Should we expect clouds to look different as global warming proceeds?
鈥� The role of clouds and oceans are the two biggest uncertainties in mathematical models of the climate. But one would expect a warmer world to lead to an enhanced hydrological cycle, with more evaporation and an increase in globally averaged precipitation from more rain-bearing clouds.
The physics is complicated as clouds can simultaneously cool the planet through reflection of solar radiation and warm it by absorption of infrared radiation emitted from Earth鈥檚 surface.
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Whether warming or cooling wins is partly dictated by the altitude at which water vapour condenses or water freezes. Feathery, high-altitude cirrus clouds have a warming effect, so more of these would increase the anthropogenic greenhouse effect. Stratus is the layer of clouds that blankets the whole sky on overcast days 鈥� more of these will reduce any warming. This is partly because they are at low altitude and only slightly cooler than Earth鈥檚 surface.
Mike Follows, Sutton Coldfield, West Midlands, UK
鈥� I suspect the answer is 鈥渘ot particularly鈥�, because clouds are varied and they affect each other鈥檚 appearance. For example, a white cloud shading another equally white cloud can make it look grey or even black, and sunset clouds look golden or red because some of the sunlight they reflect has been filtered by other clouds.
A warmer climate might produce either more or less cloud regionally, with updraught and concentrated wind patterns favouring currently unusual shapes, such as more dramatic cumulus or lenticular clouds, or more rippled bars.
Feathery high-altitude cirrus might become more common, though obscured by lower cloud banks, and if turbulence carries microscopic dust to great altitudes, we might expect more Turner-esque cloudy sunsets, but most such effects would be variants of familiar patterns.
鈥淎 warmer climate might produce more or less cloud with wind patterns favouring unusual shapes鈥�
Of course, if Earth鈥檚 water evaporated to such an extent that our entire atmosphere clouded over 鈥� with the kind of purple cloud ceilings seen over Kansas in tornado weather or the solid black cloud ceilings seen on Venus 鈥� we would notice. But plenty of other concerns would distract our attention before that happened.
Jon Richfield, Somerset West, South Africa
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