greenhouse gas

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{{pp-pc1}}{{pp-move-indef}}{{short description|Gas in an atmosphere that absorbs and emits radiation within the thermal infrared range}}{{Use dmy dates|date=June 2019}}(File:Greenhouse-effect-t2.svg|thumb|upright=1.5|The greenhouse effect of solar radiation on the Earth's surface caused by greenhouse gases)A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gases cause the greenhouse effect.WEB,weblink IPCC AR4 SYR Appendix Glossary, 14 December 2008, The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone. Without greenhouse gases, the average temperature of Earth's surface would be about {{convert|-18|°C|°F}},WEB,weblink NASA GISS: Science Briefs: Greenhouse Gases: Refining the Role of Carbon Dioxide,, 2016-04-26, rather than the present average of {{convert|15|°C|°F}}.JOURNAL, 2003, Modern global climate change, Science, 302, 5651, 1719–23, 2003Sci...302.1719K, 10.1126/science.1090228, 14657489, Karl TR, Trenberth KE,weblink BOOK,weblink Historical overview of climate change science., Le Treut H., Somerville R., Cubasch U., Ding Y., Mauritzen C., Mokssit A., Peterson T., Prather M., 14 December 2008, in {{harvnb|IPCC AR4 WG1|2007}}WEB,weblink NASA Science Mission Directorate article on the water cycle,, 2010-10-16, dead,weblink" title="">weblink 17 January 2009, The atmospheres of Venus, Mars and Titan also contain greenhouse gases.Human activities since the beginning of the Industrial Revolution (around 1750) have produced a 45% increase in the atmospheric concentration of carbon dioxide ({{CO2}}), from 280 ppm in 1750 to 415 ppm in 2019.WEB,weblink 31 August 2019, CO2 in the atmosphere just exceeded 415 parts per million for the first time in human history, This increase has occurred despite the uptake of more than half of the emissions by various natural "sinks" involved in the carbon cycle.WEB,weblink Frequently asked global change questions, Carbon Dioxide Information Analysis Center, WEB,weblink Trends in carbon dioxide, 14 January 2008,, ESRL Web Team, 2011-09-11, The vast majority of anthropogenic carbon dioxide emissions come from combustion of fossil fuels, principally coal, oil, and natural gas, with additional contributions coming from deforestation, changes in land use, soil erosion and agriculture (including livestock).WEB,weblink Global Greenhouse Gas Emissions Data – US EPA, US, EPA,OA, US EPA, 12 January 2016, WEB,weblink AR4 SYR Synthesis Report Summary for Policymakers – 2 Causes of change,, 9 October 2015,weblink" title="">weblink 28 February 2018, dead, Should greenhouse gas emissions continue at their rate in 2019, global warming could cause Earth's surface temperature to exceed historical values as early as 2047, with potentially harmful effects on ecosystems, biodiversity and human livelihoods.JOURNAL, 2013, The projected timing of climate departure from recent variability, Nature, 502, 7470, 183–87, 10.1038/nature12540, Mora, C, 2013Natur.502..183M, 24108050, At current emission rates, temperatures could increase by 2 Â°C, which the United Nations' IPCC designated as the upper limit to avoid "dangerous" levels, by 2036.NEWS,weblink Earth Will Cross the Climate Danger Threshold by 2036, 2014-04-01, Scientific American, Mann, Michael E., 30 August 2016, {{TOC limit|3}}

Gases in Earth's atmosphere

The most common gases in Earth's atmosphere are nitrogen (78%), oxygen (21%), and argon (0.9%). The next most common gases are carbon dioxide (0.04%), nitrous oxide, methane, and ozone. They are trace gases that account for almost one tenth of 1% of Earth's atmosphere.{{see also|Global warming|Carbon dioxide in Earth's atmosphere}}File:Atmospheric Transmission.png|right|thumb|upright=1.75|alt=refer to caption and adjacent text|Atmospheric absorption and scattering at different wavelengths of electromagnetic waves. The largest absorption band of carbon dioxide is not far from the maximum in the thermal emission from ground, and it partly closes the window of transparency of water; hence its major effect.]]

Greenhouse gases

Greenhouse gases are those that absorb and emit infrared radiation in the wavelength range emitted by Earth. In order, the most abundant{{clarify|reason=Please quantify the atmospheric concentration of each of the listed greenhouse gases.|date=April 2019}} greenhouse gases in Earth's atmosphere are:{{citation needed|date=April 2019}} 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).NEWS, FAQ 7.1, 14, in {{harvnb|IPCC AR4 WG1|2007}} 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 Â± 0.21% per year over the period 1959–2006.JOURNAL, Canadell, J.G., Le Quere, C., Raupach, M.R., Field, C.B., Buitenhuis, E.T., Ciais, P., Conway, T.J., Gillett, N.P., Houghton, R.A., Marland, G., 2007, Contributions to accelerating atmospheric {{CO2, growth from economic activity, carbon intensity, and efficiency of natural sinks| journal = Proc. Natl. Acad. Sci. USA| volume = 104| issue = 47| pages = 18866–70 | pmid = 17962418| doi = 10.1073/pnas.0702737104| pmc = 2141868| bibcode = 2007PNAS..10418866C }}

Non-greenhouse gases

The major atmospheric constituents: nitrogen ({{chem|N|2}}), oxygen ({{chem|O|2}}), and argon (Ar) are not greenhouse gases because molecules containing two atoms of the same element such as {{chem|N|2}} and {{chem|O|2}} have no net change in the distribution of their electrical charges when they vibrate, and monatomic gases such as Ar do not have vibrational modes. Hence they are almost totally unaffected by infrared radiation. Some molecules containing just two atoms of different elements, such as carbon monoxide (CO) and hydrogen chloride (HCl), do absorb infrared radiation, but these molecules are short-lived in the atmosphere owing to their reactivity and solubility. Therefore, they do not contribute significantly to the greenhouse effect and often are omitted when discussing greenhouse gases.

Indirect radiative effects

(File:Mopitt first year carbon monoxide.jpg|thumb|alt=world map of carbon monoxide concentrations in the lower atmosphere|The false colors in this image represent concentrations of carbon monoxide in the lower atmosphere, ranging from about 390 parts per billion (dark brown pixels), to 220 parts per billion (red pixels), to 50 parts per billion (blue pixels).WEB, The Chemistry of Earth's Atmosphere, Earth Observatory,weblinkweblink" title="">weblink 20 September 2008, dead, NASA, )Some gases have indirect radiative effects (whether or not they are greenhouse gases themselves). This happens in two main ways. One way is that when they break down in the atmosphere they produce another greenhouse gas. For example, methane and carbon monoxide (CO) are oxidized to give carbon dioxide (and methane oxidation also produces water vapor). Oxidation of CO to {{CO2}} directly produces an unambiguous increase in radiative forcing although the reason is subtle. The peak of the thermal IR emission from Earth's surface is very close to a strong vibrational absorption band of {{CO2}} (wavelength 15 microns, or wavenumber 667 cm−1). On the other hand, the single CO vibrational band only absorbs IR at much shorter wavelengths (4.7 microns, or 2145 cm−1), where the emission of radiant energy from Earth's surface is at least a factor of ten lower. Oxidation of methane to {{CO2}}, which requires reactions with the OH radical, produces an instantaneous reduction in radiative absorption and emission since {{CO2}} is a weaker greenhouse gas than methane. However, the oxidations of CO and {{chem|CH|4}} are entwined since both consume OH radicals. In any case, the calculation of the total radiative effect includes both direct and indirect forcing.A second type of indirect effect happens when chemical reactions in the atmosphere involving these gases change the concentrations of greenhouse gases. For example, the destruction of non-methane volatile organic compounds (NMVOCs) in the atmosphere can produce ozone. The size of the indirect effect can depend strongly on where and when the gas is emitted.BOOK,weblink 2.10.3 Indirect GWPs, Changes in Atmospheric Constituents and in Radiative Forcing, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, 2007, Forster, P., 2012-12-02, etal, Methane has indirect effects in addition to forming {{CO2}}. The main chemical that reacts with methane in the atmosphere is the hydroxyl radical (OH), thus more methane means that the concentration of OH goes down. Effectively, methane increases its own atmospheric lifetime and therefore its overall radiative effect. The oxidation of methane can produce both ozone and water; and is a major source of water vapor in the normally dry stratosphere. CO and NMVOCs produce {{CO2}} when they are oxidized. They remove OH from the atmosphere, and this leads to higher concentrations of methane. The surprising effect of this is that the global warming potential of CO is three times that of {{CO2}}.WEB, MacCarty, N., Laboratory Comparison of the Global-Warming Potential of Six Categories of Biomass Cooking Stoves,weblink Approvecho Research Center, dead,weblink" title="">weblink 11 November 2013, The same process that converts NMVOCs to carbon dioxide can also lead to the formation of tropospheric ozone. Halocarbons have an indirect effect because they destroy stratospheric ozone. Finally, hydrogen can lead to ozone production and {{chem|CH|4}} increases as well as producing stratospheric water vapor.

