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.