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The Main Greenhouse Gases

Resources
Carbon Dioxide Information Analysis Center: http://cdiac.esd.ornl.gov
CO2 emissions from industrial processes: www.grida.no/climate/vital/09.htm
CO2 emissions from land-use changes: www.grida.no/climate/vital/10.htm
Global atmospheric concentration of CO2: www.grida.no/climate/vital/07.htm
Global greenhouse gases: www.grida.no/climate/vital/05.htm
Global GHG emissions (real time): www.grida.no/db/maps/collection/climate5
HFCs, PFCs, and SF6: www.epa.gov/globalwarming/emissions/national/xfcs-sf6.html
Industrial greenhouse gases: www.epa.gov/outreach/ghginfo/topic8.htm
Radiative forcing: www.grida.no/climate/vital/04.htm
Surface/atmosphere methane exchange: www.giss.nasa.gov/data/ch4fung

"There is no known geologic precedent for the transfer of carbon from the Earth's crust to atmospheric carbon dioxide, in quantities comparable to the burning of fossil fuels, without simultaneous changes in other parts of the carbon cycle and climate system. (…) The present level of scientific uncertainty does not justify inaction in the mitigation of human-induced climate change and/or the adaptation to it."
American Geophysical Union, policy statement, 1998

Footnotes:

1 - The data on concentrations and annual growth rates for the long-lived industrial gases comes from James Elkins, at the Halocarbons and other Atmospheric Trace Species Group, Oceanic and Atmospheric Research Climate Monitoring and Diagnostics Laboratory, NOAA, Boulder CO.
2 - The different gases do not suddenly disappear at the end of their lifetime, so these figures are generally approximate.
2 - GWP is an index defined as the cumulative radiative forcing between the present and some chosen time horizon (typically 100 years) caused by a unit mass of gas emitted now, expressed relative to a reference gas such as CO2, including any indirect effects of the emitted gases.
4 - The data for radiative forcing comes from the IPCC's Third Assessment Report of Working Group 1 (January 2001). The figures represent increased forcing since 1750.
5 - The percentages are based on the radiative forcings of the different gases, excluding the aerosols.
6 - It is likely that total atmospheric water vapour has increased by several percent per decade over many regions of the Northern Hemisphere. (IPCC)
7 - The increased water vapor is caused by increased ocean precipitation, which is caused indirectly by human activities. There is uncertainty about the extent to which it causes increased radiative forcing due to an increase in high level cirrus cloud cover (which traps heat), or decreased forcing due to increased albedo on lower stratus clouds (which reflect heat back into space).
8 - Water vapour feedback approximately doubles the warming from the warming for fixed water vapour. (IPCC)
9 - Overall global methane sources and methane sinks are not well understood. Methane emissions are continuing, but the accumulation of methane in the atmosphere has slowed since 1990 for reasons that are not clear. Methane's radiative forcing has been falling since 1987.
10 - Identified in the January 2001 IPCC Report as an additional cause of methane increase, without a number attached.
11 - James Hansen et al (see above) suggests that the radiative forcing of the CFC replacements (HCFCs and HFCs) will be similar to that of the CFCs they replace. If HFC-134a were phased out, and the stockpiles of CFC-21 were destroyed, the overall forcing might fall to 0.25W/m2. Range of uncertainty for radiative forcing: +/-0.5W/m2
12 - Yoshio Makide and a team of researchers at Tokyo University reported in 1998 that HFCs are accumulating rapidly as they are used to replace CFCs, though they are still at a very low level. In 1995 they were 2 ppt (parts per trillion); by 1997 they had reached 6 ppt. The figure of 12 for the year 2000 is based on an increase of 2ppt per year.
13 - As authors, we were not able to locate data for the growth rate of tropospheric ozone.
14 - The principal emissions that cause the accumulation of tropospheric ozone (known as the 'precursors') are volatile organic compounds and nitrogen oxides (NOx), which result from transportation, power plants and industrial processes. It is also caused by the break-up of methane in the atmosphere.
15 - Research on the different aerosols if difficult, partly because they are so short-lived.
16 - The direct radiative forcing of the different aerosols is estimated by the IPCC to be -0.4 Wm2 for sulfate, -0.2 Wm2 for biomass burning aerosols, -0.1 Wm2 for fossil fuel organic carbon and +0.2 Wm2 for fossil fuel black carbon. The radiative forcing of indirect aerosol effects (eg on clouds) is very uncertain, and ranges from 0 to - 2.0.

Last updated 2001

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