Water high in Earth's atmosphere said source of climate warming

Water vapor in Earth's stratosphere contributes to warmer temperatures and likely played an important role in the evolution of Earth's climate, researchers say. Scientists at Texas A&M University, working with other researchers, report they've found increased surface temperatures, such as from the addition of carbon dioxide to the atmosphere, lead to increased humidity in the stratosphere, and because stratospheric water vapor acts as a greenhouse gas, this leads in turn to additional warming. Such a cycle is commonly referred to as a climate feedback. The stratosphere is the layer of the atmosphere generally considered to stretch from 30,000 feet to 160,000 feet above the Earth's surface. "We find that this stratospheric water vapor feedback is probably responsible for 5-10 percent of the total warming you get from adding carbon dioxide to the climate," A&M atmospheric scientist Andrew Dessler explained. "While it's not really surprising that this process is going on, we were surprised at how important the process is for our climate system." Some climate models already include this process, but while some models predict large increases in stratospheric humidity others don't, the researchers say. "It's clear to us that, if models want to make accurate predictions of climate change, they should get stratospheric water vapor right," study co-author Sean Davis of the University of Colorado at Boulder said. "A better understanding of the stratospheric water vapor feedback could help explain some of the spread among predictions of future climate change from different models."