Main Greenhouse Gases

The tables below present characteristics of major greenhouse gases. The Global Warming Potential (GWP) indicates the warming effect of a greenhouse gas, while the atmospheric lifetime expresses the total effect of a specific greenhouse gas after taking into account global sink availability. The lifetime indicates how long the gas remains in the atmosphere and increased radiative forcing quantifies the contribution to additional heating over an area. The vast majority of emissions  are carbon dioxide followed by methane and nitrous oxide. Lesser amounts of CFC-12, HCFC-22, Perflouroethane and Sulfur Hexaflouride are also emitted and their contribution to global warming is magnified by their high GWP, although there total contribution is still small compared to the other gasses.



Chemical Formula

 Anthropogenic Sources

Atmospheric Lifetime1(years)

 GWP2 (100 Year Time Horizon)



Fossil-fuel combustion, Land-use conversion, Cement Production





Fossil fuels,
Rice paddies,
Waste dumps





Industrial processes, Combustion



Tropospheric Ozone O3Fossil fuel combustion, Industrial emissions, Chemical solventshours-daysN.A.



Liquid coolants,








Sulfur Hexaflouride


Dielectric fluid




Pre-1750 Tropospheric
(parts per billion)

Current Tropospheric
(parts per billion) 






1,870 / 1,7488



 323 / 3228

Tropospheric Ozone 2534



.534 / .5328



.218 / .19410

Sulfur Hexaflouride


.00712 /.006738, 10

Source of graphical information and notes:
Blasing, T.J. ad K. Smith 2011.  "Recent Greenhouse Gas Concentrations."  In Trends: A Compendium of Data on Global Change.  Carbon Dioxide Information Analysis Cetner, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, TN, USA.


  1. The atmospheric lifetime is used to characterize the decay of an instanenous pulse input to the atmosphere, and can be likened to the time it takes that pulse input to decay to 0.368 (l/e) of its original value. The analogy would be strictly correct if every gas decayed according to a simple expotential curve, which is seldom the case. For example, CH4 is removed from the atmosphere by a single process, oxidation by the hydroxyl radical (OH), but the effect of an increase in atmospheric concentration of CH4 is to reduce the OH concentration, which, in turn, reduces destruction of the additional methane, effectively lengthening its atmospheric lifetime. An opposite kind of feedback may shorten the atmospheric lifetime of N2O (IPCC 2007, Section 2.10.3).
  2. The Global Warming Potential (GWP) provides a simple measure of the radiative effects of emissions of various greenhouse gases, integrated over a specified time horizon, relative to an equal mass of CO2 emissions.
  3. 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 which, unmixed with the rest of the atmosphere, would be 10 micrometers thick at standard temperature and pressure.
  4. Because 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).
  5. The value given by IPCC 2001, page 185, is 280 ± 10 ppm. This is supported by measurements of CO2 in old, confined, and reasonably well-dated air. Such air is found in bubbles trapped in annual layers of ice in Antarctica, in sealed brass buttons on old uniforms, airtight bottles of wine of known vintage, etc. Additional support comes from well-dated carbon-isotope signatures, for example, in annual tree rings. Estimates of "pre-industrial" CO2 can also be obtained by first calculating the ratio of the recent atmospheric CO2 increases to recent fossil-fuel use, and using past records of fossil-fuel use to extrapolate past atmospheric CO2 concentrations on an annual basis. Estimates of "pre-industrial" CO2 concentrations obtained in this way are higher than those obtained by more direct measurements; this is believed to be because the effects of widespread land clearing are not accounted for. Ice-core data provide records of earlier concentrations. For concentrations back to about 1775, see A. Neftel et al.
  6. Recent CO2 concentration (388.5 ppm) is the 2010 average taken from globally averaged marine surface data given by the National Oceanic and Atmospheric Administration Earth System Research Laboratory, web site:
  7. Pre-industrial concentrations of CH4 are evident in the "1000-year" ice-core records in CDIAC's Trends Online However, those values need to be multiplied by a scaling factor of 1.0119 to make them compatible with the AGAGE measurements of current methane concentrations, which have already been adjusted to the Tohoku University scale. Ten thousand-year records of CH4, CO2 and N2O, from ice-core data, are also presented graphically in IPCC 2007, (Figure SPM.1).
  8. The first value in a cell represents Mace Head, Ireland, a mid-latitude Northern-Hemisphere site, and the second value represents Cape Grim, Tasmania, a mid-latitude Southern-Hemisphere site. "Current" values given for these gases are annual arithmetic averages based on monthly background concentrations for October 2009 through September 2010. The SF6 values are from the AGAGE gas chromatography - mass spectrometer (gc-ms) Medusa measuring system.
  9. Source: IPCC (2007). The pre-1750 value for N2O is consistent with ice-core records from 10,000 B.C.E. through 1750 C.E. shown graphically in figure SPM.1 on page 3.
  10. For SF6 data from January 2004 onward see For data from 1995 through 2004, see the National Oceanic and Atmospheric Administration (NOAA), Halogenated and other Atmospheric Trace Species (HATS) site at:

