Geophys. Res. Lett. 35, L20704 (2008)


Scientists have obtained the most detailed ever measurements of atmospheric water vapour — an abundant greenhouse gas — from unique sensors aboard a NASA satellite. The observational data validate what scientists have inferred from climate models for some time — that the heat-trapping properties of water vapour could double the effect of greenhouse warming from other sources such as carbon dioxide.

A team led by Andrew Dessler at Texas A&M University used data measured by the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite from 2003 to 2008 to calculate the amount of water vapour throughout the lowest 10 miles of the atmosphere. AIRS is the first instrument capable of differentiating the amount of water vapour at different levels in the atmosphere, enabling these detailed observations. Dessler and colleagues combined the satellite data with global-average surface temperature readings for the same period to determine how water vapour both affects, and responds to, temperature. They found that if the Earth warms by 1°C, rising humidity will trap an additional 2 Watts of energy per square metre, similar to the estimates simulated by climate models.

The results suggest that the feedback effect of water vapour on climate warming is both large and positive.