Greenhouse gas emissions (abbreviated as GHG emissions) from human activities strengthen the greenhouse effect, contributing to climate change. Carbon dioxide (CO₂), from burning fossil fuels such as coal, oil, and natural gas, is one of the most important factors in causing climate change. The largest emitters are China followed by the US, although the United States has higher emissions per capita. The main producers fueling the emissions globally are large oil and gas companies. Human-caused emissions have increased atmospheric carbon dioxide by about 50% over pre-industrial levels. The growing levels of emissions have varied, but have been consistent among all greenhouse gases. Emissions in the 2010s averaged 56 billion tons a year, higher than any decade before.^[2] Total cumulative emissions from 1870 to 2017 were 425±20 GtC (1539 GtCO₂) from fossil fuels and industry, and 180±60 GtC (660 GtCO₂) from land use change. Land-use change, such as deforestation, caused about 31% of cumulative emissions over 1870–2017, coal 32%, oil 25%, and gas 10%.^[3]

Carbon dioxide (CO₂) is the dominant-emitted greenhouse gas (by humans), is the next-most important greenhouse gas (accounting for more than half of the warming), while methane (CH₄) emissions have almost the same short-term impact.^[4] Nitrous oxide (N₂O) and fluorinated gases (F-gases) play a lesser role in comparison.

Electricity generation, heat and transport are major emitters; overall energy is responsible for around 73% of emissions.^[5] Deforestation and other changes in land use also emit carbon dioxide and methane. The largest source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil-fuel industry. The largest agricultural methane source is livestock. Agricultural soils emit nitrous oxide partly due to fertilizers. Similarly, fluorinated gases from refrigerants play an outsized role in total human emissions.

The current CO₂-equivalent emission rates averaging 6.6 tonnes per person per year,^[6] are well over twice the estimated rate 2.3 tons^[7][8] required to stay within the 2030 Paris Agreement increase of 1.5 °C (2.7 °F) over pre-industrial levels.^[9] Annual per capita emissions in the industrialized countries are typically as much as ten times the average in developing countries.^[10]

The carbon footprint (or greenhouse gas footprint) serves as an indicator to compare the amount of greenhouse gases emitted over the entire life cycle from the production of a good or service along the supply chain to its final consumption.^[11][12] Carbon accounting (or greenhouse gas accounting) is a framework of methods to measure and track how much greenhouse gas an organization emits.^[13]

Overview of main sources

Relevant greenhouse gases

The major anthropogenic (human origin) sources of greenhouse gases are carbon dioxide (CO₂), nitrous oxide (N
₂O), methane, three groups of fluorinated gases (sulfur hexafluoride (SF
₆), hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs, sulphur hexafluoride (SF₆), and nitrogen trifluoride (NF₃)).^[15] Though the greenhouse effect is heavily driven by water vapor,^[16] human emissions of water vapor are not a significant contributor to warming.

Although CFCs are greenhouse gases, they are regulated by the Montreal Protocol which was motivated by CFCs' contribution to ozone depletion rather than by their contribution to global warming. Note that ozone depletion has only a minor role in greenhouse warming, though the two processes are sometimes confused in the media. In 2016, negotiators from over 170 nations meeting at the summit of the United Nations Environment Programme reached a legally binding accord to phase out hydrofluorocarbons (HFCs) in the Kigali Amendment to the Montreal Protocol.^[17][18][19]

Human activities

Since about 1750, human activity has increased the concentration of carbon dioxide and other greenhouse gases. As of 2021, measured atmospheric concentrations of carbon dioxide were almost 50% higher than pre-industrial levels.^[20]

Natural sources of carbon dioxide are nearly 20 times greater than sources due to human activity,^[21] but over periods longer than a few years natural sources are closely balanced by natural sinks, mainly photosynthesis of carbon compounds by plants and marine plankton. Absorption of terrestrial infrared radiation by longwave absorbing gases makes Earth a less efficient emitter. Therefore, in order for Earth to emit as much energy as is absorbed, global temperatures must increase.^[22]

The main sources of greenhouse gases due to human activity (also called carbon sources) are:

• Burning of fossil fuels and deforestation: Burning fossil fuels is estimated to have emitted 62% of the human-caused greenhouse gases in 2015.^[23] The largest single source is coal-fired power stations, with 20% of greenhouse gases (GHG) as of 2021.^[24]
• Land use change (mainly deforestation in the tropics) accounts for about a quarter of total anthropogenic GHG emissions.^[25]
• Livestock enteric fermentation and manure management,^[26] paddy rice farming, land use and wetland changes, man-made lakes,^[27] pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane.
• Use of chlorofluorocarbons (CFCs) in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes.
• Agricultural soils emit nitrous oxide (N₂O) partly due to application of fertilizers.^[28]
• The largest source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil-fuel industry.^[29][30] The largest agricultural methane source is livestock. Cattle (raised for both beef and milk, as well as for inedible outputs like manure and draft power) are the animal species responsible for the most emissions, representing about 65% of the livestock sector's emissions.^[31]

Global estimates

Global greenhouse gas emissions are about 50 Gt per year^[14] and for 2019 have been estimated at 57 Gt CO₂ eq including 5 Gt due to land use change.^[32] In 2019, approximately 34% [20 GtCO₂-eq] of total net anthropogenic GHG emissions came from the energy supply sector, 24% [14 GtCO₂-eq] from industry, 22% [13 GtCO₂-eq]from agriculture, forestry and other land use (AFOLU), 15% [8.7 GtCO₂-eq] from transport and 6% [3.3 GtCO₂-eq] from buildings.^[33]

The current CO₂-equivalent emission rates averaging 6.6 tonnes per person per year,^[6] are well over twice the estimated rate 2.3 tons^[7][8] required to stay within the 2030 Paris Agreement increase of 1.5 °C (2.7 °F) over pre-industrial levels.^[9]

While cities are sometimes considered to be disproportionate contributors to emissions, per-capita emissions tend to be lower for cities than the averages in their countries.^[34]

