View source for Earth:Climate change in the Arctic

{{Short description|Impacts of climate change on the Arctic}}
[[File:Arctic Sea Ice Minimum Comparison.png|thumb|The maps above compare the Arctic ice minimum extents from 2012 (top) and 1984 (bottom).]]
[[File:Climate Change and Arctic.pdf|thumb|Climate change in the Arctic.pdf]]
Major environmental issues caused by contemporary [[Earth:Climate change|climate change]] in the Arctic region range from the well-known, such as the [[Physics:Arctic sea ice decline|loss of sea ice]] or melting of the [[Earth:Greenland ice sheet|Greenland ice sheet]], to more obscure, but deeply significant issues, such as [[Earth:Permafrost|permafrost]] thaw,<ref>{{Cite journal|last=Kessler|first=Louise|date=May 2017|title=Estimating the Economic Impact of the Permafrost Carbon Feedback|url=http://dx.doi.org/10.1142/s2010007817500087|journal=Climate Change Economics|volume=08|issue=2|pages=1750008|doi=10.1142/s2010007817500087|issn=2010-0078}}</ref> as well as related social consequences for locals and the [[Earth:Geopolitics|geopolitical]] ramifications of these changes.<ref name=":0">{{Cite conference|last=Arvelo|first=Juan|date=2011|title=An Under-Ice Arctic Geophysical Exploration Sonar System Concept To Resolve International Territorial Claims|series=Proceedings of Meetings on Acoustics|volume=12|issue=1|page=070002|url=http://dx.doi.org/10.1121/1.3626896|publisher=Acoustical Society of America|doi=10.1121/1.3626896}}</ref> The Arctic is likely to be especially affected by climate change because of the high projected rate of regional warming and associated impacts.<ref name="IPCC_4th_assessment_a">{{cite book|author=Intergovernmental Panel on Climate Change|url=https://archive.ipcc.ch/site/assets/uploads/2018/02/ar4_syr.pdf|title=Synthesis report|publisher=IPCC|year=2007|series=Climate Change 2007: Synthesis Report. A Contribution of Working Groups I, II, and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC)|location=Geneva, Switzerland|contribution=3.3.3 Especially affected systems, sectors and regions|access-date=2011-09-15}}</ref> Temperature projections for the Arctic region were assessed in 2007:<ref name="IPCC_4th_assessment_c">{{cite book|last=Anisimov|first=O.A.|url=http://archive.ipcc.ch/publications_and_data/ar4/wg2/en/ch15s15-3-2.html|title=Chapter 15: Polar Regions (Arctic and Antarctic)|publisher=Print version: CUP. This version: IPCC website|year=2007|isbn=978-0-521-88010-7|editor1=Parry, M.L.|series=Climate change 2007: impacts, adaptation and vulnerability: contribution of Working Group II to the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC)|location=Cambridge University Press (CUP): Cambridge, UK|contribution=15.3.2 Projected atmospheric changes|access-date=2011-09-15|display-editors=etal}}</ref> These suggested already averaged warming of about 2&nbsp;°C to 9&nbsp;°C by the year 2100. The range reflects different projections made by different [[Earth:Climate model|climate model]]s, run with different forcing [[Software:Climate change scenario|scenarios]]. [[Astronomy:Radiative forcing|Radiative forcing]] is a measure of the effect of natural and human activities on the climate. Different forcing scenarios reflect things such as different projections of future human [[Earth:Greenhouse gas emissions|greenhouse gas emissions]].

These effects are wide-ranging and can be seen in many Arctic systems, from [[Earth:Fauna|fauna]] and [[Earth:Flora|flora]] to territorial claims.<ref name=":0" /> According to a July 2022 article in ''[[Earth:Geophysical Research Letters|Geophysical Research Letters]]'', temperatures in the Arctic region are rising four times as fast as elsewhere on Earth,<ref name="Chylek_20220716">{{cite journal |last1=Chylek |first1=Petr |last2=Folland |first2=Chris |last3=Klett |first3=James D. |last4=Wang |first4=Muyin |last5=Hengartner |first5=Nick |last6=Lesins |first6=Glen |last7=Dubey |first7=Manvendra K. |title=Annual Mean Arctic Amplification 1970–2020: Observed and Simulated by CMIP6 Climate Models |journal=Geophysical Research Letters |date=16 July 2022 |volume=49 |issue=13 |doi=10.1029/2022GL099371 |bibcode=2022GeoRL..4999371C |s2cid=250097858 |language=en |issn=0094-8276 }} via Wikipedia Library and EBSCOhost</ref>{{rp|1}}<ref name="LANL_202207">{{cite news |title=Arctic temperatures are increasing four times faster than global warming |url=https://phys.org/news/2022-07-arctic-temperatures-faster-global.html |access-date=18 July 2022 |work=Los Alamos National Laboratory |language=en}}</ref> leading to these effects worsening year on year and causing significant concern. The changing Arctic has global repercussions, perhaps via [[Earth:Shutdown of thermohaline circulation|ocean circulation changes]]<ref name="dx.doi.org">{{Cite journal|date=2015|title=Atlantic Ocean circulation shows "exceptional" slowdown|url=http://dx.doi.org/10.1063/pt.5.028751|journal=Physics Today|doi=10.1063/pt.5.028751|issn=1945-0699}}</ref> or [[Earth:Polar amplification|arctic amplification]].<ref>{{Cite journal|last1=Francis|first1=Jennifer A.|last2=Vavrus|first2=Stephen J.|date=2012-03-17|title=Evidence linking Arctic amplification to extreme weather in mid-latitudes|url=http://dx.doi.org/10.1029/2012gl051000|journal=Geophysical Research Letters|volume=39|issue=6|pages=n/a|doi=10.1029/2012gl051000|bibcode=2012GeoRL..39.6801F|s2cid=15383119|issn=0094-8276}}</ref>


==Current trends and impacts==
The 2021 [[Organization:Arctic Monitoring and Assessment Programme|Arctic Monitoring and Assessment Programme]] (AMAP) report by an international team of more than 60 experts, scientists, and indigenous knowledge keepers from Arctic communities, was prepared from 2019 to 2021.<ref name="AMAP_2021">{{cite report |title=AMAP Arctic Climate Change Update 2021: Key Trends and Impacts |pages=viii + 148 |work=[[Organization:Arctic Monitoring and Assessment Programme|Arctic Monitoring and Assessment Programme]] (AMAP) |date=2021 |location= Tromsø, Norway |isbn=978-82-7971-201-5 }}</ref>{{rp|vii}} It is a follow-up report of the 2017 assessment, "Snow, Water, Ice and Permafrost in the Arctic" (SWIPA).<ref name="AMAP_2021"/>{{rp|vii}} The 2021 IPCC AR6 WG1 Technical Report confirmed that "[o]bserved and projected warming" were ""strongest in the Arctic".<ref name="IPCC_AR6_WG1_2021">{{Cite book |chapter= Technical Summary |last1=Arias |first1=Paola A. |last2 = Bellouin |first2= Nicolas |last3 = Coppola |first3 = Erika |last4 = Jones |first4 = Richard G. |last5 = Krinner |first5 = Gerhard |display-authors=4 |chapter-url= https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf |year= 2021 |title= IPCC AR6 WG1 |pages=76 }}</ref>{{rp|29}} According to an August 11, 2022 article published in ''Nature'', there have been numerous reports that the Arctic is warming from twice to three times as fast as the global average since 1979, but the co-authors cautioned that the recent report of the "four-fold Arctic warming ratio" was potentially an "extremely unlikely event".<ref name="Rantanen_Karpechko_20220811">{{Cite journal |last1=Rantanen |first1=Mika |last2=Karpechko |first2=Alexey Yu |last3=Lipponen |first3=Antti |last4=Nordling |first4=Kalle |last5=Hyvärinen |first5=Otto |last6=Ruosteenoja |first6=Kimmo |last7=Vihma |first7=Timo |last8=Laaksonen |first8=Ari |date=11 August 2022 |title=The Arctic has warmed nearly four times faster than the globe since 1979 |url=https://www.nature.com/articles/s43247-022-00498-3 |journal=Communications Earth & Environment |language=en |volume=3 |issue=1 |page=168 |doi=10.1038/s43247-022-00498-3 |bibcode=2022ComEE...3..168R |s2cid=251498876 |issn=2662-4435}}</ref> The annual mean Arctic Amplification (AA) index had "reached values exceeding four" from c. 2002 through 2022, according to a July 2022 article in ''[[Earth:Geophysical Research Letters|Geophysical Research Letters]]''.<ref name="Chylek_20220716"/>{{rp|1}}<ref name="LANL_202207"/>

The December 14, 2021 16th Arctic Report Card produced by the United States's [[Organization:National Oceanic and Atmospheric Administration|National Oceanic and Atmospheric Administration]] (NOAA) and released annually, examined the "interconnected physical, ecological and human components" of the circumpolar Arctic.<ref name="ARC_2021">{{cite report |url=http://www.arctic.noaa.gov/Report-Card/Report-Card-2021 |series=Arctic Report Card: Update for 2021 |title=Rapid and pronounced warming continues to drive the evolution of the Arctic environment |publisher=NOAA}}</ref><ref name="Druckenmiller_20211214">{{cite news |last1=Druckenmiller |first1=Matthew |last2=Thoman |first2=Rick |last3=Moon |first3=Twila |title=2021 Arctic Report Card reveals a (human) story of cascading disruptions, extreme events and global connections |url=https://theconversation.com/2021-arctic-report-card-reveals-a-human-story-of-cascading-disruptions-extreme-events-and-global-connections-172136 |access-date=30 January 2022 |agency=The Conversation |date=14 December 2021}}</ref> The report said that the 12 months between October 2020 and September 2021 were the "seventh warmest over Arctic land since the record began in 1900".<ref name="ARC_2021"/> The 2017 report said that the melting ice in the warming Arctic was unprecedented in the past 1500 years.<ref name="Freedman_2017">{{cite web |url=https://mashable.com/2017/12/12/arctic-ice-melt-warming-unprecedented-1500-years-report-card |title=Arctic warming, ice melt 'unprecedented' in at least the past 1,500 years |first=Andrew |last=Freedman |date=12 December 2017 |work=Mashable |access-date=13 December 2017}}</ref><ref name="ARC_2017">{{cite web |url=https://www.arctic.noaa.gov/Report-Card/Report-Card-2017 |title=Arctic Report Card: Update for 2017; Arctic shows no sign of returning to reliably frozen region of recent past decades   |work=NOAA |access-date=13 December 2017}}</ref> NOAA's State of the Arctic Reports, starting in 2006, updates some of the records of the original 2004 and 2005 [[Earth:Arctic Climate Impact Assessment|Arctic Climate Impact Assessment]] (ACIA) reports by the intergovernmental [[Organization:Arctic Council|Arctic Council]] and the non-governmental [[Organization:International Arctic Science Committee|International Arctic Science Committee]].<ref name="ACIA_20041015">{{cite report |work=[[Earth:Arctic Climate Impact Assessment|Arctic Climate Impact Assessment]] (ACIA) |date=15 October 2004 |title=Impacts of a Warming Arctic: Arctic Climate Impact Assessment |isbn=0-521-61778-2 |series= Overview report |publisher=Cambridge University Press |pages=140}}</ref>

A 2022 [[Organization:United Nations Environment Programme|United Nations Environment Programme]] (UNEP) report "Spreading Like Wildfire: The Rising Threat Of Extraordinary Landscape Fires" said that smoke from wildfires around the world created a positive feedback loop that is a contributing factor to Arctic melting.<ref name="UNEP_2022">{{cite report |work=United Nations Environment Programme (UNEP) |date=2022 |title=Spreading like Wildfire – The Rising Threat of Extraordinary Landscape Fires |series=A UNEP Rapid Response Assessment |location=Nairobi, Kenya |pages=122}}</ref><ref name="McGrath_20220319">{{cite news |last1=McGrath |first1=Matt |title=Climate change: Wildfire smoke linked to Arctic melting |url=https://www.bbc.com/news/science-environment-60782084 |access-date=20 March 2022 |agency=BBC |date=19 March 2022}}</ref> The 2020 Siberian heatwave was "associated with extensive burning in the Arctic Circle".<ref name="UNEP_2022"/>{{rp|36}} Report authors said that this extreme heat event was the first to demonstrate that it would have been "almost impossible" without anthropogenic emissions and climate change.<ref name="Ciavarella_2021">{{cite journal |last1=Ciavarella |first1=A. |last2=Cotterill |first2=D. |last3=Stott |first3=P. |title=Prolonged Siberian heat of 2020 almost impossible without human influence |journal=Climatic Change |volume=166 |number=9 |date=2021 |page=9 |doi=10.1007/s10584-021-03052-w|pmid=34720262 |pmc=8550097 |bibcode=2021ClCh..166....9C |s2cid=233875870 }}</ref><ref name="UNEP_2022"/>{{rp|36}}

