One of the most complicated problems in climate science is slowly but surely becoming a little better understood. The influence of a warming climate on clouds -- and the impact of clouds on climate -- is one of those puzzles that has had climate modelers scratching their heads for years.
There are different daytime and nighttime responses to clouds as the Earth heats up and then cools down. There are different inputs from different cloud types, based on their height and structure in the atmosphere. There are global net effects and different local and regional ones as well. But the truth is, because clouds are often relatively small and ephemeral features, the big global models are almost blind to their existence.
Led by atmospheric scientist Evgueni Kassianov, a research team from the Department of Energy's Pacific Northwest National Laboratory took a bunch of ordinary summer days in the flat landscape of Oklahoma and some everyday white billowy cumulus clouds and examined in unprecedented detail the sunlight they were casting about.
The clouds cast cooling shadows irregularly over the land, of course, and their bright white surfaces reflected some sunlight back into space, another cooling effect. But their water droplets and aerosols scattered sunlight between their irregular surfaces and down across other clouds' shadows -- causing a significant warming effect.
Sunlight scattered from cumulus clouds accounted for roughly 15-20 percent of the sun's heat reaching the ground on a cloudy day.
While the net effect of clouds on sunlight reaching the ground is usually negative on cloudy days, Kassionov said the study "demonstrated that for days with cumulus clouds there are many cases (about 20 percent of total population) with positive cloud effect. And this effect is associated with cloud-scattered sunlight."
"We all know that we can still get sunburned on cloudy days," said Kassianov. "This explains why."
by "environment clean generations"
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