A 2017 survey of corporations responsible for global emissions found that 100 companies were responsible for 71% of global direct and indirect emissions, and that state-owned companies were responsible for 59% of their emissions.^[35][36]

China is, by a significant margin, Asia's and the world's largest emitter: it emits nearly 10 billion tonnes each year, more than one-quarter of global emissions.^[37] Other countries with fast growing emissions are South Korea, Iran, and Australia (which apart from the oil rich Persian Gulf states, now has the highest per capita emission rate in the world). On the other hand, annual per capita emissions of the EU-15 and the US are gradually decreasing over time.^[38] Emissions in Russia and Ukraine have decreased fastest since 1990 due to economic restructuring in these countries.^[39]

2015 was the first year to see both total global economic growth and a reduction of carbon emissions.^[40]

High income countries compared to low income countries

Annual per capita emissions in the industrialized countries are typically as much as ten times the average in developing countries.^[10]: 144 Due to China's fast economic development, its annual per capita emissions are quickly approaching the levels of those in the Annex I group of the Kyoto Protocol (i.e., the developed countries excluding the US).^[38]

Africa and South America are both fairly small emitters: accounting for 3-4% of global emissions each. Both have emissions almost equal in size to international aviation and shipping.^[37]

Calculations and reporting

[[File:Annual CO₂ emissions, OWID.svg|thumb|upright=1.5|Annual CO₂ emissions, total by country, not per capita (2017 data)]]

Variables

There are several ways of measuring greenhouse gas emissions. Some variables that have been reported include:^[44]

• Definition of measurement boundaries: Emissions can be attributed geographically, to the area where they were emitted (the territory principle) or by the activity principle to the territory that produced the emissions. These two principles result in different totals when measuring, for example, electricity importation from one country to another, or emissions at an international airport.
• Time horizon of different gases: The contribution of given greenhouse gas is reported as a CO₂ equivalent. The calculation to determine this takes into account how long that gas remains in the atmosphere. This is not always known accurately^{[clarification needed]} and calculations must be regularly updated to reflect new information.
• The measurement protocol itself: This may be via direct measurement or estimation. The four main methods are the emission factor-based method, mass balance method, predictive emissions monitoring systems, and continuous emissions monitoring systems. These methods differ in accuracy, cost, and usability. Public information from space-based measurements of carbon dioxide by Climate Trace is expected to reveal individual large plants before the 2021 United Nations Climate Change Conference.^[45]

These measures are sometimes used by countries to assert various policy/ethical positions on climate change.^[46]: 94The use of different measures leads to a lack of comparability, which is problematic when monitoring progress towards targets. There are arguments for the adoption of a common measurement tool, or at least the development of communication between different tools.^[44]

Emissions may be tracked over long time periods, known as historical or cumulative emissions measurements. Cumulative emissions provide some indicators of what is responsible for greenhouse gas atmospheric concentration build-up.^[47]: 199

National accounts balance

The national accounts balance tracks emissions based on the difference between a country's exports and imports. For many richer nations, the balance is negative because more goods are imported than they are exported. This result is mostly due to the fact that it is cheaper to produce goods outside of developed countries, leading developed countries to become increasingly dependent on services and not goods. A positive account balance would mean that more production was occurring within a country, so more operational factories would increase carbon emission levels.^[48]

Emissions may also be measured across shorter time periods. Emissions changes may, for example, be measured against the base year of 1990. 1990 was used in the United Nations Framework Convention on Climate Change (UNFCCC) as the base year for emissions, and is also used in the Kyoto Protocol (some gases are also measured from the year 1995).^{[10]: 146, 149} A country's emissions may also be reported as a proportion of global emissions for a particular year.

Another measurement is of per capita emissions. This divides a country's total annual emissions by its mid-year population.^[49]: 370 Per capita emissions may be based on historical or annual emissions.^{[46]: 106–107}

Embedded emissions

One way of attributing greenhouse gas emissions is to measure the embedded emissions (also referred to as "embodied emissions") of goods that are being consumed. Emissions are usually measured according to production, rather than consumption.^[50] For example, in the main international treaty on climate change (the UNFCCC), countries report on emissions produced within their borders, e.g., the emissions produced from burning fossil fuels.^{[51]: 179 [52]: 1} Under a production-based accounting of emissions, embedded emissions on imported goods are attributed to the exporting, rather than the importing, country. Under a consumption-based accounting of emissions, embedded emissions on imported goods are attributed to the importing country, rather than the exporting, country.

A substantial proportion of CO₂ emissions is traded internationally. The net effect of trade was to export emissions from China and other emerging markets to consumers in the US, Japan, and Western Europe.^[52]: 4

Carbon footprint

Emission intensity

Emission intensity is a ratio between greenhouse gas emissions and another metric, e.g., gross domestic product (GDP) or energy use. The terms "carbon intensity" and "emissions intensity" are also sometimes used.^[53] Emission intensities may be calculated using market exchange rates (MER) or purchasing power parity (PPP).^[46]: 96 Calculations based on MER show large differences in intensities between developed and developing countries, whereas calculations based on PPP show smaller differences.

Example tools and websites

Carbon accounting (or greenhouse gas accounting) is a framework of methods to measure and track how much greenhouse gas an organization emits.^[13]

Climate TRACE

Historical trends

Cumulative and historical emissions

Cumulative anthropogenic (i.e., human-emitted) emissions of CO₂ from fossil fuel use are a major cause of global warming,^[62] and give some indication of which countries have contributed most to human-induced climate change. In particular, CO₂ stays in the atmosphere for at least 150 years and up to 1000 years,^[63] whilst methane disappears within a decade or so,^[64] and nitrous oxides last about 100 years.^[65] The graph gives some indication of which regions have contributed most to human-induced climate change.^{[66][67]: 15} When these numbers are calculated per capita cumulative emissions based on then-current population the situation is shown even more clearly. The ratio in per capita emissions between industrialized countries and developing countries was estimated at more than 10 to 1.

