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Subject: Clouds

How much would clouds affect the current predictions of global warming? the current global warming models that i am aware of do not include clouds. I think that as the Earth would warm, more clouds would develop that would reflect more light, so clouds would ack as a safety valve for heat, am I right, is there any data?

    You are right: clouds do play a role in global heat retention. In a sense, cloud cover is only one of the aspects of light and heat reflectivity of Earth known as "albedo". Many aspects of the albedo's supposed response to global warming or cooling, and its mitigating or exagerating effects, are very poorly understood. There are a large number of feedbacks between various surfaces on Earth that contribute to our albedo. Clouds do in fact reflect more light back to space (and thus incident heat) than does blue sky. However, the increased water vapor required to make extra clouds will absorb more infrared radiation that would have otherwise made it out of our atmosphere and into space, thus potentially negating their own beneficial effects. Other surfaces that may contribute or detract from the intensity of our albedo are forest cover vs sparsely vegetated terranes (the latter reflect more light than the former) and the proportion of ice cap to liquid water on the surface of the Earth. Both are supposed to be affected by changing CO2 levels and potential warming or cooling of the Earth in response to this increase, yet predicting how much the albedo will change and what overall effect this has on a) mean global temperature AND b) the distribution of heat on the planet, is very difficult. There are climate models that take clouds into effect. In fact, one very prominent climatologist, by the name of Ramanathan has recently written a number of papers on what he believes to be the moderating effects of clouds during periods of global warming.

Dr. Ken Rubin, Asst. Professor
Department of Geology and Geophysics
University of Hawaii, Honolulu, HI 96822


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