# Earth:Carbon footprint

Short description: Environmental impact
CO₂ emissions by world region (Our World in Data)

A carbon footprint is the total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, place or product, expressed as carbon dioxide equivalent (CO2e).[1] Greenhouse gases, including the carbon-containing gases carbon dioxide and methane, can be emitted through the burning of fossil fuels, land clearance, and the production and consumption of food, manufactured goods, materials, wood, roads, buildings, transportation and other services.[2]

In most cases, the total carbon footprint cannot be calculated exactly because of inadequate knowledge of data about the complex interactions between contributing processes, including the influence of natural processes that store or release carbon dioxide. For this reason, Wright, Kemp, and Williams proposed the following definition of a carbon footprint:

A measure of the total amount of carbon dioxide (CO2) and methane (CH4) emissions of a defined population, system or activity, considering all relevant sources, sinks and storage within the spatial and temporal boundary of the population, system or activity of interest. Calculated as carbon dioxide equivalent using the relevant 100-year global warming potential (GWP100).[3]

The Greenhouse Gas Protocol has extended the range of gases.

The standard covers the accounting and reporting of seven greenhouse gases covered by the Kyoto Protocol – carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PCFs), sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3).[4]

The global average annual carbon footprint per person in 2014 was about 5 tonnes CO2e.[5] Although there are many ways to calculate a carbon footprint, the Nature Conservancy suggests that the average carbon footprint for a U.S. citizen is 16 tons.[6] This is one of the highest rates in the world,[7] leading to new policies implemented to reduce carbon footprint. Scholars estimated that New York City can eliminate the carbon footprint of its buildings by 2050. Based on city documents and national statistics, a significant measure directly controlled by New York is the elimination of carbon emissions from municipal district heating, which may account for up to 30% of New York city’s reported carbon emissions and 58% of the energy-related carbon emissions.[8]

The use of household carbon footprint calculators originated when oil producer BP hired Ogilvy to create an "effective propaganda" campaign to shift responsibility of climate change-causing pollution away from the corporations and institutions that created a society where carbon emissions are unavoidable and onto personal lifestyle choices. The term "carbon footprint" was also popularized by BP.[9][10]

## Background

Human activities are one of the main causes of greenhouse gas emissions. These increase the earth's temperature and are emitted from the use of fossil fuels (coal, oil and gas), particularly in energy and transportation. The major effects of such practices mainly consist of climate changes, such as extreme precipitation and acidification and warming of oceans. Climate change has been occurring since the start of the Industrial Revolution in the 1820s. Due to humans' heavy reliance on fossil fuels, energy usage, and constant deforestation, the amount of greenhouse gas in the atmosphere is increasing, which makes reducing a greenhouse gas footprint harder to achieve. However, there are several ways to reduce one's greenhouse gas footprint, such as changing eating habits (reducing meat and dairy, as well as food waste), using more energy efficient appliances at home, buying less in general (particularly throwaway items, such as fast fashion) and travelling less (particularly reducing air travel).[11]

Greenhouse gases (GHGs) are gases that increase the temperature of the Earth due to their absorption of infrared radiation.[12] Although some emissions are natural, the rate of which they are being produced has increased because of humans. These gases are emitted from fossil fuel usage in electricity, in heat and transportation, as well as being emitted as byproducts of manufacturing. The most common GHGs are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and many fluorinated gases.[13] A greenhouse gas footprint is the numerical quantity of these gases that a single entity emits. The calculations can be computed ranging from a single person to the entire world.[14]

The latest climate science is published in the IPCC Sixth Assessment Report. The report presents key scientific findings linking the increase in anthropogenic GHGs emissions in current climate change. According to the report, it is only possible to avoid warming of 1.5 °C or 2 °C if massive and immediate cuts in greenhouse gas emissions are made.

### Origin of the concept

The concept and name of the carbon footprint was derived from the ecological footprint concept,[15] which was developed by William E. Rees and Mathis Wackernagel in the 1990s at the University of British Columbia. While carbon footprints are usually reported in tons of emissions (CO2-equivalent) per year, ecological footprints are usually reported in comparison to what the planet can renew. This assesses the number of "earths" that would be required if everyone on the planet consumed resources at the same level as the person calculating their ecological footprint. The carbon footprint is one part of the ecological footprint. Carbon footprints are more focused than ecological footprints since they merely measure emissions of gases that cause climate change into the atmosphere.