== Impacts on the natural environment ==

=== Temperature and weather changes ===
[[File: ArcticYearlongTempAnom HR.jpg|thumb|The image above shows where average air temperatures (October 2010 – September 2011) were up to 2 degrees Celsius above (red) or below (blue) the long-term average (1981–2010).]]
According to the [[Organization:Intergovernmental Panel on Climate Change|Intergovernmental Panel on Climate Change]], "surface air temperatures (SATs) in the Arctic have warmed at approximately twice the global rate".<ref>{{Cite web|title=Polar Regions (Arctic and Antarctic) — IPCC|url=https://archive.ipcc.ch/report/ar4/wg2/polar-regions-arctic-and-antarctic/|access-date=2021-05-18}}</ref> The period of 1995–2005 was the warmest decade in the Arctic since at least the 17th century, with temperatures {{convert|2|C-change|1}} above the 1951–1990 average.<ref name="Przybylak 2007">{{cite journal | last1 = Przybylak | first1 = Rajmund | year = 2007 | title = Recent air-temperature changes in the Arctic | url = http://www.igsoc.org/annals/46/a46a005.pdf | journal = Annals of Glaciology | volume = 46 | issue = 1 | pages = 316–324 | doi = 10.3189/172756407782871666 | bibcode = 2007AnGla..46..316P | s2cid = 129155170 | doi-access = free | access-date = 14 September 2013 | archive-date = 28 September 2007 | archive-url = https://web.archive.org/web/20070928080017/http://www.igsoc.org/annals/46/a46a005.pdf | url-status = dead }}</ref> In addition, since 2013, Arctic annual mean SAT has been at least 1&nbsp;°C (1.8&nbsp;°F) warmer than the 1981-2010 mean. With 2020 having the second warmest SAT anomaly after 2016, being 1.9&nbsp;°C (3.4&nbsp;°F) warmer than the 1981–2010 average.<ref>{{Cite web|title=Surface Air Temperature|url=https://arctic.noaa.gov/Report-Card/Report-Card-2020/ArtMID/7975/ArticleID/878/Surface-Air-Temperature|access-date=2021-05-18|website=Arctic Program|language=en-US}}</ref> In 2016, there were extreme anomalies from January to February with the temperature in the Arctic being estimated to be between 4-5.8 degrees Celsius more than it was between 1981 and 2010, and has shown to not have cooled years followed.<ref>{{cite journal |last1=Yu |first1=Yining |last2=Xiao |first2=Wanxin |last3=Zhang |first3=Zhilun |last4=Cheng |first4=Xiao |last5=Hui |first5=Fengming |last6=Zhao |first6=Jiechen |title=Evaluation of 2-m Air Temperature and Surface Temperature from ERA5 and ERA-I Using Buoy Observations in the Arctic during 2010–2020|journal=Remote Sensing |date=17 July 2021 |volume=13 |issue=Polar Sea Ice: Detection, Monitoring and Modeling|page=2813 |doi=10.3390/rs13142813 |bibcode=2021RemS...13.2813Y |doi-access=free }}</ref>

Some regions within the Arctic have warmed even more rapidly, with Alaska and western Canada's temperature rising by {{convert|3|to|4|C-change|2}}.<ref name="ACIA 2004">Arctic Climate Impact Assessment (2004): ''Arctic Climate Impact Assessment''. Cambridge University Press, {{ISBN|0-521-61778-2}}, siehe [http://www.acia.uaf.edu/pages/scientific.html online] {{Webarchive|url=https://web.archive.org/web/20130628144322/http://www.acia.uaf.edu/pages/scientific.html |date=28 June 2013 }}</ref> This warming has been caused not only by the rise in [[Chemistry:Greenhouse gas|greenhouse gas]] concentration, but also the  deposition of [[Earth:Soot|soot]] on Arctic ice.<ref name="Quinn et al. 2007">Quinn, P.K., T. S. Bates, E. Baum et al. (2007): ''Short-lived pollutants in the Arctic: their climate impact and possible mitigation strategies'', in: Atmospheric Chemistry and Physics, Vol. 7, S. 15669–15692, siehe [http://www.atmos-chem-phys-discuss.net/7/15669/2007/acpd-7-15669-2007.html online]</ref> The smoke from wildfires defined as "[[Chemistry:Brown carbon|brown carbon]]" also increases arctic warming. Its warming effect is around 30% from the effect of [[Earth:Black carbon|black carbon]] (soot). As wildfires increases with warming this create a positive feedback loop.<ref name="McGrath_20220319"/> A 2013 article published in [[Earth:Geophysical Research Letters|Geophysical Research Letters]] has shown that temperatures in the region haven't been as high as they currently are since at least 44,000 years ago and perhaps as long as 120,000 years ago. The authors conclude that "anthropogenic increases in greenhouse gases have led to unprecedented regional warmth."<ref>[http://www.livescience.com/40676-arctic-temperatures-record-high.html Arctic Temperatures Highest in at Least 44,000 Years], Livescience, 24 October 2013</ref><ref>{{Cite journal | last1 = Miller | first1 = G. H. | last2 = Lehman | first2 = S. J. | last3 = Refsnider | first3 = K. A. | last4 = Southon | first4 = J. R. | last5 = Zhong | first5 = Y. | title = Unprecedented recent summer warmth in Arctic Canada | doi = 10.1002/2013GL057188 | journal = Geophysical Research Letters | volume = 40 | issue = 21 | pages = 5745–5751 | year = 2013 | bibcode = 2013GeoRL..40.5745M | s2cid = 128849141 }}</ref>

On 20 June 2020, for the first time, a temperature measurement was made inside the Arctic Circle of 38&nbsp;°C, more than 100&nbsp;°F. This kind of weather was expected in the region only by 2100. In March, April and May the average temperature in the Arctic was 10&nbsp;°C higher than normal.<ref>{{cite news |last1=Rosane |first1=Olivia |title=A Siberian Town Just Hit 100 F Degrees |url=https://www.ecowatch.com/siberia-100-degrees-2646222137.html |access-date=23 June 2020 |agency=Ecowatch |date=22 June 2020}}</ref><ref>{{cite news |last1=King |first1=Simon |last2=Rowlatt |first2=Justin |title=Arctic Circle sees 'highest-ever' recorded temperatures |url=https://www.bbc.com/news/science-environment-53140069 |access-date=23 June 2020 |agency=BBC |date=22 June 2020}}</ref>  This heat wave, without human – induced warming, could happen only one time in 80,000 years, according to an attribution study published in July 2020. It is the strongest link of a weather event to anthropogenic climate change that had been ever found, for now.<ref name="bbc.com">{{cite news |last1=Rowlatt |first1=Justin |title=Climate change: Siberian heatwave 'clear evidence' of warming |url=https://www.bbc.com/news/science-environment-53415297 |access-date=17 July 2020 |agency=BBC |date=15 July 2020}}</ref> Such heat waves are generally a result of an unusual state of the [[Earth:Jet stream|jet stream]].

Some scientists suggest that climate change will slow the [[Earth:Jet stream|jet stream]] by reducing the difference in temperature between the Arctic and more southern territories, because the Arctic is warming faster. This can facilitate the occurring of such heat waves.<ref>{{cite news |last1=Kuebler |first1=Martin |last2=Schauenberg |first2=Tim |title=Record heat wave in Siberia: What happens when climate change goes extreme? |url=https://www.dw.com/en/siberia-heatwave-climate-change/a-54120019 |access-date=28 July 2020 |agency=Deutch Welle |date=13 July 2020}}</ref> The scientists do not know if the 2020 heat wave is the result of such change.<ref>{{cite web |last1=Serreze |first1=Mark |title=5 ways the extreme Arctic heat wave follows a disturbing pattern |url=https://phys.org/news/2020-06-ways-extreme-arctic-disturbing-pattern.html#:~:text=The%20Arctic%20heat%20wave%20that,underway%20for%20about%2030%20years.&text=The%20Arctic%20is%20warming%20at,the%20globe%20as%20a%20whole. |website=Phys.org |access-date=28 July 2020}}</ref>

A rise of 1.5 degrees in global temperature from the pre-industrial level will probably change the type of precipitation in the Arctic from snow to rain in summer and autumn, which will increase glaciers melting and [[Earth:Permafrost|permafrost]] thawing. Both effects lead to more warming.<ref name="Druckenmiller_20211214"/>

One of the effects of climate change is a strong increase in the number of lightnings in the Arctic. Lightnings increase the risk for wildfires.<ref>{{cite news |last1=Chao-Fong |first1=Léonie |title='Drastic' rise in high Arctic lightning has scientists worried |url=https://www.theguardian.com/environment/2022/jan/07/lightning-high-arctic-rise-scientists-worried |access-date=30 January 2022 |agency=The Guardian |date=7 January 2021}}</ref>

====Arctic amplification====
{{excerpt|Ice–albedo feedback#Current role}}

{{excerpt|Polar amplification#Recent Arctic amplification|paragraphs=2-3}}

====Black carbon====
{{Main|Earth:Black carbon}}
[[Earth:Black carbon|Black carbon]] deposits (from the combustion of heavy fuel oil (HFO) of Arctic shipping) absorb solar radiation in the atmosphere and strongly reduce the albedo when deposited on snow and ice, thus accelerating the effect of the melting of snow and sea ice.<ref name="Qi 442–454">{{Cite journal|last1=Qi|first1=Ling|last2=Wang|first2=Shuxiao|date=November 2019|title=Sources of black carbon in the atmosphere and in snow in the Arctic|url=http://dx.doi.org/10.1016/j.scitotenv.2019.07.073|journal=Science of the Total Environment|volume=691|pages=442–454|doi=10.1016/j.scitotenv.2019.07.073|pmid=31323589|bibcode=2019ScTEn.691..442Q|s2cid=198135020|issn=0048-9697}}</ref> A 2013 study quantified that gas flaring at petroleum extraction sites contributed over 40% of the black carbon deposited in the Arctic.<ref>{{Citation |author=Stohl, A. |author2=Klimont, Z. |author3=Eckhardt, S. |author4=Kupiainen, K. |author5=Chevchenko, V.P. |author6=Kopeikin, V.M. |author7=Novigatsky, A.N. |title=Black carbon in the Arctic: the underestimated role of gas flaring and residential combustion emissions |journal=Atmos. Chem. Phys. |volume=13 |issue=17 |pages=8833–8855 |year=2013 |doi=10.5194/acp-13-8833-2013 |bibcode=2013ACP....13.8833S |doi-access=free }}</ref><ref>{{Cite web |url=https://arctic-council.org/images/PDF_attachments/COP24_2018/2018-11-10-COP24-Stanley-flaring-World-Bank-BC.pdf |title=Gas flaring: An industry practice faces increasing global attention |first=Michael |last=Stanley |publisher=World Bank |date=2018-12-10 |access-date=2020-01-20 |archive-date=15 February 2019 |archive-url=https://web.archive.org/web/20190215231453/https://www.arctic-council.org/images/PDF_attachments/COP24_2018/2018-11-10-COP24-Stanley-flaring-World-Bank-BC.pdf |url-status=dead }}</ref> Recent studies attributed the majority (56%) of Arctic surface black carbon to emissions from Russia, followed by European emissions, and Asia also being a large source.<ref>{{Cite journal|last1=Zhu|first1=Chunmao|last2=Kanaya|first2=Yugo|last3=Takigawa|first3=Masayuki|last4=Ikeda|first4=Kohei|last5=Tanimoto|first5=Hiroshi|last6=Taketani|first6=Fumikazu|last7=Miyakawa|first7=Takuma|last8=Kobayashi|first8=Hideki|last9=Pisso|first9=Ignacio|title=Flexpart v10.1 simulation of source contributions to Arctic black carbon|date=2019-09-24|journal=Atmospheric Chemistry and Physics |doi=10.5194/acp-2019-590|s2cid=204117555 |doi-access=free }}</ref><ref name="Qi 442–454"/>

According to a 2015 study, reductions in black carbon emissions and other minor greenhouse gases, by roughly 60 percent, could cool the Arctic up to 0.2&nbsp;°C by 2050.<ref>{{cite web|url=http://www.climatecentral.org/news/race-to-understand-black-carbons-climate-impact-21458|title=The Race to Understand Black Carbon's Climate Impact|publisher=ClimateCentral|year=2017|access-date=21 May 2017|archive-date=22 November 2017|archive-url=https://web.archive.org/web/20171122113008/http://www.climatecentral.org/news/race-to-understand-black-carbons-climate-impact-21458|url-status=dead}}</ref> However, a 2019 study indicates that "Black carbon emissions will continuously rise due to increased shipping activities", specifically fishing vessels.<ref>{{Cite journal|last1=Zhang|first1=Qiang|last2=Wan|first2=Zheng|last3=Hemmings|first3=Bill|last4=Abbasov|first4=Faig|date=December 2019|title=Reducing black carbon emissions from Arctic shipping: Solutions and policy implications|url=http://dx.doi.org/10.1016/j.jclepro.2019.118261|journal=Journal of Cleaner Production|volume=241|pages=118261|doi=10.1016/j.jclepro.2019.118261|s2cid=203303955|issn=0959-6526}}</ref>

=== Decline of sea ice ===
[[File:Seaice-1870-part-2009.png|thumb|1870–2009 Northern Hemisphere sea ice extent in million square kilometers. Blue shading indicates the pre-satellite era; data then is less reliable.]]{{excerpt|Arctic sea ice decline|paragraphs=1-2|file=no}}

====Changes in extent and area====
Reliable [[Earth:Measurement of sea ice|measurement of sea ice]] edges began with the satellite era in the late 1970s. Before this time, sea ice area and extent were monitored less precisely by a combination of ships, [[Earth:Ice mass balance buoy|buoys]] and aircraft.<ref name="2005gl025080">{{Cite journal|last1=Lawrence|first1=D. M.|last2=Slater|first2=A.|year=2005|title=A projection of severe near-surface permafrost degradation during the 21st century|journal=[[Earth:Geophysical Research Letters|Geophysical Research Letters]]|volume=32|issue=24|pages=L24401|bibcode=2005GeoRL..3224401L|doi=10.1029/2005GL025080|s2cid=128425266}}</ref> The data show a long-term negative trend in recent years, attributed to global warming, although there is also a considerable amount of variation from year to year.<ref name="2007gl029703">{{Cite journal|last1=Stroeve|first1=J.|last2=Holland|first2=M. M.|last3=Meier|first3=W.|last4=Scambos|first4=T.|last5=Serreze|first5=M.|year=2007|title=Arctic sea ice decline: Faster than forecast|journal=Geophysical Research Letters|volume=34|issue=9|pages=L09501|bibcode=2007GeoRL..34.9501S|doi=10.1029/2007GL029703|doi-access=free}}</ref> Some of this variation may be related to effects such as the [[Earth:Arctic oscillation|Arctic oscillation]], which may itself be related to global warming.<ref name="Accelerated decline in Arctic sea ice cover">{{cite journal|author1=Comiso, Josefino C.|author2=Parkinson, Claire L.|author3=Gersten, Robert|author4=Stock, Larry|year=2008|title=Accelerated decline in Arctic sea ice cover|journal=Geophysical Research Letters|volume=35|issue=1|pages=L01703|bibcode=2008GeoRL..35.1703C|doi=10.1029/2007GL031972|s2cid=129445545}}</ref>

[[File:Oldest Arctic Sea Ice is Disappearing.png|thumb|Sea ice coverage in 1980 (bottom) and 2012 (top), as observed by passive microwave sensors from NASA. Multi-year ice is shown in bright white, while average sea ice cover is shown in light blue to milky white.]]

