Atmospheric Science

Certainly Warmer

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Science  18 Oct 2002:
Vol. 298, Issue 5593, pp. 497
DOI: 10.1126/science.298.5593.497d

How much global warming occurs as a result of human additions of radiatively active agents like greenhouse gases and sulfate aerosols depends on how sensitive climate is to these species. “Climate sensitivity” is a measure of how much global average surface temperature can be expected to change in response to an increase in radiative forcing equivalent to that which would be produced by doubling the concentration of atmospheric CO2 from pre-industrial levels (280 ppm). The best estimates of climate sensitivity suggest that its value lies between 1.5° and 4.5°C, but they do not generally include any information about how certain those bounds are. Gregory et al. use a model that includes observations of temperature changes in the ocean and the atmosphere to evaluate the probable lower bound of climate sensitivity, and find that there is a 95% chance that it is at least 1.6°C. Thus, unless greenhouse gas emissions are abated, substantial climate change will occur in response to warming during the next century. The large uncertainty in the amount of radiative forcing prevents the determination of an upper bound for climate sensitivity. — HJS

J. Clim.15, 3117 (2002).

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