Greenhouse gases are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. What distinguishes them from other gases is that they absorb the wavelengths of radiation that a planet emits, resulting in the greenhouse effect. [1] The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about −18 °C (0 °F), [2] rather than the present average of 15 °C (59 °F). [3] [4]
The most abundant greenhouse gases in Earth's atmosphere, listed in decreasing order of average global mole fraction, are: [5] [6] Water vapor (H
2O), Carbon dioxide (CO
2), Methane (CH
4), Nitrous oxide (N
2O), Ozone (O
3), Chlorofluorocarbons (CFCs and HCFCs), Hydrofluorocarbons (HFCs), Perfluorocarbons (CF
4, C
2F
6, etc.), SF
6, and NF
3. Yet, while water vapor is a potent greenhouse gas, humans are not directly adding to its concentrations, [7] . so it is not one of the primary drivers of climate change, but rather one of the feedbacks. [8] On the other hand, carbon dioxide is causing about three quarters of global warming and can take thousands of years to be fully absorbed by the carbon cycle. [9] [10] Methane causes most of the remaining warming and lasts in the atmosphere for an average of 12 years. [11]
Human activities since the beginning of the Industrial Revolution (around 1750) have increased atmospheric methane concentrations by over 150% and carbon dioxide by over 50%, [12] [13] up to a level not seen in over 3 million years. [14] The vast majority of carbon dioxide emissions by humans come from the combustion of fossil fuels, principally coal, petroleum (including oil) and natural gas. Additional contributions come from cement manufacturing, fertilizer production, and changes in land use like deforestation. [15] : 687 [16] [17] Methane emissions originate from agriculture, fossil fuel production, waste, and other sources. [18]
According to Berkeley Earth, average global surface temperature has risen by more than 1.2 °C (2.2 °F) since the pre-industrial (1850–1899) period as a result of greenhouse gas emissions. If current emission rates continue then temperature rises will surpass 2.0 °C (3.6 °F) sometime between 2040 and 2070, which is the level the United Nations' Intergovernmental Panel on Climate Change (IPCC) says is "dangerous". [19]
Greenhouse gases are infrared active, meaning that they absorb and emit infrared radiation in the same long wavelength range as what is emitted by the Earth's surface, clouds and atmosphere. [20] : 2233
99% of the Earth's dry atmosphere (excluding water vapor) is made up of nitrogen (N
2) (78%) and oxygen (O
2) (21%). Because their molecules contain two atoms of the same element, they have no asymmetry in the distribution of their electrical charges, [21] and so are almost totally unaffected by infrared thermal radiation, [22] with only an extremely minor effect from collision-induced absorption. [23] [24] [25] A further 0.9% of the atmosphere is made up by argon (Ar), which is monatomic, and so completely transparent to thermal radiation. On the other hand, carbon dioxide (0.04%), methane, nitrous oxide and even less abundant trace gases account for less than 0.1% of Earth's atmosphere, but because their molecules contain atoms of different elements, there is an asymmetry in electric charge distribution which allows molecular vibrations to interact with electromagnetic radiation. This makes them infrared active, and so their presence causes greenhouse effect. [21]
Earth absorbs some of the radiant energy received from the sun, reflects some of it as light and reflects or radiates the rest back to space as heat. A planet's surface temperature depends on this balance between incoming and outgoing energy. When Earth's energy balance is shifted, its surface becomes warmer or cooler, leading to a variety of changes in global climate. [26] Radiative forcing is a metric calculated in watts per square meter, which characterizes the impact of an external change in a factor that influences climate. It is calculated as the difference in top-of-atmosphere (TOA) energy balance immediately caused by such an external change A positive forcing, such as from increased concentrations of greenhouse gases, means more energy arriving than leaving at the top-of-atmosphere, which causes additional warming, while negative forcing, like from sulfates forming in the atmosphere from sulfur dioxide, leads to cooling. [20] : 2245 [27]
Within the lower atmosphere, greenhouse gases exchange thermal radiation with the surface and limit radiative heat flow away from it, which reduces the overall rate of upward radiative heat transfer. [28] : 139 [29] The increased concentration of greenhouse gases is also cooling the upper atmosphere, as it is much thinner than the lower layers, and any heat re-emitted from greenhouse gases is more likely to travel further to space than to interact with the fewer gas molecules in the upper layers. The upper atmosphere is also shrinking as the result. [30]
Global warming potential (GWP) is an index to measure of how much infrared thermal radiation a greenhouse gas would absorb over a given time frame after it has been added to the atmosphere (or emitted to the atmosphere). The GWP makes different greenhouse gases comparable with regards to their "effectiveness in causing radiative forcing". [31] : 2232 It is expressed as a multiple of the radiation that would be absorbed by the same mass of added carbon dioxide (CO2), which is taken as a reference gas. Therefore, the GWP is one for CO2. For other gases it depends on how strongly the gas absorbs infrared thermal radiation, how quickly the gas leaves the atmosphere, and the time frame being considered.
