Global Cooling during 2007:  An Examination of the Water-Vapor Climate Feedback

Andrew Dessler, Department of Atmospheric Sciences, TAMU

Abstract

Between 2003 and 2008, the global-average surface temperature of the Earth varied by 0.6°C.  We have analyzed the response of atmospheric water vapor to these variations. Over most of the troposphere, specific humidity increased with increasing global average surface temperature, although some regions showe dthe opposite response. Relative humidity increased in some regions and decreased in others, with the global average remaining nearly constant at most altitudes. The water-vapor feedback implied by these observations is strongly positive, with an average magnitude of 2.04 W/m2/K, similar to that simulated by climate models.  The magnitude is also similar to that obtained if the atmosphere maintained constant RH.  The existence of a strong and positive water-vapor feedback means that projected business-as-usual greenhouse-gas emissions over the next century are virtually guaranteed to produce warming of several degrees Celsius.