Ice Sheets

The effects of past and present climate changes on ice sheets are manifest in their current state of mass balance. Assessing that balance has been and continues to be a priority of the Earth Science Enterprise. Since 1995, NASA's Program for Arctic Regional Climate Assessment (PARCA) has focused a coordinated effort on determining the mass balance of the Greenland ice sheet through a combination of targeted field campaigns, satellite data analysis, aircraft observations, and process modeling. PARCA has been successful in advancing our knowledge of the Greenland ice sheet mass balance, and providing crucial insight into the processes that control mass balance. Results from PARCA indicate that the high-elevation regions of the Greenland ice sheet have generally been in overall balance in recent years, but there is considerable spatial and temporal variability. At lower elevations, nearer the ice sheets margins, thinning has been observed in the mid to late 1990's and a negative mass balance has been estimated, also with large spatial variability. A variety of PARCA data sets have been developed and are being made available through links at the National Snow and Ice Data Center (NSIDC) at URL: http://nsidc.org/NASA/PARCA/. A report from the last PARCA meeting identifying considerations for future directions for Greenland mass balance research is also available from NSIDC at the same URL.

NASA has historically not supported field activities in Antarctica because of budget limitations, and such activities have been the purview of the National Science Foundation. However, there have been extensive satellite observations of all or parts of the continent, which are valuable for mass balance studies. Among the more notable ones recently have been Landsat-7 observations, and the first and second Radarsat Antarctic Mapping Missions. These measurements will be further enhanced following the launch of ICESat (Ice Cloud and land Elevation Satellite), scheduled for the end of 2002, which has as its primary function the assessment of ice sheet elevation changes.

Additional satellite remote sensing investigations of both Greenland and Antarctica have made use of scatterometry, passive microwave radiometry, synthetic aperture radar (SAR) backscatter and interferometry, and various visible and thermal sensors. All of these measurements, along with aircraft remote sensing data, in situ observations, and modeling activities have significantly increased our capabilities in studying glaciers and ice sheets. However, large uncertainties remain in the mass balance characteristics, and the processes that control these balances must be better quantified and understood. This program seeks to reduce those uncertainties.