Decadal variability in the lower-tropospheric lapse rate.

Climate models predict that the surface and the troposphere will warm in re sponse to increasing concentrations of greenhouse gases. Both have warmed s ince 1958, but radiosonde and satellite observations suggest that the atmos phere has not followed the strong surface warming over the last 20 years es pecially in the tropics. In the light of this, we investigate observed trop ical lower-tropospheric lapse rate variability on decadal and longer time s cales using radiosonde data since 1958. We find evidence of interdecadal ch anges in the surface minus 700 hPa temperature difference with reduced valu es throughout the tropics in the late 1970s to mid 1980s followed by an inc rease to the present day. This ubiquitous signal implies that the lapse rat e changes are real rather than artefacts of the radiosonde record. Thus, re al variability may explain much of the discrepancy in tropical temperature trends.