Global Surface Temperature Trends

The global average surface temperature fluctuates over time, but recently it has increased dramatically. From 1920 to the present, the Earth’s average surface temperature has increased by around 1.4 °F. The current warming trend is proceeding at a rate that is unprecedented in at least the past 1,300 years. (IPCC AR4)

The sharpest rise occurred between 1975 and 2010, when temperature rose steadily by over 1 °F. The graph below holds 1880-1920 as the baseline climate period and temperatures are expressed as the difference from that era.


The Greenhouse Effect

The greenhouse effect naturally keeps the earth warm enough to be habitable; without it, the earth’s surface would be about 60 degrees Fahrenheit colder on average. 

Scientists refer to what has been happening in the earth’s atmosphere over the past century as the “enhanced greenhouse effect.” By pumping man-made greenhouse gases into the atmosphere, humans are altering and enhancing the process by which the atmosphere traps the sun’s heat before it can be released back into space.

Greenhouse Effect

United States Emissions

In this section, you can find information about the main sources of greenhouse gases emitted in the United States.

Click on the images below to view additional information on each figure.



U.S. Greenhouse Gas Emissions by Gas

Greenhouse Gas Emissions by Sector

U.S. Trends in Greenhouse Gas Emissions

Trends in CO2 Emissions

U.S. CO2 Emissions from the Electric Power Sector


Observed Temperature & Greenhouse Gas Trends

This section illustrates the relationship between average global surface temperature and greenhouse gas concentration in the atmosphere.

Click on the images below to view additional information on each figure.


Global Surface Temperature Trends

CO2 and Temp Trends S

Atmospheric GHG Concentrations & Global Surface Temperature Trends

The Last 150 Years

Vostok Ice Core S
Trends in Atmospheric GHG Concentrations & Global Surface Temperature

The Last 400,000 Years

Comparison of Modeled and Observed Temperature

Trends in Ocean Heat Penetration


The Physical Basis of Global Warming

This section explains the mechanism of the greenhouse effect, the role of anthropogenic (human produced) greenhouse gas emissions in generating the enhanced greenhouse effect, and the basic characteristics of the main anthropogenic greenhouse gases.

Click on the images below to view additional information on each figure.

greenhouse effect

The Greenhouse Effect

Main Greenhouse Gases

Main Greenhouse Gases

Also, from our FAQs: 
What are the most important greenhouse gases and their sources?

Global CO2 Flows Carbon Reservoirs and

Global CO2 Flows, Carbon Reservoirs, and Reservoir Changes



The physical basis of the greenhouse gas effect and the role of human emissions in global warming.

Adaptation to Climate Change: International Policy Options

Adaptation to Climate Change cover

Adaptation to Climate Change: International Policy Options

Prepared for the Pew Center on Global Climate Change
November 2006

Ian Burton, University of Toronto
Elliot Diringer, Pew Center on Global Climate Change
Joel Smith, Stratus Consulting Inc.

This report examines options for future international efforts to help vulnerable countries adapt to the impacts of climate change both within and outside the climate framework. Options outlined in the report include stronger funding and action under the UN Framework Convention on Climate Change, mandatory climate risk assessments for multilateral development finance, and donor country support for climate "insurance" in vulnerable countries.

Press release

Download entire report (pdf)



From its inception, the international climate effort has focused predominantly on mitigation—reducing greenhouse gas (GHG) emissions to prevent dangerous climate change. The next stage of the international effort must deal squarely with adaptation—coping with those impacts that cannot be avoided. This is both a matter of need, as climate change is now underway, and a matter of equity, as its impacts fall disproportionately on those least able to bear them. It also may be a condition for further progress on mitigation. Indeed, substantial new mitigation commitments post-2012 may be politically feasible only if accompanied by stronger support for adaptation.

