez Aguilar, C.A.F. Enquist, E.A. Gilmore, D.S. Gutzler, S. Harper, K. Holsman, E.B. Jewett, T.A. Kohler, and KA. Miller, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter14.pdf Chapter 14: North America]. In [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability] [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, US, pp. 1929–2042</ref>

==== Island nations ====
[[File:Malé.jpg|thumb|left|[[Place:Malé|Malé]], the capital island of Maldives.]]
Small island states are nations whose populations are concentrated on [[Earth:Atoll|atoll]]s and other [[Earth:Low island|low island]]s. Atolls on average reach {{convert|3-6|ft|m|1|order=flip|abbr=on}} above sea level.<ref>{{Cite web|title=Many Low-Lying Atoll Islands Will Be Uninhabitable by Mid-21st Century {{!}} U.S. Geological Survey|url=https://www.usgs.gov/news/national-news-release/many-low-lying-atoll-islands-will-be-uninhabitable-mid-21st-century|access-date=2021-12-17|website=www.usgs.gov}}</ref> This means that no other place is more vulnerable to [[Earth:Coastal erosion|coastal erosion]], flooding and salt intrusion into soils and freshwater caused by sea level rise. The latter may render an island uninhabitable well before it is completely flooded.<ref>{{Cite journal|last1=Zhu|first1=Bozhong|last2=Bai|first2=Yan|last3=He|first3=Xianqiang|last4=Chen|first4=Xiaoyan|last5=Li|first5=Teng|last6=Gong|first6=Fang|date=2021-09-18|title=Long-Term Changes in the Land–Ocean Ecological Environment in Small Island Countries in the South Pacific: A Fiji Vision|journal=Remote Sensing|language=en|volume=13|issue=18|page=3740|doi=10.3390/rs13183740|bibcode=2021RemS...13.3740Z|issn=2072-4292|doi-access=free}}</ref> Already, children in small island states are encountering hampered access to food and water and are suffering an increased rate of mental and social disorders due to these stressors.<ref>{{Cite journal|last1=Sly|first1=Peter D|last2=Vilcins|first2=Dwan|date=November 2021|title=Climate impacts on air quality and child health and wellbeing: Implications for Oceania|url=https://onlinelibrary.wiley.com/doi/10.1111/jpc.15650|journal=Journal of Paediatrics and Child Health|language=en|volume=57|issue=11|pages=1805–1810|doi=10.1111/jpc.15650|pmid=34792251|s2cid=244271480|issn=1034-4810}}</ref> At current rates, sea level would be high enough to make the Maldives uninhabitable by 2100,<ref>{{cite web |author=Megan Angelo |date=1 May 2009 |title=Honey, I Sunk the Maldives: Environmental changes could wipe out some of the world's most well-known travel destinations |url=http://travel.yahoo.com/p-interests-27384279;_ylc=X3oDMTFxcWIyczFpBF9TAzI3MTYxNDkEX3MDMjcxOTQ4MQRzZWMDZnAtdG9kYXltb2QEc2xrA21hbGRpdmVzLTQtMjgtMDk- |archive-url=https://web.archive.org/web/20120717041919/http://travel.yahoo.com/p-interests-27384279 |archive-date=17 July 2012 |access-date=29 September 2009}}</ref><ref>{{cite web |author=Kristina Stefanova |date=19 April 2009 |title=Climate refugees in Pacific flee rising sea |url=http://www.washingtontimes.com/news/2009/apr/19/rising-sea-levels-in-pacific-create-wave-of-migran/ |website=The Washington Times}}</ref> while five of the Solomon Islands have already disappeared due to the combined effects of sea level rise and stronger trade winds that were pushing water into the Western Pacific.<ref>{{Cite web |last=Klein |first=Alice |title=Five Pacific islands vanish from sight as sea levels rise |url=https://www.newscientist.com/article/2087356-five-pacific-islands-vanish-from-sight-as-sea-levels-rise/ |access-date=2016-05-09 |website=New Scientist}}</ref>
[[File:Island area change in the Central Pacific and Solomon Islands - erlaa21eff7 hr.jpg|thumb|Surface area change of islands in the Central Pacific and Solomon Islands<ref name="Albeert2016">{{Cite Q|Q29028186}}</ref>]]

