IN 1978 Mercer(1) discussed the probable effects of climate warming on
the Antarctic Ice Sheet, predicting that one sign of a warming trend
in this region would be the retreat of ice shelves on the Antarctic Pe
ninsula. Analyses of 50-year meteorological records have since reveale
d atmospheric warming on the Antarctic Peninsula(2,3), and a number of
ice shelves have retreated(4-8). Here we present time-series of obser
vations of the areal extent of nine ice shelves on the Antarctic Penin
sula, showing that five northerly ones have retreated dramatically in
the past fifty years, while those further south show no clear trend. C
omparison with air-temperature data shows that the pattern and magnitu
de of ice-shelf retreat is consistent with the existence of an abrupt
thermal limit on ice-shelf viability, the isotherm associated with thi
s limit having been driven south by the atmospheric warming. Ice shelv
es therefore appear to be sensitive indicators of climate change.