Arctic Sea Ice Changes under Global Warming

In this review we summarise the latest results on the rapid changes that are occurring to Arctic sea ice thickness and extent, the reasons for them, and the methods being used to monitor the changing ice thickness. Arctic sea ice extent has been reducing at a relatively modest rate of 3-4% per decade (annually averaged) but since 1996 this has speeded up to 10% per decade and in summer 2007 there was a massive collapse of ice extent to a new record minimum of only 4.1 million sq km. Thickness has been falling at a more rapid rate (43% in the 25 years from the early 1970s to late 1990s) with a specially rapid loss of mass from pressure ridges. The summer 2007 event may arise from an interaction between the long-term retreat and more rapid thinning rates. We review thickness monitoring techniques which show the greatest promise on different spatial and temporal scales, and for different purposes. We show results from some very recent work from submarines.