For example, methane has a GWP over 20 years (GWP-20) of 81.2 [32] meaning that, for example, a leak of a tonne of methane is equivalent to emitting 81.2 tonnes of carbon dioxide measured over 20 years. As methane has a much shorter atmospheric lifetime than carbon dioxide, its GWP is much less over longer time periods, with a GWP-100 of 27.9 and a GWP-500 of 7.95. [32] : 7SM-24
The carbon dioxide equivalent (CO2e or CO2eq or CO2-e) can be calculated from the GWP. For any gas, it is the mass of CO2 that would warm the earth as much as the mass of that gas. Thus it provides a common scale for measuring the climate effects of different gases. It is calculated as GWP times mass of the other gas.This table shows the most important contributions to the overall greenhouse effect, without which the average temperature of Earth's surface would be about −18 °C (0 °F), [2] instead of around 15 °C (59 °F). [3] This table also specifies tropospheric ozone, because this gas has a cooling effect in the stratosphere, but a warming influence comparable to nitrous oxide and CFCs in the troposphere. [34]
K&T (1997) [35] | Schmidt (2010) [36] | |||
---|---|---|---|---|
Contributor | Clear Sky | With Clouds | Clear Sky | With Clouds |
Water vapor | 60 | 41 | 67 | 50 |
Clouds | 31 | 25 | ||
CO2 | 26 | 18 | 24 | 19 |
Tropospheric ozone (O3) | 8 | |||
N2O + CH4 | 6 | |||
Other | 9 | 9 | 7 | |
K&T (1997) used 353 ppm CO2 and calculated 125 W/m2 total clear-sky greenhouse effect; relied on single atmospheric profile and cloud model. "With Clouds" percentages are from Schmidt (2010) interpretation of K&T (1997). |
Anthropogenic changes to the natural greenhouse effect are sometimes referred to as the enhanced greenhouse effect. [20] : 2223 The contribution of each gas to the enhanced greenhouse effect is determined by the characteristics of that gas, its abundance, and any indirect effects it may cause. For example, the direct radiative effect of a mass of methane is about 84 times stronger than the same mass of carbon dioxide over a 20-year time frame. [40] Since the 1980s, greenhouse gas forcing contributions (relative to year 1750) are also estimated with high accuracy using IPCC-recommended expressions derived from radiative transfer models. [41]
The concentration of a greenhouse gas is typically measured in parts per million (ppm) or parts per billion (ppb) by volume. A CO2 concentration of 420 ppm means that 420 out of every million air molecules is a CO2 molecule. The first 30 ppm increase in CO2 concentrations took place in about 200 years, from the start of the Industrial Revolution to 1958; however the next 90 ppm increase took place within 56 years, from 1958 to 2014. [13] [42] [43] Similarly, the average annual increase in the 1960s was only 37% of what it was in 2000 through 2007. [44]