Carbon footprint is one of a family of footprint indicators,[16] which also include ecological footprints, water footprints and land footprints.

The idea of a personal carbon footprint was popularized by a large advertising campaign of the fossil fuel company BP in 2005, designed by Ogilvy.[10][15] It instructed people to calculate their personal footprints and provided ways for people to "go on a low-carbon diet".[17] This strategy, also employed by other major fossil fuel companies[18] borrowed heavily from previous campaigns by the tobacco industry[19] and plastics industry to shift the blame for negative consequences of those industries (under-age smoking,[20] cigarette butt pollution,[21] and plastic pollution[22]) onto individual choices.

BP made no attempt to reduce its own carbon footprint, instead expanding its oil drilling into the 2020s.[23][24] However, the strategy had some success, with a rise in consumers concerned about their own personal actions, and creation of multiple carbon footprint calculators.[10]

## Measuring carbon footprints

Common Greenhouse Gases

Carbon Dioxide (84%)
Methane (9%)
Nitrous Oxide (5%)
Fluorinated Gases (2%)

An individual's, nation's, or organization's carbon footprint can be measured by undertaking a GHG emissions assessment,[25] a life cycle assessment, or other calculative activities denoted as carbon accounting. Once the size of a carbon footprint is known, a strategy can be devised to reduce it, for example, by technological developments, energy efficiency improvements, better process and product management, changed Green Public or Private Procurement (GPP), carbon capture, consumption strategies, carbon offsetting and others.[26]

For calculating personal carbon footprints, several free online carbon footprint calculators exist[27][28] including a few supported by publicly available peer-reviewed data and calculations including the University of California, Berkeley's CoolClimate Network research consortium and CarbonStory.[29][30][31] These websites ask you to answer more or less detailed questions about your diet, transportation choices, home size, shopping and recreational activities, usage of electricity, heating, and heavy appliances such as dryers and refrigerators, and so on. The website then estimates your carbon footprint based on your answers to these questions. A systematic literature review was conducted to objectively determine the best way to calculate individual/household carbon footprints. This review identified 13 calculation principles and subsequently used the same principles to evaluate the 15 most popular online carbon footprint calculators. A recent study's results by Carnegie Mellon's Christopher Weber found that the calculation of carbon footprints for products is often filled with large uncertainties. The variables of owning electronic goods such as the production, shipment, and previous technology used to make that product, can make it difficult to create an accurate carbon footprint. It is important to question, and address the accuracy of Carbon Footprint techniques, especially due to its overwhelming popularity.[32]

Calculating the carbon footprint of industry, product, or service is a complex task. One tool industry uses Life-cycle assessment (LCA), where carbon footprint may be one of many factors taken into consideration when assessing a product or service. The International Organization for Standardization has a standard called ISO 14040:2006 that has the framework for conducting an LCA study.[33] ISO 14060 family of standards provides further sophisticated tools for quantifying, monitoring, reporting and validating or verifying of GHG emissions and removals.[34] Another method is through the Greenhouse Gas Protocol,[35] a set of standards for tracking greenhouse gas emissions (GHG) across scope 1, 2 and 3 emissions within the value chain.[36]

Predicting the carbon footprint of a process is also possible through estimations using the above standards. By using Emission intensities/Carbon intensities and the estimated annual use of fuel, chemical, or other inputs, the carbon footprint can be determined while a process is being planned/designed.

### Direct carbon emissions

Direct or 'scope 1' carbon emissions come from sources that are directly from the site that is producing a product or delivering a service.[37][38] An example for industry would be the emissions related to burning a fuel on site. On the individual level, emissions from personal vehicles or gas burning stoves would fall under scope 1.

