State and variability of mass balance of Greenland Ice Sheet since 1957, and links with climate

Concerted observational and modelling programmes are underway to determine thecurrent state and variability of mass balance of the Greenland Ice Sheet, hence helppredict its response to future climatic change. Here we present the results of new meteorologicalmodelling based on ERA-40 reanalysis data from the European Centre forMedium RangeWeather Forecasts (ECMWF). This gives us valuable insights into thepast and present state and variability of the Greenland ice mass and links with climate.Here we show for the first time a validated annual and seasonal surface-mass-balancehistory of the ice sheet for 1957-2003. This is based on a novel monthly melt-waterrunoff model by Janssens Huybrechts (Huybrechts 2002). We show considerable interannualvariability in snow accumulation, runoff and mass balance over the last 45years, with some intriguing recent results. By comparing with long-term temperature,precipitation and accumulation records from the met. stations and ice cores, we discusspossible climatic factors forcing the ice in this period. We also derive sensitivityof the ice sheet to climatic forcing, based on real meteorological observations (ERA-40). The intriguing results include massive snow accumulation over south-east Greenlandduring winter 2002/03, which led to unprecedented thickening in the most recentNASA aircraft surveys. Is this recent thickening signal a sign of more extreme weatherconditions over the Ice Sheet, more storminess and higher accumulation events, dueto global warming?