Non-OECD countries accounted for 42% of cumulative energy-related CO₂ emissions between 1890 and 2007.^{[51]: 179–80} Over this time period, the US accounted for 28% of emissions; the EU, 23%; Japan, 4%; other OECD countries 5%; Russia, 11%; China, 9%; India, 3%; and the rest of the world, 18%.^{[51]: 179–80}

Overall, developed countries accounted for 83.8% of industrial CO₂ emissions over this time period, and 67.8% of total CO₂ emissions. Developing countries accounted for industrial CO₂ emissions of 16.2% over this time period, and 32.2% of total CO₂ emissions.

However, what becomes clear when we look at emissions across the world today is that the countries with the highest emissions over history are not always the biggest emitters today. For example, in 2017, the UK accounted for just 1% of global emissions.^[37]

In comparison, humans have emitted more greenhouse gases than the Chicxulub meteorite impact event which caused the extinction of the dinosaurs.^[68]

Transport, together with electricity generation, is the major source of greenhouse gas emissions in the EU. Greenhouse gas emissions from the transportation sector continue to rise, in contrast to power generation and nearly all other sectors. Since 1990, transportation emissions have increased by 30%. The transportation sector accounts for around 70% of these emissions. The majority of these emissions are caused by passenger vehicles and vans. Road travel is the first major source of greenhouse gas emissions from transportation, followed by aircraft and maritime.^[69][70] Waterborne transportation is still the least carbon-intensive mode of transportation on average, and it is an essential link in sustainable multimodal freight supply chains.^[71]

Buildings, like industry, are directly responsible for around one-fifth of greenhouse gas emissions, primarily from space heating and hot water consumption. When combined with power consumption within buildings, this figure climbs to more than one-third.^[72][73][74]

Within the EU, the agricultural sector presently accounts for roughly 10% of total greenhouse gas emissions, with methane from livestock accounting for slightly more than half of 10%.^[75]

Estimates of total CO₂ emissions do include biotic carbon emissions, mainly from deforestation.^[46]: 94 Including biotic emissions brings about the same controversy mentioned earlier regarding carbon sinks and land-use change.^{[46]: 93–94} The actual calculation of net emissions is very complex, and is affected by how carbon sinks are allocated between regions and the dynamics of the climate system.

The graphic shows the logarithm of 1850–2019 fossil fuel CO₂ emissions;^[76] natural log on left, actual value of Gigatons per year on right. Although emissions increased during the 170-year period by about 3% per year overall, intervals of distinctly different growth rates (broken at 1913, 1945, and 1973) can be detected. The regression lines suggest that emissions can rapidly shift from one growth regime to another and then persist for long periods of time. The most recent drop in emissions growth - by almost 3 percentage points - was at about the time of the 1970s energy crisis. Percent changes per year were estimated by piecewise linear regression on the log data and are shown on the plot; the data are from The Integrated Carbon Observation system.^[77]

Changes since a particular base year

The sharp acceleration in CO₂ emissions since 2000 to more than a 3% increase per year (more than 2 ppm per year) from 1.1% per year during the 1990s is attributable to the lapse of formerly declining trends in carbon intensity of both developing and developed nations. China was responsible for most of global growth in emissions during this period. Localised plummeting emissions associated with the collapse of the Soviet Union have been followed by slow emissions growth in this region due to more efficient energy use, made necessary by the increasing proportion of it that is exported.^[78] In comparison, methane has not increased appreciably, and N
₂O by 0.25% y⁻¹.

Using different base years for measuring emissions has an effect on estimates of national contributions to global warming.^{[67]: 17–18 [79]} This can be calculated by dividing a country's highest contribution to global warming starting from a particular base year, by that country's minimum contribution to global warming starting from a particular base year. Choosing between base years of 1750, 1900, 1950, and 1990 has a significant effect for most countries.^{[67]: 17–18} Within the G8 group of countries, it is most significant for the UK, France and Germany. These countries have a long history of CO₂ emissions (see the section on Cumulative and historical emissions).

Data from Global Carbon Project

The Global Carbon Project continuously releases data about CO₂ emissions, budget and concentration.

Emissions by type of greenhouse gas

Carbon dioxide (CO₂) is the dominant emitted greenhouse gas, while methane (CH₄) emissions almost have the same short-term impact.^[4] Nitrous oxide (N₂O) and fluorinated gases (F-gases) play a lesser role in comparison.

Greenhouse gas emissions are measured in CO₂ equivalents determined by their global warming potential (GWP), which depends on their lifetime in the atmosphere. Estimations largely depend on the ability of oceans and land sinks to absorb these gases. Short-lived climate pollutants (SLCPs) including methane, hydrofluorocarbons (HFCs), tropospheric ozone and black carbon persist in the atmosphere for a period ranging from days to 15 years; whereas carbon dioxide can remain in the atmosphere for millennia.^[83] Reducing SLCP emissions can cut the ongoing rate of global warming by almost half and reduce the projected Arctic warming by two-thirds.^[84]

Greenhouse gas emissions in 2019 were estimated at 57.4 GtCO₂e, while CO₂ emissions alone made up 42.5 Gt including land-use change (LUC).^[85]

While mitigation measures for decarbonization are essential on the longer term, they could result in weak near-term warming because sources of carbon emissions often also co-emit air pollution. Hence, pairing measures that target carbon dioxide with measures targeting non-CO₂ pollutants – short-lived climate pollutants, which have faster effects on the climate, is essential for climate goals.^[86]

Carbon dioxide (CO₂)

• Fossil fuel: oil, gas and coal (89%) are the major driver of anthropogenic global warming with annual emissions of 35.6 GtCO₂ in 2019.^[87]: 20
• Cement production (4%) is estimated at 1.42 GtCO₂
• Land-use change (LUC) is the imbalance of deforestation and reforestation. Estimations are very uncertain at 4.5 GtCO₂. Wildfires alone cause annual emissions of about 7 GtCO₂^[88][89]
• Non-energy use of fuels, carbon losses in coke ovens, and flaring in crude oil production.^[87]

Methane (CH₄)

Methane has a high immediate impact with a 5-year global warming potential of up to 100.^[4] Given this, the current 389 Mt of methane emissions^[87]: 6 has about the same short-term global warming effect as CO₂ emissions, with a risk to trigger irreversible changes in climate and ecosystems. For methane, a reduction of about 30% below current emission levels would lead to a stabilization in its atmospheric concentration.