The rate of the decline in entire Arctic ice coverage is accelerating. From 1979 to 1996, the average per decade decline in entire ice coverage was a 2.2% decline in ice extent and a 3% decline in ice area. For the decade ending 2008, these values have risen to 10.1% and 10.7%, respectively. These are comparable to the September to September loss rates in year-round ice (i.e., perennial ice, which survives throughout the year), which averaged a retreat of 10.2% and 11.4% per decade, respectively, for the period 1979–2007.<ref>{{Cite journal|last1=Comiso|first1=Josefino C.|last2=Parkinson|first2=Claire L.|last3=Gersten|first3=Robert|last4=Stock|first4=Larry|date=2008-01-03|title=Accelerated decline in the Arctic sea ice cover|url=http://dx.doi.org/10.1029/2007gl031972|journal=Geophysical Research Letters|volume=35|issue=1|pages=L01703|doi=10.1029/2007gl031972|bibcode=2008GeoRL..35.1703C|s2cid=129445545|issn=0094-8276}}</ref>

The Arctic sea ice September minimum extent (SIE) (i.e., area with at least 15% sea ice coverage) reached new record lows in 2002, 2005, 2007, 2012 (5.32 million km2), 2016 and 2019 (5.65 million km2).<ref>{{cite web|url= http://www.metoffice.gov.uk/news/releases/archive/2012/sea-ice-minimum|title= Record Arctic sea ice minimum confirmed by NSIDC|url-status= dead|archive-url= https://web.archive.org/web/20130729155912/http://www.metoffice.gov.uk/news/releases/archive/2012/sea-ice-minimum|archive-date= 29 July 2013|df= dmy-all}}</ref><ref>{{Cite journal|last1=Petty|first1=Alek A.|last2=Stroeve|first2=Julienne C.|last3=Holland|first3=Paul R.|last4=Boisvert|first4=Linette N.|last5=Bliss|first5=Angela C.|last6=Kimura|first6=Noriaki|last7=Meier|first7=Walter N.|date=2018-02-06|title=The Arctic sea ice cover of 2016: a year of record-low highs and higher-than-expected lows|journal=The Cryosphere|volume=12|issue=2|pages=433–452|doi=10.5194/tc-12-433-2018|bibcode=2018TCry...12..433P|issn=1994-0424 |doi-access=free }}</ref><ref name=":3">{{Cite journal|last1=Yadav|first1=Juhi|last2=Kumar|first2=Avinash|last3=Mohan|first3=Rahul|date=2020-05-21|title=Dramatic decline of Arctic sea ice linked to global warming|url=http://dx.doi.org/10.1007/s11069-020-04064-y|journal=Natural Hazards|volume=103|issue=2|pages=2617–2621|doi=10.1007/s11069-020-04064-y|s2cid=218762126|issn=0921-030X}}</ref> The 2007 melt season let to a minimum 39% below the 1979–2000 average, and for the first time in human memory, the fabled [[Earth:Northwest Passage|Northwest Passage]] opened completely.<ref name="Arctic summer sea ice loss may not 'tip' over the edge">{{cite web|date=30 January 2009|title=Arctic summer sea ice loss may not 'tip' over the edge|url=http://environmentalresearchweb.org/cws/article/research/37591|url-status=dead|archive-url=https://web.archive.org/web/20090202155122/http://environmentalresearchweb.org/cws/article/research/37591|archive-date=2 February 2009|access-date=26 July 2010|publisher=environmentalresearchweb|df=dmy-all}}</ref> During July 2019 the warmest month in the Arctic was recorded, reaching the lowest SIE (7.5 million km2) and sea ice volume (8900 km3). Setting a decadal trend of SIE decline of −13%.<ref name=":3" /> As for now, the SIE has shrink by 50% since the 1970s.<ref name=":2">{{Cite journal|last1=Senftleben|first1=Daniel|last2=Lauer|first2=Axel|last3=Karpechko|first3=Alexey|date=2020-02-15|title=Constraining Uncertainties in CMIP5 Projections of September Arctic Sea Ice Extent with Observations|url=http://dx.doi.org/10.1175/jcli-d-19-0075.1|journal=Journal of Climate|volume=33|issue=4|pages=1487–1503|doi=10.1175/jcli-d-19-0075.1|bibcode=2020JCli...33.1487S|s2cid=210273007|issn=0894-8755}}</ref>

From 2008 to 2011, Arctic sea ice minimum extent was higher than 2007, but it did not return to the levels of previous years.<ref name="Arcticseaiceextent">{{cite web|date=6 October 2009|title=Arctic sea ice extent remains low; 2009 sees third-lowest mark|url=http://nsidc.org/news/press/20091005_minimumpr.html|access-date=26 July 2010|publisher=NSIDC|archive-date=26 December 2012|archive-url=https://web.archive.org/web/20121226072828/http://nsidc.org/news/press/20091005_minimumpr.html|url-status=dead}}</ref><ref name="Black">{{cite news|last=Black|first=Richard|date=18 May 2007|title=Earth – melting in the heat?|work=BBC News|url=http://news.bbc.co.uk/2/hi/science/nature/4315968.stm|access-date=3 January 2008}}</ref> In 2012 however, the 2007 record low was broken in late August with three weeks still left in the melt season.<ref name="Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Chapter 10">{{cite book|last=Meehl|first=G.A.|url=http://archive.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter10.pdf|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, Chapter 10|publisher={{wipe|Cambridge University Press}}|year=2007|location=New York|display-authors=0}}</ref> It continued to fall, bottoming out on 16 September 2012 at 3.42 million square kilometers (1.32 million square miles), or 760,000 square kilometers (293,000 square miles) below the previous low set on 18 September 2007 and 50% below the 1979–2000 average.<ref name="Climatology: threatened loss of the Greenland ice-sheet">{{cite journal|author1=Gregory JM|author2=Huybrechts P|author3=Raper SC|date=April 2004|title=Climatology: threatened loss of the Greenland ice-sheet|url=http://homepages.vub.ac.be/~phuybrec/pdf/Nature.Green.2004.pdf|journal=Nature|volume=428|issue=6983|page=616|bibcode=2004Natur.428..616G|doi=10.1038/428616a|pmid=15071587|quote=The Greenland ice-sheet would melt faster in a warmer climate and is likely to be eliminated — except for residual glaciers in the mountains — if the annual average temperature in [[Place:Greenland|Greenland]] increases by more than about 3 °C. This would raise the global average sea-level by 7 metres over a period of 1000 years or more. We show here that concentrations of greenhouse gasses will probably have reached levels before the year 2100 that are sufficient to raise the temperature past this warming threshold.|s2cid=4421590|access-date=5 April 2008|archive-date=9 August 2017|archive-url=https://web.archive.org/web/20170809085231/http://homepages.vub.ac.be/~phuybrec/pdf/Nature.Green.2004.pdf|url-status=dead}}</ref><ref name="Record Arctic sea ice minimum confirmed by NSIDC">Record Arctic sea ice minimum confirmed by NSIDC</ref>

Temperatures in the Arctic region are increasing four times faster than elsewhere on Earth, according to a July 2022 ''[[Earth:Geophysical Research Letters|Geophysical Research Letters]]'' article.<ref name="Chylek_20220716"/>{{rp|1}}<ref name="LANL_202207"/>

====Changes in volume====
[[File:Plot arctic sea ice volume.svg|thumb|Seasonal variation and long-term decrease of Arctic sea ice volume as determined by measurement backed numerical modelling.<ref name="zhangrothrock1">{{cite journal|author1=Zhang, Jinlun  |author2=D.A. Rothrock|title=Modeling global sea ice with a thickness and enthalpy distribution model in generalized curvilinear coordinates|journal=Mon. Wea. Rev.|volume=131|issue=5|pages=681–697|year=2003|doi=10.1175/1520-0493(2003)131<0845:MGSIWA>2.0.CO;2|citeseerx=10.1.1.167.1046|bibcode=2003MWRv..131..845Z}}</ref>]]
The sea ice thickness field and accordingly the ice volume and mass, is much more difficult to determine than the extension. Exact measurements can be made only at a limited number of points. Because of large variations in ice and snow thickness and consistency air- and spaceborne-measurements have to be evaluated carefully.  Nevertheless, the studies made support the assumption of a dramatic decline in ice age and thickness.<ref name="Arcticseaiceextent" /> While the Arctic ice area and extent show an accelerating downward trend, arctic ice volume shows an even sharper decline than the ice coverage. Since 1979, the ice volume has shrunk by 80% and in just the past decade the volume declined by 36% in the autumn and 9% in the winter.<ref>{{cite news|last=Masters|first=Jeff|title=Arctic sea ice volume now one-fifth its 1979 level|url=http://www.wunderground.com/blog/JeffMasters/article.html?entrynum=2352|work=weather underground|date=19 February 2013|access-date=14 September 2013|url-status=dead|archive-url=https://web.archive.org/web/20131219012233/http://www.wunderground.com/blog/JeffMasters/article.html?entrynum=2352|archive-date=19 December 2013|df=dmy-all}}</ref> And currently, 70% of the winter sea ice has turned into seasonal ice.<ref name=":2" />

====An end to summer sea ice?====

The IPCC's Fourth Assessment Report in 2007 summarized the current state of sea ice projections: "the projected reduction <nowiki>[in global sea ice cover]</nowiki> is accelerated in the Arctic, where some models project summer sea ice cover to disappear entirely in the high-emission A2 scenario in the latter part of the 21st century."<ref name="Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Chapter 10"/> However, current [[Earth:Climate model|climate model]]s frequently underestimate the rate of sea ice retreat.<ref name="2007gl029703"/> A summertime ice-free Arctic would be unprecedented in recent geologic history, as currently [[Scientific evidence|scientific evidence]] does not indicate an ice-free polar sea anytime in the last 700,000 years.<ref name="overpeck">{{cite journal |last1=Overpeck |first1=Jonathan T. |title=Arctic System on Trajectory to New, Seasonally Ice-Free State |journal=Eos, Transactions, American Geophysical Union |volume=86 |issue=34 |pages=309–316 |date=23 August 2005 |doi=10.1029/2005EO340001 |display-authors=3 |last2=Sturm |first2=Matthew |last3=Francis |first3=Jennifer A. |last4=Perovich |first4=Donald K. |last5=Serreze |first5=Mark C. |last6=Benner |first6=Ronald |last7=Carmack |first7=Eddy C. |last8=Chapin |first8=F. Stuart |last9=Gerlach |first9=S. Craig |bibcode=2005EOSTr..86..309O |df=dmy-all |doi-access=free }}</ref><ref name="Ottera">{{cite journal | last = Butt | first = F. A. | author2 = H. Drange | author3 = A. Elverhoi | author4 = O. H. Ottera | author5 = A. Solheim | url = http://www.nersc.no/~oddho/Thesis/chapter3.pdf | title = The Sensitivity of the North Atlantic Arctic Climate System to Isostatic Elevation Changes, Freshwater and Solar Forcings | journal = Quaternary Science Reviews | volume = 21 | pages = 1643–1660 | year = 2002 | oclc = 108566094 | issue = 14–15 | doi = 10.1016/S0277-3791(02)00018-5 | url-status = dead | archive-url = https://web.archive.org/web/20080910213953/http://www.nersc.no/~oddho/Thesis/chapter3.pdf | archive-date = 10 September 2008 | df = dmy-all }}</ref>

The Arctic ocean will likely be free of summer [[Earth:Sea ice|sea ice]] before the year 2100, but many different dates have been projected, with models showing near-complete to complete loss in September from 2035 to some time around 2067.<ref>{{Cite web|last=Reich|first=Katharine|date=2019-11-15|title=Arctic Ocean could be ice-free for part of the year as soon as 2044|url=https://phys.org/news/2019-11-arctic-ocean-ice-free-year.html|access-date=2020-09-03|website=phys.org|language=en}}</ref><ref>{{Cite web|last=Kirby|first=Alex|date=2020-08-11|title=End of Arctic sea ice by 2035 possible, study finds|url=https://climatenewsnetwork.net/end-of-arctic-sea-ice-by-2035-possible-study-finds/|access-date=2020-09-03|website=Climate News Network|language=en-GB}}</ref>

