Observations show large and coordinated changes are occurring in theArctic climate system. Perhaps the most dramatic of these is a significantdecline in the summer Arctic ice cover. The summer of 2007 wasparticularly striking, being 23% lower than the previous minimum set in2005. Model projections suggest continued and possibly accelerated iceloss into the future.

Here we explore projected changes in Arctic sea ice conditions through the 21st century and how they relate to observed change. Particular attentionis paid to instances of rapid summer ice loss and the mechanisms andfeedbacks that are important in driving that loss. The possibility thatthese simulated rapid ice loss events represent a "tipping point" in thesystem is explored and mechanisms of potential recovery of the perennialice cover are addressed. Finally we discuss the implications of the lossof seasonal ice cover for other aspects of the climate system.