Wetter atmosphere linked to warming

MIAMI — Scientists analyzing 20 years of satellite data have confirmed an atmospheric spike in a prime fuel behind global warming, according to a study in the current issue of the journal Science.

The finding is important because it used real-world readings to verify what computer simulations have predicted is happening in a key zone of Earth's atmosphere, said Brian Soden, a University of Miami scientist and lead author of the study.

It's getting wetter up there, which means it's getting hotter down here.

"This is one of the first studies to show it is increasing at the same rate as the models suggest," said Soden, an associate professor of meteorology at the University of Miami's Rosenstiel School of Marine & Atmospheric Science.

Researchers did not focus on pollutants typically blamed for global warming but on water vapor, which climatologists recognize as the "dominant greenhouse gas," Soden said.

Water vapor occurs naturally, driving the rain cycle and keeping the planet from being too cold, he said. But as global temperatures rise — from carbon-dioxide emissions from burning fossil fuel, other industrial emissions and deforestation — moisture in the atmosphere builds up with it, forming a blanket that further raises temperatures, Soden said.

"The CO2 [carbon dioxide] is the trigger," he said, "and water vapor acts as an amplifier."

Models suggest the impact is profound. Current projections predict average global temperatures rising five degrees Fahrenheit by century's end, Soden said. Without the water-vapor increase, he said, models predict a 2-degree rise.

Though the study is being published in one of the world's most-respected academic journals, Soden did not anticipate it would necessarily sway skeptics. The Bush administration, for one, has questioned global-warming theories, and critics, including some scientists, think the effect is cyclical and not linked to human activity.

"I don't think there will ever be a single study that provides the smoking gun," he said. "It is all incremental evidence that accumulates. The consensus has developed toward global warming. What role this study will play in convincing people who are still skeptical, that's impossible for me to say."