• Fossil fuels (32%), again, account for most of the methane emissions including coal mining (12% of methane total), gas distribution and leakages (11%) as well as gas venting in oil production (9%).^{[87]: 6 [87]: 12}
• Livestock (28%) with cattle (21%) as the dominant source, followed by buffalo (3%), sheep (2%), and goats (1.5%).^{[87]: 6, 23}
• Human waste and wastewater (21%): When biomass waste in landfills and organic substances in domestic and industrial wastewater is decomposed by bacteria in anaerobic conditions, substantial amounts of methane are generated.^[87]: 12
• Rice cultivation (10%) on flooded rice fields is another agricultural source, where anaerobic decomposition of organic material produces methane.^[87]: 12

Nitrous oxide (N
₂O)

N₂O has a high GWP and significant Ozone Depleting Potential. It is estimated that the global warming potential of N₂O over 100 years is 265 times greater than CO₂.^[90] For N₂O, a reduction of more than 50% would be required for a stabilization.

Most emissions (56%) of nitrous oxide comes from agriculture, especially meat production: cattle (droppings on pasture), fertilizers, animal manure.^[87]: 12Further contributions come from combustion of fossil fuels (18%) and biofuels^[91] as well as industrial production of adipic acid and nitric acid.

F-gases

Fluorinated gases include hydrofluorocarbons (HFC), perfluorocarbons (PFC), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃). They are used by switchgear in the power sector, semiconductor manufacture, aluminum production and a largely unknown source of SF₆.^[87]: 38 Continued phase down of manufacture and use of HFCs under the Kigali Amendment to the Montreal Protocol will help reduce HFC emissions and concurrently improve the energy efficiency of appliances that use HFCs like air conditioners, freezers and other refrigeration devices.

Hydrogen

Hydrogen leakages contribute to indirect global warming.^[92] When hydrogen is oxidized in the atmosphere, the result is an increase in concentrations of greenhouse gases in both the troposphere and the stratosphere.^[93]

While grey hydrogen indirectly contributes to global warming, green hydrogen has the opposite effect. Green hydrogen, in the form of hydrogen fuel cells, can reduce greenhouse gas emissions from cars and trucks by replacing fossil-based fuels, such as gasoline and diesel.^[94]

Black carbon

Black carbon is formed through the incomplete combustion of fossil fuels, biofuel, and biomass. It is not a greenhouse gas but a climate forcing agent. Black carbon can absorb sunlight and reduce albedo when deposited on snow and ice. Indirect heating can be caused by the interaction with clouds.^[95] Black carbon stays in the atmosphere for only several days to weeks.^[96] Emissions may be mitigated by upgrading coke ovens, installing particulate filters on diesel-based engines, reducing routine flaring, and minimizing open burning of biomass.

Emissions by sector

Global greenhouse gas emissions can be attributed to different sectors of the economy. This provides a picture of the varying contributions of different types of economic activity to climate change, and helps in understanding the changes required to mitigate climate change.

Greenhouse gas emissions can be divided into those that arise from the combustion of fuels to produce energy, and those generated by other processes. Around two thirds of greenhouse gas emissions arise from the combustion of fuels.^[98]

Energy may be produced at the point of consumption, or by a generator for consumption by others. Thus emissions arising from energy production may be categorized according to where they are emitted, or where the resulting energy is consumed. If emissions are attributed at the point of production, then electricity generators contribute about 25% of global greenhouse gas emissions.^[99] If these emissions are attributed to the final consumer then 24% of total emissions arise from manufacturing and construction, 17% from transportation, 11% from domestic consumers, and 7% from commercial consumers.^[100] Around 4% of emissions arise from the energy consumed by the energy and fuel industry itself.

The remaining third of emissions arise from processes other than energy production. 12% of total emissions arise from agriculture, 7% from land use change and forestry, 6% from industrial processes, and 3% from waste.^[98]

Electricity generation

Coal-fired power stations are the single largest emitter, with over 20% of global greenhouse gas emissions in 2018.^[101] Although much less polluting than coal plants, natural gas-fired power plants are also major emitters,^[102] taking electricity generation as a whole over 25% in 2018.^[103] Notably, just 5% of the world's power plants account for almost three-quarters of carbon emissions from electricity generation, based on an inventory of more than 29,000 fossil-fuel power plants across 221 countries.^[104] In the 2022 IPCC report, it is noted that providing modern energy services universally would only increase greenhouse gas emissions by a few percent at most. This slight increase means that the additional energy demand that comes from supporting decent living standards for all would be far lower than current average energy consumption.^[105]

Agriculture, forestry and land use

Agriculture

Deforestation

Deforestation is a major source of greenhouse gas emissions. A study shows annual carbon emissions (or carbon loss) from tropical deforestation have doubled during the last two decades and continue to increase. (0.97 ±0.16 PgC per year in 2001–2005 to 1.99 ±0.13 PgC per year in 2015–2019)^[122][121]

Land-use change

Land-use change, e.g., the clearing of forests for agricultural use, can affect the concentration of greenhouse gases in the atmosphere by altering how much carbon flows out of the atmosphere into carbon sinks.^[124] Accounting for land-use change can be understood as an attempt to measure "net" emissions, i.e., gross emissions from all sources minus the removal of emissions from the atmosphere by carbon sinks.^{[46]: 92–93}

There are substantial uncertainties in the measurement of net carbon emissions.^[125] Additionally, there is controversy over how carbon sinks should be allocated between different regions and over time.^[46]: 93 For instance, concentrating on more recent changes in carbon sinks is likely to favour those regions that have deforested earlier, e.g., Europe.