Ambitious mitigation efforts can lessen, but not prevent, future climate change. While steep reductions in emissions could stabilize atmospheric GHG concentrations at lower levels than under “business as usual,” they likely would be well above current, let alone pre-industrial, levels.2 With higher concentrations will come further rises in temperatures and sea level, changes in precipitation, and more extreme weather. The early impacts of climate change already are being felt worldwide.3 Future impacts will affect a broad array of human and natural systems, with consequences for human health, food and fiber production, water supplies, and many other areas vital to economic and social well being. While certain impacts may in the nearer term prove beneficial to some, in the long term, the effects will be largely detrimental.4

Anticipating and adapting to these impacts in order to minimize their human and environmental toll is a significant challenge for all nations. Meeting it requires action at multiple levels, from the local to the international, within both public and private spheres. This paper explores one critical dimension of this multifaceted challenge—how adaptation can be best promoted and facilitated through future multilateral efforts.

Among the many issues confronting governments, two are especially daunting. The first is equity and its relation to cost. Difficult questions of fairness suffuse the climate debate but are particularly stark in the case of adaptation: those most vulnerable to climate change are the ones least responsible for it. Stronger international adaptation efforts—whatever form they might take, and whether understood as assistance or as compensation—will be possible, let alone effective, only insofar as affluent countries are prepared to commit resources. This is a question not of policy design but, rather, of negotiation and political will. Second, reliable information and relevant experience are in short supply. Relative to mitigation, the adaptation challenge is much less well understood—needs as well as solutions. A high priority in the near term is strengthening the knowledge base with better data and modeling to refine projections of future impacts, and with early insights from the field on the most effective responses.

It is at the same time essential to begin considering how future international efforts can best be structured. This paper examines underlying issues and lays out an array of possibilities. To set the issue in context, it looks first at the history and evolving nature of human adaptation to climate. It then highlights key issues in the design of adaptation policy, and summarizes and assesses international adaptation efforts to date. Finally, the paper outlines three broad and potentially complementary approaches to future international efforts:

  • Adaptation Under the UNFCCC—Initiating new steps under the UN Framework Convention on Climate Change (UNFCCC) to facilitate comprehensive national adaptation strategies and to provide reliable assistance for high-priority implementation projects.
  • Integration with Development—Integrating adaptation across the full range of development-related assistance through measures such as mandatory climate risk assessments for projects financed with bilateral or multilateral support.
  • Climate “Insurance”—Committing stable funding for an international response fund or to support insurance-type approaches covering climate-related losses and promoting proactive adaptation in vulnerable countries.

1. This report was prepared initially as input to the Climate Dialogue at Pocantico convened by the PewCenterin 2004-5, and in its final form reflects contributions from the dialogue. The Pocantico dialogue brought together 25 senior policymakers and stakeholders from 15 countries to recommend options for advancing the international climate change effort beyond 2012. The group’s report is available at: /global-warming-in-depth/all_reports/climate_dialogue_at_ pocantico/index.cfm.

2. Metz et al. (2001).

3. Parmesan, C. and G. Yohe (2003); Root, T. L. et al. (2003); Stott et al. (2004).

4. McCarthy et al. (2001).


Elliot Diringer
Ian Burton
Joel Smith

Climate Change Institute to Engage State Legislatures

Promoted in Energy Efficiency section: 
Pew Center on Global Climate Change hosts a conference on understanding climate change science and the status of relevant technologies.

November 29 - December 1, 2006
Wingspread Conference Center
33 East Four Mile Road
Racine, Wisconsin 53402

From November 29 to December 1, 2006, the Pew Center on Global Climate Change, in collaboration with the National Conference of State Legislatures and the Johnson Foundation, hosted a climate change institute for state legislators. The conference covered many issues including understanding climate change science, the status of relevant technologies, and how other levels of government and various states across the country are responding to climate change. The conference offered attendees a chance to meet experts in fields related to climate change as well as colleagues who are considering climate change issues throughout the nation.


November 29, 2006

Dinner Keynote Speaker

  • An Alaskan Perspective on Climate Change - Reggie Joule, State Representative, Alaska
November 30, 2006

Climate Change 101

  • Jerry Mahlman, Senior Research Associate, Institute for the Study of Society and the Environment and the National Center of Atmospheric Research

Technology Update

  • M. Granger Morgan, Professor and Department Head, Department of Engineering and Public Policy, Carnegie Mellon University (pdf)
  • Patrick Hughes, Building Technologies Integration Manager, Engineering Science and Technology Division, Oak Ridge National Laboratory (pdf)
  • Sally Benson, Earth Sciences Division, Lawrence Berkeley National Laboratory (pdf)
  • Keith Paustian, Professor of Soil and Crop Sciences, Natural Resource Ecology Laboratory, Colorado State University (pdf)
  • David Greene, Corporate Fellow, Oak Ridge National Laboratory (pdf)

Business Perspectives

  • Lewis L. Falbo, Director, Worldwide Safetey, Health, and Environmental Operations, S.C. Johnson & Son, Inc. (pdf)
  • Barbara J. Swan, Executive Vice President and General Counsel, Alliant Energy (pdf)

Keynote Speaker

  • A Wisconsin Perspective on Climate Change - Robert W. Wirch, State Senator, Wisconsin
December 1st, 2006

What Are Other Countries Doing?

