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Will Clouds Keep a Lid on Climate Change?

(Originally published on's Ecocentric blog)

Unique clouds known as hole-punch clouds, such as this one, can result when aircraft fly through clouds containing supercooled water droplets.
Photo credit: NCAR

Clouds cool the planet by reflecting sunlight back into space. Clouds warm the planet by trapping heat. Both statements can be true, depending on what kind of clouds you're talking about.

Add to that the fact that some types of clouds might increase in a warming world and some might decrease, and it becomes clear why clouds are such a headache for people trying to project where temperatures are likely to go over the next century. If the net effect is to trap heat, clouds will act as a positive feedback, amplifying the underlying warming from greenhouse gases. If the main effect is to reflect sunlight, their feedback will be negative, tamping the warming down.

So far, computer climate models generally agree that cloud feedbacks will be positive, but they don't agree on how much — and even that general agreement isn't a guarantee. Models are constructed differently, but, says Andrew Dessler, an atmospheric scientist at Texas A&M University, "they share DNA. One's a baboon and one's an organgutan. They could all agree and the answer could still be wrong."

It's also hard to make actual measurements of what clouds do in the real world, because their structures are so complex and varied, and they change so rapidly (that's why they're hard to model in the first place). So Dessler came at the problem in an entirely different way: he analyzed cloud feedbacks by looking at everything but clouds. The result, described in a paper just published in Science: overall, clouds are likely to amplify warming — or at the very least, to hold it back by the tiniest amount.

Read more at Time's Ecocentric blog


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