Influence of Patterns of Climate Variability on the Difference between Satellite and Surface Temperature Trends

Abstract

During the past 20 years, satellite measurements of tropospheric temperature have shown a slower rate of global temperature increase than surface air temperature, yielding an increase in the surface to lower-troposphere lapse rate of 0.12 K decade?1 from 1979 to August 2001. This increase in lapse rate was preceded by a decrease over the previous 15-yr interval. The influence of patterns of climate variability on the global- and hemispheric-scale lapse rate was investigated, based on observations of surface and tropospheric temperature from satellite, radiosonde, surface air, and sea surface data. It was found that a substantial fraction of winter-to-winter lapse rate variability in the Northern Hemisphere mid- to high latitudes is dynamically induced. In the Tropics and subtropics, a distinctive signature of El Niño is apparent in the interannual variations in lapse rate. A small additional amount of month-to-month variability can be attributed to zonally symmetric circulation changes at lower latitudes that are linearly independent of ENSO. Trends in these patterns can account only for a small fraction of the observed trend in lapse rate. The combination of strong surface warming and very small tropospheric warming in the Tropics and subtropics over the recent 21 yr is extremely unusual in the context of data from a coupled climate model. The same can be said of the observed trends of the previous 15 yr. Thus, it is concluded that structured patterns of climate variability account for much of the variability in lapse rate on monthly and interannual timescales, but not on interdecadal timescales.