==== Melting of the Greenland ice sheet ====
[[File:Greenland Albedo Change.png|thumb|Albedo Change on Greenland]]
Models predict a sea-level contribution of about {{convert|5|cm|in|0}} from melting of the [[Earth:Greenland ice sheet|Greenland ice sheet]] during the 21st century.<ref name="ipcc">[[Organization:Intergovernmental Panel on Climate Change|IPCC]] AR4 chapter 10 [http://archive.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter10.pdf] Table 10.7</ref> It is also predicted that [[Place:Greenland|Greenland]] will become warm enough by 2100 to begin an almost complete melt during the next 1,000 years or more.<ref name="Climatology: threatened loss of the Greenland ice-sheet" /><ref name="Regional Sea Level Change">{{cite web|title=Regional Sea Level Change|url=http://www.grida.no/climate/ipcc_tar/wg1/432.htm#fig1116|publisher=Intergovernmental Panel on Climate Change|format=Figure 11.16|access-date=4 April 2008|archive-date=19 January 2017|archive-url=https://web.archive.org/web/20170119092619/http://www.grida.no/climate/ipcc_tar/wg1/432.htm#fig1116|url-status=dead}}</ref> In early July 2012, 97% percent of the ice sheet experienced some form of surface melt, including the summits.<ref name="nasa">{{cite web|title=NASA – Satellites See Unprecedented Greenland Ice Sheet Surface Melt|url=http://www.nasa.gov/topics/earth/features/greenland-melt.html|access-date=4 November 2012|archive-date=24 June 2023|archive-url=https://web.archive.org/web/20230624023317/https://www.nasa.gov/topics/earth/features/greenland-melt.html|url-status=dead}}</ref>

Ice thickness measurements from the [[Physics:Gravity Recovery and Climate Experiment|GRACE]] satellite indicate that ice mass loss is accelerating. For the period 2002–2009, the rate of loss increased from 137 Gt/yr to 286 Gt/yr, with every year seeing on average 30 gigatonnes more mass lost than in the preceding year.<ref name="Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE">{{cite journal|author=Velicogna, I.|year=2009|title=Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE|journal=Geophysical Research Letters|volume=36|issue=19|pages=L19503|bibcode=2009GeoRL..3619503V|citeseerx=10.1.1.170.8753|doi=10.1029/2009GL040222|s2cid=14374232}}</ref> The rate of melting was 4 times higher in 2019 than in 2003. In the year 2019 the melting contributed 2.2 millimeters to sea level rise in just 2 months.<ref name="ScienceDaily">{{cite web|title=Ohio State University. "Warming Greenland ice sheet passes point of no return: Even if the climate cools, study finds, glaciers will continue to shrink."|url=https://www.sciencedaily.com/releases/2020/08/200813123550.htm|access-date=1 September 2020|website=ScienceDaily}}</ref><ref name="livescience.com">{{cite web|last1=Pappas|first1=Stephanie|title=Nothing will stop Greenland's ice sheet from shrinking now|url=https://www.livescience.com/greenland-melt-point-of-no-return.html|access-date=1 September 2020|website=Live Science|date=17 August 2020}}</ref> Overall, the signs are overwhelming that melting is not only occurring, but accelerating year on year.

[[File:Greenland Ice Mass Trend.jpg|thumb|Greenland ice sheet mass trend (2003–2005)]]
According to a study published in "Nature Communications Earth and Environment" the Greenland ice sheet is possibly past the point of no return, meaning that even if the rise in temperature were to completely stop and even if the climate were to become a little colder, the melting would continue. This outcome is due to the movement of ice from the middle of Greenland to the coast, creating more contact between the ice and warmer coastal water and leading to more melting and calving. Another climate scientist says that after all the ice near the coast melts, the contact between the seawater and the ice will stop what can prevent further warming.<ref name="ScienceDaily" /><ref name="livescience.com" />

In September 2020, [[Astronomy:Satellite imagery|satellite imagery]] showed that a big chunk of ice shattered into many small pieces from the last remaining ice shelf in Nioghalvfjerdsfjorden, Greenland.<ref>{{cite web|date=14 September 2020|title=Climate change: Warmth shatters section of Greenland ice shelf|url=https://www.bbc.com/news/science-environment-54127279|website=BBC}}</ref> This ice sheet is connected to the interior ice sheet, and could prove a hotspot for deglaciation in coming years.

Another unexpected effect of this melting relates to activities by the United States military in the area. Specifically, Camp Century, a nuclear powered base which has been producing nuclear waste over the years.<ref>{{cite news|date=9 March 2019|title=A Top-Secret US Military Base Will Melt Out of the Greenland Ice Sheet|work=VICE Magazine|url=https://www.vice.com/en_asia/article/d3wdb7/cold-war-era-nuclear-base-camp-century-melting-climate-change-greenland}}</ref> In 2016, a group of scientists evaluated the environmental impact and estimated that due to changing weather patterns over the next few decades, melt water could release the [[Physics:Nuclear waste|nuclear waste]], 20,000 liters of [[Chemistry:Chemical waste|chemical waste]] and 24 million liters of untreated sewage into the environment. However, so far neither US or {{wipe|Denmark}} has taken responsibility for the clean-up.<ref>{{Cite magazine|last=Laskow|first=Sarah|date=2018-02-27|title=America's Secret Ice Base Won't Stay Frozen Forever|magazine=Wired|url=https://www.wired.com/story/americas-secret-ice-base-wont-stay-frozen-forever/|issn=1059-1028}}</ref>

===Changes in vegetation===
[[File:Arctic Vegetation Index Trend (WH).png|right|thumb|Western Hemisphere Arctic Vegetation Index Trend]] 
[[File:Arctic Vegetation Index Trend (EH).png|right|thumb|Eastern Hemisphere Vegetation Index Trend]]
Climate change is expected to have a strong effect on the Arctic's flora, some of which is already being seen. These changes in vegetation are associated with the increases in landscape scale [[Chemistry:Methane emissions|methane emissions]],<ref>{{Cite journal|last=Christensen|first=Torben R.|date=2004|title=Thawing sub-arctic permafrost: Effects on vegetation and methane emissions|url=http://dx.doi.org/10.1029/2003gl018680|journal=Geophysical Research Letters|volume=31|issue=4|pages=L04501|bibcode=2004GeoRL..31.4501C|doi=10.1029/2003gl018680|s2cid=129023294|issn=0094-8276}}</ref> as well as increases in {{CO2}}, Tº and the disruption of ecological cycles which affect patterns in nutrient cycling, humidity and other key ecological factors that help shape plant communities.<ref>{{Cite journal|last1=Bjorkman|first1=Anne D.|last2=García Criado|first2=Mariana|last3=Myers-Smith|first3=Isla H.|last4=Ravolainen|first4=Virve|last5=Jónsdóttir|first5=Ingibjörg Svala|last6=Westergaard|first6=Kristine Bakke|last7=Lawler|first7=James P.|last8=Aronsson|first8=Mora|last9=Bennett|first9=Bruce|last10=Gardfjell|first10=Hans|last11=Heiðmarsson|first11=Starri|date=2019-03-30|title=Status and trends in Arctic vegetation: Evidence from experimental warming and long-term monitoring|url=http://dx.doi.org/10.1007/s13280-019-01161-6|journal=Ambio|volume=49|issue=3|pages=678–692|doi=10.1007/s13280-019-01161-6|issn=0044-7447|pmc=6989703|pmid=30929249}}</ref>

A large source of information for how vegetation has adapted to climate change over the last years comes from satellite records, which help quantify shifts in vegetation in the Arctic region. For decades, NASA and NOAA satellites have continuously monitored vegetation from space. The Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Very High-Resolution Radiometer (AVHRR) instruments, as well as others, measure the intensity of visible and near-infrared light reflecting off of plant leaves.<ref>{{Cite journal|last=Gutman|first=G.Garik|date=February 1991|title=Vegetation indices from AVHRR: An update and future prospects|url=http://dx.doi.org/10.1016/0034-4257(91)90005-q|journal=Remote Sensing of Environment|volume=35|issue=2–3|pages=121–136|bibcode=1991RSEnv..35..121G|doi=10.1016/0034-4257(91)90005-q|issn=0034-4257}}</ref> Scientists use this information to calculate the Normalized Difference Vegetation Index (NDVI),<ref name=":7">{{Cite book|last=Sonja|first=Myers-Smith, Isla H. Kerby, Jeffrey T. Phoenix, Gareth K. Bjerke, Jarle W. Epstein, Howard E. Assmann, Jakob J. John, Christian Andreu-Hayles, Laia Angers-Blondin, Sandra Beck, Pieter S. A. Berner, Logan T. Bhatt, Uma S. Bjorkman, Anne D. Blok, Daan Bryn, Anders Christiansen, Casper T. Cornelissen, J. Hans C. Cunliffe, Andrew M. Elmendorf, Sarah C. Forbes, Bruce C. Goetz, Scott J. Hollister, Robert D. de Jong, Rogier Loranty, Michael M. Macias-Fauria, Marc Maseyk, Kadmiel Normand, Signe Olofsson, Johan Parker, Thomas C. Parmentier, Frans-Jan W. Post, Eric Schaepman-Strub, Gabriela Stordal, Frode Sullivan, Patrick F. Thomas, Haydn J. D. Tommervik, Hans Treharne, Rachael Tweedie, Craig E. Walker, Donald A. Wilmking, Martin Wipf|url=http://worldcat.org/oclc/1234747430|title=Complexity revealed in the greening of the Arctic|date=2020|publisher=Umeå universitet, Institutionen för ekologi, miljö och geovetenskap|oclc=1234747430}}</ref> an indicator of photosynthetic activity or "greenness" of the landscape, which is most often used. There also exist other indices, such as the Enhanced Vegetation Index (EVI) or Soil-Adjusted Vegetation Index (SAVI).<ref name=":7" />

These indices can be used as proxies for vegetation productivity, and their shifts over time can provide information on how vegetation changes over time. One of the two most used ways to define shifts in vegetation in the Arctic are the concepts of Arctic greening and Arctic browning. The former refers to a positive trend in the aforementioned greenness indices, indicating increases in plant cover or biomass whereas browning can be broadly understood as a negative trend, with decreases in those variables.<ref name=":7" />

Recent studies have allowed us to get an idea of how these two processes have progressed in recent years. It has been found that from 1985 to 2016, greening has occurred in 37.3% of all sites sampled in the tundra, whereas browning was observed only in 4.7% of them.<ref name=":8">{{Cite journal|last1=Berner|first1=Logan T.|last2=Massey|first2=Richard|last3=Jantz|first3=Patrick|last4=Forbes|first4=Bruce C.|last5=Macias-Fauria|first5=Marc|last6=Myers-Smith|first6=Isla|last7=Kumpula|first7=Timo|last8=Gauthier|first8=Gilles|last9=Andreu-Hayles|first9=Laia|last10=Gaglioti|first10=Benjamin V.|last11=Burns|first11=Patrick|date=December 2020|title=Summer warming explains widespread but not uniform greening in the Arctic tundra biome|journal=Nature Communications|language=en|volume=11|issue=1|pages=4621|bibcode=2020NatCo..11.4621B|doi=10.1038/s41467-020-18479-5|issn=2041-1723|pmc=7509805|pmid=32963240}}</ref> Certain variables influenced this distribution, as greening was mostly associated with sites with higher summer air temperature, soil temperature and soil moisture.<ref name=":8" /> On the other hand, browning was found to be linked with colder sites that were experiencing cooling and drying.<ref name=":8" /> Overall, this paints the picture of widespread greening occurring throughout significant portions of the arctic tundra, as a consequence of increases in plant productivity, height, biomass and shrub dominance in the area.