### Indirect carbon emissions

Consumption-based CO₂ emissions per capita, 2017

Indirect carbon emissions are emissions from sources upstream or downstream from the process being studied, also known as scope 2 or scope 3 emissions.[37]

Examples of upstream, indirect carbon emissions may include:[39]

• Transportation of materials/fuels
• Any energy used outside of the production facility
• Wastes produced outside of the production facility

Examples of downstream, indirect carbon emissions may include:[13]

• Any end-of-life process or treatments
• Product and waste transportation
• Emissions associated with selling the product

Scope 2 emissions are the other indirect related to purchased electricity, heat, and/or steam used on site.[38]

Scope 3 emissions are all other indirect emissions derived from the activities of an organisation but from sources which they do not own or control.[40] The GHG Protocol's Corporate Value Chain (Scope 3) Accounting and Reporting Standard allows companies to assess their entire value chain emissions impact and identify where to focus reduction activities.[41]

### Reporting

In the US, the EPA has broken down electricity emission factors by state.[42]

In the UK, DEFRA provides emission factors going back to 2002 covering scope 1, 2 and 3.[43] DEFRA no longer provide international emission factors and refer visitors to the IEA who provide free highlights and paid for details covering Scope 1 and 2.[44]

## Carbon footprints of geographical areas

CO₂ emissions per person by country, 2017 (Our World in Data).

### National Carbon Footprints

According to The World Bank, the global average carbon footprint in 2014 was 4.97 metric tons CO2/cap.[5] The EU average for 2007 was about 13.8 tons CO2e/cap, whereas for the U.S., Luxembourg and Australia it was over 25 tons CO2e/cap. In 2017, the average for the USA was about 20 metric tons CO2e.[lower-alpha 1]

Mobility (driving, flying & small amount from public transit), shelter (electricity, heating, construction) and food are the most important consumption categories determining the carbon footprint of a person. In the EU, the carbon footprint of mobility is evenly split between direct emissions (e.g. from driving private cars) and emissions embodied in purchased products related to mobility (air transport service, emissions occurring during the production of cars and during the extraction of fuel). In low carbon economies such as Sweden and France the majority of household carbon is in imported goods 65% and 51% respectively.[47]

The carbon footprint of U.S. households is about 5 times greater than the global average. For most U.S. households the single most important action to reduce their carbon footprint is driving less or switching to a more efficient vehicle.[48]

### Sub-national or local Carbon Footprints

As well as calculating carbon footprints for whole countries, it is also possible to calculate the footprint of regions, cities, and neighbourhoods.[49]

## Carbon footprints of energy consumption

Main page: Physics:Life-cycle greenhouse gas emissions of energy sources

Three studies concluded that hydroelectric, wind, and nuclear power produced the least CO2 per kilowatt-hour of any other electricity sources. These figures do not include emissions due to accidents or terrorism. Wind power and solar power emit no carbon from their operation, but do leave a footprint during construction and maintenance. Hydropower from reservoirs also has large footprints from initial removal of vegetation and ongoing methane (stream detritus decays anaerobically to methane in bottom of reservoir, rather than aerobically to CO2 if it had stayed in an unrestricted stream).[50]

The generation of electricity accounts for about half of the world's man-made CO2 output. The CO2 footprint for heat is equally significant and research shows that using waste heat from power generation in combined heat and power district heating, chp/dh has the lowest carbon footprint,[51] much lower than micro-power or heat pumps.

Coal production has been refined to greatly reduce carbon emissions; since the 1980s, the amount of energy used to produce a ton of steel has decreased by 50%.[52]

## Carbon footprints of transport

This section gives representative figures for the carbon footprint of the fuel burned by different transport types (not including the carbon footprints of the vehicles or related infrastructure themselves). The precise figures vary according to a wide range of factors.

### Flight

Main page: Earth:Environmental effects of aviation

Some representative figures for CO2 emissions are provided by LIPASTO's survey of average direct emissions (not accounting for high-altitude radiative effects) of airliners expressed as CO2 and CO2 equivalent per passenger kilometre:[53]

• Domestic, short distance, less than 463 km (288 mi): 257 g/km CO2 or 259 g/km (14.7 oz/mile) CO2e
• Long-distance flights: 113 g/km CO2 or 114 g/km (6.5 oz/mile) CO2e

However, emissions per unit distance travelled is not necessarily the best indicator for the carbon footprint of air travel, because the distances covered are commonly longer than by other modes of travel. It is the total emissions for a trip that matters for a carbon footprint, not merely the rate of emissions. For example, because air travel makes rapid long-distance travel feasible, a holiday destination may be chosen that is much more distant than if another mode of travel were used.[54]

