PerspectiveClimate Change

Constraining Cloud Feedbacks

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Science  09 Nov 2012:
Vol. 338, Issue 6108, pp. 755-756
DOI: 10.1126/science.1231083

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Despite decades of improvements in computer models of Earth's climate, estimates of the climate sensitivity—the change in global average surface air temperature in response to a doubling of carbon dioxide concentration—remain uncertain (1). Much of the uncertainty results from radiative feedbacks that amplify or dampen climate changes. Particular attention has been given to the cloud feedback. Global warming is expected to change the cloud cover, but these changes and their effects on global temperature are very difficult to predict. On page 792 of this issue, Fasullo and Trenberth (2) present an observational test of the cloud feedback based on satellite measurements of relative humidity (RH) in cloud-free subtropical regions. The authors focus on environmental conditions that are easier to observe than the cloud properties themselves.