Contribution of clouds to Earth's greenhouse effect

The major non-gas contributor to Earth's greenhouse effect, clouds, also absorb and emit infrared radiation and thus have an effect on greenhouse gas radiative properties. Clouds are water droplets or ice crystals suspended in the atmosphere.JOURNAL,weblink Earth's annual global mean energy budget, J.T., Kiehl, Kevin E. Trenberth, Bulletin of the American Meteorological Society, 197–208, 78, 2, 1997, 1 May 2006, 10.1175/1520-0477(1997)0782.0.CO;2,weblink" title="">weblink 30 March 2006, 1997BAMS...78..197K, WEB,weblink 6 April 2005, Water vapour: feedback or forcing?, RealClimate, 1 May 2006,

Impacts on the overall greenhouse effect

File:Attribution of individual atmospheric component contributions to the terrestrial greenhouse effect, separated into feedback and forcing categories (NASA).png|right|thumb|alt=refer to caption and adjacent text|Schmidt et al. (2010){{citation | author1=Schmidt, G.A. | author2=R. Ruedy | author3=R.L. Miller | author4=A.A. Lacis | authorlink1=Gavin Schmidt | year=2010 | title=The attribution of the present-day total greenhouse effect | url= | work=J. Geophys. Res. | volume=115 | issue=D20 | pages=D20106 | doi=10.1029/2010JD014287 | bibcode=2010JGRD..11520106S | url-status=dead | archiveurl= | archivedate=22 October 2011 | df=dmy-all }}, D20106. Web page analysed how individual components of the atmosphere contribute to the total greenhouse effect. They estimated that water vapor accounts for about 50% of Earth's greenhouse effect, with clouds contributing 25%, carbon dioxide 20%, and the minor greenhouse gases and aerosols accounting for the remaining 5%. In the study, the reference model atmosphere is for 1980 conditions. Image credit: (NASA]].{{citation | author=Lacis, A. | date=October 2010 | title=NASA GISS: CO2: The Thermostat that Controls Earth's Temperature | url= | publisher=NASA GISS | location=New York}})The contribution of each gas to the 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 but it is present in much smaller concentrations so that its total direct radiative effect is smaller, in part due to its shorter atmospheric lifetime. On the other hand, in addition to its direct radiative impact, methane has a large, indirect radiative effect because it contributes to ozone formation. Shindell et al. (2005)JOURNAL, 10.1029/2004GL021900,weblink An emissions-based view of climate forcing by methane and tropospheric ozone, 2005, Shindell, Drew T., Geophysical Research Letters, 32, L04803, 2005GeoRL..32.4803S, 4, argue that the contribution to climate change from methane is at least double previous estimates as a result of this effect.WEB,weblink Methane's Impacts on Climate Change May Be Twice Previous Estimates,, 30 November 2007, 2010-10-16, When ranked by their direct contribution to the greenhouse effect, the most important are:{{Failed verification|date=April 2016}}{| class="wikitable" style="text-align:center" id-"GHG-ranking"! Compound  ! style="text-align:left;"| Formula  ! Concentration in atmosphereWEB
, Climate Change Indicators: Atmospheric Concentrations of Greenhouse Gases
, United States Environmental Protection Agency
, Climate Change Indicators, 2017-01-20
,weblink 27 June 2016
, (ppm)
! Contribution (%)
Water vapor#In Earth's atmosphere>Water vapor and clouds {{chem2| 36–72%  
Carbon dioxide in Earth's atmosphere>Carbon dioxide {{CO2}} ~400 9–26%
Atmospheric methane>Methane {{chem4}} ~1.8 4–9%  
Ozone layer>Ozone {{chem3}} 2–8(B) 3–7%  
! colspan=4 style="font-size: 0.85em; padding: 5px 2px 5px 10px; text-align: left; font-weight: normal;" | notes:(A) Water vapor strongly varies locallyWallace, John M. and Peter V. Hobbs. Atmospheric Science; An Introductory Survey. Elsevier. Second Edition, 2006. {{ISBN|978-0127329512}}. Chapter 1(B) The concentration in stratosphere. About 90% of the ozone in Earth's atmosphere is contained in the stratosphere.
In addition to the main greenhouse gases listed above, other greenhouse gases include sulfur hexafluoride, hydrofluorocarbons and perfluorocarbons (see IPCC list of greenhouse gases). Some greenhouse gases are not often listed. For example, nitrogen trifluoride has a high global warming potential (GWP) but is only present in very small quantities.JOURNAL, Prather, Michael J., J Hsu, {{chem, NF, 3, , the greenhouse gas missing from Kyoto |journal= Geophysical Research Letters |volume=35 |pages=L12810 |year=2008 |doi=10.1029/2008GL034542 |bibcode=2008GeoRL..3512810P |issue= 12|url=weblink }}

Proportion of direct effects at a given moment

It is not possible to state that a certain gas causes an exact percentage of the greenhouse effect. This is because some of the gases absorb and emit radiation at the same frequencies as others, so that the total greenhouse effect is not simply the sum of the influence of each gas. The higher ends of the ranges quoted are for each gas alone; the lower ends account for overlaps with the other gases. In addition, some gases, such as methane, are known to have large indirect effects that are still being quantified.JOURNAL, Isaksen, Ivar S.A., Michael Gauss, Gunnar Myhre, Katey M. Walter Anthony, Carolyn Ruppel, Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions, Global Biogeochemical Cycles, 20 April 2011, 25, 10.1029/2010GB003845,weblink 29 July 2011, 2011GBioC..25.2002I, 2, n/a, 1912/4553,

Atmospheric lifetime

Aside from water vapor, which has a residence time of about nine days,WEB,weblink AGU Water Vapor in the Climate System,, 27 April 1995, 2011-09-11, major greenhouse gases are well mixed and take many years to leave the atmosphere.BOOK,weblink 6.3 Well-mixed Greenhouse Gases, Chapter 6 Radiative Forcing of Climate Change, Working Group I: The Scientific Basis IPCC Third Assessment Report – Climate Change 2001, UNEP/GRID-Arendal – Publications, 2001, Betts, 2010-10-16, dead,weblink" title="">weblink 29 June 2011, 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) defines the lifetime tau of an atmospheric species X in a one-box model as the average time that a molecule of X remains in the box. Mathematically tau canbe defined as the ratio of the mass m (in kg) of X in the box to its removal rate, which is the sum of the flow of X out of the box(F_{out}),chemical loss of X(L),and deposition of X(D)(all in kg/s):tau = frac{m}{F_{out}+L+D}.BOOK, Jacob, Daniel, Introduction to atmospheric chemistry, Princeton University Press, 1999,weblink 978-0691001852, 25–26, dead,weblink" title="">weblink 2 September 2011, dmy-all, If output of this gas into the box ceased, then after time tau, 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.WEB,weblink How long will global warming last?, RealClimate, 2012-06-12, The atmospheric lifetime of {{CO2}} is estimated of the order of 30–95 years.NEWS, Jacobson, M.Z., Correction to "Control of fossil-fuel particulate black carbon and organic matter, possibly the most effective method of slowing global warming." volume = 110 year = 2005 url = weblink 2005JGRD..11014105J, This figure accounts for {{CO2}} molecules being removed from the atmosphere by mixing into the ocean, photosynthesis, and other processes. However, this excludes the balancing fluxes of {{CO2}} into the atmosphere from the geological reservoirs, which have slower characteristic rates.NEWS, Archer, David, Atmospheric lifetime of fossil fuel carbon dioxide volume = 37 year = 2009 bibcode = 2009AREPS..37..117A, Although more than half of the {{CO2}} emitted is removed from the atmosphere within a century, some fraction (about 20%) of emitted {{CO2}} remains in the atmosphere for many thousands of years.BOOK, Frequently Asked Question 10.3: If emissions of greenhouse gases are reduced, how quickly do their concentrations in the atmosphere decrease?, Global Climate Projections,weblink 2011-06-01IPCC AR4 WG1|2007}}See also: JOURNAL,weblink David, Archer, Fate of fossil fuel {{CO2, in geologic time |journal= Journal of Geophysical Research |volume= 110 |issue= C9 |pages= C09S05.1–6 |year = 2005|doi= 10.1029/2004JC002625 |accessdate= 27 July 2007 |bibcode= 2005JGRC..11009S05A}}See also: JOURNAL, Ken, Caldeira, Michael E., Wickett,weblink Ocean model predictions of chemistry changes from carbon dioxide emissions to the atmosphere and ocean, Journal of Geophysical Research, 110, C9, C09S04.1–12, 2005, 10.1029/2004JC002671, 27 July 2007,weblink" title="">weblink 10 August 2007, 2005JGRC..11009S04C, 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.

Radiative forcing

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.Edited quote from public-domain source: WEB, 2010, U.S. Environmental Protection Agency (EPA), Climate Change Indicators in the United States url =weblink . PDF (p. 18)
Earth's surface temperature depends on this balance between incoming and outgoing energy. If this energy balance is shifted, Earth's surface becomes warmer or cooler, leading to a variety of changes in global climate.
A number of natural and man-made mechanisms can affect the global energy balance and force changes in Earth's climate. Greenhouse gases are one such mechanism. Greenhouse gases absorb and emit some of the outgoing energy radiated from Earth's surface, causing that heat to be retained in the lower atmosphere. As explained above, some greenhouse gases remain in the atmosphere for decades or even centuries, and therefore can affect Earth's energy balance over a long period. Radiative forcing quantifies the effect of factors that influence Earth's energy balance, including changes in the concentrations of greenhouse gases. Positive radiative forcing leads to warming by increasing the net incoming energy, whereas negative radiative forcing leads to cooling.

Global warming potential

The global warming potential (GWP) depends on both the efficiency of the molecule as a greenhouse gas and its atmospheric lifetime. GWP is measured relative to the same mass of {{CO2}} and evaluated for a specific timescale. Thus, if a gas has a high (positive) radiative forcing but also a short lifetime, it will have a large GWP on a 20-year scale but a small one on a 100-year scale. Conversely, if a molecule has a longer atmospheric lifetime than {{CO2}} its GWP will increase when the timescale is considered. Carbon dioxide is defined to have a GWP of 1 over all time periods.Methane has an atmospheric lifetime of 12 ± 3 years. The 2007 IPCC report lists the GWP as 72 over a time scale of 20 years, 25 over 100 years and 7.6 over 500 years. A 2014 analysis, however, states that although methane's initial impact is about 100 times greater than that of {{CO2}}, because of the shorter atmospheric lifetime, after six or seven decades, the impact of the two gases is about equal, and from then on methane's relative role continues to decline.NEWS,weblink How to count methane emissions, MIT News, 2018-08-20, David L., Chandler, Referenced paper is JOURNAL, Jessika, Trancik, Morgan, Edwards,weblink Climate impacts of energy technologies depend on emissions timing,weblink 16 January 2015, Nature Climate Change, 4, 25 April 2014, 347, 15 January 2015, The decrease in GWP at longer times is because methane is degraded to water and {{CO2}} through chemical reactions in the atmosphere.Examples of the atmospheric lifetime and GWP relative to {{CO2}} for several greenhouse gases are given in the following table:{| class="wikitable" style="text-align: right"global warming potential>GWP relative to {{CO2}} at different time horizon for various greenhouse gases! rowspan="2" style="text-align:left;" | Gas name! rowspan="2" | Chemical formula !! rowspan="2" | Lifetime (years)BOOK, Intergovernmental Panel on Climate Change Fifth Assessment Report,weblink Appendix 8.A, 731, ! colspan="3" | Global warming potential (GWP) for given time horizon
! 20-yr !! 100-yr!! 500-yrBOOK, IPCC Fourth Assessment Report,weblink Table 2.14, 212,
Carbon dioxide {{CO2}} 30–95 1 1 1
Methane {{chem4}} 12 84 28 7.6
Nitrous oxide {{chem2| 153
CFC-12 {{chem22}} 100 10 800 10 200 5 200
HCFC-22 {{chem2}} 12 5 280 1 760 549
Tetrafluoromethane        {{chem4}} 50 000 4 880 6 630 11 200
Hexafluoroethane {{chem26}} 10 000 8 210 11 100 18 200
Sulfur hexafluoride {{chem6}} 3 200 17 500 23 500 32 600
Nitrogen trifluoride {{chem3}} 500 12 800 16 100 20 700
The use of CFC-12 (except some essential uses) has been phased out due to its ozone depleting properties.{{citation
|title=Use of ozone depleting substances in laboratories
|archivedate=6 August 2011
}} The phasing-out of less active HCFC-compounds will be completed in 2030.Montreal Protocol{{multiple image |caption_align=center |align=center |width= |direction=horizontal|image1=M15-162b-EarthAtmosphere-CarbonDioxide-FutureRoleInGlobalWarming-Simulation-20151109.jpgCarbon dioxide in Earth's atmosphere if half of Global warming>global-warming emissionsST. FLEUR >FIRST=NICHOLAS URL=HTTPS://WWW.NYTIMES.COM/2015/11/11/SCIENCE/ATMOSPHERIC-GREENHOUSE-GAS-LEVELS-HIT-RECORD-REPORT-SAYS.HTML WORK=NEW YORK TIMES TITLE=UK: IN 1ST, GLOBAL TEMPS AVERAGE COULD BE 1 DEGREE C HIGHER DATE=9 NOVEMBER 2015 AP NEWS >ACCESSDATE=11 NOVEMBER 2015, are not absorbed.(NASA simulation; 9 November 2015)|width1=315}}