Adaptation to sea level rise is costly for small island nations as a large portion of their population lives in areas that are at risk.<ref>{{Cite book|chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar5/wg2/WGIIAR5-Chap29_FINAL.pdf|title=AR5 WGII|last1=Nurse|first1=Leonard A.|last2=McLean|first2=Roger|publisher=Cambridge University Press|year=2014|editor-last=Barros|editor-first=VR|chapter=29: Small Islands|editor-last2=Field|access-date=2018-09-02|archive-date=2018-04-30|archive-url=https://web.archive.org/web/20180430194832/http://www.ipcc.ch/pdf/assessment-report/ar5/wg2/WGIIAR5-Chap29_FINAL.pdf}}</ref> Nations like [[History:Maldives|Maldives]], Kiribati and Tuvalu are already forced to consider controlled international migration of their population in response to rising seas,<ref name="Grecequet2017" /> since the alternative of uncontrolled migration threatens to exacerbate the humanitarian crisis of climate refugees.<ref>{{Cite web|last=Nations|first=United|title=Small Islands, Rising Seas|url=https://www.un.org/en/chronicle/article/small-islands-rising-seas|access-date=2021-12-17|website=United Nations|language=en}}</ref> In 2014, Kiribati had purchased 20 square kilometers of land (about 2.5% of Kiribati's current area) on the Fijian island of Vanua Levu to relocate its population there once their own islands are lost to the sea.<ref>{{cite news|url=https://www.theguardian.com/environment/2014/jul/01/kiribati-climate-change-fiji-vanua-levu|title=Besieged by the rising tides of climate change, Kiribati buys land in Fiji|last1=Caramel|first1=Laurence|date=July 1, 2014|access-date=9 January 2023|agency=The Guardian}}</ref>

While Fiji is also impacted by sea level rise,<ref>{{Cite journal |last=Long |first=Maebh |year=2018 |title=Vanua in the Anthropocene: Relationality and Sea Level Rise in Fiji |url=https://muse.jhu.edu/article/710005 |journal=Symplokē |volume=26 |issue=1–2 |pages=51–70 |doi=10.5250/symploke.26.1-2.0051 |s2cid=150286287}}</ref> it is in a comparatively safer position, and its residents continue to rely on local adaptation like moving further inland and increasing [[Earth:Sediment|sediment]] supply to combat erosion instead of relocating entirely.<ref name="Grecequet2017">{{Cite web|url=http://theconversation.com/many-small-island-nations-can-adapt-to-climate-change-with-global-support-86820|title=Many small island nations can adapt to climate change with global support|last1=Grecequet|first1=Martina|last2=Noble|first2=Ian|date=2017-11-16|website=The Conversation|access-date=2019-02-02|last3=Hellmann|first3=Jessica}}</ref> Fiji has also issued a green bond of $50&nbsp;million to invest in green initiatives and use the proceeds to fund adaptation efforts, and it is restoring [[Earth:Coral reef|coral reef]]s and [[Earth:Mangrove|mangrove]]s to protect itself flooding and erosion as a more cost-efficient alternative to building sea walls, with the nations of Palau and Tonga adopting similar efforts.<ref name="Grecequet2017" /><ref>{{Cite web|url=http://www.unenvironment.org/news-and-stories/video/adaptation-sea-level-rise|title=Adaptation to Sea Level Rise|date=2018-01-11|website=UN Environment|access-date=2019-02-02}}</ref> At the same time, even when an island is not threatened with complete disappearance due to flooding, tourism and local economies may end up devastated. For instance, a sea level rise of {{cvt|1.0|m|ftin|0}} would cause partial or complete inundation of 29% of coastal resorts in the Caribbean, while a further 49&ndash;60% of coastal resorts would be at risk from resulting coastal erosion.<ref>{{Cite journal|last1=Thomas|first1=Adelle|last2=Baptiste|first2=April|last3=Martyr-Koller|first3=Rosanne|last4=Pringle|first4=Patrick|last5=Rhiney|first5=Kevon|date=2020-10-17|title=Climate Change and Small Island Developing States|journal=Annual Review of Environment and Resources|language=en|volume=45|issue=1|pages=1–27|doi=10.1146/annurev-environ-012320-083355|issn=1543-5938|doi-access=free}}</ref>

