Some climate forecasts might be exaggerating estimations of global warming, according to a study funded by NASA.

NASA says the models possibly are overestimating the amount of water vapor entering the atmosphere as the Earth warms.

Study used satellite data from 6-9 miles above Earth (NASA graphic)

Because water vapor is the most important heat-trapping gas in the atmosphere, the calculations consequently would overestimate future temperature increases.

The study, published in the March 15 issue of the American Meteorological Society’s Journal of Climate, was conducted by Ken Minschwaner, a physicist at the New Mexico Institute of Mining and Technology, Socorro, N.M., and Andrew Dessler, a researcher with the University of Maryland, College Park, and NASA’s Goddard Space Flight Center, Greenbelt, Md.

The researchers used satellite data on water vapor in the upper troposphere, about 6-9 miles above Earth.

The theory many scientists work with says the Earth warms in response to human emissions of greenhouse gases such as carbon dioxide, causing more water to evaporate from the ocean into the atmosphere.

But the existence and size of this effect, known as “positive water vapor feedback,” have been contentiously argued for several years, NASA noted.

The new study indicated an increase in water vapor but not as high as many climate-forecasting computer models have assumed.

“One of the responsibilities of science is making good predictions of the future climate, because that’s what policy-makers use to make their decisions,” Dessler said. “This study is another incremental step toward improving those climate predictions.”

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