In 1997, human-caused Indonesian peat fires were estimated to have released between 13% and 40% of the average annual global carbon emissions caused by the burning of fossil fuels.^{[126][127][128]}

Transport of people and goods

Transportation accounts for 15% of emissions worldwide.^[129] Over a quarter of global transport CO₂ emissions are from road freight,^[130] so many countries are further restricting truck CO₂ emissions to help limit climate change.^[131]

Maritime transport accounts for 3.5% to 4% of all greenhouse gas emissions, primarily carbon dioxide.^[132][133] In 2022, the shipping industry's 3% of global greenhouse gas emissions made it "the sixth largest greenhouse gas emitter worldwide, ranking between Japan and Germany."^{[134][135][136]}

Aviation

Jet airliners contribute to climate change by emitting carbon dioxide (CO₂), nitrogen oxides, contrails and particulates.In 2018, global commercial operations generated 2.4% of all CO₂ emissions.^[137]

In 2020, approximately 3.5% of the overall human impacts on climate are from the aviation sector. The impact of the sector on climate in the late 20 years had doubled, but the part of the contribution of the sector in comparison to other sectors did not change because other sectors grew as well.^[138]

Some representative figures for CO₂ average direct emissions (not accounting for high-altitude radiative effects) of airliners expressed as CO₂ and CO₂ equivalent per passenger kilometer:^[139]

• 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

Buildings and construction

In 2018, manufacturing construction materials and maintaining buildings accounted for 39% of carbon dioxide emissions from energy and process-related emissions. Manufacture of glass, cement, and steel accounted for 11% of energy and process-related emissions.^[140] Because building construction is a significant investment, more than two-thirds of buildings in existence will still exist in 2050. Retrofitting existing buildings to become more efficient will be necessary to meet the targets of the Paris Agreement; it will be insufficient to only apply low-emission standards to new construction.^[141] Buildings that produce as much energy as they consume are called zero-energy buildings, while buildings that produce more than they consume are energy-plus. Low-energy buildings are designed to be highly efficient with low total energy consumption and carbon emissions—a popular type is the passive house.^[140]

The global design and construction industry is responsible for approximately 39 percent of greenhouse gas emissions.^[142] Green building practices that avoid emissions or capture the carbon already present in the environment, allow for reduced footprint of the construction industry, for example, use of hempcrete, cellulose fiber insulation, and landscaping.^[143]

In 2019, the building sector was responsible for 12 GtCO₂-eq emissions. More than 95% of these emissions were carbon, and the remaining 5% were CH₄, N₂O, and halocarbon.^[144]

Embodied carbon emissions, or upfront carbon emissions (UCE), are the result of creating and maintaining the materials that form a building.^[145] As of 2018, "Embodied carbon is responsible 11% of global greenhouse gas emissions and 28% of global building sector emissions ... Embodied carbon will be responsible for almost half of total new construction emissions between now and 2050."^[146]

It has been suggested that buildings with "high carbon frames should be taxed like cigarettes"^[147] to create a presumption in favour of timber, stone, and other zero-carbon architectural design techniques."^[147][148]

Industrial processes

As of 2020^[update] Secunda CTL is the world's largest single emitter, at 56.5 million tonnes CO₂ a year.^[149]

Around 6% of emissions are fugitive emissions, which are waste gases released by the extraction of fossil fuels.

Steel and aluminum

Steel and aluminum are key economic sectors for the carbon capture and storage. According to a 2013 study, "in 2004, the steel industry along emits about 590M tons of CO₂, which accounts for 5.2% of the global anthropogenic GHG emissions. CO₂ emitted from steel production primarily comes from energy consumption of fossil fuel as well as the use of limestone to purify iron oxides."^[150]

Plastics

Plastics are produced mainly from fossil fuels. It was estimated that between 3% and 4% of global GHG emissions are associated with plastics' life cycles.^[151] The EPA estimates^[152] as many as five mass units of carbon dioxide are emitted for each mass unit of polyethylene terephthalate (PET) produced—the type of plastic most commonly used for beverage bottles,^[153] the transportation produce greenhouse gases also.^[154] Plastic waste emits carbon dioxide when it degrades. In 2018 research claimed that some of the most common plastics in the environment release the greenhouse gases methane and ethylene when exposed to sunlight in an amount that can affect the earth climate.^[155][156]

Due to the lightness of plastic versus glass or metal, plastic may reduce energy consumption. For example, packaging beverages in PET plastic rather than glass or metal is estimated to save 52% in transportation energy, if the glass or metal package is single-use, of course.

In 2019 a new report "Plastic and Climate" was published. According to the report, the production and incineration of plastics will contribute in the equivalent of 850 million tonnes of carbon dioxide (CO₂) to the atmosphere in 2019. With the current trend, annual life cycle greenhouse gas emissions of plastics will grow to 1.34 billion tonnes by 2030. By 2050, the life cycle emissions of plastics could reach 56 billion tonnes, as much as 14 percent of the Earth's remaining carbon budget.^[157] The report says that only solutions which involve a reduction in consumption can solve the problem, while others like biodegradable plastic, ocean cleanup, using renewable energy in plastic industry can do little, and in some cases may even worsen it.^[158]

Pulp and paper

The global print and paper industry accounts for about 1% of global carbon dioxide emissions.^[159] Greenhouse gas emissions from the pulp and paper industry are generated from the combustion of fossil fuels required for raw material production and transportation, wastewater treatment facilities, purchased power, paper transportation, printed product transportation, disposal and recycling.

