While the summer sea ice extent has beendecreasing in the Artic by 8% per decade for the past 30 years,the ice extent has actually increased slightlyin the Antarctic. Ice thickness changes are less well known. In the central Arctic, sea ice thinned by 43%between 19581976 and 19931997. In the Transpolar Drift, level ice thickness decreased by 20% between1991 and 2001. The interpretation of those changes is difficult, however, as both air and water temperatures,as well as the direction and strength of the wind-driven ice drift, have a strong impact on ice thickness.