Global Climate Models and 20th and 21st Century Arctic Climate Change

We review the history of global climate model (GCM) development with regard to Arctic climate beginning with the ACSYS era. This was a time of rapid improvement in many models. We focus on those aspects of the Arctic climate system that are most likely to amplify the Arctic response to anthropogenic greenhouse gas forcing in the 20th and 21st centuries. Lessons from past GCM modeling and the most likely near-future model developments are discussed. We present highlights of GCM simulations from two sophsiticated climate models that have the highest Arctic amplification among the the models that participated in the World Climate Research Programme’s third Coupled Model Intercomparison Project (CMIP3). The two models are the Hadley Center Global Environmental Model (HadGEM1) and the Community Climate System Model version 3 (CCSM3). These two models have considerably larger climate change in the Arctic than the CMIP3 model mean by mid 21st century. Thus the surface warms by about 50% more on average north of 75◦N in HadGEM1 and CCSM3 than in the CMIP3 model mean, which amounts to more than three times the global average warming. The sea ice thins and retreats 50-100% more in HadGEM1 and CCSM3 than in the CMIP3 model mean. Further, the oceanic transport of heat into the Arctic increases much more in HadGEM1 and CCSM3 than in other CMIP3 models and contributes to the larger climate change.