This expansion of vegetation in the Arctic is not equivalent across types of vegetation. One of the most dramatic changes arctic tundras are currently facing is the expansion of [[Biology:Shrub|shrub]]s,<ref>{{Cite journal|last1=Martin|first1=Andrew|last2=Petrokofsky|first2=Gillian|date=2018-05-24|title=Shrub growth and expansion in the Arctic tundra: an assessment of controlling factors using an evidence-based approach.|url=http://dx.doi.org/10.17011/conference/eccb2018/108642|journal=Proceedings of the 5th European Congress of Conservation Biology|location=Jyväskylä|publisher=Jyvaskyla University Open Science Centre|doi=10.17011/conference/eccb2018/108642|s2cid=134164370 }}</ref> which, thanks to increases in air temperature and, to a lesser extent, precipitation have contributed to an Arctic-wide trend known as "shrubification", where shrub type plants are taking over areas previously dominated by moss and lichens. This change contributes to the consideration that the tundra biome is currently experiencing the most rapid change of any terrestrial biomes on the planet.<ref>{{Cite journal|last1=Myers-Smith|first1=Isla H.|last2=Hik|first2=David S.|date=2017-09-25|title=Climate warming as a driver of tundra shrubline advance|url=http://dx.doi.org/10.1111/1365-2745.12817|journal=Journal of Ecology|volume=106|issue=2|pages=547–560|doi=10.1111/1365-2745.12817|issn=0022-0477|hdl=20.500.11820/f12e7d9d-1c24-4b5f-ad86-96715e071c7b|s2cid=90390767}}</ref>

The direct impact on mosses and lichens is unclear as there exist very few studies at species level, but climate change is more likely to cause increased fluctuation and more frequent extreme events.<ref>{{Cite journal|last1=Alatalo|first1=Juha M.|last2=Jägerbrand|first2=Annika K.|last3=Molau|first3=Ulf|date=2014-08-14|title=Climate change and climatic events: community-, functional- and species-level responses of bryophytes and lichens to constant, stepwise, and pulse experimental warming in an alpine tundra|url=http://dx.doi.org/10.1007/s00035-014-0133-z|journal=Alpine Botany|volume=124|issue=2|pages=81–91|doi=10.1007/s00035-014-0133-z|issn=1664-2201|s2cid=6665119}}</ref> The expansion of shrubs could affect permafrost dynamics, but the picture is quite unclear at the moment. In the winter, shrubs trap more snow, which insulates the permafrost from extreme cold spells, but in the summer they shade the ground from direct sunlight, how these two effects counter and balance each other is not yet well understood.<ref>{{Cite journal|last1=TAPE|first1=KEN|last2=STURM|first2=MATTHEW|last3=RACINE|first3=CHARLES|date=2006-03-24|title=The evidence for shrub expansion in Northern Alaska and the Pan-Arctic|url=http://dx.doi.org/10.1111/j.1365-2486.2006.01128.x|journal=Global Change Biology|volume=12|issue=4|pages=686–702|bibcode=2006GCBio..12..686T|doi=10.1111/j.1365-2486.2006.01128.x|s2cid=86278724|issn=1354-1013}}</ref> Warming is likely to cause changes in plant communities overall, contributing to the rapid changes tundra ecosystems are facing. While shrubs may increase in range and biomass, warming may also cause a decline in [[Biology:Cushion plant|cushion plant]]s such as moss campion, and since cushion plants act as facilitator species across [[Earth:Trophic level|trophic level]]s and fill important ecological niches in several environments, this could cause cascading effects in these ecosystems that could severely affect the way in which they function and are structured.<ref>{{Cite journal|last1=Alatalo|first1=Juha M|last2=Little|first2=Chelsea J|date=2014-03-22|title=Simulated global change: contrasting short and medium term growth and reproductive responses of a common alpine/Arctic cushion plant to experimental warming and nutrient enhancement|journal=SpringerPlus|volume=3|issue=1|page=157|doi=10.1186/2193-1801-3-157|issn=2193-1801|pmc=4000594|pmid=24790813 |doi-access=free }}</ref>

The expansion of these shrubs can also have strong effects on other important ecological dynamics, such as the [[Earth:Albedo|albedo effect]].<ref>{{Cite journal|last1=Loranty|first1=Michael M|last2=Goetz|first2=Scott J|last3=Beck|first3=Pieter S A|date=2011-04-01|title=Tundra vegetation effects on pan-Arctic albedo|url=http://dx.doi.org/10.1088/1748-9326/6/2/024014|journal=Environmental Research Letters|volume=6|issue=2|pages=024014|bibcode=2011ERL.....6b4014L|doi=10.1088/1748-9326/6/2/024014|s2cid=250681995 |issn=1748-9326}}</ref> These shrubs change the winter surface of the tundra from undisturbed, uniform snow to mixed surface with protruding branches disrupting the snow cover,<ref name=":9">{{Cite journal|last1=Belke-Brea|first1=M.|last2=Domine|first2=F.|last3=Barrere|first3=M.|last4=Picard|first4=G.|last5=Arnaud|first5=L.|date=2020-01-15|title=Impact of Shrubs on Winter Surface Albedo and Snow Specific Surface Area at a Low Arctic Site: In Situ Measurements and Simulations|url=http://dx.doi.org/10.1175/jcli-d-19-0318.1|journal=Journal of Climate|volume=33|issue=2|pages=597–609|bibcode=2020JCli...33..597B|doi=10.1175/jcli-d-19-0318.1|s2cid=210295151|issn=0894-8755}}</ref> this type of snow cover has a lower albedo effect, with reductions of up to 55%, which contributes to a positive feedback loop on regional and global climate warming.<ref name=":9" /> This reduction of the albedo effect means that more radiation is absorbed by plants, and thus, surface temperatures increase, which could disrupt current surface-atmosphere energy exchanges and affect thermal regimes of permafrost.<ref name=":9" /> Carbon cycling is also being affected by these changes in vegetation, as parts of the tundra increase their shrub cover, they behave more like boreal forests in terms of carbon cycling.<ref name=":10">{{Cite journal|last1=Jeong|first1=Su-Jong|last2=Bloom|first2=A. Anthony|last3=Schimel|first3=David|last4=Sweeney|first4=Colm|last5=Parazoo|first5=Nicholas C.|last6=Medvigy|first6=David|last7=Schaepman-Strub|first7=Gabriela|last8=Zheng|first8=Chunmiao|last9=Schwalm|first9=Christopher R.|last10=Huntzinger|first10=Deborah N.|last11=Michalak|first11=Anna M.|date=July 2018|title=Accelerating rates of Arctic carbon cycling revealed by long-term atmospheric CO 2 measurements|url=http://dx.doi.org/10.1126/sciadv.aao1167|journal=Science Advances|volume=4|issue=7|pages=eaao1167|bibcode=2018SciA....4.1167J|doi=10.1126/sciadv.aao1167|issn=2375-2548|pmc=6040845|pmid=30009255}}</ref> This is speeding up the carbon cycle, as warmer temperatures lead to increased permafrost thawing and carbon release, but also carbon capturing from plants that have increased growth.<ref name=":10" /> It is not certain whether this balance will go in one direction or the other, but studies have found that it is more likely that this will eventually lead to increased {{CO2}} in the atmosphere.<ref name=":10" />

For a more graphic and geographically focused overview of the situation, maps above show the Arctic Vegetation Index Trend between July 1982 and December 2011 in the Arctic Circle. Shades of green depict areas where plant productivity and abundance increased; shades of brown show where photosynthetic activity declined, both according to the NDVI index. The maps show a ring of greening in the treeless tundra ecosystems of the circumpolar Arctic—the northernmost parts of Canada, Russia, and Scandinavia. Tall shrubs and trees started to grow in areas that were previously dominated by tundra grasses, as part of the previously mentioned "shrubification" of the tundra. Researchers concluded that plant growth had increased by 7% to 10% overall.

However, boreal forests, particularly those in North America, showed a different response to warming. Many boreal forests greened, but the trend was not as strong as it was for tundra of the circumpolar Arctic, mostly characterized by shrub expansion and increased growth.<ref>{{Cite journal|last1=Martin|first1=Andrew C.|last2=Jeffers|first2=Elizabeth S.|last3=Petrokofsky|first3=Gillian|last4=Myers-Smith|first4=Isla|last5=Macias-Fauria|first5=Marc|date=August 2017|title= Shrub growth and expansion in the Arctic tundra: An assessment of controlling factors using an evidence-based approach|url=https://iopscience.iop.org/article/10.1088/1748-9326/aa7989|journal=Environmental Research Letters|language=en|volume=12|issue=8|page=085007|doi=10.1088/1748-9326/aa7989|bibcode=2017ERL....12h5007M|s2cid=134164370 }}</ref> In North America, some boreal forests actually experienced browning over the study period. Droughts, increased forest fire activity, animal behavior, industrial pollution, and a number of other factors may have contributed to browning.<ref name=":7" />

Another important change affecting flora in the arctic is the increase of wildfires in the Arctic Circle, which in 2020 broke its record of {{CO2}} emissions, peaking at 244 megatonnes of carbon dioxide emitted.<ref name=":11">{{Cite journal|last=Witze|first=Alexandra|date=2020-09-10|title=The Arctic is burning like never before — and that's bad news for climate change|url=http://dx.doi.org/10.1038/d41586-020-02568-y|journal=Nature|volume=585|issue=7825|pages=336–337|bibcode=2020Natur.585..336W|doi=10.1038/d41586-020-02568-y|issn=0028-0836|pmid=32913318|s2cid=221625701}}</ref>  This is due to the burning of peatlands, carbon-rich soils that originate from the accumulation of waterlogged plants which are mostly found at Arctic latitudes.<ref name=":11" /> These peatlands are becoming more likely to burn as temperatures increase, but their own burning and releasing of {{CO2}} contributes to their own likelihood of burning in a positive feedback loop.<ref name=":11" />

In terms of aquatic vegetation, reduction of sea ice has boosted the productivity of [[Earth:Phytoplankton|phytoplankton]] by about twenty percent over the past thirty years. However, the effect on [[Earth:Marine ecosystem|marine ecosystem]]s is unclear, since the larger types of phytoplankton, which are the preferred food source of most [[Earth:Zooplankton|zooplankton]], do not appear to have increased as much as the smaller types. So far, Arctic phytoplankton have not had a significant impact on the global [[Earth:Carbon cycle|carbon cycle]].<ref>{{Cite journal|last1=Lee|first1=Sang H.|last2=Whitledge|first2=Terry E.|last3=Kang|first3=Sung-Ho|date=2009-08-25|title=Carbon Uptake Rates of Sea Ice Algae and Phytoplankton under Different Light Intensities in a Landfast Sea Ice Zone, Barrow, Alaska|url=http://dx.doi.org/10.14430/arctic25|journal=Arctic|volume=61|issue=3|doi=10.14430/arctic25|issn=1923-1245}}</ref> In summer, the melt ponds on young and thin ice have allowed sunlight to penetrate the ice, in turn allowing [[Biology:Ice algae|ice algae]] to bloom in unexpected concentrations, although it is unknown just how long this phenomenon has been occurring, or what its effect on broader ecological cycles is.<ref>{{Cite journal|last=Wu|first=Qiang|date=2019-12-24|title=Satellite observations of unprecedented phytoplankton blooms in the Southern Ocean |journal=The Cryosphere Discuss |doi=10.5194/tc-2019-282-sc1 |s2cid=243147775 |doi-access=free }}</ref>

===Changes for animals===
[[File:Polar Bear Habitat.png|thumb|Projected change in polar bear habitat from 2001–2010 to 2041–2050]]
The northward shift of the [[Earth:Subarctic climate|subarctic climate]] zone is allowing animals that are adapted to that climate to move into the far north, where they are replacing species that are more adapted to a pure Arctic climate. Where the Arctic species are not being replaced outright, they are often interbreeding with their southern relations. Among slow-breeding [[Biology:Vertebrate|vertebrate]] species, this usually has the effect of reducing the [[Biology:Genetic diversity|genetic diversity]] of the [[Biology:Genus|genus]]. Another concern is the spread of [[Medicine:Infection|infectious diseases]], such as [[Medicine:Brucellosis|brucellosis]] or phocine distemper virus, to previously untouched populations. This is a particular danger among [[Biology:Marine mammal|marine mammal]]s who were previously segregated by sea ice.<ref>{{cite web|last=Struzik|first=Ed|date=14 February 2011|title=Arctic Roamers: The Move of Southern Species into Far North|url=http://e360.yale.edu/feature/arctic_roamers_the_move_of_southern_species_into_far_north/2370/|access-date=19 July 2016|website=Environment360|publisher=Yale University|quote=Grizzly bears mating with polar bears. Red foxes out-competing Arctic foxes. Exotic diseases making their way into once-isolated polar realms. These are just some of the worrisome phenomena now occurring as Arctic temperatures soar and the Arctic Ocean, a once-impermeable barrier, melts.}}</ref>

On 3 April 2007, the National Wildlife Federation urged the United States Congress to place polar bears under the Endangered Species Act.<ref name="Protection For Polar Bears Urged By National Wildlife Federation">{{cite web|date=3 April 2008|title=Protection For Polar Bears Urged By National Wildlife Federation|url=https://www.sciencedaily.com/releases/2008/04/080402210456.htm|access-date=3 April 2008|website=Science Daily}}</ref>
Four months later, the United States Geological Survey completed a year-long study<ref name="Uncertainty in Climate Model Projections of Arctic Sea Ice Decline: An Evaluation Relevant to Polar Bears">{{cite web|last=DeWeaver|first=Eric|author2=U.S. Geological Survey|year=2007|title=Uncertainty in Climate Model Projections of Arctic Sea Ice Decline: An Evaluation Relevant to Polar Bears|url=http://www.usgs.gov/newsroom/special/polar_bears/docs/USGS_PolarBear_DeWeaver_GCM-Uncertainty.pdf|url-status=dead|archive-url=https://web.archive.org/web/20090509072101/http://www.usgs.gov/newsroom/special/polar_bears/docs/USGS_PolarBear_DeWeaver_GCM-Uncertainty.pdf|archive-date=9 May 2009|publisher=United States Department of the Interior|oclc=183412441|df=dmy-all}}</ref> which concluded in part that the floating Arctic sea ice will continue its rapid shrinkage over the next 50 years, consequently wiping out much of the polar bear [[Earth:Habitat|habitat]]. The bears would disappear from Alaska, but would continue to exist in the [[Place:Canadian Arctic Archipelago|Canadian Arctic Archipelago]] and areas off the northern Greenland coast.<ref name="Warming Is Seen as Wiping Out Most Polar Bears">{{cite news|last=Broder|first=John|author2=Revkin, Andrew C.|date=8 July 2007|title=Warming Is Seen as Wiping Out Most Polar Bears|work=The New York Times|url=https://www.nytimes.com/2007/09/08/science/earth/08polar.html?_r=1&hp=&adxnnl=1&oref=slogin&adxnnlx=1190574637-aS0VOr2klykTSNwK91tiDg|access-date=23 September 2007}}</ref> Secondary ecological effects are also resultant from the shrinkage of sea ice; for example, [[Biology:Polar bear|polar bear]]s are denied their historic length of seal hunting season due to late formation and early thaw of pack ice.