Various services

Digital services

In 2020, data centers (excluding cryptocurrency mining) and data transmission each used about 1% of world electricity.^[160] The digital sector produces between 2% and 4% of global GHG emissions,^[161] a large part of which is from chipmaking.^[162] However the sector reduces emissions from other sectors which have a larger global share, such as transport of people,^[163] and possibly buildings and industry.^[164]

Mining for proof-of-work cryptocurrencies requires enormous amounts of electricity and consequently comes with a large carbon footprint.^[165] Proof-of-work blockchains such as Bitcoin, Ethereum, Litecoin, and Monero were estimated to have added between 3 million and 15 million tonnes of carbon dioxide (CO₂) to the atmosphere in the period from 1 January 2016 to 30 June 2017.^[166] By the end of 2021, Bitcoin was estimated to produce 65.4 million tonnes of CO₂, as much as Greece,^[167] and consume between 91 and 177 terawatt-hours annually. Bitcoin is the least energy-efficient cryptocurrency, using 707.6 kilowatt-hours of electricity per transaction.^{[168][169][170]}

Health care

The healthcare sector produces 4.4–4.6% of global greenhouse gas emissions.^[171]

Based on the 2013 life cycle emissions in the health care sector, it is estimated that the GHG emissions associated with US health care activities may cause an additional 123,000 to 381,000 DALYs annually.^[172]

Water supply and sanitation

Tourism

According to UNEP, global tourism is a significant contributor to the increasing concentrations of greenhouse gases in the atmosphere.^[175]

Emissions by other characteristics

The responsibility for anthropogenic climate change differs substantially among individuals, e.g. between groups or cohorts.

By type of energy source

Generational

Researchers report that, on average, the elderly played "a leading role in driving up greenhouse gas emissions in the past decade and are on the way to becoming the largest contributor" due to factors such as demographic transition, low informed concern about climate change and high expenditures on carbon-intensive products like energy which is used i.a. for heating rooms and private transport.^[179][180] They are less affected by climate change impacts,^[181] but have e.g. the same vote-weights for the available electoral options.

By socio-economic class

Emissions of the richest 1% are more than twice that of the poorest 50%. Compliance with the Paris Agreement's 1.5 °C goal would require the richest 1% to reduce emissions by at least 30 times, while per-person emissions of the poorest 50% could approximately triple.^[182]

Though total CO₂ emissions (size of pie charts) differ substantially among high-emitting regions, the pattern of higher income classes emitting more than lower income classes is consistent across regions.^[183] The world's top 1% of emitters emit over 1000 times more than the bottom 1%.^[183]

Fueled by the consumptive lifestyle of wealthy people, the wealthiest 5% of the global population has been responsible for 37% of the absolute increase in greenhouse gas emissions worldwide. It can be seen that there is a strong relationship between income and per capita carbon dioxide emissions.^[37] Almost half of the increase in absolute global emissions has been caused by the richest 10% of the population.^[185] In the newest report from the IPCC 2022, it states that the lifestyle consumptions of the poor and middle class in emerging economies produce approximately 5–50 times less the amount that the high class in already developed high-income countries.^[186][187] Variations in regional, and national per capita emissions partly reflect different development stages, but they also vary widely at similar income levels. The 10% of households with the highest per capita emissions contribute a disproportionately large share of global household greenhouse gas emissions.^[187]

Studies find that the most affluent citizens of the world are responsible for most environmental impacts, and robust action by them is necessary for prospects of moving towards safer environmental conditions.^[188][189]

According to a 2020 report by Oxfam and the Stockholm Environment Institute,^[190][191] the richest 1% of the global population have caused twice as much carbon emissions as the poorest 50% over the 25 years from 1990 to 2015.^{[192][193][182]} This was, respectively, during that period, 15% of cumulative emissions compared to 7%.^[194] The bottom half of the population is directly-responsible for less than 20% of energy footprints and consume less than the top 5% in terms of trade-corrected energy. The largest disproportionality was identified to be in the domain of transport, where e.g. the top 10% consume 56% of vehicle fuel and conduct 70% of vehicle purchases.^[195] However, wealthy individuals are also often shareholders and typically have more influence^[196] and, especially in the case of billionaires, may also direct lobbying efforts, direct financial decisions, and/or control companies.

Reducing greenhouse gas emissions

Climate change mitigation

Governments have taken action to reduce greenhouse gas emissions to mitigate climate change. Countries and regions listed in Annex I of the United Nations Framework Convention on Climate Change (UNFCCC) (i.e., the OECD and former planned economies of the Soviet Union) are required to submit periodic assessments to the UNFCCC of actions they are taking to address climate change.^[197]: 3 Policies implemented by governments include for example national and regional targets to reduce emissions, promoting energy efficiency, and support for an energy transition.

Projections for future reductions

Country examples

Lists of countries

In 2019, China, the United States, India, the EU27+UK, Russia, and Japan - the world's largest CO₂ emitters - together accounted for 51% of the population, 62.5% of global gross domestic product, 62% of total global fossil fuel consumption and emitted 67% of total global fossil CO₂. Emissions from these five countries and the EU28 show different changes in 2019 compared to 2018: the largest relative increase is found for China (+3.4%), followed by India (+1.6%). On the contrary, the EU27+UK (-3.8%), the United States (-2.6%), Japan (-2.1%) and Russia (-0.8%) reduced their fossil CO₂ emissions.^[206]