Many observations are available online in a variety of atmospheric chemistry observational databases. The table below shows the most influential long-lived, well-mixed greenhouse gases, along with their tropospheric concentrations and direct radiative forcings, as identified by the Intergovernmental Panel on Climate Change (IPCC). [45] Abundances of these trace gases are regularly measured by atmospheric scientists from samples collected throughout the world. [46] [47] [48] It excludes water vapor because changes in its concentrations are calculated as a climate change feedback indirectly caused by changes in other greenhouse gases, as well as ozone, whose concentrations are only modified indirectly by various refrigerants that cause ozone depletion. Some short-lived gases (e.g. carbon monoxide, NOx) and aerosols (e.g. mineral dust or black carbon) are also excluded because of limited role and strong variation, alongside with minor refrigants and other halogenated gases, which have been mass-produced in smaller quantities than those in the table. [45] : 731–738 and Annex III of the 2021 IPCC WG1 Report [49] : 4–9
Species | Lifetime (years) [45] : 731 | 100-yr | Mole Fraction [ppt - except as noted]a + Radiative forcing [W m−2] [B] | Concentrations up to year 2022 | ||||
---|---|---|---|---|---|---|---|---|
Baseline Year 1750 | TAR [52] Year 1998 | AR4 [53] Year 2005 | AR5 [45] : 678 Year 2011 | AR6 [49] : 4–9 Year 2019 | ||||
CO2 [ppm] | [A] | 1 | 278 | 365 (1.46) | 379 (1.66) | 391 (1.82) | 410 (2.16) | |
CH4 [ppb] | 12.4 | 28 | 700 | 1,745 (0.48) | 1,774 (0.48) | 1,801 (0.48) | 1866 (0.54) | |
N2O [ppb] | 121 | 265 | 270 | 314 (0.15) | 319 (0.16) | 324 (0.17) | 332 (0.21) | |
CFC-11 | 45 | 4,660 | 0 | 268 (0.07) | 251 (0.063) | 238 (0.062) | 226 (0.066) | |
CFC-12 | 100 | 10,200 | 0 | 533 (0.17) | 538 (0.17) | 528 (0.17) | 503 (0.18) | |
CFC-13 | 640 | 13,900 | 0 | 4 (0.001) | - | 2.7 (0.0007) | 3.28 (0.0009) | cfc13 |
CFC-113 | 85 | 6,490 | 0 | 84 (0.03) | 79 (0.024) | 74 (0.022) | 70 (0.021) | |
CFC-114 | 190 | 7,710 | 0 | 15 (0.005) | - | - | 16 (0.005) | cfc114 |
CFC-115 | 1,020 | 5,860 | 0 | 7 (0.001) | - | 8.37 (0.0017) | 8.67 (0.0021) | cfc115 |
HCFC-22 | 11.9 | 5,280 | 0 | 132 (0.03) | 169 (0.033) | 213 (0.0447) | 247 (0.0528) | |
HCFC-141b | 9.2 | 2,550 | 0 | 10 (0.001) | 18 (0.0025) | 21.4 (0.0034) | 24.4 (0.0039) | |
HCFC-142b | 17.2 | 5,020 | 0 | 11 (0.002) | 15 (0.0031) | 21.2 (0.0040) | 22.3 (0.0043) | |
CH3CCl3 | 5 | 160 | 0 | 69 (0.004) | 19 (0.0011) | 6.32 (0.0004) | 1.6 (0.0001) | |
CCl4 | 26 | 1,730 | 0 | 102 (0.01) | 93 (0.012) | 85.8 (0.0146) | 78 (0.0129) | |
HFC-23 | 222 | 12,400 | 0 | 14 (0.002) | 18 (0.0033) | 24 (0.0043) | 32.4 (0.0062) | |
HFC-32 | 5.2 | 677 | 0 | - | - | 4.92 (0.0005) | 20 (0.0022) | |
HFC-125 | 28.2 | 3,170 | 0 | - | 3.7 (0.0009) | 9.58 (0.0022) | 29.4 (0.0069) | |
HFC-134a | 13.4 | 1,300 | 0 | 7.5 (0.001) | 35 (0.0055) | 62.7 (0.0100) | 107.6 (0.018) | |
HFC-143a | 47.1 | 4,800 | 0 | - | - | 12.0 (0.0019) | 24 (0.0040) | |
HFC-152a | 1.5 | 138 | 0 | 0.5 (0.0000) | 3.9 (0.0004) | 6.4 (0.0006) | 7.1 (0.0007) | |
CF4 (PFC-14) | 50,000 | 6,630 | 40 | 80 (0.003) | 74 (0.0034) | 79 (0.0040) | 85.5 (0.0051) | |
C2F6 (PFC-116) | 10,000 | 11,100 | 0 | 3 (0.001) | 2.9 (0.0008) | 4.16 (0.0010) | 4.85 (0.0013) | |
SF6 | 3,200 | 23,500 | 0 | 4.2 (0.002) | 5.6 (0.0029) | 7.28 (0.0041) | 9.95 (0.0056) | |
SO2F2 | 36 | 4,090 | 0 | - | - | 1.71 (0.0003) | 2.5 (0.0005) | |
NF3 | 500 | 16,100 | 0 | - | - | 0.9 (0.0002) | 2.05 (0.0004) | |
a Mole fractions: μmol/mol = ppm = parts per million (106); nmol/mol = ppb = parts per billion (109); pmol/mol = ppt = parts per trillion (1012).
