The possibility of a global warming induced by increasing levels of atmospheric carbon dioxide has led to increased interest in monitoring global temperatures. Polar regions are of particular interest because temperature changes may be amplified in these regions by the complex feedback mechanisms which operate in the atmosphere-ice-ocean system1. Monthly mean station surface air-temperature data have been objectively analysed to produce time series of temperature anomalies for the Northern Hemisphere (1881-1980)2,3, the Arctic (1881-1980)4 and the Antarctic (1957-82)5. A comparison of recent changes in these three regions is made here. Previously published series have been updated to 1982. Changes in Arctic temperatures since about 1966 and in Antarctic temperatures since 1960 show significant warming trends. For the period from 1975 to 1982 there is a high positive correlation between temperature variations in the Arctic and Antarctic.