Similarly, Arctic warming negatively affects the foraging and breeding ecology many other species of arctic marine mammals, such as [[Biology:Walrus|walrus]]es,<ref>{{Cite web|title=Walruses in a Time of Climate Change|url=https://www.arctic.noaa.gov/Report-Card/Report-Card-2015/ArtMID/5037/ArticleID/226/Walruses-in-a-Time-of-Climate-Change|access-date=2021-05-19|website=Arctic Program|language=en-US}}</ref> seals, [[Biology:Arctic fox|foxes]] or reindeers.<ref>{{Cite journal|last1=Descamps|first1=Sébastien|last2=Aars|first2=Jon|last3=Fuglei|first3=Eva|last4=Kovacs|first4=Kit M.|last5=Lydersen|first5=Christian|last6=Pavlova|first6=Olga|last7=Pedersen|first7=Åshild Ø.|last8=Ravolainen|first8=Virve|last9=Strøm|first9=Hallvard|date=2016-06-28|title=Climate change impacts on wildlife in a High Arctic archipelago – Svalbard, Norway|url=http://dx.doi.org/10.1111/gcb.13381|journal=Global Change Biology|volume=23|issue=2|pages=490–502|doi=10.1111/gcb.13381|issn=1354-1013|pmid=27250039|s2cid=34897286}}</ref>  In July 2019, 200 [[Biology:Svalbard reindeer|Svalbard reindeer]] were found starved to death apparently due to low precipitation related to climate change.<ref>[https://www.livescience.com/66047-200-dead-reindeer-norway.html More Than 200 Reindeer Found Dead in Norway, Starved by Climate Change] By Mindy Weisberger. Live Science, July 29, 2019</ref>

In the short-term, climate warming may have neutral or positive effects on the nesting cycle of many Arctic-breeding shorebirds.<ref>{{cite journal|author1=Weiser, E.L.|author2=Brown, S.C.|author3=Lanctot, R.B.|author4=River Gates, H.|author5=Abraham, K.F.|author6=Bentzen, R.L.|author7=Bêty, J.|author8=Boldenow, M.L.|author9=Brook, R.W.|author10=Donnelly, T.F.|author11=English, W.B.|display-authors=5|year=2018|title=Effects of environmental conditions on reproductive effort and nest success of Arctic‐breeding shorebirds|journal=Ibis|volume=160|issue=3|pages=608–623|doi=10.1111/ibi.12571|hdl-access=free|author20=Kwon, E.|author35=Solovyeva, D.|hdl=10919/99313|author12=Flemming, S.A.|author13=Franks, S.E.|author14=Gilchrist, H.G.|author15=Giroux, M.|author16=Johnson, A.|author17=Kendall, S.|author18=Kennedy, L.V.|s2cid=53514207|author38=Sandercock, B.K.|author37=Woodard, P.F.|author36=Ward, D.H.|author34=Soloviev, M.|author21=Lamarre, J.|author33=Smith, P.A.|author32=Senner, N.R.|author31=Saalfeld, S.T.|author30=Robards, M.|author29=Rausch, J.|author28=Perz, J.|author27=Nol, E.|author26=McKinnon, L.|author25=Liebezeit, J.R.|author19=Koloski, L.|author23=Latty, C.J.|author22=Lank, D.B.|author24=Lecomte, N.}}</ref>

==Permafrost thaw==
[[File:Beaufort Permafrost1.JPG|thumb|right|Rapidly thawing Arctic permafrost and coastal erosion on the Beaufort Sea, Arctic Ocean, near Point Lonely, AK. Photo Taken in August 2013]]
[[File:Permafrost thaw ponds in Hudson Bay Canada near Greenland.jpg|thumb|Permafrost thaw ponds on Baffin Island]]
[[Earth:Permafrost|Permafrost]] is an important component of hydrological systems and ecosystems within the Arctic landscape.<ref>{{Cite web|title=Terrestrial Permafrost|url=https://arctic.noaa.gov/Report-Card/Report-Card-2017/ArtMID/7798/ArticleID/694/Terrestrial-Permafrost|access-date=2021-05-18|website=Arctic Program|language=en-US}}</ref> In the Northern Hemisphere the terrestrial permafrost domain comprises around 18 million km<sup>2</sup>.<ref name=":4">{{Cite journal|last1=Sayedi|first1=Sayedeh Sara|last2=Abbott|first2=Benjamin W|last3=Thornton|first3=Brett F|last4=Frederick|first4=Jennifer M|last5=Vonk|first5=Jorien E|last6=Overduin|first6=Paul|last7=Schädel|first7=Christina|last8=Schuur|first8=Edward A G|last9=Bourbonnais|first9=Annie|last10=Demidov|first10=Nikita|last11=Gavrilov|first11=Anatoly|date=2020-12-01|title=Subsea permafrost carbon stocks and climate change sensitivity estimated by expert assessment|url=http://dx.doi.org/10.1088/1748-9326/abcc29|journal=Environmental Research Letters|volume=15|issue=12|pages=B027-08|doi=10.1088/1748-9326/abcc29|bibcode=2020AGUFMB027...08S|s2cid=234515282|issn=1748-9326}}</ref> Within this permafrost region, the total soil organic carbon (SOC) stock is estimated to be 1,460-1,600 Pg (where 1 Pg = 1 billion tons), which constitutes double the amount of carbon currently contained in the atmosphere.<ref>{{Cite journal|last1=Hugelius|first1=G.|last2=Strauss|first2=J.|last3=Zubrzycki|first3=S.|last4=Harden|first4=J. W.|last5=Schuur|first5=E. A. G.|last6=Ping|first6=C.-L.|last7=Schirrmeister|first7=L.|last8=Grosse|first8=G.|last9=Michaelson|first9=G. J.|last10=Koven|first10=C. D.|last11=O'Donnell|first11=J. A.|date=2014-12-01|title=Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified data gaps|journal=Biogeosciences|volume=11|issue=23|pages=6573–6593|doi=10.5194/bg-11-6573-2014|bibcode=2014BGeo...11.6573H|s2cid=14158339 |issn=1726-4189 |doi-access=free }}</ref><ref>{{Cite web|title=Permafrost and the Global Carbon Cycle|url=https://arctic.noaa.gov/Report-Card/Report-Card-2019/ArtMID/7916/ArticleID/844/Permafrost-and-the-Global-Carbon-Cycle|access-date=2021-05-18|website=Arctic Program|language=en-US}}</ref>

{{excerpt|Permafrost carbon cycle#Carbon release from the permafrost|paragraphs=2-3}}

{{excerpt|Permafrost carbon cycle#Cumulative|hat=no}}

{{excerpt|Permafrost#Construction on permafrost|paragraphs=6}}

===Subsea permafrost===
Subsea permafrost occurs beneath the seabed and exists in the continental shelves of the polar regions.<ref>{{cite web|author=IPCC AR4|title=Climate Change 2007: Working Group I: The Physical Science Basis|date=2007|url=http://archive.ipcc.ch/publications_and_data/ar4/wg1/en/ch4s4-7-2-4.html|access-date=12 April 2014|archive-url=https://web.archive.org/web/20140413125748/http://archive.ipcc.ch/publications_and_data/ar4/wg1/en/ch4s4-7-2-4.html|archive-date=13 April 2014|url-status=dead}}</ref> Thus, it can be defined as "the unglaciated continental shelf areas exposed during the [[Earth:Last Glacial Maximum|Last Glacial Maximum]] (LGM, ~26 500 BP) that are currently inundated". Large stocks of organic matter (OM) and methane ({{CH4}}) are accumulated below and within the subsea permafrost deposits. This source of methane is different from [[Chemistry:Methane clathrate|methane clathrate]]s, but contributes to the overall outcome and feedbacks in the Earth's climate system.<ref name=":4" />

Sea ice serves to stabilise methane deposits on and near the shoreline,<ref name="2005gl022751">{{Cite journal|last1=Shakhova|first1=N.|last2=Semiletov|first2=I.|last3=Panteleev|first3=G.|year=2005|title=The distribution of methane on the Siberian Arctic shelves: Implications for the marine methane cycle|journal=Geophysical Research Letters|volume=32|issue=9|pages=L09601|bibcode=2005GeoRL..32.9601S|doi=10.1029/2005GL022751|doi-access=free}}</ref> preventing the clathrate breaking down and venting into the water column and eventually reaching the atmosphere. Methane is released through bubbles from the subsea permafrost into the Ocean (a process called ebullition). During storms, methane levels in the water column drop dramatically, when wind-driven air-sea gas exchange accelerates the ebullition process into the atmosphere. This observed pathway suggests that methane from seabed permafrost will progress rather slowly, instead of abrupt changes. However, Arctic cyclones, fueled by [[Earth:Global warming|global warming]] and further accumulation of greenhouse gases in the atmosphere could contribute to more release from this methane cache, which is really important for the Arctic.<ref>{{cite journal|last1=Shakhova|first1=Natalia|last2=Semiletov|first2=Igor|last3=Leifer|first3=Ira|last4=Sergienko|first4=Valentin|last5=Salyuk|first5=Anatoly|last6=Kosmach|first6=Denis|last7=Chernykh|first7=Denis|last8=Stubbs|first8=Chris|last9=Nicolsky|first9=Dmitry|last10=Tumskoy|first10=Vladimir|last11=Gustafsson|first11=Örjan|date=24 November 2013|title=Ebullition and storm-induced methane release from the East Siberian Arctic Shelf|url=http://www.homepages.ed.ac.uk/shs/Methane/Shakhova%202013.pdf|journal=Nature|volume=7|issue=1|pages=64–70|bibcode=2014NatGe...7...64S|doi=10.1038/ngeo2007|access-date=12 April 2014}}</ref> An update to the mechanisms of this permafrost degradation was published in 2017.<ref>{{Cite journal|last1=Shakhova|first1=Natalia|last2=Semiletov|first2=Igor|last3=Gustafsson|first3=Orjan|last4=Sergienko|first4=Valentin|last5=Lobkovsky|first5=Leopold|last6=Dudarev|first6=Oleg|last7=Tumskoy|first7=Vladimir|last8=Grigoriev|first8=Michael|last9=Mazurov|first9=Alexey|last10=Salyuk|first10=Anatoly|last11=Ananiev|first11=Roman|year=2017|title=Current rates and mechanisms of subsea permafrost degradation in the East Siberian Arctic Shelf|journal=Nature Communications|volume=8|pages=15872|bibcode=2017NatCo...815872S|doi=10.1038/ncomms15872|pmc=5489687|pmid=28639616|first12=Andrey|last13=Kosmach|first13=Denis|last14=Charkin|first14=Alexander|last15=Dmitrevsky|last12=Koshurnikov|last16=Karnaukh|first16=Victor|last17=Gunar|first17=Alexey|last18=Meluzov|first18=Alexander|last19=Chernykh|first19=Denis|first15=Nicolay}}</ref>

The size of today's subsea permafrost has been estimated at 2 million km<sup>2</sup> (~1/5 of the terrestrial permafrost domain size), which constitutes a 30–50% reduction since the LGM. Containing around 560 GtC in OM and 45 GtC in CH<sub>4</sub>, with a current release of 18 and 38 MtC per year respectively, which is due to the warming and thawing that the subsea permafrost domain has been experiencing since after the LGM (~14000 years ago). In fact, because the subsea permafrost systems responds at millennial timescales to climate warming, the current carbon fluxes it is emitting to the water are in response to climatic changes occurring after the LGM. Therefore, human-driven climate change effects on subsea permafrost will only be seen hundreds or thousands of years from today. According to predictions under a business-as-usual emissions scenario RCP 8.5, by 2100, 43 GtC could be released from the subsea permafrost domain, and 190 GtC by the year 2300. Whereas for the low emissions scenario RCP 2.6, 30% less emissions are estimated. This constitutes a significant anthropogenic-driven acceleration of carbon release in the upcoming centuries.<ref name=":4" />

===Methane clathrate deposits ===
{{excerpt|Clathrate gun hypothesis|paragraphs=1}}
{{excerpt|Clathrate gun hypothesis#Modern deposits|paragraphs=1-3|hat=no}}
{{excerpt|Clathrate gun hypothesis#East Siberian Arctic Shelf|hat=no}}
{{excerpt|Clathrate gun hypothesis#Svalbard|paragraphs=2-4|hat=no}}

{{excerpt|Clathrate gun hypothesis#Current outlook|paragraphs=2-3|hat=no}}

==Effects on other parts of the world==
===On ocean circulation===

Although this is now thought unlikely in the near future, it has also been suggested that there could be a [[Earth:Shutdown of thermohaline circulation|shutdown of thermohaline circulation]], similar to that which is believed to have driven the [[Earth:Younger Dryas|Younger Dryas]], an [[Earth:Abrupt climate change|abrupt climate change]] event.<ref>{{Cite report|last=Hill|first=Christopher|date=2015-06-15|title=Abrupt Climate Change and the Atlantic Meridional Overturning Circulation: sensitivity and non-linear response to Arctic/sub-Arctic freshwater pulses. Collaborative research. Final report|doi=10.2172/1184378|osti=1184378}}</ref> Even if a full shutdown is unlikely, a slowing down of this current and a weakening of its effects on climate has already been seen, with a 2015 study finding that the [[Earth:Atlantic meridional overturning circulation|Atlantic meridional overturning circulation]] (AMOC) has weakened by 15% to 20% over the last 100 years.<ref name="dx.doi.org"/> This slowing could lead to cooling in the North Atlantic, although this could be mitigated by global warming, but it is not clear up to what extent.<ref name=":12">{{Cite journal|last=Nelson|first=Daniel|date=2018-04-19|title=The Gulf Stream May Be Weaker Than It Has Been In 1600 Years, Could Exacerbate Climate Change|url=http://dx.doi.org/10.31988/scitrends.15937|journal=Science Trends|doi=10.31988/scitrends.15937}}</ref> Additional effects of this would be felt around the globe, with changes in tropical patterns, stronger storms in the North Atlantic and reduced European crop productivity among the potential repercussions.<ref name=":12" />