Natural and anthropogenic sources

File:Carbon History and Flux Rev.png|thumb|right|alt=refer to caption and article text|Top: Increasing atmospheric carbon dioxide levels as measured in the atmosphere and reflected in ice cores. Bottom: The amount of net carbon increase in the atmosphere, compared to carbon emissions from burning fossil fuelfossil fuelFile:Diagram showing a simplified representation of the Earth's annual carbon cycle (US DOE).png|thumb|alt=refer to caption and image description|right|This diagram shows a simplified representation of the contemporary global carbon cycle. Changes are measured in gigatons of carbon per year (GtC/y). Canadell et al. (2007) estimated the growth rate of global average atmospheric {{CO2}} for 2000–2006 as 1.93 parts-per-million per year (4.1 petagrams of carbon per year).{{citation
| author=Canadell, J.G.
| title=Contributions to Accelerating Atmospheric CO2 Growth from Economic Activity, Carbon Intensity, and Efficiency of Natural Sinks (Results and Discussion: Growth in Atmospheric CO2)
| date=20 November 2007
| journal=Proceedings of the National Academy of Sciences of the United States of America
| volume=104
| issue=47
| pages=18866–70
| doi=10.1073/pnas.0702737104
| pmid=17962418
| pmc=2141868| bibcode = 2007PNAS..10418866C |display-authors=etal}}
petagramAside from purely human-produced synthetic halocarbons, most greenhouse gases have both natural and human-caused 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.WEB,weblink Historical Overview of Climate Change Science – FAQ 1.3 Figure 1, 116, in {{harvnb|IPCC AR4 WG1|2007}}WEB,weblink Chapter 3, IPCC Special Report on Emissions Scenarios, 2000, Intergovernmental Panel on Climate Change, 2000, 2010-10-16, live, The 2007 Fourth Assessment Report compiled by the IPCC (AR4) noted that "changes in atmospheric concentrations of greenhouse gases and aerosols, land cover and solar radiation alter the energy balance of the climate system", and concluded that "increases in anthropogenic greenhouse gas concentrations is very likely to have caused most of the increases in global average temperatures since the mid-20th century".WEB
, Climate Change 2007: Synthesis Report, 5
, Intergovernmental Panel on Climate Change, 17 November 2007
, 2017-01-20, In AR4, "most of" is defined as more than 50%.
Abbreviations used in the two tables below: ppm = parts-per-million; ppb = parts-per-billion; ppt = parts-per-trillion; W/m2 = watts per square metre{| class="wikitable"Blasing, T.J.|2013}}! Gas! Pre-1750troposphericconcentration{{citation | url= | contribution=Table 4.1 | title=Atmospheric Chemistry and Greenhouse Gases | author=Ehhalt, D. | display-authors=etal | url-status=dead | archiveurl= | archivedate=3 January 2013 | df=dmy-all }}, in {{harvnb|IPCC TAR WG1|2001|pp=244–45}}. Referred to by: {{citation
|title = Current Greenhouse Gas Concentrations
|author = Blasing, T.J.
|doi = 10.3334/CDIAC/atg.032
|date = February 2013
|url =weblink
}}, on {{harvnb|Blasing, T.J.|2013}}. Based on Blasing et al. (2013): Pre-1750 concentrations of CH4,N2O and current concentrations of O3, are taken from Table 4.1 (a) of the IPCC Intergovernmental Panel on Climate Change), 2001. Following the convention of IPCC (2001), inferred global-scale trace-gas concentrations from prior to 1750 are assumed to be practically uninfluenced by human activities such as increasingly specialized agriculture, land clearing, and combustion of fossil fuels. Preindustrial concentrations of industrially manufactured compounds are given as zero. The short atmospheric lifetime of ozone (hours-days) together with the spatial variability of its sources precludes a globally or vertically homogeneous distribution, so that a fractional unit such as parts per billion would not apply over a range of altitudes or geographical locations. Therefore a different unit is used to integrate the varying concentrations of ozone in the vertical dimension over a unit area, and the results can then be averaged globally. This unit is called a Dobson Unit (D.U.), after G.M.B. Dobson, one of the first investigators of atmospheric ozone. A Dobson unit is the amount of ozone in a column that, unmixed with the rest of the atmosphere, would be 10 micrometers thick at standard temperature and pressure.!! RecenttroposphericconcentrationBecause atmospheric concentrations of most gases tend to vary systematically over the course of a year, figures given represent averages over a 12-month period for all gases except ozone (O3), for which a current global value has been estimated (IPCC, 2001, Table 4.1a). {{CO2}} averages for year 2012 are taken from the National Oceanic and Atmospheric Administration, Earth System Research Laboratory, web site: maintained by Dr. Pieter Tans. For other chemical species, the values given are averages for 2011. These data are found on the CDIAC AGAGE web site:weblink or the AGAGE home page:weblink Absolute increasesince 1750 !! Percentageincreasesince 1750 !! Increasedradiative forcing(W/m2){{citation | url= | contribution=Table 2.1 | title=Changes in Atmospheric Constituents and in Radiative Forcing | author=Forster, P. | display-authors=etal | access-date=30 October 2012 | archive-url= | archive-date=12 October 2012 | url-status=dead }}, in {{harvnb|IPCC AR4 WG1|2007|p=141}}. Referred to by: {{harvnb|Blasing, T.J.|2013}}
Carbon dioxide in Earth's atmosphere>Carbon dioxide ({{CO2}}) 280 ppmBOOK
, Executive summary
, The Carbon Cycle and Atmospheric Carbon Dioxide
, Prentice, I.C.
, etal
, dead
,weblink" title="">weblink
, 7 December 2009
, , in {{harvnb|IPCC TAR WG1|2001|p=185}}. Referred to by: {{citation
|title=Current Greenhouse Gas Concentrations
|author=Blasing, T.J.
|date=February 2013
}}, on {{harvnb|Blasing, T.J.|2013}}
|| 395.4 ppmRecent {{CO2}} concentration (395.4 ppm) is the 2013 average taken from globally averaged marine surface data given by the National Oceanic and Atmospheric Administration Earth System Research Laboratory, website:weblink Please read the material on that web page and reference Dr. Pieter Tans when citing this average (Dr. Pieter Tans, NOAA/ESRLweblink The oft-cited Mauna Loa average for 2012 is 393.8 ppm, which is a good approximation although typically about 1 ppm higher than the spatial average given above. Refer toweblink for records back to the late 1950s.
|| 115.4 ppm || 41.2% || 1.88
Methane ({{chem>CHCape Grim, Tasmania, a mid-latitude Southern-Hemisphere site. "Current" values given for these gases are annual arithmetic averages based on monthly background concentrations for year 2011. The {{chem>SFAUTHOR1=PRINN YEAR=2000, 1762 ppb || 1193 ppb /1062 ppb || 170.4% /151.7% || 0.49
Nitrous oxide ({{chem>NO}}) 270 ppbThe pre-1750 value for {{chem2|O}} is consistent with ice-core records from 10,000 BCE through 1750 CE: {{citation
| chapter-url= |title=Figure SPM.1
| chapter=Summary for policymakers
| publisher=IPCC
}}, in {{harvnb|IPCC AR4 WG1|2007|p=3}}. Referred to by: {{citation
| title=Current Greenhouse Gas Concentrations
| author=Blasing, T.J.
| doi=10.3334/CDIAC/atg.032
| date=February 2013
| url=
}}, on {{harvnb|Blasing, T.J.|2013}}
|| 326 ppb /324 ppb || 56 ppb /54 ppb || 20.7% /20.0% || 0.17
Troposphericozone ({{chem>O| 0.4Changes in stratospheric ozone have resulted in a decrease in radiative forcing of 0.05 W/m2: {{citation
| url= |contribution=Table 2.12
| title=Changes in Atmospheric Constituents and in Radiative Forcing
| author=Forster, P.
IPCC AR4 WG1p=204}}. Referred to by: {{harvnb2013}}
{| class="wikitable"|+ Relevant to radiative forcing and/or ozone depletion; all of the following have no natural sources and hence zero amounts pre-industrial! Gas !! Recenttroposphericconcentration !! Increasedradiative forcing(W/m2)
CFC-11(trichlorofluoromethane)({{chem>CClF}}) 236 ppt /234 ppt 0.061
CFC-12 ({{chem>CClF| 0.169
CFC-113 ({{chem>ClFC-CClF| 0.022
HCFC-22 ({{chem>CHClF| 0.046
HCFC-141b ({{chem>CHCClF}}) 24 ppt /21 ppt 0.0036
HCFC-142b ({{chem>CHCClF| 0.0042
Halon 1211 ({{chem>CBrClF| 0.0012
Halon 1301 ({{chem>CBrClF| 0.001
HFC-134a ({{chem>CHFCF| 0.0108
Carbon tetrachloride ({{chem>CCl| 0.0143
Sulfur hexafluoride ({{chem>SF6, data from January 2004 6, from 1970 through 1999, obtained from Antarctic firn (consolidated deep snow) air sampleslast=Sturges display-authors= et al.}}7.39 ppt || 0.0043
halocarbons >| collectively0.02
| 0.3574
(File:Vostok Petit data.svg|thumb|right|alt=refer to caption and article text|400,000 years of ice core data)Ice cores provide evidence for greenhouse gas concentration variations over the past 800,000 years (see the following section). Both {{CO2}} and {{chem|CH|4}} vary between glacial and interglacial phases, and concentrations of these gases correlate strongly with temperature. Direct data does not exist for periods earlier than those represented in the ice core record, a record that indicates {{CO2}} mole fractions stayed within a range of 180 ppm to 280 ppm throughout the last 800,000 years, until the increase of the last 250 years. However, various proxies and modeling suggests larger variations in past epochs; 500 million years ago {{CO2}} levels were likely 10 times higher than now.(:File:Phanerozoic Carbon Dioxide.png) Indeed, higher {{CO2}} concentrations are thought to have prevailed throughout most of the Phanerozoic eon, with concentrations four to six times current concentrations during the Mesozoic era, and ten to fifteen times current concentrations during the early Palaeozoic era until the middle of the Devonian period, about 400 Ma.JOURNAL, Berner, Robert A., January 1994, GEOCARB II: a revised model of atmospheric {{CO2, over Phanerozoic time |url= |journal=American Journal of Science |volume=294 |issue=1 |pages=56–91 |doi=10.2475/ajs.294.1.56 |bibcode=1994AmJS..294...56B }}{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }}JOURNAL, Royer, D.L., R.A. Berner, D.J. Beerling, David Beerling, 2001, Phanerozoic atmospheric {{CO2, change: evaluating geochemical and paleobiological approaches |journal=Earth-Science Reviews |volume=54 |pages=349–92 |doi=10.1016/S0012-8252(00)00042-8 |bibcode=2001ESRv...54..349R |issue=4}}JOURNAL, Berner, Robert A., Kothavala, Zavareth, 2001, GEOCARB III: a revised model of atmospheric {{CO2, over Phanerozoic time |url= |journal=American Journal of Science |volume=301 |issue=2 |pages=182–204 |doi=10.2475/ajs.301.2.182 |url-status=dead |archiveurl= |archivedate=6 August 2004 |bibcode=2001AmJS..301..182B |citeseerx= }} The spread of land plants is thought to have reduced {{CO2}} concentrations during the late Devonian, and plant activities as both sources and sinks of {{CO2}} have since been important in providing stabilising feedbacks.JOURNAL, Beerling, D.J., David Beerling, Berner, R.A., 2005, Feedbacks and the co-evolution of plants and atmospheric {{CO2, |journal=Proc. Natl. Acad. Sci. USA |volume=102 |pages=1302–05 |doi=10.1073/pnas.0408724102 |pmid=15668402 |issue=5 |pmc=547859|bibcode = 2005PNAS..102.1302B }}Earlier still, a 200-million year period of intermittent, widespread glaciation extending close to the equator (Snowball Earth) appears to have been ended suddenly, about 550 Ma, by a colossal volcanic outgassing that raised the {{CO2}} concentration of the atmosphere abruptly to 12%, about 350 times modern levels, causing extreme greenhouse conditions and carbonate deposition as limestone at the rate of about 1 mm per day.JOURNAL, Hoffmann, PF, AJ Kaufman, GP Halverson, DP Schrag, 1998, A neoproterozoic snowball earth, Science, 281, 5381, 1342–46, 10.1126/science.281.5381.1342, 9721097, 1998Sci...281.1342H, This episode marked the close of the Precambrian eon, and was succeeded by the generally warmer conditions of the Phanerozoic, during which multicellular animal and plant life evolved. No volcanic carbon dioxide emission of comparable scale has occurred since. In the modern era, emissions to the atmosphere from volcanoes are approximately 0.645 billion tonnes of {{CO2}} per year, whereas humans contribute 29 billion tonnes of {{CO2}} each year.NEWS,weblink How Much CO2 Does A Single Volcano Emit?, Siegel, Ethan, Forbes, 2018-09-06, en, JOURNAL, Gerlach, TM, 1991, Present-day {{CO2, emissions from volcanoes |journal=Transactions of the American Geophysical Union |volume=72 |pages=249–55 |doi=10.1029/90EO10192 |bibcode=1991EOSTr..72..249. |issue=23}}See also: WEB,weblink
, U.S. Geological Survey
, 14 June 2011
, 15 October 2012

