The doubling of the moisture content in the stratosphere over the last 50 years was caused, at least in part, by tropical biomass burning, a Yale researcher has concluded from examining satellite weather data.

"In the stratosphere, there has been a cooling trend that is now believed to be contributing to milder winters in parts of the northern hemisphere; the cooling is caused as much by the increased humidity as by carbon dioxide," said Steven Sherwood, assistant professor of geology and geophysics whose article appears in this month's issue of the journal, Science. "Higher humidity also helps catalyze the destruction of the ozone layer."