== Adaptation ==
{{further|Earth:Climate change adaptation|Earth:Coastal management}}
[[File:Oosterscheldekering-pohled.jpg|thumb|left|Oosterscheldekering, the largest barrier of the Dutch Delta Works.]]
[[Earth:Climate change mitigation|Cutting greenhouse gas emissions]] can slow and stabilize the rate of sea level rise after 2050, greatly reducing its costs and damages, but cannot stop it outright. Thus, [[Earth:Climate change adaptation|climate change adaptation]] to sea level rise is inevitable.<ref>Cooley, S., D. Schoeman, L. Bopp, P. Boyd, S. Donner, D.Y. Ghebrehiwet, S.-I. Ito, W. Kiessling, P. Martinetto, E. Ojea, M.-F. Racault, B. Rost, and M. Skern-Mauritzen, 2022: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_FinalDraft_Chapter03.pdf Ocean and Coastal Ecosystems and their Services (Chapter 3)]. In: ''Climate Change 2022: Impacts, Adaptation, and Vulnerability.'' Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. In Press. - Cross-Chapter Box SLR: Sea Level Rise</ref>{{rp||page=3–127}} The most straightforward approach is to first cease development in vulnerable areas and ultimately move the people and [[Physics:Infrastructure|infrastructure]] away from them. Such ''retreat'' from sea level rise often results in the loss of livelihoods, and the displacement of newly impoverished people could burden their new homes and accelerate social tensions.<ref>{{Cite journal |last1=Dasgupta |first1=Susmita |last2=Wheeler |first2=David |last3=Bandyopadhyay |first3=Sunando |last4=Ghosh |first4=Santadas |last5=Roy |first5=Utpal |date=February 2022 |title=Coastal dilemma: Climate change, public assistance and population displacement |url=https://linkinghub.elsevier.com/retrieve/pii/S0305750X21003223 |journal=World Development |language=en |volume=150 |page=105707 |doi=10.1016/j.worlddev.2021.105707 |issn=0305-750X |s2cid=244585347}}</ref>

