Remote Sensing Observations of Ice Sheet Mass Balance: Challenges and Interpretation

Of all of the factors that contribute to sea level change, the ice sheets have the potential by far to be the most significant, both in terms of quantity of change and rate of change. For this reason, a number of scientific investigations have sought to assess the mass balance of Greenland and Antarctic ice sheets, which contain the equivalent of approximately 7 and 65 m of sea level respectively. It has only been through advances in satellite and aircraft remote sensing over the last fifteen years that such large-scale estimates have been enabled, and since 2000, when the first observationally based mass balance assessment of an ice sheet - Greenland - was made, roughly a dozen satellite- and aircraft-derived mass balance estimates have followed. These estimates vary widely, largely as a result of the different techniques used and the different time periods examined. For Greenland they have ranged from a very slight gain of 11 gigatons per year to a loss of over 200 gigatons per year. In Antarctica, the disparity among estimates is smaller, but there are still considerable differences among them. Despite the large variations among the estimates, the pictures they paint of the behavior of the two great ice sheets are not as different as the numbers suggest. This presentation will review recent remote-sensing-based mass balance assessments of the Greenland and Antarctic ice sheets in the context of the strengths and limitations of the various techniques used, provide an interpretation the differences among the estimates, and discuss new observations that contribute to our understanding of just what the mass balances of the ice sheets are and their implications for the future.