Detection of Human Influence on 20th Century Precipitation Trends


Human influence on climate has been detected in surface air temperature, sea level pressure, free atmospheric temperature, tropopause height and ocean heat content. Human-induced changes have not, however, previously been detected in precipitation at the global scale, partly because changes in precipitation in different regions cancel each other out and thereby reduce the strength of the global average value. In a study published in this week’s issue of Nature, and sponsored in part by the Office of Science, BER, the authors demonstrate anthropogenic forcing has had a detectable influence on observed changes in average precipitation within latitudinal bands, and that these changes cannot be explained by internal climate variability or natural forcing. The authors estimate that anthropogenic forcing contributed significantly to observed increases in precipitation in the Northern Hemisphere mid-latitudes, drying in the Northern Hemisphere subtropics and tropics, and moistening in the Southern Hemisphere subtropics and deep tropics.


Zhang, Xuebin, F.W. Zwiers, G.C. Hegerl, H.F. Lambert, N.P. Gillett, S. Solomon, P.A. Stott, and T. Nozawa. 2007. “Detection of human influence on twentieth-century precipitation trends,” Nature 448, 461-466.