There is also potentially a possibility of a more general disruption of ocean circulation, which may lead to an ocean anoxic event; these are believed to be much more common in the distant past. It is unclear whether the appropriate pre-conditions for such an event exist today, but these ocean anoxic events are thought to have been mainly caused by nutrient run-off, which was driven by increased {{CO2}} emissions in the distant past.<ref>{{Cite journal|last=Vaughan|first=Adam|date=November 2020|title=Arctic ice loss could trigger huge extra global warming|url=http://dx.doi.org/10.1016/s0262-4079(20)31956-4|journal=New Scientist|volume=248|issue=3307|pages=21|doi=10.1016/s0262-4079(20)31956-4|bibcode=2020NewSc.248...21V|s2cid=228974766|issn=0262-4079}}</ref> This draws an unsettling parallel with current climate change, but the amount of {{CO2}} that's thought to have caused these events is far higher than the levels we're currently facing, so effects of this magnitude are considered unlikely on a short time scale.<ref>{{Cite journal|last1=Chen|first1=Xi|title=Supplemental Material: Zinc isotope evidence for paleoenvironmental changes during Cretaceous Oceanic Anoxic Event 2|display-authors=0|date=2020-11-12|journal=Geology |url=http://dx.doi.org/10.1130/geol.s.13232360.v1|access-date=2021-05-19 |doi=10.1130/geol.s.13232360.v1|s2cid=240757224}}</ref>

===On mid-latitude weather===
As the Arctic continues to warm, the temperature gradient between it and the warmer parts of the globe will continue to diminish with every decade of global warming due to Arctic amplification. If this gradient has a strong influence on the jet stream, then it will eventually become weaker and more variable in its course, which would allow more cold air from the polar vortex to leak mid-latitudes and slow the progression of Rossby Waves, leading to more persistent and more [[Earth:Extreme weather|extreme weather]].

{{excerpt|Jet stream#Longer-term climatic changes|paragraphs=2-7|file=yes}}

== Impacts on people ==

===Territorial claims===
Growing evidence that global warming is shrinking polar ice has added to the urgency of several nations' Arctic territorial claims in hopes of establishing resource development and [[Earth:Arctic shipping routes|new shipping lanes]], in addition to protecting sovereign rights.<ref name="WashPost">{{cite news | first = Mike | last = Eckel | title = Russia: Tests Show Arctic Ridge Is Ours | url = https://www.washingtonpost.com/wp-dyn/content/article/2007/09/20/AR2007092001703.html |agency=Associated Press | newspaper = The Washington Post | date = 20 September 2007 | access-date = 21 September 2007}}{{dead link|date=June 2021|bot=medic}}{{cbignore|bot=medic}}</ref>

As ice sea coverage decreases more and more, year on year, Arctic countries (Russia, Canada, Finland, Iceland, Norway, Sweden, the United States and Denmark representing Greenland) are making moves on the geopolitical stage to ensure access to potential [[Earth:Arctic shipping routes|new shipping lanes]], oil and gas reserves, leading to overlapping claims across the region.<ref name=":13">{{Cite web|title=Territorial Claims in the Arctic Circle: An Explainer|url=https://theobserver-qiaa.org/territorial-claims-in-the-arctic-circle-an-explainer|access-date=2021-05-19|website=The Observer|language=en-US}}</ref> However, there is only one single land border dispute in the Arctic, with all others relating to the sea, that is Hans Island.<ref name=":14">{{Cite web|date=2013-09-15|title=Evolution of Arctic Territorial Claims and Agreements: A Timeline (1903–Present) • Stimson Center|url=https://www.stimson.org/2013/evolution-arctic-territorial-claims-and-agreements-timeline-1903-present/|access-date=2021-05-19|website=Stimson Center|language=en-US}}</ref>  This small uninhabited island lies in the Nares strait, between Canada's Ellesmere Island and the northern coast of Greenland. Its status comes from its geographical position, right between the equidistant boundaries determined in a 1973 treaty between Canada and Denmark.<ref name=":14" />  Even though both countries have acknowledged the possibility of splitting the island, no agreement on the island has been reached, with both nations still claiming it for themselves.<ref name=":14" />

There is more activity in terms of maritime boundaries between countries, where overlapping claims for [[Earth:Internal waters|internal waters]], [[Earth:Territorial waters|territorial seas]] and particularly [[Earth:Exclusive economic zone|Exclusive Economic Zones]] (EEZs) can cause frictions between nations. Currently, official maritime borders have an unclaimed triangle of international waters lying between them, that is at the centerpoint of international disputes.<ref name=":13" />

This unclaimed land can be obtainable by submitting a claim to the United Nations Convention on the Law of the Sea, these claims can be based on geological evidence that continental shelves extend beyond their current maritime borders and into international waters.<ref name=":13" />

Some overlapping claims are still pending resolution by international bodies, such as a large portion containing the [[Earth:North Pole|north pole]] that is both claimed by Denmark and Russia, with some parts of it also contested by Canada.<ref name=":13" /> Another example is that of the [[Earth:Northwest Passage|Northwest Passage]], globally recognized as international waters, but technically in Canadian waters.<ref name=":13" /> This has led to Canada wanting to limit the number of ships that can go through for environmental reasons but the United States disputes that they have the authority to do so, favouring unlimited passage of vessels.<ref name=":13" />

=== Impacts on indigenous peoples ===
As climate change speeds up, it is having more and more of a direct impact on societies around the world. This is particularly true of people that live in the Arctic, where increases in temperature are occurring at faster rates than at other latitudes in the world, and where traditional ways of living, deeply connected with the natural arctic environment are at particular risk of environmental disruption caused by these changes.<ref name="ClimateImpactAssessment">{{cite book |last=Hassol |first=Susan Joy |url=https://archive.org/details/impactsofwarming0000hass |title=Impacts of a warming Arctic |publisher=Cambridge University Press |year=2004 |isbn=978-0-521-61778-9 |edition=Reprinted |location=Cambridge, UK |url-access=registration}}</ref>

The warming of the atmosphere and ecological changes that come alongside it presents challenges to local communities such as the Inuit. Hunting, which is a major way of survival for some small communities, will be changed with increasing temperatures.<ref name="ethz.ch">{{cite journal |last1=Berkes |first1=Fikret |last2=Jolly |first2=Dyanna |title=Adapting to climate change: social-ecological resilience in a Canadian western Arctic community |url=https://www.ecologyandsociety.org/vol5/iss2/art18/print.pdf |journal=Conservation Ecology |volume=5 |issue=2 |date=2001}}</ref> The reduction of sea ice will cause certain species populations to decline or even become extinct.<ref name="ClimateImpactAssessment" />  Inuit communities are deeply reliant on seal hunting, which is dependent on sea ice flats, where seals are hunted.<ref name=":15">{{Cite journal|last=Farquhar|first=Samantha D.|date=2020-03-18|title=Inuit Seal Hunting in Canada: Emerging Narratives in an Old Controversy|url=http://dx.doi.org/10.14430/arctic69833|journal=Arctic|volume=73|issue=1|pages=13–19|doi=10.14430/arctic69833|s2cid=216308832|issn=1923-1245}}</ref>

Unsuspected changes in river and snow conditions will cause herds of animals, including reindeer, to change migration patterns, [[Biology:Birth#Cattle|calving]] grounds, and forage availability.<ref name="ClimateImpactAssessment" /> In good years, some communities are fully employed by the commercial harvest of certain animals.<ref name="ethz.ch" /> The harvest of different animals fluctuates each year and with the rise of temperatures it is likely to continue changing and creating issues for Inuit hunters, as unpredictability and disruption of ecological cycles further complicate life in these communities, which already face significant problems, such as Inuit communities being the poorest and most unemployed of North America.<ref name=":15" />

Other forms of transportation in the Arctic have seen negative impacts from the current warming, with some transportation routes and pipelines on land being disrupted by the melting of ice.<ref name="ClimateImpactAssessment" /> Many Arctic communities rely on frozen roadways to transport supplies and travel from area to area.<ref name="ClimateImpactAssessment" /> The changing landscape and unpredictability of weather is creating new challenges in the Arctic.<ref>{{Cite journal|last=Timonin|first=Andrey|date=2021|title=Climate Change in the Arctic and Future Directions for Adaptation: Views From Non-Arctic States|url=http://dx.doi.org/10.2139/ssrn.3802303|journal=SSRN Electronic Journal|doi=10.2139/ssrn.3802303|s2cid=233756936|issn=1556-5068}}</ref> Researchers have documented historical and current trails created by the Inuit in the Pan Inuit Trails Atlas, finding that the change in sea ice formation and breakup has resulted in changes to the routes of trails created by the Inuit.<ref>{{Cite web |last=Rogers |first=Sarah |date=2014-06-13 |title=New online atlas tracks Nunavut's centuries-old Inuit trails |url=https://nunatsiaq.com/stories/article/65674new_online_atlas_tracks_centuries-old_inuit_trails/ |access-date=2021-05-19 |website=Nunatsiaq News |language=en}}</ref>

===Navigation===
The [[Earth:Transpolar Sea Route|Transpolar Sea Route]] is a future Arctic shipping lane running from the Atlantic Ocean to the Pacific Ocean across the center of the Arctic Ocean. The route is also sometimes called Trans-Arctic Route. In contrast to the [[Earth:Northeast Passage|Northeast Passage]] (including the [[Earth:Northern Sea Route|Northern Sea Route]]) and the North-West Passage it largely avoids the territorial waters of Arctic states and lies in international high seas.<ref>{{cite journal|last1=Humpert|first1=Malte|last2=Raspotnik|first2=Andreas|title=The Future of Shipping Along the Transpolar Sea Route|journal=The Arctic Yearbook|year=2012|volume=1|issue=1|pages=281–307|url=http://www.arcticyearbook.com/images/Articles_2012/Humpert_and_Raspotnik.pdf|access-date=18 November 2015|archive-url=https://web.archive.org/web/20160121203700/http://www.arcticyearbook.com/images/Articles_2012/Humpert_and_Raspotnik.pdf|archive-date=21 January 2016|url-status=dead|df=dmy-all}}</ref>

Governments and private industry have shown a growing interest in the Arctic.<ref>{{cite web|url=http://www.popsci.com/science/article/2013-01/energy-development-arctic|title=As The Earth Warms, The Lure Of The Arctic's Natural Resources Grows|date=18 March 2019}}</ref> Major new shipping lanes are opening up: [[Earth:Northern Sea Route|the northern sea route]] had 34 passages in 2011 while the [[Earth:Northwest Passage|Northwest Passage]] had 22 traverses, more than any time in history.<ref>{{cite web|url=http://www.aljazeera.com/indepth/opinion/2011/12/2011121913304370977.html|title=Melting Arctic brings new opportunities|first=Michael|last=Byers|website=aljazeera.com}}</ref> Shipping companies may benefit from the shortened distance of these northern routes. Access to natural resources will increase, including valuable minerals and offshore oil and gas.<ref name="ClimateImpactAssessment" /> Finding and controlling these resources will be difficult with the continually moving ice.<ref name="ClimateImpactAssessment" /> Tourism may also increase as less sea ice will improve safety and accessibility to the Arctic.<ref name="ClimateImpactAssessment" />

The melting of Arctic ice caps is likely to increase traffic in and the commercial viability of the Northern Sea Route. One study, for instance, projects, "remarkable shifts in trade flows between Asia and Europe, diversion of trade within Europe, heavy shipping traffic in the Arctic and a substantial drop in Suez traffic. Projected shifts in trade also imply substantial pressure on an already threatened Arctic ecosystem."<ref>{{Cite journal|last1=Bekkers|first1=Eddy|last2=Francois|first2=Joseph F.|last3=Rojas-Romagosa|first3=Hugo|date=2016-12-01|title=Melting Ice Caps and the Economic Impact of Opening the Northern Sea Route|journal=The Economic Journal|volume=128|issue=610|language=en|pages=1095–1127|doi=10.1111/ecoj.12460|s2cid=55162828|issn=1468-0297|url=https://boris.unibe.ch/89212/1/Melting%20Ice%20Caps.pdf}}</ref>

== Adaptation ==

=== Research ===

====National====
Individual countries within the Arctic zone, {{wipe|Canada}}, Denmark (Greenland), {{wipe|Finland}}, Iceland, {{wipe|Norway}}, {{wipe|Russia}}, Sweden, and the {{wipe|United States}} ([[Earth:Alaska|Alaska]]) conduct independent research through a variety of organizations and agencies, public and private, such as Russia's [[Organization:Arctic and Antarctic Research Institute|Arctic and Antarctic Research Institute]]. Countries who do not have Arctic claims, but are close neighbors, conduct Arctic research as well, such as the [[Organization:Chinese Arctic and Antarctic Administration|Chinese Arctic and Antarctic Administration]] (CAA).  The United States's [[Organization:National Oceanic and Atmospheric Administration|National Oceanic and Atmospheric Administration]] (NOAA) produces an [[Earth:Arctic Report Card|Arctic Report Card]] annually, containing peer-reviewed information on recent observations of environmental conditions in the Arctic relative to historical records.<ref name="Freedman_2017"/><ref name="ARC_2017"/>