Ice cores

Measurements from Antarctic ice coresshow that before industrial emissions started atmospheric {{CO2}} mole fractions were about 280 parts per million (ppm), and stayed between 260 and 280 during the preceding ten thousand years.JOURNAL, 10.1029/2001GB001417, High-resolution Holocene {{chem, N, 2, O, ice core record and its relationship with {{chem|CH|4}} and {{CO2}}|year=2002|last1=Flückiger|first1=Jacqueline|journal=Global Biogeochemical Cycles|volume=16|page=1010|bibcode=2002GBioC..16a..10F}} Carbon dioxide mole fractions in the atmosphere have gone up by approximately 35 percent since the 1900s, rising from 280 parts per million by volume to 387 parts per million in 2009. One study using evidence from stomata of fossilized leaves suggests greater variability, with carbon dioxide mole fractions above 300 ppm during the period seven to ten thousand years ago,JOURNAL, Friederike Wagner, Bent Aaby, Henk Visscher, Rapid atmospheric {{CO2, changes associated with the 8,200-years-B.P. cooling event |journal=Proc. Natl. Acad. Sci. USA |volume=99 |issue=19 |year=2002 |pages=12011–14 |doi=10.1073/pnas.182420699 |pmid=12202744 |pmc=129389|bibcode = 2002PNAS...9912011W }} though others have argued that these findings more likely reflect calibration or contamination problems rather than actual {{CO2}} variability.JOURNAL, Andreas Indermühle, Bernhard Stauffer, Thomas F. Stocker, Early Holocene Atmospheric {{CO2, Concentrations |journal=Science |volume=286 |issue=5446 |year=1999 |page=1815 |doi=10.1126/science.286.5446.1815a}} JOURNAL, Early Holocene atmospheric {{CO2, concentrations|journal=Science|doi=10.1126/science.286.5446.1815a|volume=286|issue=5446|pages=1815a–15|year=1999|last1=IndermÃœhle|first1=A}}JOURNAL, H. J. Smith, M. Wahlen, D. Mastroianni, The {{CO2, concentration of air trapped in GISP2 ice from the Last Glacial Maximum-Holocene transition| journal=Geophysical Research Letters| volume=24| issue=1| year=1997| pages=1–4| doi=10.1029/96GL03700| bibcode=1997GeoRL..24....1S}} Because of the way air is trapped in ice (pores in the ice close off slowly to form bubbles deep within the firn) and the time period represented in each ice sample analyzed, these figures represent averages of atmospheric concentrations of up to a few centuries rather than annual or decadal levels.

Changes since the Industrial Revolution

(File:CO2 increase rate.png|thumb|left|alt=Refer to caption|Recent year-to-year increase of atmospheric {{CO2}}.)(File:Major greenhouse gas trends.png|alt=Refer to caption|thumb|right|Major greenhouse gas trends.)Since the beginning of the Industrial Revolution, the concentrations of most of the greenhouse gases have increased. For example, the mole fraction of carbon dioxide has increased from 280 ppm to 415 ppm, or 120 ppm over modern pre-industrial levels. The first 30 ppm increase 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.BOOK, Charles J. Kibert, Sustainable Construction: Green Building Design and Delivery, {{google books, y, qv3iCwAAQBAJ, 698, |year=2016|publisher=Wiley|isbn=978-1119055327|chapter=Background}}WEB,weblink Full Mauna Loa CO2 record, 2005, Earth System Research Laboratory, 6 May 2017, Recent data also shows that the concentration is increasing at a higher rate. In the 1960s, the average annual increase was only 37% of what it was in 2000 through 2007.WEB, Pieter, Tans, 3 May 2008,weblink Annual {{CO2, mole fraction increase (ppm) for 1959–2007 |publisher=National Oceanic and Atmospheric Administration Earth System Research Laboratory, Global Monitoring Division}} WEB,weblink additional details, ; see also JOURNAL, K.A., Masarie, P.P., Tans, 1995, Extension and integration of atmospheric carbon dioxide data into a globally consistent measurement record, J. Geophys. Res., 100, D6, 11593–610, 10.1029/95JD00859, 1995JGR...10011593M,weblink 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%.WEB,weblink Global Carbon Project (GCP),, en, 2019-05-19, Today,{{when|date=May 2019}} the stock of carbon in the atmosphere increases by more than 3 million tonnes per annum (0.04%) compared with the existing stock.{{clarify|date=April 2011|reason=in what year was this measurement made?}} This increase is the result of human activities by burning fossil fuels, deforestation and forest degradation in tropical and boreal regions.JOURNAL, Dumitru-Romulus Târziu, Victor-Dan Păcurar, Pădurea, climatul È™i energia, ro, Revista pădurilor, Rev. pădur., 1583-7890, 126, 1, 34–39, Jan 2011,weblinkweblink" title="">weblink dead, 2013-04-16, 16720, 2012-06-11, (webpage has a translation button)The other greenhouse gases produced from human activity show similar increases in both amount and rate of increase. Many observations are available online in a variety of Atmospheric Chemistry Observational Databases.{{Clear}}