A The IPCC states that "no single atmospheric lifetime can be given" for CO2. [45] : 731 This is mostly due to the rapid growth and cumulative magnitude of the disturbances to Earth's carbon cycle by the geologic extraction and burning of fossil carbon. [54] As of year 2014, fossil CO2 emitted as a theoretical 10 to 100 GtC pulse on top of the existing atmospheric concentration was expected to be 50% removed by land vegetation and ocean sinks in less than about a century, as based on the projections of coupled models referenced in the AR5 assessment. [55] A substantial fraction (20-35%) was also projected to remain in the atmosphere for centuries to millennia, where fractional persistence increases with pulse size. [56] [57]
B Values are relative to year 1750. AR6 reports the effective radiative forcing which includes effects of rapid adjustments in the atmosphere and at the surface. [58]
Atmospheric concentrations are determined by the balance between sources (emissions of the gas from human activities and natural systems) and sinks (the removal of the gas from the atmosphere by conversion to a different chemical compound or absorption by bodies of water). [60] : 512
The proportion of an emission remaining in the atmosphere after a specified time is the "airborne fraction" (AF). The annual airborne fraction is the ratio of the atmospheric increase in a given year to that year's total emissions.
As of 2006 the annual airborne fraction for CO2 was about 0.45. The annual airborne fraction increased at a rate of 0.25 ± 0.21% per year over the period 1959–2006. [61]
Aside from water vapor, which has a residence time of about nine days, [62] major greenhouse gases are well mixed and take many years to leave the atmosphere. [63] Although it is not easy to know with precision how long it takes greenhouse gases to leave the atmosphere, there are estimates for the principal greenhouse gases. Jacob (1999) [64] defines the lifetime of an atmospheric species X in a one-box model as the average time that a molecule of X remains in the box. Mathematically can be defined as the ratio of the mass (in kg) of X in the box to its removal rate, which is the sum of the flow of X out of the box (), chemical loss of X (), and deposition of X () (all in kg/s):
If input of this gas into the box ceased, then after time , its concentration would decrease by about 63%.
The atmospheric lifetime of a species therefore measures the time required to restore equilibrium following a sudden increase or decrease in its concentration in the atmosphere. Individual atoms or molecules may be lost or deposited to sinks such as the soil, the oceans and other waters, or vegetation and other biological systems, reducing the excess to background concentrations. The average time taken to achieve this is the mean lifetime.
Carbon dioxide has a variable atmospheric lifetime, and cannot be specified precisely. [65] [40] [20] : 2237 Similar issues apply to other greenhouse gases, many of which have longer mean lifetimes than CO2, e.g. N2O has a mean atmospheric lifetime of 121 years. [40]
Water vapor concentrations fluctuate regionally, but human activity does not directly affect water vapor concentrations except at local scales, such as near irrigated fields. Indirectly, human activity that increases global temperatures will increase water vapor concentrations, because Clausius–Clapeyron relation establishes that more water vapor will be present per unit volume at elevated temperatures. This process known as water vapor feedback. [66] The atmospheric concentration of vapor is highly variable and depends largely on temperature, from less than 0.01% in extremely cold regions up to 3% by mass in saturated air at about 32 °C. [67]
Most greenhouse gases have both natural and human-caused sources. An exception are purely human-produced synthetic halocarbons which have no natural sources. During the pre-industrial Holocene, concentrations of existing gases were roughly constant, because the large natural sources and sinks roughly balanced. In the industrial era, human activities have added greenhouse gases to the atmosphere, mainly through the burning of fossil fuels and clearing of forests. [68] [4] : 115
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)). [69] Though the greenhouse effect is heavily driven by water vapor, [70] human emissions of water vapor are not a significant contributor to warming.
