As these cumulus convective clouds grow taller, water droplets inside them collide and combine into raindrops that either fall out of the cloud or continue rising until they freeze into ice crystals forming cirrus clouds. The researchers noticed that when the temperature of the sea was rising, the coverage of cirrus clouds decreased, allowing the release of more infrared energy into space. This had the effect of cooling the ocean. More of the cloud droplets form raindrops and fewer are left in the cloud to form ice crystals. As a result, the area of cirrus cloud is reduced.
Clouds play a critical and complicated role in regulating the temperature of the Earth.
Thick, bright, watery clouds like cumulus shield the atmosphere from incoming solar radiation by reflecting much of it back into space. Thin, icy cirrus clouds are poor sunshields but very efficient insulators that trap energy rising from the Earth's warmed surface. A decrease in cirrus cloud area would have a cooling effect by allowing more heat energy, or infrared radiation, to leave the planet. If the effect is found to be widespread, the Earth may be much less sensitive to the warming effects of rising greenhouse gas concentrations in the atmosphere. The researchers estimate that this effect could cut by two-thirds the projected increase in global temperatures initiated by a doubling of carbon dioxide in the atmosphere.