| Summary: | As a result of global warming, the Greenland Ice Sheet (GrIS) will bemajor contributor to the future mean sea level rise (SLR). Its contribution will be led by the meltwater production at the surface of the ice sheet, gauged by the surface mass balance (SMB, the sum of surface ice mass gains and losses). Various physical processes enhanced the current melt of the ice sheet through positive feedbacks. These feedbacks add uncertainties to SMB projections due to their poor representation in climate modelling. The purpose of this thesis is to estimate the uncertainties related to the influence of two of these feedbacks on the GrIS SMB projections. The SMB is computed in this work by a regional climate model, the Modèle Atmosphérique Régional (MAR), developed at ULiège and specifically designed to represent the interactions of the atmosphere with snow-covered or ice-covered surfaces. The first objective was to evaluate the influence of recent circulation changes associated with summer blocking events on the SMB in a context of atmospheric warming up to + 2°C. We highlighted that if such events continue to occur, the increase in SMB due to global warming alone may be underestimated by a factor of 2 in the current projections. We then assessed the representation of such circulation changes in the new generation of global climate models (the CMIP6 models) used to perform the climate projections to 2100. We concluded that none of these models can represent the currently observed circulation changes, nor do they project such changes to 2100. Finally, the last objective was to study the long-term (2200) influence of extreme atmospheric warming (+ 7 °C compared to 1961-1990) on the GrIS contribution to SLR, and on the method to represent the feedback between melt and surface elevation, causing an enhancing of melt. This was achieved by coupling MAR with an ice sheet model (PISM), thus enabling the explicit consideration of the melt-elevation feedback. While not considering this feedback results in an underestimation of more ...
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