It is possible to avoid or at least delay the ''retreat'' from sea level rise with enhanced ''protections'' like dams, [[Earth:Levee|levee]]s or improved natural defenses,<ref name="Thomsen-2012" /> or through ''accommodation'' like [[Engineering:Building code|building standards]] updated to reduce damage from floods, addition of storm water valves to address more frequent and severe flooding at high tide,<ref name="US EPA">{{cite web |date=2 May 2016 |title=Climate Adaptation and Sea Level Rise |url=https://www.epa.gov/arc-x/climate-adaptation-and-sea-level-rise |website=US EPA, Climate Change Adaptation Resource Center (ARC-X) |language=en}}</ref> or [[Earth:Agriculture|cultivating]] crops more tolerant of saltwater mixing into the soil, even at an increased cost.<ref name="Nagothu-2017" /><ref name="Thomsen-2012" /><ref name="Fletcher-2013">{{cite journal |last1=Fletcher |first1=Cameron |date=2013 |title=Costs and coasts: an empirical assessment of physical and institutional climate adaptation pathways |url=https://apo.org.au/node/34006 |journal=Apo}}</ref> These options can be further divided into ''hard'' and ''soft'' adaptation. The former generally involves large-scale changes to human societies and ecological systems, often through the construction of capital-intensive infrastructure. Soft adaptation involves strengthening [[Earth:Nature-based solutions|natural defenses]] and local community adaptation, usually with simple, modular and locally owned technology. The two types of adaptation might be complementary or mutually exclusive.<ref name="Fletcher-2013" /><ref>{{Cite journal |last=Sovacool |first=Benjamin K. |date=2011 |title=Hard and soft paths for climate change adaptation |url=http://www.adaptation-undp.org/sites/default/files/downloads/sovacool-cp-hardsoft.pdf |journal=Climate Policy |volume=11 |issue=4 |pages=1177–1183 |doi=10.1080/14693062.2011.579315 |bibcode=2011CliPo..11.1177S |s2cid=153384574}}</ref> Adaptation options often require significant investment, but the costs of doing nothing are far greater. For instance, effective adaptation measures are predicted to reduce future annual costs of flooding in 136 of the world's largest coastal cities from $1 trillion by 2050 if no adaptation was done, to a little over $60 billion annually, while costing $50 billion per year.<ref>{{cite web |date=18 August 2013 |title=Coastal cities face rising risk of flood losses, study says |url=https://phys.org/news/2013-08-coastal-cities-losses.html |access-date=17 April 2023 |publisher=Phys.org}}</ref><ref>{{cite journal |last1=Hallegatte |first1=Stephane |last2=Green |first2=Colin |last3=Nicholls |first3=Robert J. |last4=Corfee-Morlot |first4=Jan |date=18 August 2013 |title=Future flood losses in major coastal cities |url=https://www.nature.com/articles/nclimate1979 |journal=Nature Climate Change |language=en |volume=3 |issue=9 |pages=802–806 |bibcode=2013NatCC...3..802H |doi=10.1038/nclimate1979}}</ref> However, it has been suggested that in the case of very high sea level rise, retreat away from the coast would have a lower impact on the [[Finance:GDP|GDP]] of {{wipe|India}} and [[Place:Southeast Asia|Southeast Asia]] then attempting to protect every coastline.<ref>{{cite journal |last1=Bachner |first1=Gabriel |last2=Lincke |first2=Daniel |last3=Hinkel |first3=Jochen |date=29 September 2022 |title=The macroeconomic effects of adapting to high-end sea-level rise via protection and migration |journal=Nature Communications |language=en |volume=13 |issue=1 |page=5705 |bibcode=2022NatCo..13.5705B |doi=10.1038/s41467-022-33043-z |pmc=9522673 |pmid=36175422}}</ref> 
[[File:Hurk_2022_UK_SLR_adaptation.jpg|thumb|Planning for the future sea level rise used in the {{wipe|United Kingdom}}.<ref name="Hurk2022" />]]
To be successful, adaptation needs to anticipate sea level rise well ahead of time. As of 2023, the global state of adaptation planning is mixed. A survey of 253 planners from 49 countries found that while 98% are aware of sea level rise projections, 26% have not yet formally integrated them into their policy documents. Only around a third of respondents from Asian and South American countries have done so, compared to 50% in Africa, and >75% in Europe, Australasia and North America. 56% of all surveyed planners have structured plans which account for 2050 and 2100 sea level rise, but 53% only plan using a single projection, rather than a range of two or three projections. Just 14% plan using four projections, including that of the "extreme" or "high-end" sea level rise.<ref>{{cite journal |last1=Hirschfeld |first1=Daniella |last2=Behar |first2=David |last3=Nicholls |first3=Robert J. |last4=Cahill |first4=Niamh |last5=James |first5=Thomas |last6=Horton |first6=Benjamin P. |last7=Portman |first7=Michelle E. |last8=Bell |first8=Rob |last9=Campo |first9=Matthew |last10=Esteban |first10=Miguel |last11=Goble |first11=Bronwyn |last12=Rahman |first12=Munsur |last13=Appeaning Addo |first13=Kwasi |last14=Chundeli |first14=Faiz Ahmed |last15=Aunger |first15=Monique |date=3 April 2023 |title=Global survey shows planners use widely varying sea-level rise projections for coastal adaptation |journal=Communications Earth & Environment |language=en |volume=4 |issue=1 |page=102 |bibcode=2023ComEE...4..102H |doi=10.1038/s43247-023-00703-x |doi-access=free |last16=Babitsky |first16=Orly |last17=Beal |first17=Anders |last18=Boyle |first18=Ray |last19=Fang |first19=Jiayi |last20=Gohar |first20=Amir |last21=Hanson |first21=Susan |last22=Karamesines |first22=Saul |last23=Kim |first23=M. J. |last24=Lohmann |first24=Hilary |last25=McInnes |first25=Kathy |last26=Mimura |first26=Nobuo |last27=Ramsay |first27=Doug |last28=Wenger |first28=Landis |last29=Yokoki |first29=Hiromune}} [[File:CC-BY_icon.svg|50x50px]] Text and images are available under a Creative Commons Attribution 4.0 International License.</ref> Another study found that while >75% of regional sea level rise assessments from the West and Northeastern United States included at least three estimates (usually RCP2.6, RCP4.5 and RCP8.5), and sometimes included extreme scenarios, 88% of projections from the American South had only a single estimate. Similarly, no assessment from the South went beyond 2100, while 14 assessments from the West went up to 2150, and three from the Northeast went to 2200. 56% of all localities were also found to underestimate the upper end of sea level rise relative to [[Earth:IPCC Sixth Assessment Report|IPCC Sixth Assessment Report]].<ref>{{cite journal |last1=Garner |first1=Andra J. |last2=Sosa |first2=Sarah E. |last3=Tan |first3=Fangyi |last4=Tan |first4=Christabel Wan Jie |last5=Garner |first5=Gregory G. |last6=Horton |first6=Benjamin P. |date=23 January 2023 |title=Evaluating Knowledge Gaps in Sea-Level Rise Assessments From the United States |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022EF003187 |journal=Earth's Future |volume=11 |issue=2 |pages=e2022EF003187 |bibcode=2023EaFut..1103187G |doi=10.1029/2022EF003187 |s2cid=256227421}}</ref>

