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We derive mass changes of the Greenland ice sheet (GIS) for 2003-07 from ICESat laser altimetry and compare them with results for 1992-2002 from ERS radar and airborne laser altimetry. The GIS continued to grow inland and thin at the margins during 2003 07, but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s. The net balance changed from a small loss of 7 plus or minus 3 Gt a 1(sup -1) in the 1990s to 171 plus or minus 4 Gt a (sup -1) for 2003-07, contributing 0.5 mm a(sup -1) to recent global sea-level rise. We divide the derived mass changes into two components: (1) from changes in melting and ice dynamics and (2) from changes in precipitation and accumulation rate. We use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation-driven changes to mass changes. Increased losses from melting and ice dynamics (17-206 Gt a(sup-1) are over seven times larger than increased gains from precipitation (10 35 Gt a(sup-1) during a warming period of approximately 2 K (10 a)(sup -1) over the GIS. Above 2000m elevation, the rate of gain decreased from 44 to 28 Gt a(sup-1), while below 2000m the rate of loss increased from 51 to 198 Gt a(sup-1). Enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers, as well as accelerating ice flow. Increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales.

Changes in ice mass are estimated from elevation changes derived from 10.5 years (Greenland) and 9 years (Antarctica) of satellite radar altimetry data from the European Remote-sensing Satellites ERS-1 and -2. For the first time, the dH/dt values are adjusted for changes in surface elevation resulting from temperature-driven variations in the rate of fun compaction. The Greenland ice sheet is thinning at the margins (-42 plus or minus 2 Gta(sup -1) below the equilibrium line altitude (ELA)) and growing inland (+53 plus or minus 2 Gt a(sup -1)above the ELA) with a small overall mass gain (+11 plus or minus 3 Gt a(sup -1); -0.03 mm a(sup -1) SLE (sea level equivalent)). The ice sheet in West Antarctica (WA) is losing mass (-47 (dot) 4 GT a(sup -1) and the ice sheet in East Antarctica (EA) shows a small mass gain (+16 plus or minus 11 Gt a(sup -1) for a combined net change of -31 plus or minus 12 Gt a(sup -1) (+0.08 mm a(sup -1) SLE)). The contribution of the three ice sheets to sea level is +0.05 plus or minus 0.03 mm a(sup -1). The Antarctic ice shelves show corresponding mass changes of -95 (dot) 11 Gt a(sup -1) in WA and +142 plus or minus 10 Gt a(sup -1) in EA. Thinning at the margins of the Greenland ice sheet and growth at higher elevations is an expected response to increasing temperatures and precipitation in a warming climate. The marked thinnings in the Pine Island and Thwaites Glacier basins of WA and the Totten Glacier basin in EA are probably ice-dynamic responses to long-term climate change and perhaps past removal of their adjacent ice shelves. The ice growth in the southern Antarctic Peninsula and parts of EA may be due to increasing precipitation during the last century.