The surface mass balance for Greenland and Antarctica has been calculated using model data from an AMIP-type experiment for the period 1979-2001 using the ECHAM5 spectral transform model at different triangular truncations. There is a significant reduction in the calculated ablation for the highest model resolution, T319 with an equivalent grid distance of ca 40 km. As a consequence the T319 model has a positive surface mass balance for both ice sheets during the period. For Greenland, the models at lower resolution, T106 and T63, on the other hand, have a much stronger ablation leading to a negative surface mass balance. Calculations have also been undertaken for a climate change experiment using the IPCC scenario A1B, with a T213 resolution (corresponding to a grid distance of some 60 km) and comparing two 30-year periods from the end of the twentieth century and the end of the twenty-first century, respectively. For Greenland there is change of 495 km(3)/year, going from a positive to a negative surface mass balance corresponding to a sea level rise of 1.4 mm/year. For Antarctica there is an increase in the positive surface mass balance of 285 km(3)/year corresponding to a sea level fall by 0.8 mm/year. The surface mass balance changes of the two ice sheets lead to a sea level rise of 7 cm at the end of this century compared to end of the twentieth century. Other possible mass losses such as due to changes in the calving of icebergs are not considered. It appears that such changes must increase significantly, and several times more than the surface mass balance changes, if the ice sheets are to make a major contribution to sea level rise this century. The model calculations indicate large inter-annual variations in all relevant parameters making it impossible to identify robust trends from the examined periods at the end of the twentieth century. The calculated inter-annual variations are similar in magnitude to observations. The 30-year trend in SMB at the end of the twenty-first century is significant. The increase in precipitation on the ice sheets follows closely the Clausius-Clapeyron relation and is the main reason for the increase in the surface mass balance of Antarctica. On Greenland precipitation in the form of snow is gradually starting to decrease and cannot compensate for the increase in ablation. Another factor is the proportionally higher temperature increase on Greenland leading to a larger ablation. It follows that a modest increase in temperature will not be sufficient to compensate for the increase in accumulation, but this will change when temperature increases go beyond any critical limit. Calculations show that such a limit for Greenland might well be passed during this century. For Antarctica this will take much longer and probably well into following centuries.
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NASA, Goddard Space Flight Ctr, Cryospher Sci Lab, Greenbelt, MD 20771 USA
Univ Buffalo, Geol Dept, Buffalo, NY 14260 USA
Univ Buffalo, RENEW Inst, Buffalo, NY 14260 USAUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
Nowicki, Sophie
Abe-Ouchi, Ayako
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Univ Tokyo, Atmosphere & Ocean Res Inst, Kashiwa, Chiba, JapanUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
Abe-Ouchi, Ayako
Agosta, Cecile
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Univ Paris Saclay, CEA CNRS UVSQ, LSCE IPSL, Lab Sci Climat & Environm, Gif Sur Yvette, FranceUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
Agosta, Cecile
Alexander, Patrick
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Columbia Univ, Lamont Doherty Earth Observ, Palisades, NY USA
NASA, Goddard Inst Space Studies, New York, NY 10025 USAUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
Alexander, Patrick
Albrecht, Torsten
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Leibniz Assoc, Potsdam Inst Climate Impact Res PIK, Potsdam, GermanyUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
Albrecht, Torsten
Asay-Davis, Xylar
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Los Alamos Natl Lab, Theoret Div, Los Alamos, NM USAUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
Asay-Davis, Xylar
Aschwanden, Andy
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Univ Alaska, Inst Geophys, Fairbanks, AK USAUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
Aschwanden, Andy
Barthel, Alice
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Los Alamos Natl Lab, Theoret Div, Los Alamos, NM USAUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
Barthel, Alice
Bracegirdle, Thomas J.
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British Antarctic Survey, Cambridge, EnglandUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
Bracegirdle, Thomas J.
Calov, Reinhard
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Leibniz Assoc, Potsdam Inst Climate Impact Res PIK, Potsdam, GermanyUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England
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Australian Antarctic Div, Kingston, Tas, Australia
Univ Tasmania, Inst Marine & Antarctic Studies, Australian Antarctic Program Partnership, Hobart, Tas, AustraliaUniv Bristol, Ctr Polar Observat & Modelling, Bristol, Avon, England