2019 Fossil CO₂ emissions by country^[206]

Country	total emissions (Mton)	Share (%)	per capita (ton)	per GDP (ton/k$)
Global Total	38,016.57	100.00	4.93	0.29
China	11,535.20	30.34	8.12	0.51
United States	5,107.26	13.43	15.52	0.25
EU27+UK	3,303.97	8.69	6.47	0.14
India	2,597.36	6.83	1.90	0.28
Russia	1,792.02	4.71	12.45	0.45
Japan	1,153.72	3.03	9.09	0.22
International Shipping	730.26	1.92	-	-
Germany	702.60	1.85	8.52	0.16
Iran	701.99	1.85	8.48	0.68
South Korea	651.87	1.71	12.70	0.30
International Aviation	627.48	1.65	-	-
Indonesia	625.66	1.65	2.32	0.20
Saudi Arabia	614.61	1.62	18.00	0.38
Canada	584.85	1.54	15.69	0.32
South Africa	494.86	1.30	8.52	0.68
Mexico	485.00	1.28	3.67	0.19
Brazil	478.15	1.26	2.25	0.15
Australia	433.38	1.14	17.27	0.34
Turkey	415.78	1.09	5.01	0.18
United Kingdom	364.91	0.96	5.45	0.12
Italy,  San Marino and the Holy See	331.56	0.87	5.60	0.13
Poland	317.65	0.84	8.35	0.25
France and  Monaco	314.74	0.83	4.81	0.10
Vietnam	305.25	0.80	3.13	0.39
Kazakhstan	277.36	0.73	14.92	0.57
Taiwan	276.78	0.73	11.65	0.23
Thailand	275.06	0.72	3.97	0.21
Spain and Andorra	259.31	0.68	5.58	0.13
Egypt	255.37	0.67	2.52	0.22
Malaysia	248.83	0.65	7.67	0.27
Pakistan	223.63	0.59	1.09	0.22
United Arab Emirates	222.61	0.59	22.99	0.34
Argentina	199.41	0.52	4.42	0.20
Iraq	197.61	0.52	4.89	0.46
Ukraine	196.40	0.52	4.48	0.36
Algeria	180.57	0.47	4.23	0.37
Netherlands	156.41	0.41	9.13	0.16
Philippines	150.64	0.40	1.39	0.16
Bangladesh	110.16	0.29	0.66	0.14
Venezuela	110.06	0.29	3.36	0.39
Qatar	106.53	0.28	38.82	0.41
Czechia	105.69	0.28	9.94	0.25
Belgium	104.41	0.27	9.03	0.18
Nigeria	100.22	0.26	0.50	0.10
Kuwait	98.95	0.26	23.29	0.47
Uzbekistan	94.99	0.25	2.90	0.40
Oman	92.78	0.24	18.55	0.67
Turkmenistan	90.52	0.24	15.23	0.98
Chile	89.89	0.24	4.90	0.20
Colombia	86.55	0.23	1.74	0.12
Romania	78.63	0.21	4.04	0.14
Morocco	73.91	0.19	2.02	0.27
Austria	72.36	0.19	8.25	0.14
Serbia and Montenegro	70.69	0.19	7.55	0.44
Israel and  Palestine	68.33	0.18	7.96	0.18
Belarus	66.34	0.17	7.03	0.37
Greece	65.57	0.17	5.89	0.20
Peru	56.29	0.15	1.71	0.13
Singapore	53.37	0.14	9.09	0.10
Hungary	53.18	0.14	5.51	0.17
Libya	52.05	0.14	7.92	0.51
Portugal	48.47	0.13	4.73	0.14
Myanmar	48.31	0.13	0.89	0.17
Norway	47.99	0.13	8.89	0.14
Sweden	44.75	0.12	4.45	0.08
Hong Kong	44.02	0.12	5.88	0.10
Finland	43.41	0.11	7.81	0.16
Bulgaria	43.31	0.11	6.20	0.27
North Korea	42.17	0.11	1.64	0.36
Ecuador	40.70	0.11	2.38	0.21
Switzerland and  Liechtenstein	39.37	0.10	4.57	0.07
New Zealand	38.67	0.10	8.07	0.18
Ireland	36.55	0.10	7.54	0.09
Slovakia	35.99	0.09	6.60	0.20
Azerbaijan	35.98	0.09	3.59	0.25
Mongolia	35.93	0.09	11.35	0.91
Bahrain	35.44	0.09	21.64	0.48
Bosnia and Herzegovina	33.50	0.09	9.57	0.68
Trinidad and Tobago	32.74	0.09	23.81	0.90
Tunisia	32.07	0.08	2.72	0.25
Denmark	31.12	0.08	5.39	0.09
Cuba	31.04	0.08	2.70	0.11
Syria	29.16	0.08	1.58	1.20
Jordan	28.34	0.07	2.81	0.28
Sri Lanka	27.57	0.07	1.31	0.10
Lebanon	27.44	0.07	4.52	0.27
Dominican Republic	27.28	0.07	2.48	0.14
Angola	25.82	0.07	0.81	0.12
Bolivia	24.51	0.06	2.15	0.24
Sudan and  South Sudan	22.57	0.06	0.40	0.13
Guatemala	21.20	0.06	1.21	0.15
Kenya	19.81	0.05	0.38	0.09
Croatia	19.12	0.05	4.62	0.16
Estonia	18.50	0.05	14.19	0.38
Ethiopia	18.25	0.05	0.17	0.07
Ghana	16.84	0.04	0.56	0.10
Cambodia	16.49	0.04	1.00	0.23
New Caledonia	15.66	0.04	55.25	1.67
Slovenia	15.37	0.04	7.38	0.19
Nepal	15.02	0.04	0.50	0.15
Lithuania	13.77	0.04	4.81	0.13
Côte d'Ivoire	13.56	0.04	0.53	0.10
Georgia	13.47	0.04	3.45	0.24
Tanzania	13.34	0.04	0.22	0.09
Kyrgyzstan	11.92	0.03	1.92	0.35
Panama	11.63	0.03	2.75	0.09
Afghanistan	11.00	0.03	0.30	0.13
Yemen	10.89	0.03	0.37	0.17
Zimbabwe	10.86	0.03	0.63	0.26
Honduras	10.36	0.03	1.08	0.19
Cameroon	10.10	0.03	0.40	0.11
Senegal	9.81	0.03	0.59	0.18
Luxembourg	9.74	0.03	16.31	0.14
Mozambique	9.26	0.02	0.29	0.24
Moldova	9.23	0.02	2.29	0.27
Costa Rica	8.98	0.02	1.80	0.09
North Macedonia	8.92	0.02	4.28	0.26
Tajikistan	8.92	0.02	0.96	0.28
Paraguay	8.47	0.02	1.21	0.09
Latvia	8.38	0.02	4.38	0.14
Benin	8.15	0.02	0.69	0.21
Mauritania	7.66	0.02	1.64	0.33
Zambia	7.50	0.02	0.41	0.12
Jamaica	7.44	0.02	2.56	0.26
Cyprus	7.41	0.02	6.19	0.21
El Salvador	7.15	0.02	1.11	0.13
Botswana	7.04	0.02	2.96	0.17
Brunei	7.02	0.02	15.98	0.26
Laos	6.78	0.02	0.96	0.12
Uruguay	6.56	0.02	1.89	0.09
Armenia	5.92	0.02	2.02	0.15
Curaçao	5.91	0.02	36.38	1.51
Nicaragua	5.86	0.02	0.92	0.17
Congo	5.80	0.02	1.05	0.33
Albania	5.66	0.01	1.93	0.14
Uganda	5.34	0.01	0.12	0.06
Namibia	4.40	0.01	1.67	0.18
Mauritius	4.33	0.01	3.41	0.15
Madagascar	4.20	0.01	0.16	0.09
Papua New Guinea	4.07	0.01	0.47	0.11
Iceland	3.93	0.01	11.53	0.19
Puerto Rico	3.91	0.01	1.07	0.04
Barbados	3.83	0.01	13.34	0.85
Burkina Faso	3.64	0.01	0.18	0.08
Haiti	3.58	0.01	0.32	0.18
Gabon	3.48	0.01	1.65	0.11
Equatorial Guinea	3.47	0.01	2.55	0.14
Réunion	3.02	0.01	3.40	-
Democratic Republic of the Congo	2.98	0.01	0.03	0.03
Guinea	2.92	0.01	0.22	0.09
Togo	2.85	0.01	0.35	0.22
Bahamas	2.45	0.01	6.08	0.18
Niger	2.36	0.01	0.10	0.08
Bhutan	2.12	0.01	2.57	0.24
Suriname	2.06	0.01	3.59	0.22
Martinique	1.95	0.01	5.07	-
Guadeloupe	1.87	0.00	4.17	-
Malawi	1.62	0.00	0.08	0.08
Guyana	1.52	0.00	1.94	0.20
Sierra Leone	1.40	0.00	0.18	0.10
Fiji	1.36	0.00	1.48	0.11
Palau	1.33	0.00	59.88	4.09
Macao	1.27	0.00	1.98	0.02
Liberia	1.21	0.00	0.24	0.17
Rwanda	1.15	0.00	0.09	0.04
Eswatini	1.14	0.00	0.81	0.11
Djibouti	1.05	0.00	1.06	0.20
Seychelles	1.05	0.00	10.98	0.37
Malta	1.04	0.00	2.41	0.05
Mali	1.03	0.00	0.05	0.02
Cabo Verde	1.02	0.00	1.83	0.26
Somalia	0.97	0.00	0.06	0.57
Maldives	0.91	0.00	2.02	0.09
Chad	0.89	0.00	0.06	0.04
Aruba	0.78	0.00	7.39	0.19
Eritrea	0.75	0.00	0.14	0.08
Lesotho	0.75	0.00	0.33	0.13
Gibraltar	0.69	0.00	19.88	0.45
French Guiana	0.61	0.00	2.06	-
French Polynesia	0.60	0.00	2.08	0.10
The Gambia	0.59	0.00	0.27	0.11
Greenland	0.54	0.00	9.47	0.19
Antigua and Barbuda	0.51	0.00	4.90	0.24
Central African Republic	0.49	0.00	0.10	0.11
Guinea-Bissau	0.44	0.00	0.22	0.11
Cayman Islands	0.40	0.00	6.38	0.09
Timor-Leste	0.38	0.00	0.28	0.10
Belize	0.37	0.00	0.95	0.14
Bermuda	0.35	0.00	5.75	0.14
Burundi	0.34	0.00	0.03	0.04
Saint Lucia	0.30	0.00	1.65	0.11
Western Sahara	0.30	0.00	0.51	-
Grenada	0.23	0.00	2.10	0.12
Comoros	0.21	0.00	0.25	0.08
Saint Kitts and Nevis	0.19	0.00	3.44	0.14
São Tomé and Príncipe	0.16	0.00	0.75	0.19
Saint Vincent and the Grenadines	0.15	0.00	1.32	0.11
Samoa	0.14	0.00	0.70	0.11
Solomon Islands	0.14	0.00	0.22	0.09
Tonga	0.13	0.00	1.16	0.20
Turks and Caicos Islands	0.13	0.00	3.70	0.13
British Virgin Islands	0.12	0.00	3.77	0.17
Dominica	0.10	0.00	1.38	0.12
Vanuatu	0.09	0.00	0.30	0.09
Saint Pierre and Miquelon	0.06	0.00	9.72	-
Cook Islands	0.04	0.00	2.51	-
Falkland Islands	0.03	0.00	10.87	-
Kiribati	0.03	0.00	0.28	0.13
Anguilla	0.02	0.00	1.54	0.12
Saint Helena,  Ascension and  Tristan da Cunha	0.02	0.00	3.87	-
Faroes	0.00	0.00	0.04	0.00

