Clouds, which act as thermal regulators for Earth, have altered in character and global distribution due to climate change, and could in turn make warming worse, a study said.
A trawl of satellite images has revealed reduced cloudiness in Earth's temperate mid-latitude zones, which lie between the poles and subtropics in both hemispheres, accompanied by a poleward expansion of the subtropical dry zones.
The tops of clouds everywhere rose higher, according to data that stretched over more than two decades from the early 1980s.
"These cloud changes enhance absorption of solar radiation by the Earth and reduce emission of thermal radiation to space," said a statement from the Scripps Institution of Oceanography at the University of California San Diego, which took part in the study.
"This exacerbates global warming caused by increasing greenhouse gas concentration."
Clouds regulate Earth's temperature by reflecting some solar radiation back into space before it can hit the ground, while also acting as a blanket to limit heat loss from the planet at night.