Greenhouse gas monitoring involves the direct measurement of greenhouse gas emissions and levels. There are several different methods of measuring carbon dioxide concentrations in the atmosphere, including infrared analyzing and manometry. Methane and nitrous oxide are measured by other instruments. Greenhouse gases are measured from space such as by the Orbiting Carbon Observatory and networks of ground stations such as the Integrated Carbon Observation System.[ citation needed ]
The Annual Greenhouse Gas Index (AGGI) is defined by atmospheric scientists at NOAA as the ratio of total direct radiative forcing due to long-lived and well-mixed greenhouse gases for any year for which adequate global measurements exist, to that present in year 1990. [39] [76] These radiative forcing levels are relative to those present in year 1750 (i.e. prior to the start of the industrial era). 1990 is chosen because it is the baseline year for the Kyoto Protocol, and is the publication year of the first IPCC Scientific Assessment of Climate Change.
As such, NOAA states that the AGGI "measures the commitment that (global) society has already made to living in a changing climate. It is based on the highest quality atmospheric observations from sites around the world. Its uncertainty is very low." [77]
Carbon dioxide is removed from the atmosphere primarily through photosynthesis and enters the terrestrial and oceanic biospheres. Carbon dioxide also dissolves directly from the atmosphere into bodies of water (ocean, lakes, etc.), as well as dissolving in precipitation as raindrops fall through the atmosphere. When dissolved in water, carbon dioxide reacts with water molecules and forms carbonic acid, which contributes to ocean acidity. It can then be absorbed by rocks through weathering. It also can acidify other surfaces it touches or be washed into the ocean. [82]
A number of technologies remove greenhouse gases emissions from the atmosphere. Most widely analyzed are those that remove carbon dioxide from the atmosphere, either to geologic formations such as bio-energy with carbon capture and storage and carbon dioxide air capture, [85] or to the soil as in the case with biochar. [85] Many long-term climate scenario models require large-scale human-made negative emissions to avoid serious climate change. [86] Negative emissions approaches are also being studied for atmospheric methane, called atmospheric methane removal. [87]
Carbon dioxide is believed to have played an important effect in regulating Earth's temperature throughout its 4.54 billion year history. Early in the Earth's life, scientists have found evidence of liquid water indicating a warm world even though the Sun's output is believed to have only been 70% of what it is today. Higher carbon dioxide concentrations in the early Earth's atmosphere might help explain this faint young sun paradox. When Earth first formed, Earth's atmosphere may have contained more greenhouse gases and CO2 concentrations may have been higher, with estimated partial pressure as large as 1,000 kPa (10 bar), because there was no bacterial photosynthesis to reduce the gas to carbon compounds and oxygen. Methane, a very active greenhouse gas, may have been more prevalent as well. [88] [89]
Carbon dioxide concentrations have shown several cycles of variation from about 180 parts per million during the deep glaciations of the Holocene and Pleistocene to 280 parts per million during the interglacial periods. Carbon dioxide concentrations have varied widely over the Earth's history. It is believed to have been present in Earth's first atmosphere, shortly after Earth's formation. The second atmosphere, consisting largely of nitrogen and COIn the late 19th century, scientists experimentally discovered that N
2 and O
2 do not absorb infrared radiation (called, at that time, "dark radiation"), while water (both as true vapor and condensed in the form of microscopic droplets suspended in clouds) and CO2 and other poly-atomic gaseous molecules do absorb infrared radiation. [92] [93] In the early 20th century, researchers realized that greenhouse gases in the atmosphere made Earth's overall temperature higher than it would be without them. The term greenhouse was first applied to this phenomenon by Nils Gustaf Ekholm in 1901. [94] [95]
During the late 20th century, a scientific consensus evolved that increasing concentrations of greenhouse gases in the atmosphere cause a substantial rise in global temperatures and changes to other parts of the climate system, [96] with consequences for the environment and for human health.