United States

China

China has the most total annual emissions (area of rectangle) of any nation, and has higher than average per capita emissions.^[219]

Cumulatively over time, emissions from China have caused more economic damage globally than any other nation except the U.S.^[220]

Greenhouse gas emissions by China are the largest of any country in the world both in production and consumption terms, and stem mainly from coal burning in China, including coal-fired power stations, coal mining,^[221] and blast furnaces producing iron and steel.^[222] When measuring production-based emissions, China emitted over 14 gigatonnes (Gt) CO_2eq of greenhouse gases in 2019,^[223] 27% of the world total.^[224][225] When measuring in consumption-based terms, which adds emissions associated with imported goods and extracts those associated with exported goods, China accounts for 13 gigatonnes (Gt) or 25% of global emissions.^[226]

India

Society and culture

Impacts of the COVID-19 pandemic

In 2020, carbon dioxide emissions fell by 6.4% or 2.3 billion tonnes globally.^[233] In April 2020, NO_x emissions fell by up to 30%.^[234] In China, lockdowns and other measures resulted in a 26% decrease in coal consumption, and a 50% reduction in nitrogen oxide emissions.^[235] Greenhouse gas emissions rebounded later in the pandemic as many countries began lifting restrictions, with the direct impact of pandemic policies having a negligible long-term impact on climate change.^[233][236]