Anthropogenic greenhouse gases

{{see also|Climate change and ecosystems}}{{Multiple image| direction = vertical| align = right| image1 = NOAA Annual Greenhouse Gas Index 2012.png| image2 = Global greenhouse gas emissions by sector, 1990-2005, in carbon dioxide equivalents (EPA, 2010).png| image3 = Global Carbon Emissions.svg| width = 250| caption1 = This graph shows changes in the annual greenhouse gas index (AGGI) between 1979 and 2011.WEB, 2012, Climate Change Indicators in the United Statespublisher= NOAA,weblink The AGGI measures the levels of greenhouse gases in the atmosphere based on their ability to cause changes in Earth's climate.| caption2 = This bar graph shows global greenhouse gas emissions by sector from 1990 to 2005, measured in carbon dioxide equivalents.WEB, 2010, US Environmental Protection Agency (EPA), Climate Change Indicators in the United States url = weblink | caption3 = Modern global CO2 emissions from the burning of fossil fuels.| total_width = | alt1 = }}Since about 1750 human activity has increased the concentration of carbon dioxide and other greenhouse gases. Measured atmospheric concentrations of carbon dioxide are currently 100 ppm higher than pre-industrial levels.WEB,weblink Climate Change 2001: Working Group I: The Scientific Basis: figure 6-6, 1 May 2006, dead,weblink" title="">weblink 14 June 2006, dmy-all, Natural sources of carbon dioxide are more than 20 times greater than sources due to human activity,WEB,weblink The present carbon cycle – Climate Change,, 2010-10-16, 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. As a result of this balance, the atmospheric mole fraction of carbon dioxide remained between 260 and 280 parts per million for the 10,000 years between the end of the last glacial maximum and the start of the industrial era.It is likely that anthropogenic (i.e., human-induced) warming, such as that due to elevated greenhouse gas levels, has had a discernible influence on many physical and biological systems.BOOK, 2007d title = 6 Robust findings, key uncertainties publisher = IPCC, Geneva url =weblink
Future warming is projected to have a range of impacts, including sea level rise,
BOOK, 2007d title = 6 Robust findings, key uncertainties publisher = IPCC url =weblink
increased frequencies and severities of some extreme weather events, loss of biodiversity,
BOOK, 2007d, 3.3.1 Impacts on systems and sectors, 3 Climate change and its impacts in the near and long term under different scenarios, Climate Change 2007: Synthesis Report. A Contribution of Working Groups I, II, and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), IPCC, Geneva,weblink 31 August 2012,weblink" title="">weblink 3 November 2018, dead, dmy-all,
and regional changes in agricultural productivity.
The main sources of greenhouse gases due to human activity are:
  • burning of fossil fuels and deforestation leading to higher carbon dioxide concentrations in the air. Land use change (mainly deforestation in the tropics) account for up to one third of total anthropogenic {{CO2}} emissions.BOOK, Couplings Between Changes in the Climate System and Biogeochemistry
accessdate = 13 May 2008, in {{harvnb|IPCC AR4 WG1|2007}}
  • livestock enteric fermentation and manure management,JOURNAL, Livestock's long shadow,weblink H., Steinfeld, P., Gerber, T., Wassenaar, V., Castel, M., Rosales, C., de Haan, 2006, FAO Livestock, Environment and Development (LEAD) Initiative, paddy rice farming, land use and wetland changes, man-made lakes,BOOK, Ciais, Phillipe, Sabine, Christopher, etal, Stocker Thomas F., etal, Climate Change 2013: The Physical Science Basis, Carbon and Other Biogeochemical Cycles,weblink IPCC, 473, 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 activities, including the use of fertilizers, that lead to higher nitrous oxide ({{chem|N|2|O}}) concentrations.
{{Bar chart|title=Mean greenhouse gas emissions for different food typesJOURNAL, Michael Clark, Tilman, David, November 2014, Global diets link environmental sustainability and human health, Nature, 515, 7528, 518–522, 10.1038/nature13959, 1476-4687, 2014Natur.515..518T, |float=right|label_type=Food Types|data_type=Greenhouse Gas Emissions (g CO2-Ceq per g protein)|bar_width=20|width_units=em|data_max=62|label1=Ruminant Meat|data1=62|label2=Recirculating Aquaculture|data2=30|label3=Trawling Fishery|data3=26|label4=Non-recirculating Aquaculture|data4=12|label5=Pork|data5=10|label6=Poultry|data6=10|label7=Dairy|data7=9.1|label8=Non-trawling Fishery|data8=8.6|label9=Eggs|data9=6.8|label10=Starchy Roots|data10=1.7|label11=Wheat|data11=1.2|label12=Maize|data12=1.2|label13=Legumes|data13=0.25}}The seven sources of {{CO2}} from fossil fuel combustion are (with percentage contributions for 2000–2004):{| class="wikitable" style="text-align:center"! Seven main fossil fuel combustion sources !! Contribution (%)
Liquid fuels (e.g., gasoline, fuel oil) 36%
Solid fuels (e.g., coal) 35%
Gaseous fuels (e.g., natural gas) 20%
Cement production  3 %
< 1%  
Gas flare gas industrially and at wells >|
< 1%  
Non-fuel hydrocarbons
"International bunker fuels" of transport not included in national inventoriesJOURNAL
, Schrooten
, L
, Inventory and forecasting of maritime emissions in the Belgian sea territory, an activity based emission model
, Atmospheric Environment
, 42
, 4
, 667–76
, 2008
, 10.1016/j.atmosenv.2007.09.071
, De Vlieger
, Ina
, Int Panis
, Luc
, Styns, R. Torfs
, K
, Torfs
, R, 2008AtmEn..42..667S
, ||  4 %
Carbon dioxide, methane, nitrous oxide ({{chem|N|2|O}}) and three groups of fluorinated gases (sulfur hexafluoride ({{chem|SF|6}}), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs)) are the major anthropogenic greenhouse gases,JOURNAL
, The economics of the Kyoto protocol
, Grubb, M.
, July–September 2003
, World Economics
, 4
, 3
, dead
,weblink" title="">weblink
, 17 July 2011
, {{Rp|147}}WEB, Lerner & K. Lee Lerner, Brenda Wilmoth, 2006,weblink Environmental issues: essential primary sources accessdate = 11 September 2006,
and are regulated under the Kyoto Protocol international treaty, which came into force in 2005.
WEB, Kyoto Protocol publisher = United Nations Framework Convention on Climate Change, Home > Kyoto Protocol,
Emissions limitations specified in the Kyoto Protocol expired in 2012. The Cancún agreement, agreed on in 2010, includes voluntary pledges made by 76 countries to control emissions.
|date=July 2011
|author=King, D.
|chapter=Copenhagen and Cancún
|title=International climate change negotiations: Key lessons and next steps
|publisher=Smith School of Enterprise and the Environment, University of Oxford
|archivedate=1 August 2013
}} WEB,weblink PDF available,weblink" title="">weblink 13 January 2012,
At the time of the agreement, these 76 countries were collectively responsible for 85% of annual global emissions.
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 often are confused in the media. On 15 October 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 an amendment to the Montreal Protocol.WEB,weblink Climate change: global deal reached to limit use of hydrofluorocarbons, Johnston, Chris, Milman, Oliver, The Guardian, en, 2018-08-21, Vidal, John, 15 October 2016, WEB,weblink Climate change: 'Monumental' deal to cut HFCs, fastest growing greenhouse gases, BBC News, 15 October 2016, 15 October 2016, WEB,weblink Nations, Fighting Powerful Refrigerant That Warms Planet, Reach Landmark Deal, New York Times, 15 October 2016, 15 October 2016,

Greenhouse gases emissions per sector

The section presents information about Greenhouse gas emissions from different sectors of the economy.{{Expand section|1=Information on emissions from other sectors|date=July 2013}}(File:Greenhouse Gas by Sector.png|thumb|This figure shows the relative fraction of anthropogenic greenhouse gases coming from each of eight categories of sources, as estimated by the Emission Database for Global Atmospheric Research version 4.2, fast track 2010 project. These values are intended to provide a snapshot of global annual greenhouse gas emissions in the year 2010. The top panel shows the sum over all anthropogenic greenhouse gases, weighted by their global warming potential over the next 100 years. This consists of 72% carbon dioxide, 20% methane, 5% nitrous oxide and 3% other gases. Lower panels show the comparable information for each of these three primary greenhouse gases, with the same coloring of sectors as used in the top chart. Segments with less than 1% fraction are not labeled.)

Electricity generation

{{See also|Life-cycle greenhouse-gas emissions of energy sources}}Electricity generation emits over a quarter of global greenhouse gases.WEB,weblink March: Tracking the decoupling of electricity demand and associated CO2 emissions,, 2019-09-21, Coal-fired power stations are the single largest emitter, with over 10 Gt {{CO2}} in 2018.WEB,weblink Emissions,, 2019-09-21, Although much less polluting than coal plants, natural gas-fired power plants are also major emitters.WEB,weblink We have too many fossil-fuel power plants to meet climate goals, 2019-07-01, Environment, en, 2019-09-21,


According to UNEP, global tourism is closely linked to climate change. Tourism is a significant contributor to the increasing concentrations of greenhouse gases in the atmosphere. Tourism accounts for about 50% of traffic movements. Rapidly expanding air traffic contributes about 2.5% of the production of {{CO2}}. The number of international travelers is expected to increase from 594 million in 1996 to 1.6 billion by 2020, adding greatly to the problem unless steps are taken to reduce emissions.WEB,weblink Environmental Impacts of Tourism – Global Level, UNEP,

Trucking and haulage

{{update section|date=September 2019}}The trucking and haulage industry plays a part in production of {{CO2}}, contributing around 20% of the UK's total carbon emissions a year, with only the energy industry having a larger impact at around 39%.WEB,weblink A Cheaper and More Efficient Freight Industry In and Out of the UK,, 13 September 2015, {{dead link |date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }}Average carbon emissions within the haulage industry are falling—in the thirty-year period from 1977 to 2007, the carbon emissions associated with a 200-mile journey fell by 21 percent; NOx emissions are also down 87 percent, whereas journey times have fallen by around a third.{{citation
| first1=Richard | last1=Newbold | date=19 May 2014
| title=A practical guide for fleet operators |
| url=
| accessdate=2017-01-20 | postscript=. }} Due to their size, HGVs often receive criticism regarding their CO2 emissions; however, rapid development in engine technology and fuel management is having a largely positive effect.


