Science
Long-term Trends in Carbon Dioxide and Surface Temperature
As can been seen in this figure, throughout the millennia, there has been a clear correlation between carbon dioxide levels and average global surface temperatures. This provides strong evidence that CO2 is a major driver of global temperatures.
Scientists say the world is entering largely uncharted territory as atmospheric levels of greenhouse gases continue to rise. Today’s carbon dioxide levels are substantially higher than anything that has occurred for more than 400,000 years.
Atmospheric Carbon Dioxide & Global Surface Temperature Trends
The recent increase in concentration of carbon dioxide in the atmosphere is the result of human activities, mainly the burning of fossil fuels. As the concentration of CO2 in the atmosphere has increased, so has the average surface temperature of the Earth.
The relationship between atmospheric CO2 concentration and surface temperature is shown here for the past 130 years.
Source: NASA-GISS, CDIAC, NOAA ESRL
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.
Greenhouse | Chemical Formula | Anthropogenic Sources | Atmospheric Lifetime1(years) | GWP2 (100 Year Time Horizon) |
Carbon | CO2 | Fossil-fuel combustion, Land-use conversion, Cement Production | ~1001 | 1 |
Methane | CH4 | Fossil fuels, | 121 | 25 |
Nitrous | N2O | Fertilizer, | 1141 | 298 |
| Tropospheric Ozone | O3 | Fossil fuel combustion, Industrial emissions, Chemical solvents | hours-days | N.A. |
CFC-12 | CCL2F2 | Liquid coolants, | 100 | 10,900 |
HCFC-22 | CCl2F2 | Refrigerants | 12 | 1,810 |
Sulfur Hexaflouride | SF6 | Dielectric fluid | 3,200 | 22,800 |
Pre-1750 Tropospheric | Current Tropospheric | |
Carbon | 280,0005 | 388,5006 |
Methane | 7007 | 1,870 / 1,7488 |
Nitrous | 2709 | 323 / 3228 |
| Tropospheric Ozone | 25 | 34 |
CFC-12 | 0 | .534 / .5328 |
HCFC-22 | 0 | .218 / .19410 |
Sulfur Hexaflouride | 0 |
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. http://cdiac.ornl.gov/pns/current_ghg.html
Footnotes:
- 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).
- 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.
- 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.
- 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).
- 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.
- 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: http://www.esrl.noaa.gov/gmd/ccgg/trends/index.html#global.
- Pre-industrial concentrations of CH4 are evident in the "1000-year" ice-core records in CDIAC's Trends Online http://cdiac.ornl.gov/trends/atm_meth/lawdome_meth-graphics.html. 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).
- 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.
- 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.
- For SF6 data from January 2004 onward see http://cdiac.ornl.gov/ftp/ale_gage_Agage/AGAGE/gc-ms-medusa/monthly/. For data from 1995 through 2004, see the National Oceanic and Atmospheric Administration (NOAA), Halogenated and other Atmospheric Trace Species (HATS) site at: http://www.esrl.noaa.gov/gmd/hats/airborne/index.html.
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.
Source: NASA-GISS
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.
Impacts
This section depicts observed impacts from the enhanced greenhouse effect.
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| Summer Arctic Sea Ice Decline |
| Late Summer Arctic Sea Ice Decline |
| Drought |
| Extreme Temperature |
 | Summer Minimum Temperature |
| Extreme Precipitation |
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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.
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Greenhouse Gas Emissions by Sector |
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U.S. Trends in Greenhouse Gas Emissions |
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Trends in CO2 Emissions |
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Explore All the Facts & Figures Sections:
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.
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.
| Also, from our FAQs: |
| Global CO2 Flows, Carbon Reservoirs, and Reservoir Changes |
Adaptation to Climate Change: International Policy Options
Adaptation to Climate Change: International Policy Options
Prepared for the Pew Center on Global Climate Change
November 2006
By:
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.
Download entire report (pdf)
Introduction
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).
