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Interpretation of high projections for global-mean warming
1National Center for Atmospheric Research, Boulder, CO 80307, USA. wigley@ucar.edu
Science (New York, N.Y.)
|July 21, 2001
Summary
The latest climate change projections show a likely global warming of 1.7 to 4.9 degrees C by 2100 without mitigation policies. Extreme high or low warming scenarios are improbable, according to new analysis.
Area of Science:
- Climate science
- Environmental science
- Atmospheric science
Background:
- The Intergovernmental Panel on Climate Change (IPCC) released its Third Assessment Report (TAR) with updated global-mean warming projections.
- The TAR's projected warming range (1.4–5.8°C) is higher than previous IPCC assessments.
Purpose of the Study:
- To interpret the new IPCC TAR warming range probabilistically.
- To quantify uncertainties in climate projections, including emissions, climate sensitivity, carbon cycle, ocean mixing, and aerosol forcing.
Main Methods:
- Probabilistic analysis of IPCC TAR warming projections.
- Accounting for key climate system uncertainties.
Main Results:
- The probabilities of warming values at the extreme high and low ends of the TAR range are very low.
- The 90% probability interval for global-mean warming from 1990 to 2100, without climate-mitigation policies, is 1.7°C to 4.9°C.
Conclusions:
- The most probable range for future global warming is narrower than the full TAR range suggests.
- Urgent climate change mitigation policies are crucial to avoid the upper bounds of projected warming.
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