Cloud Cover and Climate Change

Cloud Cover and Climate Change is a short article in today's The Washington Post (scroll down to the second piece in this "Science Digest") that suggests global warming may wind up taking temperatures to the very top of the range predicted by various climate models.

Climate-change modeling has offered a range of possible temperature increases by the end of this century. In the aggregate, the predictions are that the earth will warm by 1.5 to 4.5 degrees Celsius, which is 2.7 to 8.1 degrees Fahrenheit, by the end of the 21st century.

Now a study (read its summary here) of the effects of changing cloud cover on climate change and vice versa, published in the July 24 issue of Science, indicates the heat may be turned up by global warming to the upper end of that range. The study finds that global warming does not, as hoped by some, increase low-level clouds in the atmosphere.

If that happened, the increase in cloudiness might reflect sunlight back out to space and help cool things back down. But instead, the study shows, global warming dissipates the cloud cover, lets in more (not less) sunlight, and makes things get even hotter. This is an example of what scientists call "positive feedback," though from the point of view of those worried about climate change, the news is not at all positive.

The study gives credence to Britain's Hadley Centre for Climate Prediction and Research's model — "The only model that passed this test" — as the one most predictive of the results of the study ... and therefore the one most likely to be right about what's in store for us down the road. That model predicts direly that the earth will warm by about 4.5 degrees Celsius by 2100.

The Hadley Centre is an arm of the Met Office, which is the equivalent in Britain of our National Weather Service.

More about the study on cloud cover can be read in this article from Time.com.