Science Briefs

Cloud Climatology

How Clouds Might Change with Global Warming

Although simple relations may hold between climatic conditions and the radiative properties of certain kinds of cloud, predicting how the global distribution of various kinds of clouds would change with global warming is complicated by the interaction of regional wind systems. Consider the roles of clouds in seasonal climatic change. In the midlatitudes winter brings a substantial decline in solar heating, yet the corresponding drop in air temperature near the surface is between 70 and 80 percent less than what the decline in solar heating would seem to imply. More abundant winter clouds, with slightly higher tops, trap heat.

In the tropics, despite significantly greater cloud cover in the rainy season, there is only a small seasonal variation in surface temperature. In part the variation is small because the effects of tropical clouds on thermal and solar radiation nearly cancel one another, but even more important is the controlling influence of heat transports by atmospheric winds.

The quest for more data about clouds and climate continues in parallel with the refinement of climate models. It is a slow-going process: each new piece of information must be incorporated throughout. With certain findings the models themselves may have to be reformulated. But the result should be an increasingly precise understanding of how sensitively the clouds change in response to external forces and what effect those changes would have on global warming. One must hope that the model building and data collection will lead to an understanding of climatic change before that change comes to pass.