Plastic is produced mainly from Fossil fuels. Plastic manufacturing is estimated to use 8 percent of yearly global oil production. The EPA estimates{{cn|date=September 2019}} as many as five ounces of carbon dioxide are emitted for each ounce of polyethylene terephthalate (PET) produced—the type of plastic most commonly used for beverage bottles,WEB, Glazner, Elizabeth, Plastic Pollution and Climate Change,weblink Plastic Pollution Coalition, Plastic Pollution Coalition, 6 August 2018, the transportation produce greenhouse gases also.WEB, Luise Blue, Marie-, What Is the Carbon Footprint of a Plastic Bottle?,weblink Sciencing, Leaf Group Ltd, 6 August 2018, 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.JOURNAL, Jeanne Royer, Sarah-, Ferrón, Sara, T. Wilson, Samuel, M. Karl, David, Production of methane and ethylene from plastic in the environment, PLOS ONE, 13, 1 August 2018, Plastic, Climate Change, e0200574, 10.1371/journal.pone.0200574, 30067755, 6070199, 2018PLoSO..1300574R, NEWS, Rosane, Olivia, Study Finds New Reason to Ban Plastic: It Emits Methane in the Sun,weblink 6 August 2018, Ecowatch, Plastic, Climate Change, 2 August 2018, From the other side, if it is placed in a landfill, it becomes a carbon sinkWEB, EPA, 2012,weblink Landfilling, although biodegradable plastics have caused methane emissions.JOURNAL, Levis, James W., Barlaz, Morton A., Is Biodegradability a Desirable Attribute for Discarded Solid Waste? Perspectives from a National Landfill Greenhouse Gas Inventory Model, Environmental Science & Technology, July 2011, 45, 13, 5470–5476, 10.1021/es200721s, 21615182, 2011EnST...45.5470L, 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 plastic will contribute greenhouse gases in the equivalent of 850 million tonnes of carbon dioxide (CO2) to the atmosphere in 2019. In current trend, annual emissions will grow to 1.34 billion tonnes by 2030. By 2050 plastic could emit 56 billion tonnes of Greenhouse gas emissions, as much as 14 percent of the Earth's remaining carbon budget.WEB, Sweeping New Report on Global Environmental Impact of Plastics Reveals Severe Damage to Climate,weblink Center for International Environmental Law (CIEL), 16 May 2019, 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.BOOK, Plastic & Climate The Hidden Costs of a Plastic Planet, May 2019, Center for International Environmental Law, Environmental Integrity Project, FracTracker Alliance, Global Alliance for Incinerator Alternatives, 5 Gyres, and Break Free From Plastic., 82–85,weblink 20 May 2019,

Pharmaceutical industry

The pharmaceutical industry emitted 52 megatonnes of Carbon dioxide into the atmosphere in 2015. This is more than the automotive sector. However this analysis used the combined emissions of conglomerates which produce pharmaceuticals as well as other products.WEB, Belkhir, Lotfi, Big Pharma emits more greenhouse gases than the automotive industry,weblink The Conversation, 19 July 2019,

Role of water vapor

(File:BAMS climate assess boulder water vapor 2002.png|thumb|upright=1.5|Increasing water vapor in the stratosphere at Boulder, Colorado.)Water vapor accounts for the largest percentage of the greenhouse effect, between 36% and 66% for clear sky conditions and between 66% and 85% when including clouds. 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, a process known as water vapor feedback.Held, I.M. and Soden, B.J., 2000. Water vapor feedback and global warming. Annual review of energy and the environment, 25(1), pp.441–475. 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 Â°C.BOOK, The greenhouse effect and climate change, Evans, Kimberly Masters, The environment: a revolution in attitudes, {{google books, y, DdtzAAAACAAJ, |publisher=Thomson Gale |location=Detroit |year=2005 |isbn=978-0787690823 }} (See Relative humidity#other important facts.)The average residence time of a water molecule in the atmosphere is only about nine days, compared to years or centuries for other greenhouse gases such as {{chem|CH|4}} and {{CO2}}.WEB,weblink Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2010, 15 April 2012, U.S. Environmental Protection Agency, 2 June 2012, 1.4, Thus, water vapor responds to and amplifies effects of the other greenhouse gases. The Clausius–Clapeyron relation establishes that more water vapor will be present per unit volume at elevated temperatures. This and other basic principles indicate that warming associated with increased concentrations of the other greenhouse gases also will increase the concentration of water vapor (assuming that the relative humidity remains approximately constant; modeling and observational studies find that this is indeed so). Because water vapor is a greenhouse gas, this results in further warming and so is a "positive feedback" that amplifies the original warming. Eventually other earth processes offset these positive feedbacks, stabilizing the global temperature at a new equilibrium and preventing the loss of Earth's water through a Venus-like runaway greenhouse effect.JOURNAL, Held, I.M., Soden, B.J., 10.1146/, Water Vapor Feedback and Global Warming1, Annual Review of Energy and the Environment, 25, 441–75, 2000,,

Direct greenhouse gas emissions

Between the period 1970 to 2004, greenhouse gas emissions (measured in {{CO2}}-equivalent)Includes the Kyoto "basket" of GHGs increased at an average rate of 1.6% per year, with {{CO2}} emissions from the use of fossil fuels growing at a rate of 1.9% per year.BOOK, Executive Summary, Introduction,weblink in {{harvnb|Rogner|Zhou|Bradley|Crabbé|2007}}1.3.1 REVIEW OF THE LAST THREE DECADES >CHAPTER= INTRODUCTIONRognerBradley2007}} This citation clarifies the time period (1970–2004) for the observed emissions trends. Total anthropogenic emissions at the end of 2009 were estimated at 49.5 gigatonnes {{CO2}}-equivalent.{{citation| date = November 2011| title = Bridging the Emissions Gap: A UNEP Synthesis Report publisher = United Nations Environment Programme (UNEP)Nairobi, Kenya> isbn = 978-9280732290}} UNEP Stock Number: DEW/1470/NA{{Rp|15}} These emissions include {{CO2}} from fossil fuel use and from land use, as well as emissions of methane, nitrous oxide and other greenhouse gases covered by the Kyoto Protocol.At present, the primary source of {{CO2}} emissions is the burning of coal, natural gas, and petroleum for electricity and heat.WEB,weblink Global Greenhouse Gas Emissions Data, EPA, 4 March 2014, The burning of coal, natural gas, and oil for electricity and heat is the largest single source of global greenhouse gas emissions.,

Regional and national attribution of emissions

{{See also|Kyoto Protocol and government action}}According to the Environmental Protection Agency (EPA), GHG emissions in the United States can be traced from different sectors.There are several ways of measuring greenhouse gas emissions, for example, see World Bank (2010)BOOK, 2010, Tables A1 and A2, Selected Development Indicators format = PDF, World Development Report 2010: Development and Climate Change location = Washington, DCweblink> isbn = 978-0821379875, 10.1596/978-0-8213-7987-5, {{Rp|362}} for tables of national emissions data. Some variables that have been reportedWEB,weblink Bader, N., Bleichwitz, R., 2009, Measuring urban greenhouse gas emissions: The challenge of comparability. S.A.P.I.EN.S. 2 (3),, 2011-09-11, include:
  • 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 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: Contribution of a 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 and calculations must be regularly updated to reflect new information.
  • What sectors are included in the calculation (e.g., energy industries, industrial processes, agriculture etc.): There is often a conflict between transparency and availability of data.
  • 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.
These measures are sometimes used by countries to assert various policy/ethical positions on climate change (Banuri et al., 1996, p. 94).BOOK, 1996 title = Equity and social considerations. In: Climate change 1995: Economic and social dimensions of climate change. Contribution of Working Group III to the Second Assessment Report of the Intergovernmental Panel on Climate Change (J.P. Bruce et al. Eds.) url =weblink doi = 10.2277/0521568544, The 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.Emissions may be measured over long time periods. This measurement type is called historical or cumulative emissions. Cumulative emissions give some indication of who is responsible for the build-up in the atmospheric concentration of greenhouse gases (IEA, 2007, p. 199).BOOK, 2007, World energy outlook 2007 edition – China and India insights,weblink 600, International Energy Agency (IEA), Head of Communication and Information Office, 9 rue de la Fédération, 75739 Paris Cedex 15, France, 978-9264027305, 2010-05-04,weblink" title="">weblink 15 June 2010, dead, dmy-all, The national accounts balance would be positively related to carbon emissions. The national accounts balance shows the difference between exports and imports. For many richer nations, such as the United States, the accounts balance is negative because more goods are imported than they are exported. This is mostly due to the fact that it is cheaper to produce goods outside of developed countries, leading the economies of developed countries to become increasingly dependent on services and not goods. We believed that a positive accounts balance would means that more production was occurring in a country, so more factories working would increase carbon emission levels.JOURNAL, Stoking the fires? {{CO2, emissions and economic growth |last=Holtz-Eakin |first=D. |year=1995 |journal=Journal of Public Economics |volume=57 |issue=1 |pages=85–101 |doi=10.1016/0047-2727(94)01449-X |url= }}Emissions may also be measured across shorter time periods. Emissions changes may, for example, be measured against a 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).{{Rp|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.{{Rp|370}} Per capita emissions may be based on historical or annual emissions (Banuri et al., 1996, pp. 106–07).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.JOURNAL, Dodman, David, April 2009, Blaming cities for climate change? An analysis of urban greenhouse gas emissions inventories, Environment and Urbanization, 21, 1, 185–201, 10.1177/0956247809103016, 0956-2478,

From land-use change

(File:Greenhouse gas emissions from agriculture, forestry and other land use, 1970-2010.png|thumb|left|alt=Refer to caption.|Greenhouse gas emissions from agriculture, forestry and other land use, 1970–2010.)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.{{citation
|title=Annex I: Glossary J–P
|editor1=B. Metz
|editor2=O.R. Davidson
|editor3=P.R. Bosch
|editor4=R. Dave
|editor5=L.A. Meyer
|archivedate=3 May 2010
}} 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 (Banuri et al., 1996, pp. 92–93).There are substantial uncertainties in the measurement of net carbon emissions.BOOK
, 2001
, 7.3.5 Cost Implications of Alternative GHG Emission Reduction Options and Carbon Sinks
, Costing Methodologies
, Climate Change 2001: Mitigation. Contribution of Working Group III to the Third Assessment Report of the Intergovernmental Panel on Climate Change
, B. Metz
, Print version: Cambridge University Press, Cambridge and New York. This version: GRID-Arendal website
, 978-0521015028
, 10.2277/0521015022
, Markandya, A.
, 2011-04-11
, etal
, dead
,weblink" title="">weblink
, 5 August 2011
, dmy-all, 2019-09-23
, Additionally, there is controversy over how carbon sinks should be allocated between different regions and over time (Banuri et al., 1996, p. 93). For instance, concentrating on more recent changes in carbon sinks is likely to favour those regions that have deforested earlier, e.g., Europe.

