Observing and modelling recent climatic and glaciological changes in Southern Greenland

Coastal southern Greenland has cooled by >1degC over the past four decades, in sharp contrast to 'global warming' (a simultaneous increase ~0.5degC). This is reflected by a similar downward trend in Labrador Sea SST's. Yet it is known from previous studies (particularly the aircraft laser results of Krabill et al. 2000) that the Greenland Ice Sheet thinned around its margins during the 1990's, albeit with no major changes in surface elevation in the inland areas. The Krabill et al. (2000) results are misleadingly used by some to claim that the Ice Sheet is already responding to 'global warming'; however, this interpretation is open to question due to the short period. I'm using ERA-40 data (a new meteorological reanalysis from the European Centre for Medium-Range Weather Forecasts) to drive meteorological and glaciological models of snow accumulation and surface meltwater runoff. Model results are validated using in situ met. station and ice-core data. I aim to better define the surface mass balance of the Ice Sheet, and its response to climatic change, from 1957-2001. Questions we need to answer include: (1) Does the 1990's ice thinning reflect a sustained trend in mass balance or was it a short-term blip in the longer record?

(2) What was the main driving force: climatic change or changes in ice flow? (3) What is the current mass balance of the Ice Sheet? (4) How is the Ice Sheet likely to respond to future climatic change, particularly to 'global warming' (assuming the latter actually reaches Greenland!)? This is critical for projections of global sea-level rise. Temperatures in southern Greenland are closely correlated with the North Atlantic Oscillation, so changes in atmospheric circulation strongly influence temperature and melting rates/amounts over the Ice Sheet. The ERA-40-based modelling should yield a better insight into processes controlling snow accumulation and melt/runoff over the Ice Sheet.