 Summary : Mass changes in the Antarctic and Greenland ice sheets are of considerable interest because of their sensitivity to climate change, their contributions to sea level change, and the likelihood of changes in the rates of mass loss (or gain) with climate warming. New observations of ice sheet mass balance (growth or shrinkage) primarily by satellite laser altimetry (NASA’s ICESat) and radar altimetry (ESA’s ERS) are showing details of the spatial distributions of mass losses and gains over the ice sheets, and the changes that have taken place since the 1990's. Ice sheets respond to climate change by changes in the mass input at the surface from snow accumulation (precipitation), in the mass output from melting at the margins, and the ice velocity and discharge of icebergs into the ocean. In the last decade, the changes in Greenland are different from the changes in much of the Antarctic, because Greenland lies in a warmer climate and the climate warming in the Arctic is larger that the warming in the Antarctic. The changes are also different than predictions from climate and ice sheet modeling, mainly because most models only consider changes in the surface balance and not changes in the ice dynamics (ice flow). Observations by ICESat for 2003-2007 show that Greenland has been losing (190 km3/year) compared to a small loss of only 7 Gt/yr in the 1990's. The loss of 171 Gt/year is contributing 0.5 mm/year to global sea level rise, which is about 15% of the recent total rate of rise. Although Greenland is growing inland, perhaps from increased snowfall, the shrinkage from more melting at the margins and accelerating outlet glaciers is much greater. In contrast, the changes taking place in Antarctica may be a surprise that you will hear about when you come to this seminar. |