科学美国人60秒:Air Pollution Gives Storm Clouds a Stronger, Longer Life

Summertime in India can be unbearably hot. "And the first thing you want, is, get me some clouds, to cool down." Sudip Chakraborty grew up there, in Kolkata. Where he developed a childhood fascination with clouds. "And in like three or four months during monsoon time, it was like, rain, rain, all rain. I like the clouds, the rain, the strength they have. Their importance. It's something like I love them, you know?" 

His love of water vapor led him to study clouds, as a climate scientist at UC Davis. Clouds, he says, are built of tiny aerosol particles of dust or pollution from fossil fuel burning that suck up water vapor. "Now these cloud particles with time they combine with each other, and become big. And when they become big, due to gravity, they fall out, and we call it rain."

Chakraborty studied that process in large thunderstorm systems over the tropics, using data from geostationary and circumpolar satellites. And he found that when more aerosols seed the air, like in places with lots of industrial or agricultural pollution, the same amount of water vapor gets absorbed by a larger number of aerosols… meaning tinier-than-usual cloud particle size. 

That's important, because "it makes the cloud bigger and larger and stronger and live longer." Three to 24 hours longer. And "it can produce more extreme storms when the rain finally comes." The study is in the Proceedings of the National Academy of Sciences. [Sudip Chakraborty et al., Relative influence of meteorological conditions and aerosols on the lifetime of mesoscale convective systems]

A silver lining: he says longer-lasting clouds also reflect more light back into space, which could end up cooling the planet—and at least tap the brakes on climate change.

—Christopher Intagliata