Interpretation of high projections for global-mean warming
T. M. L. Wigley
National Center for Atmospheric Research
S. C. B. Raper
Climatic Research Unit, University of East Anglia, Norwich, NR47TJ,
U.K., and Alfred-Wegener-Institut for Polar and Marine Research, D-27515
Bremerhaven, Germany
The Intergovernmental Panel on Climate Change (IPCC) has recently released its
Third Assessment Report in which new projections are given for global-mean
warming in the absence of policies to limit climate change. These projections
are based on a new set of emissions scenarios, and incorporate recent advances
in the science of climate change. The full warming range over 1990-2100,
1.4-5.8oC, is substantially higher than the range given previously in
the IPCC Second Assessment Report, viz. 0.8-3.5oC. Here we interpret
the new warming range in probabilistic terms accounting for uncertainties in
emissions, the climate sensitivity and the carbon cycle. We show that the
probabilities of warming values at both the high and low ends of the range are
very low, and that the most likely warming in the absence of climate mitigation
policies is in a more restricted range, 1.7-5.0oC with 90%
confidence.
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Hongjun Zhang:
zhangho@ucar.edu