Greenhouse gases exist in many atmospheres, creating greenhouse effects on Mars, Titan and particularly in the thick atmosphere of Venus. [97] While Venus has been described as the ultimate end state of runaway greenhouse effect, such a process would have virtually no chance of occurring from any increases in greenhouse gas concentrations caused by humans, [98] as the Sun's brightness is too low and it would likely need to increase by some tens of percents, which will take a few billion years. [99]
Scientific studies have investigated the causes of climate change. They have found that the main cause and driver of recent climate change is elevated levels of greenhouse gases produced by human activities. Natural forces add climate variability as well. Based on many scientific studies, it is "unequivocal that human influence has warmed the atmosphere, ocean and land since pre-industrial times." Studies on attribution have focused on changes observed during the period of instrumental temperature record, particularly in the last 50 years. This is the period when human activity has grown fastest and observations of the atmosphere above the surface have become available. Some of the main human activities that contribute to global warming are: (a) increasing atmospheric concentrations of greenhouse gases, for a warming effect; (b) global changes to land surface, such as deforestation, for a warming effect; and (c) increasing atmospheric concentrations of aerosols, mainly for a cooling effect.
The greenhouse effect occurs when greenhouse gases in a planet's atmosphere insulate the planet from losing heat to space, raising its surface temperature. Surface heating can happen from an internal heat source as in the case of Jupiter, or from its host star as in the case of the Earth. In the case of Earth, the Sun emits shortwave radiation (sunlight) that passes through greenhouse gases to heat the Earth's surface. In response, the Earth's surface emits longwave radiation (heat) that is mostly absorbed by greenhouse gases. That heat absorption reduces the rate at which the Earth can cool off in response to being warmed by the Sun. Adding to greenhouse gases further reduces the rate a planet emits radiation to space, raising its average surface temperature.
Global warming potential (GWP) is an index to measure of how much infrared thermal radiation a greenhouse gas would absorb over a given time frame after it has been added to the atmosphere. The GWP makes different greenhouse gases comparable with regards to their "effectiveness in causing radiative forcing". It is expressed as a multiple of the radiation that would be absorbed by the same mass of added carbon dioxide, which is taken as a reference gas. Therefore, the GWP is one for CO2. For other gases it depends on how strongly the gas absorbs infrared thermal radiation, how quickly the gas leaves the atmosphere, and the time frame being considered.
Radiative forcing is a concept used in climate science to quantify the change in energy balance in the Earth's atmosphere caused by various factors, such as concentrations of greenhouse gases, aerosols, and changes in solar radiation. In more technical terms, it is "the change in the net, downward minus upward, radiative flux due to a change in an external driver of climate change." These external drivers are distinguished from feedbacks and variability that are internal to the climate system, and that further influence the direction and magnitude of imbalance.
This glossary of climate change is a list of definitions of terms and concepts relevant to climate change, global warming, and related topics.
Trace gases are gases that are present in small amounts within an environment such as a planet's atmosphere. Trace gases in Earth's atmosphere are gases other than nitrogen (78.1%), oxygen (20.9%), and argon (0.934%) which, in combination, make up 99.934% of its atmosphere.
Climate sensitivity is a measure of how much Earth's surface will warm for a doubling in the atmospheric carbon dioxide concentration. In technical terms, climate sensitivity is the average change in global mean surface temperature in response to a radiative forcing, which drives a difference between Earth's incoming and outgoing energy. Climate sensitivity is a key measure in climate science, and a focus area for climate scientists, who want to understand the ultimate consequences of anthropogenic global warming.
In climate science, longwave radiation (LWR) is electromagnetic thermal radiation emitted by Earth's surface, atmosphere, and clouds. It may also be referred to as terrestrial radiation. This radiation is in the infrared portion of the spectrum, but is distinct from the shortwave (SW) near-infrared radiation found in sunlight.
Greenhouse gas (GHG) emissions from human activities intensify the greenhouse effect. This contributes to climate change. Carbon dioxide, 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 United States. The United States has higher emissions per capita. The main producers fueling the emissions globally are large oil and gas companies. Emissions from human activities 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. Total cumulative emissions from 1870 to 2017 were 425±20 GtC from fossil fuels and industry, and 180±60 GtC 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%.