See also: Environmental aspects of the electric carCO2 emissions per passenger-kilometre (pkm) for all road travel for 2011 in Europe as provided by the European Environment Agency:[55]
• 109 g/km CO2 (Figure 2)

For vehicles, average figures for CO2 emissions per kilometer for road travel for 2013 in Europe, normalized to the NEDC test cycle, are provided by the International Council on Clean Transportation:[56]

• Newly registered passenger cars: 127 g CO2/km
• Hybrid-electric vehicles: 92 g CO2/km
• Light commercial vehicles (LCV): 175 g CO2/km

Average figures for the United States are provided by the US Environmental Protection Agency,[57] based on the EPA Federal Test Procedure, for the following categories:

• Passenger cars: 200 g CO2/km (322 g/mi)
• Trucks: 280 g CO2/km (450 g/mi)
• Combined: 229 g CO2/km (369 g/mi)

## Carbon footprints of products

A third of Chinese people interviewed for the European Investment Bank climate survey believe that the carbon footprint should be on every product.

Several organizations offer footprint calculators for public and corporate use, and several organizations have calculated carbon footprints of products.[58] The US Environmental Protection Agency has addressed paper, plastic (candy wrappers), glass, cans, computers, carpet and tires. Australia has addressed lumber and other building materials. Academics in Australia, Korea and the US have addressed paved roads. Companies, nonprofits and academics have addressed mailing letters and packages. Carnegie Mellon University has estimated the CO2 footprints of 46 large sectors of the economy in each of eight countries. Carnegie Mellon, Sweden and the Carbon Trust have addressed foods at home and in restaurants.

The Carbon Trust has worked with UK manufacturers on foods, shirts and detergents, introducing a CO2 label in March 2007. The label is intended to comply with a new British Publicly Available Specification (i.e. not a standard), PAS 2050,[59] and is being actively piloted by The Carbon Trust and various industrial partners.[60] As of August 2012 The Carbon Trust state they have measured 27,000 certifiable product carbon footprints.[61]

Evaluating the package of some products is key to figuring out the carbon footprint.[62] The key way to determine a carbon footprint is to look at the materials used to make the item. For example, a juice carton is made of an aseptic carton, a beer can is made of aluminum, and some water bottles either made of glass or plastic. The larger the size, the larger the footprint will be.

### Food

Food contributes 10-30% of a household’s carbon footprint, mainly attributed to agricultural practices like food production and transportation. Meat products have larger carbon footprints than plant products like vegetables and grains due to inefficient conversion of plant energy to animals, and the release of methane from manure.[63] In a 2014 study by Scarborough et al., the real-life diets of British people were surveyed and their dietary greenhouse gas footprints estimated.[64] Average dietary greenhouse-gas emissions per day (in kilograms of carbon dioxide equivalent) were:

• 7.19 for high meat-eaters
• 5.63 for medium meat-eaters
• 4.67 for low meat-eaters
• 3.91 for fish-eaters
• 3.81 for vegetarians
• 2.89 for vegans

### Textiles

The precise carbon footprint of different textiles varies considerably according to a wide range of factors. However, studies of textile production in Europe suggest the following carbon dioxide equivalent emissions footprints per kilo of textile at the point of purchase by a consumer:[65]

• Cotton: 8
• Nylon: 5.43
• PET (e.g. synthetic fleece): 5.55
• Wool: 5.48

Accounting for durability and energy required to wash and dry textile products, synthetic fabrics generally have a substantially lower carbon footprint than natural ones.[66]

### Materials

The carbon footprint of materials (also known as embodied carbon) varies widely. The carbon footprint of many common materials can be found in the Inventory of Carbon & Energy database,[67] the GREET databases and models,[68] and LCA databases via openLCA Nexus.[69] The carbon footprint of any manufactured product should be verified by a third-party.[70]

### Cement

Cement production gives a major contribution to CO2 emissions.