  • Elliot Diringer, Director of International Strategies, Pew Center on Global Climate Change (pdf)
  • James Reilly, Senior Energy and Environment Advisor, British Embassy (pdf)

What Are Local Governments Doing?

  • Julie Rosenberg, State and Local Capacity Branch, United States Environmental Protection Agency (pdf)

Next Steps for States

  • Judi Greenwald, Director of Innovative Solutions, Pew Center on Global Climate Change (pdf)
  • Paul Pinsky, State Senator, Maryland

Congressional Briefing Series on Science and Impacts: South American Glacier Loss

Promoted in Energy Efficiency section: 
Two leading experts, Dr. Mathias Vuille and Mr. Walter Vergara, will present the state of knowledge regarding the science and impacts of mountain glacier loss in tropical South America, with special focus on the Andes Mountains of Peru, where glacier retreat is particularly advanced.

October, 20, 2006

The tropical Andes is one of the regions of the globe where recent climate change is most evident.  Andean glaciers are receding rapidly, with potentially severe consequences for the availability of water for drinking, irrigation, mining, and hydropower. Climate models predict an additional warming of 7-9 °F in the region if atmospheric carbon dioxide doubles from pre-industrial levels by the end of this century. Some glaciers are already destined to disappear completely; for many more, the threshold for disappearance will be reached within the next 10 to 20 years unless conditions change quickly.

Rapid glacier retreat places in doubt the sustainability of current patterns of water use and ultimately the viability of the economies and ecologies of the Andes.  The changes induced by tropical glacier retreat constitute an early case of the need for adaptation and therefore an example of the impacts caused by climate change.

Two leading experts, Dr. Mathias Vuille and Mr. Walter Vergara, will present the state of knowledge regarding the science and impacts of mountain glacier loss in tropical South America, with special focus on the Andes Mountains of Peru, where glacier retreat is particularly advanced.

Mathias Vuille, Ph.D.
University of Massachusetts, Amherst
Dr. Vuille Research Associate Professor at the Climate System Research Center, Department of Geosciences, University of Massachusetts Amherst.  His research interests are in tropical climatology and paleoclimatology, with particular interest in linking observed modern climate dynamics to paleoclimatic interpretation of proxy data.  He is the lead investigator on a research project funded by the National Science Foundation to investigate the "Impact and consequences of predicted climate change on Andean glaciation and runoff."  He has published more than 40 peer-reviewed papers on paleoclimate and glaciology.  Dr. Vuille earned his M.S. and Ph.D. degrees from University of Bern, Switzerland.

Walter Vergara
The World Bank
Mr. Vergara is Lead Engineer in the Environmentally and Socially Sustainable Development Department of the World Bank’s Latin America and Caribbean Regional Office.  Mr. Vergara works on climate change issues and has participated in development of the carbon finance portfolio in the region, as well as initiatives on adaptation to climate change, transport and climate change, air quality, application of the Clean Development Mechanism (CDM) to wastewater, solid waste management, and renewable energy.  He is the author of four books and numerous technical articles, and currently manages an extensive portfolio of climate initiatives in the region.  Mr. Vergara is a chemical engineer and graduate of Cornell University in Ithaca, New York, and the Universidad de Colombia in Bogotá.

Jay Gulledge, Ph.D.
Pew Center on Global Climate Change
Dr. Gulledge is Senior Research Fellow for Science and Impacts at the Pew Center on Global Climate Change. He serves as the Center’s in-house scientist and coordinates its work to communicate the state of knowledge on the science and environmental impacts of global climate change to policy-makers and the public. He is also an adjunct Associate Professor at the University of Wyoming, home to his academic research on the carbon cycle. He has published more than a dozen refereed journal articles on microbial ecology and biogeochemical cycling of atmospheric greenhouse gases, and serves as an associate editor of Ecological Applications, a peer-reviewed journal published by the Ecological Society of America. Dr. Gulledge earned a PhD in Ecosystem Sciences from the University of Alaska Fairbanks.

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