In Earth's atmosphere, carbon dioxide is a trace gas that plays an integral part in the greenhouse effect, carbon cycle, photosynthesis and oceanic carbon cycle. It is one of several greenhouse gases in the atmosphere of Earth. The current global average concentration of CO2 in the atmosphere is 421 ppm as of May 2022 (0.04%). This is an increase of 50% since the start of the Industrial Revolution, up from 280 ppm during the 10,000 years prior to the mid-18th century. The increase is due to human activity. Burning fossil fuels is the main cause of these increased CO2 concentrations and also the main cause of climate change. Other large anthropogenic sources include cement production, deforestation, and biomass burning.
Fugitive emissions are leaks and other irregular releases of gases or vapors from a pressurized containment – such as appliances, storage tanks, pipelines, wells, or other pieces of equipment – mostly from industrial activities. In addition to the economic cost of lost commodities, fugitive emissions contribute to local air pollution and may cause further environmental harm. Common industrial gases include refrigerants and natural gas, while less common examples are perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride.
Atmospheric methane is the methane present in Earth's atmosphere. The concentration of atmospheric methane is increasing due to methane emissions, and is causing climate change. Methane is one of the most potent greenhouse gases. Methane's radiative forcing (RF) of climate is direct, and it is the second largest contributor to human-caused climate forcing in the historical period. Methane is a major source of water vapour in the stratosphere through oxidation; and water vapour adds about 15% to methane's radiative forcing effect. The global warming potential (GWP) for methane is about 84 in terms of its impact over a 20-year timeframe. and 28 in terms of its impact over a 100-year timeframe. The global temperature potential for methane is about 4 in terms of its impact over a 100-year timeframe.
Climate change feedbacks are effects of global warming that amplify or diminish the effect of forces that initially cause the warming. Positive feedbacks enhance global warming while negative feedbacks weaken it. Feedbacks are important in the understanding of climate change because they play an important part in determining the sensitivity of the climate to warming forces. Climate forcings and feedbacks together determine how much and how fast the climate changes. Large positive feedbacks can lead to tipping points—abrupt or irreversible changes in the climate system—depending upon the rate and magnitude of the climate change.
A Representative Concentration Pathway (RCP) is a greenhouse gas concentration trajectory adopted by the IPCC. Four pathways were used for climate modeling and research for the IPCC Fifth Assessment Report (AR5) in 2014. The pathways describe different climate change scenarios, all of which are considered possible depending on the amount of greenhouse gases (GHG) emitted in the years to come. The RCPs – originally RCP2.6, RCP4.5, RCP6, and RCP8.5 – are labelled after a possible range of radiative forcing values in the year 2100. The higher values mean higher greenhouse gas emissions and therefore higher global temperatures and more pronounced effects of climate change. The lower RCP values, on the other hand, are more desirable for humans but require more stringent climate change mitigation efforts to achieve them.
The atmospheric carbon cycle accounts for the exchange of gaseous carbon compounds, primarily carbon dioxide, between Earth's atmosphere, the oceans, and the terrestrial biosphere. It is one of the faster components of the planet's overall carbon cycle, supporting the exchange of more than 200 billion tons of carbon in and out of the atmosphere throughout the course of each year. Atmospheric concentrations of CO2 remain stable over longer timescales only when there exists a balance between these two flows. Methane, Carbon monoxide (CO), and other man-made compounds are present in smaller concentrations and are also part of the atmospheric carbon cycle.
Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% of methane released globally was from human activities, while natural sources contributed about 40%. Reducing methane emissions by capturing and utilizing the gas can produce simultaneous environmental and economic benefits.
Carbon dioxide's lifetime cannot be represented with a single value because the gas is not destroyed over time, but instead moves among different parts of the ocean–atmosphere–land system. Some of the excess carbon dioxide is absorbed quickly (for example, by the ocean surface), but some will remain in the atmosphere for thousands of years, due in part to the very slow process by which carbon is transferred to ocean sediments.
The concentration of methane in the atmosphere is currently over two-and-a-half times greater than its pre-industrial levels
The burning of coal, natural gas, and oil for electricity and heat is the largest single source of global greenhouse gas emissions.