====International====
International cooperative research between nations has become increasingly important:
* Arctic [[Earth:Climate change|climate change]] is summarized by the [[Organization:Intergovernmental Panel on Climate Change|Intergovernmental Panel on Climate Change]] (IPCC) in its series of Assessment Reports and the [[Earth:Arctic Climate Impact Assessment|Arctic Climate Impact Assessment]].
* [[Organization:European Space Agency|European Space Agency]] (ESA) launched [[Engineering:CryoSat#CryoSat II|CryoSat-2]] on 8 April 2010. It provides satellite data on Arctic ice cover change rates.<ref name="esa">{{cite web | url = http://www.esa.int/esaLP/ESAOMH1VMOC_LPcryosat_0.html | title = ESA's ice mission CryoSat-2 | date = 11 September 2008 | publisher = esa.int | access-date = 15 June 2009}}</ref>
* [[Earth:International Arctic Buoy Program|International Arctic Buoy Program]]: deploys and maintains buoys that provide real-time position, pressure, temperature, and interpolated ice velocity data
* [[Organization:International Arctic Research Center|International Arctic Research Center]]: Main participants are the United States and {{wipe|Japan}}.
* [[Organization:International Arctic Science Committee|International Arctic Science Committee]]: non-governmental [[Organization:Organization|organization]] (NGO) with diverse membership, including 23 countries from 3 continents.
* 'Role of the Arctic Region', in conjunction with the [[Earth:International Polar Year|International Polar Year]], was the focus of the second international conference on Global Change Research, held in Nynäshamn, Sweden, October 2007.<ref name="E SF, VR, FORMAS sign MOU to promote Global Environmental Change Research">{{cite web | first = Corinne | last = Wininger | url = http://www.innovations-report.com/html/reports/environment_sciences/report-93680.html | title = E SF, VR, FORMAS sign MOU to promote Global Environmental Change Research | publisher = innovations-report.de | date = 26 October 2007 | access-date = 26 November 2007}}</ref>
* SEARCH ([[Earth:Study of Environmental Arctic Change|Study of Environmental Arctic Change]]): A research framework originally promoted by several US agencies; an international extension is ISAC (the International Study of Arctic Change<ref>{{cite web|url=http://www.arcticchange.org/|title=Arctic Change|website=International Study of Arctic Change}}</ref>).

==See also==
{{div col}}
* [[Earth:Arctic cooperation and politics|Arctic cooperation and politics]]
* [[Earth:Arctic haze|Arctic haze]]
* [[Earth:Arctic sea ice ecology and history|Arctic sea ice ecology and history]]
* [[Earth:Atlantification of the Arctic|Atlantification of the Arctic]]
* Atmospheric Brown Cloud
* [[Earth:Climate of the Arctic|Climate of the Arctic]]
* [[Earth:Climate and vegetation interactions in the Arctic|Climate and vegetation interactions in the Arctic]]
* [[Earth:Northern Sea Route|Northern Sea Route]]
*Climate change in Antarctica
* [[Earth:Ozone depletion and climate change|Ozone depletion and climate change]]
* [[Earth:Save the Arctic|Save the Arctic]]
{{div col end}}

==References==
{{reflist|30em}}

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<ref name="Cryosphere">{{cite web | url = http://nsidc.org/sotc/sea_ice.html | title = State of the Cryosphere, Is the Cryosphere sending signals about climate change? | date = 18 February 2010 | publisher = National Snow and Ice Data Center | access-date = 26 July 2010}}</ref>

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<ref name="Global Outlook for Ice and Snow, Chapter 5: Ice in the Sea">{{cite web | url=http://www.unep.org/geo/geo_ice/PDF/GEO_C5_LowRes.pdf | title=Global Outlook for Ice and Snow, Chapter 5: Ice in the Sea | pages=75–76 | publisher=United Nations Environment Programme}}</ref>

<ref name="greenhouse effect">{{cite web |url=http://www.ciesin.org/docs/003-074/003-074.html |title=Greenhouse Effect |access-date=4 November 2012}}</ref>

<ref name="Nature Geoscience">{{cite journal|doi=10.1038/ngeo338 | volume=1 | title=Attribution of polar warming to human influence | year=2008 | journal=Nature Geoscience | pages=750–754 | last1 = Gillett | first1 = Nathan P. | bibcode=2008NatGe...1..750G}}</ref>

<ref name="New warning on Arctic sea ice melt">{{cite news|title=New warning on Arctic sea ice melt|url=http://www.bbc.co.uk/news/science-environment-13002706 | first=Jonathan|last=Amos|date=8 April 2011|work=BBC News Online}}</ref>
<ref name="NSIDC Sea Ice">{{cite web | publisher=NSIDC | url=http://www.nsidc.org/seaice/intro.html | title=All About Sea Ice | access-date=10 January 2009 | archive-url=https://web.archive.org/web/20090105023919/http://nsidc.org/seaice/intro.html | archive-date=5 January 2009 | url-status=dead | df=dmy-all }}</ref>

<ref name="nsidc4">{{cite web |url=http://nsidc.org/data/seaice_index/images/daily_images/N_stddev_timeseries.png |title=Arctic Sea Ice Extent |access-date=4 November 2012}}</ref>

<ref name="On the reliability of simulated Arctic sea ice in Global Climate Models">{{cite journal | last = Eisenman | first = Ian | author2 = Untersteiner, Norbert | author3 = Wettlaufer, J.S. | year = 2007 | title = On the reliability of simulated Arctic sea ice in Global Climate Models | journal = [[Earth:Geophysical Research Letters|Geophysical Research Letters]] | volume = 34 | issue = 10 | pages = L10501 | doi = 10.1029/2007GL029914 | url = http://pantheon.yale.edu/%7Ejw378/articles/EUW_revised_2007.pdf | bibcode = 2007GeoRL..3410501E }}{{Dead link|date=April 2019 |bot=InternetArchiveBot |fix-attempted=yes }} This is due to high sea ice thickness sensitivity to variations in downward thermal radiation, which are not reflected in outcomes of different models but seem to have been compensated by adaption of other parameters like albedo, short wave irradiation or ocean heat flux.</ref>

<ref name="planetsave">{{cite web|url=http://planetsave.com/2012/09/21/arctic-sea-ice-may-disappear-within-4-years-according-to-one-of-the-worlds-leading-sea-ice-researchers|title=Arctic Sea Ice May Disappear Within 4 Years, According To One Of The World's Leading Sea Ice Researchers – PlanetSave|date=21 September 2012}}</ref>

<ref name="Sea Ice Declines Boost Arctic Phytoplankton Productivity">{{cite web| last = Kennedy| first = Caitlyn| title = Sea Ice Declines Boost Arctic Phytoplankton Productivity| work = ClimateWatch Magazine| publisher = NOAA| date = 1 December 2011| url = http://www.climatewatch.noaa.gov/article/2011/sea-ice-declines-boost-arctic-phytoplankton-productivity| access-date = 20 January 2012}}</ref>

<ref name="Shrub Takeover One Sign of Arctic Change">{{cite web| last = Lindsey| first = Rebecca| title = Shrub Takeover One Sign of Arctic Change| work = ClimateWatch Magazine| publisher = NOAA| date = 18 January 2012| url = http://www.climatewatch.noaa.gov/article/2012/shrub-takeover-one-sign-of-arctic-change| access-date = 19 January 2012}}</ref>

<ref name="smh">{{cite news| url=http://www.smh.com.au/environment/climate-change/staggering-arctic-ice-loss-smashes-melt-records-20120917-260zu.html | work=The Sydney Morning Herald | title='Staggering' Arctic ice loss smashes melt records}}</ref>

<ref name="Study: Circulation Shift May Be Melting Arctic Sea Ice">{{cite news | url = http://www.foxnews.com/story/0,2933,311753,00.html | title = Study: Circulation Shift May Be Melting Arctic Sea Ice | date = 24 November 2007 | publisher = Fox News | access-date = 27 November 2007}}</ref>

<ref name="Thinning and volume loss of Arctic sea ice: 2003–2008">{{cite journal |author1=Kwok, R. |author2=Cunningham, G.F. |author3=Wensnahan, M. |author4=Rigor, I. |author5=Zwally, H.J. |author6=Yi D. |title=Thinning and volume loss of Arctic sea ice: 2003–2008 |journal=Journal of Geophysical Research |volume=114 |pages=C07005 |year=2009 |doi=10.1029/2009JC005312 |bibcode = 2009JGRC..11407005K }}</ref>

<ref name="Winds from Siberia reduce Arctic sea ice cover">{{cite news | url = http://www.forskningsradet.no/en/Newsarticle/Winds_from_Siberia_reduce_Arctic_sea_ice_cover/1253955174381 | title = Winds from Siberia reduce Arctic sea ice cover | date = 27 April 2010 | publisher = The Research Council of Norway | access-date = 27 April 2010}}</ref>

<ref name="uofa">{{cite journal|last=Nuttall|first=Mark |author2=Pierre-André Forest |author3=Svein D. Mathiesen|title=Adaptation to Climate Change in The Arctic|journal=University of the Arctic|date=February 2008|pages=1–5|url=http://www.uarctic.org/Adaptation_to_Climate_Change_in_the_Arctic_FIN…|access-date=5 November 2012}}</ref>
-->

===Works cited===
* {{Cite book  |ref= {{harvid|IPCC AR6 WG1|2021}}
 |year= 2021
 |title= Climate Change 2021: The Physical Science Basis
 |series= Contribution of Working Group I to the [[Earth:IPCC Sixth Assessment Report|Sixth Assessment Report]] of the Intergovernmental Panel on Climate Change
 |display-editors= 4
 |editor1-first= V.     |editor1-last= Masson-Delmotte
 |editor2-first= P.     |editor2-last= Zhai
 |editor3-first= A.	|editor3-last= Pirani
 |editor4-first= S. L.  |editor4-last= Connors
 |editor5-first= C.     |editor5-last= Péan
 |editor6-first= S.     |editor6-last= Berger
 |editor7-first= N.     |editor7-last= Caud
 |editor8-first= Y.     |editor8-last= Chen
 |editor9-first= L.     |editor9-last= Goldfarb
 |editor10-first= M. I. |editor10-last= Gomis
 |publisher= Cambridge University Press (In Press)
 |place= 
 |isbn= 
 |url= https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf
}} 
** {{Cite book
|ref= {{harvid|IPCC AR6 WG1 Ch9|2021}}
|chapter=Chapter 9: Ocean, cryosphere, and sea level change
| last1 = Fox-Kemper| first1 = Baylor| last2 = Hewitt| first2 = Helene T.| last3 = Xiao| first3 = Cunde| last4 = Aðalgeirsdóttir| first4 = Guðfinna| last5 = Drijfhout| first5 = Sybren S.| last6 = Edwards| first6 = Tamsin L.| last7 = Golledge| first7 = Nicholas R.
|chapter-url= https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_09.pdf
|display-authors=4
|title= {{Harvnb|IPCC AR6 WG1|2021}}
|year=2021 
}}

==Further reading==

*{{cite web | title=Black Carbon and Methane | website=Arctic Council | date=9 Jul 2018 | url=https://arctic-council.org/about/task-expert/egbcm/ | access-date=6 Nov 2023}} <!--quote: Despite generating just ten percent of global black carbon emissions, Arctic States are responsible for 30% of black carbon’s warming effects in the Arctic, due to the greater warming impact of local emission sources ... In developing recommendations for its Summary Reports, the Expert Group sought to identify a focused menu of priority actions from which Arctic States could select – based on their national circumstances and recognizing the need for economic development of Arctic communities. These priority actions include recommendations on how to reduce emissions from: mobile and stationary diesel-powered sources; oil and gas methane leakage, venting and flaring; residential combustion; solid waste disposal; agriculture and animal husbandry; management of wildfires.-->

*{{cite web | last=Hersher | first=Rebecca | title=The Arctic is heating up nearly four times faster than the whole planet, study finds | website=NPR | date=11 Aug 2022 | url=https://www.npr.org/2022/08/11/1116608415/the-arctic-is-heating-up-nearly-four-times-faster-than-the-rest-of-earth-study-f | access-date=6 Nov 2023}}

==External links==
* [http://www.arctic.noaa.gov/ Arctic Change website, in near-realtime]
* [http://nsidc.org/arcticseaicenews/ Arctic Sea Ice News & Analysis]
* {{Cite news |last=Smith |first=Duane |date=2007 |title=Climate Change In The Arctic: An Inuit Reality |work=UN Chronicle |url=https://www.un.org/en/chronicle/article/climate-change-arctic-inuit-reality}}
* [http://www.arctic.io/#home The Arctic ice sheet], satellite map with daily updates.
* NOAA: [http://www.arctic.noaa.gov Arctic Theme Page] – A comprehensive resource focused on the Arctic
* {{cite report |url=http://www.arctic.noaa.gov/Report-Card/Report-Card-2016 |series=Arctic Report Card: Update for 2016 |title=Persistent warming trend and loss of sea ice are triggering extensive Arctic changes |publisher=NOAA}}
* {{cite report |url=http://www.arctic.noaa.gov/Report-Card/Report-Card-2021 |series=Arctic Report Card: Update for 2021 |title=Rapid and pronounced warming continues to drive the evolution of the Arctic environment |publisher=NOAA}}
*[https://origins.osu.edu/article/pollution-climate-change-killing-arctic?language_content_entity=en Killing the Arctic] Origins: Current Events in Historical Perspective (October 2020), by John McCannon

{{Global warming}}

[[Category:Arctic Ocean|G]]
[[Category:Arctic research]]
[[Category:Environment of the Arctic]]

{{Sourceattribution|Climate change in the Arctic}}