Polar amplification in a coupled climate model with locked albedo
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In recent years, a substantial reduction of the sea ice in the Arctic has been observed. At the same time, the near-surface air in this region is warming at a rate almost twice as large as the global average—this phenomenon is known as the Arctic amplification. The role of the ice-albedo feedback for the Arctic amplification is still a matter of debate. Here the effect of the surface-albedo feedback (SAF) was studied using a coupled climate model CCSM3 from the National Center for Atmospheric Research. Experiments, where the SAF was suppressed by locking the surface albedo in the entire coupled model system, were conducted. The results reveal polar temperature amplification when this model, with suppressed albedo, is forced by a doubling of the atmospheric CO2 content. Comparisons with variable albedo experiments show that SAF amplifies the surface-temperature response in the Arctic area by about 33%, whereas the corresponding value for the global-mean surface temperature is about 15%. Even though SAF is an important process underlying excessive warming at high latitudes, the Arctic amplification is only 15% larger in the variable than in the locked-albedo experiments. It is found that an increase of water vapour and total cloud cover lead to a greenhouse effect, which is larger in the Arctic than at lower latitudes. This is expected to explain a part of the Arctic surface–air-temperature amplification.
KeywordsAlbedo feedback Polar amplification Greenhouse effect Climate-model experiment
The authors are thankful to Michael Tjernström, Erland Källén, Peter Lundberg, Thorsten Mauritsen, Heiner Körnich, and Peter Langen for useful comments on the manuscript. We will also like to thank the two reviewers: Jennifer Francis and Vladimir Alexeev for their very helpful suggestions. We acknowledge the National Center for Atmospheric Research (NCAR), Boulder, USA, for providing the community version of the CCSM3 climate model. Finally we thank the National Supercomputer Center (NSC), Linköping, Sweden, and the Knut and Alice Wallenberg Foundation for placing computer resources at our disposal.
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