Greenhouse gas intensity

{{See also|List of countries by carbon intensity}}{|thumbalt=Refer to caption.|Greenhouse gas intensity in the year 2000, including land-use change.)thumbalt=Refer to caption.|Carbon intensity of GDP (using PPP) for different regions, 1982–2011.)thumbalt=Refer to caption.|Carbon intensity of GDP (using MER) for different regions, 1982–2011.)Greenhouse gas 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.BOOK, November 2006, Herzog, T. title = Target: intensity – an analysis of greenhouse gas intensity targets publisher = World Resources Institute accessdate = 2011-04-11, Emission intensities may be calculated using market exchange rates (MER) or purchasing power parity (PPP) (Banuri et al., 1996, p. 96). Calculations based on MER show large differences in intensities between developed and developing countries, whereas calculations based on PPP show smaller differences.

Cumulative and historical emissions

{{Multiple image|direction=vertical| align=right| image1=Cumulative energy-related carbon dioxide emissions between 1850-2005 for low-income, middle-income, high-income, the EU-15, and OECD countries.png| image2=Cumulative energy-related carbon dioxide emissions between 1850-2005 for different countries.png| image3=CO2 responsibility 1950-2000.svg| image4=Yearly trends in annual regional carbon dioxide emissions from fuel combustion between 1971 and 2009.png| image5=Regional trends in annual per capita carbon dioxide emissions from fuel combustion between 1971 and 2009.png| width=220| caption1=Cumulative energy-related {{CO2}} emissions between the years 1850–2005 grouped into low-income, middle-income, high-income, the EU-15, and the OECD countries.| caption2=Cumulative energy-related {{CO2}} emissions between the years 1850–2005 for individual countries.| caption3=Map of cumulative per capita anthropogenic atmospheric {{CO2}} emissions by country. Cumulative emissions include land use change, and are measured between the years 1950 and 2000.| caption4=Regional trends in annual {{CO2}} emissions from fuel combustion between 1971 and 2009.| caption5=Regional trends in annual per capita {{CO2}} emissions from fuel combustion between 1971 and 2009.}}Cumulative anthropogenic (i.e., human-emitted) emissions of {{CO2}} from fossil fuel use are a major cause of global warming,JOURNAL, 2008 title = Cumulative {{CO2, emissions: shifting international responsibilities for climate debt volume = 8 doi = 10.3763/cpol.2008.0539| page = 570|display-authors=etal}}
and give some indication of which countries have contributed most to human-induced climate change.
JOURNAL, 24 September 2010, Höhne, N., Contributions of individual countries' emissions to climate change and their uncertainty, Climatic Change, 10.1007/s10584-010-9930-6,weblink etal, 106, 3, 359–91, dead,weblink" title="">weblink 26 April 2012, dmy-all, {{Rp|15}}{| class="wikitable" | style="text-align:center"|+ Top-5 historic {{CO2}} contributors by region over the years 1800 to 1988 (in %)! Region! Industrial {{CO2}}! Total {{CO2}}
OECD North America 33.2 29.7
OECD Europe 26.1 16.6
Former USSR 14.1 12.5
China   5.5   6.0
Eastern Europe   5.5   4.8
The table above to the left is based on Banuri et al. (1996, p. 94). 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. The estimate of total {{CO2}} emissions includes biotic carbon emissions, mainly from deforestation. Banuri et al. (1996, p. 94) calculated per capita cumulative emissions based on then-current population. The ratio in per capita emissions between industrialized countries and developing countries was estimated at more than 10 to 1.Including biotic emissions brings about the same controversy mentioned earlier regarding carbon sinks and land-use change (Banuri et al., 1996, pp. 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.Non-OECD countries accounted for 42% of cumulative energy-related {{CO2}} emissions between 1890 and 2007.{{citation| year = 2009| title = World Energy Outlook 2009| location = Paris| publisher = International Energy Agency (IEA)| pages = 179–80| isbn = 978-9264061309| url =weblink| access-date = 27 December 2011| archive-url =weblink" title="">weblink| archive-date = 24 September 2015| url-status=dead| df = dmy-all}}{{Rp|179–80}} Over this time period, the US accounted for 28% of emissions; the EU, 23%; Russia, 11%; China, 9%; other OECD countries, 5%; Japan, 4%; India, 3%; and the rest of the world, 18%.{{Rp|179–80}}

Changes since a particular base year

{{See also|Kyoto Protocol#Government action and emissions}}Between 1970 and 2004, global growth in annual {{CO2}} emissions was driven by North America, Asia, and the Middle East.{{citation chapter = Introduction weblink}} in {{harvnb>RognerBradley2007}}
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.JOURNAL
YEAR = 2007 TITLE = GLOBAL AND REGIONAL DRIVERS OF ACCELERATING {{CO2, emissions volume = 104 pages = 10288–93 pmid = 17519334 bibcode = 2007PNAS..10410288R last2 = Marland last3 = Ciais last4 = Le Quere last5 = Canadell last6 = Klepper last7 = FieldNO}} by 0.25% y−1.Using different base years for measuring emissions has an effect on estimates of national contributions to global warming.{{Rp|17–18}}The cited paper uses the term "start date" instead of "base year." 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.{{Rp|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).

Annual emissions

(File:GHG per capita 2000.svg|thumb|Per capita anthropogenic greenhouse gas emissions by country for the year 2000 including land-use change.)Annual per capita emissions in the industrialized countries are typically as much as ten times the average in developing countries.{{Rp|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).WEB, 25 June 2009, Global {{CO2, emissions: annual increase halves in 2008| url =weblink| publisher = Netherlands Environmental Assessment Agency (PBL) website| accessdate = 2010-05-05}} 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 percapita 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. Emissions in Russia and Ukraine have decreased fastest since 1990 due to economic restructuring in these countries.WEB, March 2009, Global Carbon Mechanisms: Emerging lessons and implications (CTC748) publisher = Carbon Trust accessdate = 2010-03-31, Energy statistics for fast growing economies are less accurate than those for the industrialized countries. For China's annual emissions in 2008, the Netherlands Environmental Assessment Agency estimated an uncertainty range of about 10%.The greenhouse gas footprint refers to the emissions resulting from the creation of products or services. It is more comprehensive than the commonly used carbon footprint, which measures only carbon dioxide, one of many greenhouse gases.2015 was the first year to see both total global economic growth and a reduction of carbon emissions.NEWS,weblink Global emissions to fall for first time during a period of economic growth, Vaughan, Adam, 2015-12-07, The Guardian, 0261-3077, 2016-12-23,

Top emitter countries

File:CO2 emission pie chart.svg|thumb|Global carbon dioxide emissions by country.]](File:Ghg-co2-2012.svg|thumb|upright=1.5|The top 40 countries emitting all greenhouse gases, showing both that derived from all sources including land clearance and forestry and also the CO2 component excluding those sources. Per capita figures are included. WEB,weblink World Resources Institute data, . Note that Indonesia and Brazil show very much higher than on graphs simply showing fossil fuel use.){{See also|List of countries by carbon dioxide emissions|List of countries by carbon dioxide emissions per capita|List of countries by greenhouse gas emissions|List of countries by greenhouse gas emissions per capita}}


In 2009, the annual top ten emitting countries accounted for about two-thirds of the world's annual energy-related {{CO2}} emissions.{{citation| year = 2011| publisher = International Energy Agency (IEA)| title = {{CO2}} Emissions From Fuel Combustion: Highlights (2011 edition)| url =weblink| page = 9| location = Paris, France| access-date = 7 March 2012| archive-url =weblink" title="">weblink| archive-date = 17 March 2017| url-status=dead| df = dmy-all}}{| class="wikitable" | style="text-align:center"date=August 2015}}! Country! % of global total annual emissions! Tonnes of GHG per capita
{{flag| 5.1
{{flag| 16.9
{{flag| 1.4
{{flag| 10.8
{{flag| 8.6
{{flag| 9.2
{{flag| 7.3
{{flag| 15.4
{{flag| 10.6
{{flag| 7.5


File:The C-Story of Human Civilization.webm|thumb|The C-Story of Human Civilization by PIK ]]{| class="wikitable sortable" | style="text-align:center"|+Top-10 cumulative energy-related {{CO2}} emitters between 1850 and 2008{{citation needed|date=August 2015}}! Country! % of world total! Metric tonnes {{CO2}} per person
{{flag| 1,132.7
{{flag| 85.4
{{flag| 677.2
{{flag| 998.9
{{flag| 1,127.8
{{flag| 367
{{flag| 514.9
{{flag| 26.7
{{flag| 789.2
{{flag| 556.4

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.BOOK
, 10 December 2007
, Helm, D.
, Too Good To Be True? The UK's Climate Change Record
, 3
, etal
, dead
,weblink" title="">weblink
, 15 July 2011
, dmy-all
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.{{Rp|179}}{{Rp|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.
Davis and Caldeira (2010)JOURNAL,weblink PDFauthor2=K. Caldeira date = 8 March 2010 doi = 10.1073/pnas.0906974107| pmid = 20212122bibcode = 2010PNAS..107.5687D issue = 12| pages=5687–5692| pmc = 2851800}}{{Rp|4}} found that a substantial proportion of {{CO2}} emissions are 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. Based on annual emissions data from the year 2004, and on a per-capita consumption basis, the top-5 emitting countries were found to be (in t{{CO2}} per person, per year): Luxembourg (34.7), the US (22.0), Singapore (20.2), Australia (16.7), and Canada (16.6).{{rp|5}} Carbon Trust research revealed that approximately 25% of all {{CO2}} emissions from human activities 'flow' (i.e., are imported or exported) from one country to another. Major developed economies were found to be typically net importers of embodied carbon emissions—with UK consumption emissions 34% higher than production emissions, and Germany (29%), Japan (19%) and the US (13%) also significant net importers of embodied emissions.WEB,weblink International Carbon Flows, Carbon Trust, May 2011, 12 November 2012,

