Scientists at the University of Chicago reported Wednesday they have confirmed for the first time that water vapor from the oceans can amplify global warming caused by man-made gases and perhaps could trigger a "super-greenhouse" effect above the warmest part of the Earth's oceans.
The scientists, who used temperature and radiation measurements from satellites, buoys and ocean-going ships, said they confirmed computer models indicating that as more water vapor accumulates, more energy is trapped on Earth. The study, published today in the journal Nature, also suggests that above the warmest oceans--where the water vapor would be greatest--the trapping of gases is increased at a much higher rate than models had predicted.
"I think this study is important because it offers strong support to greenhouse effect theories," said Veorabhadran Ramanathan, one of the nation's leading climate experts, who did the study with his graduate student, Ameet Raval. "Frankly, I didn't expect that our work would support the theories so strongly."
The study, coming at a time of increasing debate over the accuracy of global warming predictions, represents the most extensive testing yet of computer models.
The confirmation of what scientists describe as an essential feature of the greenhouse theory is likely to instill more public confidence in such computer modeling, but it is not expected to quell debate among scientists over the amount of warming that will occur and the precise role of industrial gases.
Scientists believe that carbon dioxide and other gases trap heat from the sun in the Earth's atmosphere, much like the panes of a greenhouse. Eventually, such trapping could produce major changes in climate, triggering more droughts, hurricanes or other cataclysmic events.
Ramanathan, interviewed by telephone, noted that relatively little warming is caused by such industrial gases as carbon dioxide. But theories developed over many decades show that atmospheric warming caused by such gases would be exaggerated by water vapor, "the most powerful greenhouse gas," coming primarily from evaporation of the Earth's oceans.
"The basis of the theory was simply pointing out that we all know from common experience that when it gets hotter, it gets more humid, and when it gets colder, it gets dry," Ramanathan said. "What is new in this study is that we went beyond that and computed the actual trapping" of the sun's infrared energy in the Earth's atmosphere.