## Carbon footprint of political choices

The concept of a political "carbon footprint" measuring individuals' political choices (e.g. voting) were first introduced in 2021 for the election in Canada[71] by Seth Wynes, Matthew Motta, and Simon Donner; and in parallel for Germany and the UK[72] by Jakob Thomä. This research represents the first attempt to expand the concept of a personal footprint beyond consumption and investment footprints. The analysis for the election in Canada suggests the median "pro-climate" vote translated to 34.2 tons of CO2e emissions reduction, compared to a 2 ton reduction of living car free. The analysis for Germany and UK measured relative footprint reductions by switching the vote to more "pro-climate parties". In the German Elections in 2021, a German voter would have reduced around 7 tons of CO2e emissions per year when switching from the SPD (Labour) party to the Green party, compared to 3 tons associated with switching to a more "sustainable lifestyle". Political carbon footprints typically find significantly higher emissions reduction potential than consumption or investment footprints, given that consumption footprints only capture effects on your own behavior whereas voters determine climate outcomes for both voters for the winning party, voters for the losing party, and non-voters.

## Solutions

### Everyday life changes

There are many simple changes that can be made to the everyday lifestyle of a person that would reduce their GHG footprint. Reducing energy consumption within a household can include lowering one's dependence on air conditioning and heating, using LED lamps, choosing ENERGY STAR appliances, recycling, using cold water to wash clothes, avoiding a dryer, and eating less meat. Another adjustment would be reducing one's reliance on gas combustion-based motor vehicles, which produce many GHGs.[37] One could also lower their footprint by taking direct flights during air traveling. While making these changes won't bring down one's carbon footprint overnight, they will make a significant difference long term.[106]

### Lifestyles and systemic changes

Sustainable living refers to ways of living that are found to be sustainable within the Earth system or by which one purposely attempts to reduce an individual's or society's use of the Earth's natural resources, and one's personal resources. Studies found that systemic change for "decarbonization" of humanity's economic structures[107] or root-cause system changes above politics are required[108] for a substantial impact on global warming. Such changes may result in sustainable lifestyles, along with associated products, services and expenditures,[109] being structurally supported and becoming sufficiently prevalent and effective in terms of collective greenhouse gas emission reductions.

### Reducing greenhouse gases

#### Reduction of carbon dioxide

In order to decrease CO2 emissions, the reliance of fossil fuels must be lowered. These fuels produce much CO2 across all forms of their usage. Alternatively, renewable sources are cleaner for the environment.[13]

Household energy conservation measures include increasing insulation in construction, using fuel-efficient vehicles and ENERGY STAR appliances, and unplugging electrical items when not in use.

#### Reduction of methane

Reducing methane gas emissions can be accomplished in several ways. Capturing CH4 emissions from coal mines and landfills, are two ways of reducing these emissions. Manure management and livestock operations is another possible solution. Motor vehicles use fossil fuels, which produces CO
2
, but fossil fuels also produce CH
4
as a byproduct. Thus, better technology for these vehicles to avoid leakage as well as technologies that reduce their use would be beneficial.[13]

#### Reduction of nitrous oxide

Nitrous oxide (N2O) is often given off as a byproduct in various ways. Nylon production and fossil fuel usage are two ways that N2O is given off as a byproduct. Thus, improving technology for nylon production and the gathering of fossil fuels would greatly reduce nitrous oxide emissions. Also, many fertilizers have a nitrogenous base. A decrease in usage of these fertilizers, or changing their components, are more ways to reduce N2O emissions.[13]

#### Reduction of fluorinated gases

Although fluorinated gases are not produced on a massive scale, they have the worst effect on the environment. A reduction of fluorinated gas emissions can be done in many ways. Many industries that emit these gases can capture or recycle them. These same industries can also invest in more advanced technology that will not produce these gases. A reduction of leakage within power grids and motor vehicles will also decrease the emissions of fluorinated gases. There are also many air conditioning systems that emit fluorinated gases, thus an update in technology would decrease these emissions.[13]

## Notes

1. The footprints per capita of countries in Africa and India were well below average. To set these numbers into context, assuming a global population around 9–10 billion by 2050 a carbon footprint of about 2–2.5 tons CO2e per capita is needed to stay within a 2 °C target. The carbon footprint calculations are based on a consumption based approach using a Multi-Regional[45] Input-Output database, which accounts for all greenhouse gas (GHG) emissions in the global supply chain and allocates them to the final consumer of the purchased commodities. GHG emissions related to land use cover change are not included.[46]

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