== See also ==
* Sea level drop
* [[Earth:Climate emergency declaration|Climate emergency declaration]]
* [[Earth:Climate engineering|Climate engineering]]
* [[Earth:Coastal development hazards|Coastal development hazards]]
* [[Earth:Effects of climate change on oceans|Effects of climate change on oceans]]
* Effects of climate change on small island countries
* [[Earth:Hydrosphere|Hydrosphere]]
* [[Organization:Islands First|Islands First]]
* List of countries by average elevation

== References ==
{{Reflist}}

== External links ==
*[https://climate.nasa.gov/vital-signs/sea-level/ Vital signs / Sea level]
*[https://sealevel.nasa.gov/ Sea level change / Observations from space] (links to multiple measurements)
*[https://science2017.globalchange.gov/chapter/12/ Fourth National Climate Assessment Sea Level Rise Key Message]
*[https://www.ngs.noaa.gov/PUBS_LIB/SLCScenariosLL.pdf Incorporating Sea Level Change Scenarios at the Local Level] Outlines eight steps a community can take to develop site-appropriate scenarios
*[https://gloss-sealevel.org/ The Global Sea Level Observing System (GLOSS)]
*[https://coast.noaa.gov/slr/ USA Sea Level Rise Viewer (NOAA)]
{{World topic|Sea level rise in|title=Sea level rise by country|noredlinks=yes|state=collapsed}}
{{Physical oceanography|expanded=other}}
{{Doomsday}}

{{DEFAULTSORT:Sea Level Rise}}
[[Category:Oceanography]]
[[Category:Coastal geography]]
[[Category:Climate change adaptation]]

{{Sourceattribution|Sea level rise}}