Effect of policy

Governments have taken action to reduce greenhouse gas emissions to mitigate climate change. Assessments of policy effectiveness have included work by the Intergovernmental Panel on Climate Change,e.g., Gupta et al. (2007) assessed the scientific literature on climate change mitigation policy: GUPTA, S.> TITLE = POLICIES, INSTRUMENTS, AND CO-OPERATIVE ARRANGEMENTS,weblinkRognerBradley2007}} WEB, Energy Policy year = 2012 location = Paris, WEB, IEA Publications on 'Energy Policy' year = 2012 location = Paris, {{citation| date = November 2011| publisher = United Nations Environment Programme (UNEP)| title = Bridging the Emissions Gap: A UNEP Synthesis Report location = Nairobi, Kenya| isbn = 978-9280732290}} UNEP Stock Number: DEW/1470/NA
Policies implemented by governments have included
BOOK, 2010, p. 192, Box 4.2: Efficient and clean energy can be good for development, 4. Energizing development without compromising the climate format = PDF, World Development Report 2010: Development and Climate Change location = Washington, DCweblink> isbn = 978-0821379875, 10.1596/978-0-8213-7987-5, BOOK, 2005, United Nations Framework Convention on Climate Change (UNFCCC), Sixth compilation and synthesis of initial national communications from Parties not included in Annex I to the Convention. Note by the secretariat. Executive summary. pages = 10–12, Geneva, Switzerland, BOOK, 2011, United Nations Framework Convention on Climate Change (UNFCCC), Compilation and synthesis of fifth national communications. Executive summary. Note by the secretariat. pages = 9–10, Geneva (Switzerland),
national and regional targets to reduce emissions, promoting energy efficiency, and support for renewable energy such as Solar energy as an effective use of renewable energy because solar uses energy from the sun and does not release pollutants into the air.
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.{{Rp|3}} Analysis by the UNFCCC (2011){{Rp|8}} suggested that policies and measures undertaken by Annex I Parties may have produced emission savings of 1.5 thousand Tg {{CO2}}-eq in the year 2010, with most savings made in the energy sector. The projected emissions saving of 1.5 thousand Tg {{CO2}}-eq is measured against a hypothetical "baseline" of Annex I emissions, i.e., projected Annex I emissions in the absence of policies and measures. The total projected Annex I saving of 1.5 thousand {{CO2}}-eq does not include emissions savings in seven of the Annex I Parties.{{Rp|8}}


{{Further|climate change scenario#Quantitative emissions projections}}{{See also|Global climate model#Projections of future climate change}}A wide range of projections of future emissions have been produced.FISHER >FIRST=B.TITLE= ISSUES RELATED TO MITIGATION IN THE LONG-TERM CONTEXTRognerBradley2007}}
Rogner et al. (2007)
BOOK, 1.3.2 Future outlook, Introduction, in {{harvnb|Rogner|Zhou|Bradley|Crabbé|2007}} assessed the scientific literature on greenhouse gas projections. Rogner et al. (2007) concluded that unless energy policies changed substantially, the world would continue to depend on fossil fuels until 2025–2030. Projections suggest that more than 80% of the world's energy will come from fossil fuels. This conclusion was based on "much evidence" and "high agreement" in the literature. Projected annual energy-related {{CO2}} emissions in 2030 were 40–110% higher than in 2000, with two-thirds of the increase originating in developing countries. Projected annual per capita emissions in developed country regions remained substantially lower (2.8–5.1 tonnes {{CO2}}) than those in developed country regions (9.6–15.1 tonnes {{CO2}}).BOOK, Total GHG emissions, Introduction,weblink 4 September 2012,weblink" title="">weblink 28 January 2013, dead, in {{harvnb|Rogner|Zhou|Bradley|Crabbé|2007}}
Projections consistently showed increase in annual world emissions of "Kyoto" gases,carbon dioxide, methane, nitrous oxide, sulfur hexafluoride measured in {{CO2}}-equivalent) of 25–90% by 2030, compared to 2000.

Relative {{CO2}} emission from various fuels

One liter of gasoline, when used as a fuel, produces {{nowrap|2.32 kg}} (about 1300 liters or 1.3 cubic meters) of carbon dioxide, a greenhouse gas. One US gallon produces 19.4 lb (1,291.5 gallons or 172.65 cubic feet)WEB,weblink Greenhouse Gas Emissions from a Typical Passenger Vehicle, US Environment Protection Agency,, 2011-09-11, WEB, Engber, Daniel,weblink How gasoline becomes {{CO2, , Slate Magazine |publisher= Slate Magazine |date= 1 November 2006 |accessdate=2011-09-11}}WEB,weblink Volume calculation for carbon dioxide,, 2011-09-11, {| class="wikitable sortable" border="1" | style="text-align:center"carbon dioxide emitted per quantity of energy for various fuelsHTTP://WWW.EIA.DOE.GOV/OIAF/1605/COEFFICIENTS.HTML,weblink" title="">weblink dead, 1 November 2004, 21 August 2009, Voluntary Reporting of Greenhouse Gases Program, Energy Information Administration, ! Fuel name! {{CO2}} emitted (lbs/106 Btu)! {{CO2}} emitted (g/MJ)! {{CO2}} emitted (g/kWh)
Natural gas| 117| 50.30|181.08
Liquefied petroleum gas| 139| 59.76|215.14
Propane| 139| 59.76|215.14
Aviation gasoline| 153| 65.78|236.81
Automobile gasoline| 156| 67.07|241.45
Kerosene| 159| 68.36|246.10
Fuel oil| 161| 69.22|249.19
Tires/tire derived fuel| 189| 81.26|292.54
Wood and wood waste| 195| 83.83|301.79
Coal (bituminous)| 205| 88.13|317.27
Coal (sub-bituminous)| 213| 91.57|329.65
Coal (lignite)| 215| 92.43|332.75
Petroleum coke| 225| 96.73|348.23
Tar-sand Bitumendate=August 2013}}date=August 2013}}date=August 2013}}
Coal (anthracite)| 227| 97.59|351.32

Life-cycle greenhouse-gas emissions of energy sources

A 2011 IPCC report included a literature review of numerous energy sources' total life cycle {{CO2}} emissions. Below are the {{CO2}} emission values that fell at the 50th percentile of all studies surveyed.JOURNAL,weblink 10, Moomaw, W., P. Burgherr, G. Heath, M. Lenzen, J. Nyboer, A. Verbruggen, 2011, Annex II: Methodology, IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation, 17 June 2016,weblink" title="">weblink 22 September 2014, dead, {|class="wikitable sortable"|+ '''Lifecycle greenhouse gas emissions by electricity source.! Technology !! Description !! 50th percentile (g {{CO2}}/kWhe)
Hydroelectricity>Hydroelectric reservoir 4
Marine energy>Ocean Energy wave and tidal 8
Wind >List of onshore wind farms>onshore 12
Nuclear power>Nuclear various generation II reactor types 16
Biomass >| 18
Concentrating solar power>Solar thermal parabolic trough 22
Geothermal >hot dry rock >| 45
Solar PV >Polycrystalline silicon photovoltaics>Polycrystalline silicon 46
Natural gas >| 469
Coal >| 1001

Removal from the atmosphere

Natural processes

Greenhouse gases can be removed from the atmosphere by various processes, as a consequence of:
  • a physical change (condensation and precipitation remove water vapor from the atmosphere).
  • a chemical reaction within the atmosphere. For example, methane is oxidized by reaction with naturally occurring hydroxyl radical, OH· and degraded to {{CO2}} and water vapor ({{CO2}} from the oxidation of methane is not included in the methane Global warming potential). Other chemical reactions include solution and solid phase chemistry occurring in atmospheric aerosols.
  • a physical exchange between the atmosphere and the other compartments of the planet. An example is the mixing of atmospheric gases into the oceans.
  • a chemical change at the interface between the atmosphere and the other compartments of the planet. This is the case for {{CO2}}, which is reduced by photosynthesis of plants, and which, after dissolving in the oceans, reacts to form carbonic acid and bicarbonate and carbonate ions (see ocean acidification).
  • a photochemical change. Halocarbons are dissociated by UV light releasing Cl· and F· as free radicals in the stratosphere with harmful effects on ozone (halocarbons are generally too stable to disappear by chemical reaction in the atmosphere).

Negative emissions

A number of technologies remove greenhouse gases emissions from the atmosphere. Most widely analysed are those that remove carbon dioxide from the atmosphere, either to geologic formations such as bio-energy with carbon capture and storageJOURNAL, Obersteiner M, Managing climate risk, Science, 294, 5543, 786–87, October 2001, 11681318, 10.1126/science.294.5543.786b, Azar C, Kauppi P, 3, Möllersten, K, Moreira, J, Nilsson, S, Read, P, Riahi, K, Schlamadinger, B, JOURNAL, Azar, C., Lindgren, K., Larson, E.D., Möllersten, K., Carbon capture and storage from fossil fuels and biomass – Costs and potential role in stabilising the atmosphere, Climatic Change, 74, 1–3, 47–79, 2006,weblink 10.1007/s10584-005-3484-7, 2006ClCh...74...47A, WEB, The Royal Society, 2009,weblink Geoengineering the climate: science, governance and uncertainty, 12 September 2009, dead,weblink" title="">weblink 7 September 2009, and carbon dioxide air capture, or to the soil as in the case with biochar. The IPCC has pointed out that many long-term climate scenario models require large-scale manmade negative emissions to avoid serious climate change.{{citation|last1=Fischer|first1=B.S.|first2=N. |last2=Nakicenovic|first3=K. |last3=Alfsen|first4=J. Corfee |last4=Morlot|first5=F. |last5=de la Chesnaye|first6=J.-Ch. |last6=Hourcade|first7=K. |last7=Jiang|first8=M. |last8=Kainuma|first9=E. |last9=La Rovere|first10=A. |last10=Matysek|first11=A. |last11=Rana|first12=K. |last12=Riahi|first13=R. |last13=Richels|first14=S. |last14=Rose|first15=D. |last15=van Vuuren|first16=R. |last16=Warren|url= |title=Issues related to mitigation in the long term context}} in {{harvnb|Rogner|Zhou|Bradley|Crabbé|2007}}

History of scientific research

In the late 19th century scientists experimentally discovered that {{chem|N|2}} and {{chem|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.{{Citation needed|date=August 2019}} 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. 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,JOURNAL, Cook, J., Nuccitelli, D., Green, S.A., Richardson, M., Winkler, B.R., Painting, R., Way, R., Jacobs, P., Skuce, A., 10.1088/1748-9326/8/2/024024, Quantifying the consensus on anthropogenic global warming in the scientific literature, Environmental Research Letters, 8, 2, 024024, 2013, 2013ERL.....8b4024C,weblink
with consequences for the environment and for human health.

See also

{hide}Columns-list|colwidth=22em| {edih}




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External links

{{Commons category|Greenhouse gases}}

Carbon dioxide emissions

{{Global warming}}{{Authority control}}

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