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The past 2,000 years provide a critical context for understanding twentieth century climate change. Due to the Past Global Changes 2k initiative, an extensive proxy database provides opportunities to assess regional climate change that have stronger ecological and societal implications than global-mean temperature changes alone. However, the various sources of paleoclimate reconstruction poses serious challenges to scientifically and statistically sound inference within a unified framework. Here we show results from the first transient simulation for the past 2,000 years with the Community Earth System Model, called past2k, and use data-model comparison to refine the interpretation of the proxy data. Our results indicate that the Atlantic Arctic was cooling at a faster rate than the Pacific Arctic over the past two millennia, in both proxy data and models. The model shows that this cooling pattern was dynamically supported by both a weakening of North Atlantic subpolar gyre and a stronger Aleutian Low.

Plain Language Summary The Arctic has become a focus for climate change studies due to the rapid Arctic changes we have already observedand their potential impacts on midlatitude weather and the North Atlantic Ocean circulation. In this study, we use a dual observation-modeling approach to elucidate the spatial pattern of Arctic cooling in the last 2,000 years and to improve the understanding of the physical mechanisms underlying this pattern. Our results indicate that greater cooling in the North Atlantic Arctic relative to the North Pacific Arctic is caused by a weakening of the northward transport of heat by Atlantic surface currents, and a strengthening of the Aleutian Low, with little or no change due to differences in reflectivity related to snow and sea ice coverage between those regions.