| Summary: | Today’s climate warming is unequivocal. Evidence from observations and satellite records show that Arctic Ocean is losing its summer sea ice cover with a rapid pace and is dominated by young and thinner ice. The ice loss has already caused heating of the overlying atmosphere. At the same time, the Greenland ice sheet (GIS) surface mass balance decreases, due to increased surface melt and runoff. These changes have an impact on global climate and sea levels. This study investigates the role of Arctic sea ice changes on GIS surface energy and mass balance, with a global climate model the Community Earth System Model (CESM). The model includes component models with 1° horizontal resolution, for the atmosphere the Community Atmospheric Model (CAM4), for the land the Community Land Model (CLM4), for the sea ice the Los Alamos Sea Ice Model (CICE4) and for the ocean the Parallel Ocean Programme (POP2). A number of simulations that have contributed to the phase 5 of the Coupled Model Intercomparison Project (CMIP5) is available to the public. The analysis in this study is mainly based on the first of the five ensemble members from the twenty-first-century simulations for the representative concentration pathway 8.5 (RCP8.5) and the twentieth-century all forcing simulations, by which the summer anomalies of sea ice, climate of Greenland and Arctic Ocean and GIS mass balance in the period 2080-2099 with respect to the 1980-1999 reference period are analysed. All five simulations project a nearly ice-free Arctic ocean in September around 2060 (mean value). The simulated 2080-2099 annual and summer mean near-surface air temperature over the Arctic increase by 7.7 K and 4.5 K respectively, with respect to 1980-1999 and summer warming is strongest in the areas of reduced sea ice. The decline in sea ice area causes open water formation with lower albedo and higher solar radiation absorption that enhances melting and heating. In addition, summer cloud cover and water vapour increase and together with the temperature increase ...
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