"The bottoms of the clouds rise with warmer temperatures, while the top of the cloud stays the same so the clouds become thinner, " explained Del Genio.

CNN: Clouds' role in global warming studied

Del Genio studied more than 3, 000 individual cloud "snapshots" collected between 1994 and 1997 at the Department of Energy's Atmospheric Radiation Measurement Southern Great Plains field station.

CNN: Clouds' role in global warming studied

"The minimum amount of warming predicted by scientists - 3 degrees Fahrenheit - should be increased by at least 1 F as a result of the new findings, " said Del Genio.

CNN: Clouds' role in global warming studied

And, Del Genio disputes a theory that rising carbon dioxide levels would have only a slight impact on global temperatures because the theory doesn't take into account real world cloud behavior.

CNN: Clouds' role in global warming studied

However, after three years of observations of low stratus, cumulus and stratocumulus clouds over land, Anthony Del Genio of NASA's Goddard Institute for Space Studies discovered that when air temperatures were higher, clouds were thinner and thus less capable of reflecting sunlight.

CNN: Clouds' role in global warming studied