Decadal variability in the lower-tropospheric lapse rate.

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