General circulation models predict that greenhouse gas induced global warming will be amplified in the Arctic as a result of temperature-albedo feedback. Whilst recent observations of decreasing Arctic sea ice extent are consistent with this scenario, the possibility that such a trend is attributable to local effects at the ice margins rather than to atmospheric warming cannot be dismissed. In the absence of direct air temperature measurements, warming over Arctic sea ice may be inferred from an increasing duration of the summer melt season. Analysis presented here of the dates of spring melt and autumn freeze-up observed over a large fraction of perennial Arctic sea ice using passive microwave data from the SMMR and SSM/I from 1979 to 1996 reveals an increase of 5.3 days (8%) per decade in the number of melt days per summer. ¿ 1998 American Geophysical Union