For each degree in Celsius that the ocean surface temperature rises, the ratio of cirrus cloud area to cumulus cloud area over the ocean dropped by 17-27 percent. The authors of the study believe that higher ocean surface temperatures directly cause the decline in cirrus clouds by changing the dynamics of cloud formation and rainfall. When these cumulus convective clouds grow taller, cloud water droplets bump into one another and combine into raindrops and fall out of the cloud or continue to rise until they freeze into ice crystals and form cirrus clouds. 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 are critically important 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 extremely 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. The researchers believe this effect could cut the projected increase in global temperatures initiated by a doubling of carbon dioxide in the atmosphere by two thirds. The American Meteorological Society is the nation's leading professional society for scientists in the atmospheric, oceanic, and related sciences.