for National Geographic News
Human activity has long made the bedroom a hot and steamy place. Now, less sexy activities like burning coal and oil—major contributors to global warming—are making the whole planet steamier, a new study says.
Scientists expect the rising humidity to cause heavier rains, stronger hurricanes, and increased human heat stress. (Get the basics on global warming.)
Climate scientists have long predicted that a warmer world will allow more water to evaporate, thus making the planet more humid.
Indeed, several studies have shown trends of increasing surface humidity around the planet, but until now scientists were uncertain what was driving the trend.
The new study combined a fresh data set of surface humidity with climate models, "and actually attribute[s] those trends to human influence," said study co-author Nathan Gillett, a climate scientist at the University of East Anglia in Norwich, England. (Related news: "Global Warming "Very Likely" Caused by Humans, World Climate Experts Say" [February 2, 2007].)
He and his colleagues report the findings in tomorrow's issue of the journal Nature.
Stormy, Steamy Future
Climate models predict that increased water vapor in the atmosphere will lead to heavier rains and raise the maximum potential intensity for hurricanes, Gillett noted.
"In heat waves, if the humidity is higher, then that results in larger heat stress on humans," he said.
And increased water vapor will accelerate the warming, said Benjamin Santer, a climate modeler at the Department of Energy's Lawrence Livermore National Laboratory in California who was not involved in the study.
"Our best understanding is as we increase greenhouse gases and warm the atmosphere, we increase the atmosphere's capacity to hold moisture. And water vapor is in itself a potent greenhouse gas.
"Therefore you accelerate the warming," he said.
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