Asymmetric changes in temperature in the Arctic during the Holocene based on a transient run with the Community Earth System Model (CESM).

The Arctic temperature changes are closely linked to midlatitude weather variability and extreme events, which has attracted much attention in recent decades. Syntheses of proxy data from poleward of 60 ∘ N indicate that there was asymmetric cooling of -1.54 and -0.61 ∘ C for the Atlantic Arctic and the Pacific Arctic during the Holocene, respectively. We also present a similar consistent cooling pattern from an accelerated transient Holocene climate simulation based on the Community Earth System Model. Our results indicate that the asymmetric Holocene Arctic cooling trend is dominated by the winter temperature variability, with -0.67 ∘ C cooling for the Atlantic Arctic and 0.09 ∘ C warming for the Pacific Arctic, which is particularly pronounced at the proxy sites. Our findings indicate that sea ice in the North Atlantic expanded significantly during the late Holocene, while a sea ice retreat is seen in the North Pacific, amplifying the cooling in the Atlantic Arctic by the sea ice feedback. The positive Arctic dipole pattern, which promotes warm southerly winds to the North Pacific, offsets parts of the cooling trend in the Pacific Arctic. The Arctic dipole pattern also causes sea ice expansion in the North Atlantic, further amplifying the cooling asymmetry. We found that the temperature asymmetry is more pronounced in a simulation driven only by orbital forcing. The accelerated simulations lead to a partial delay in the feedback of climate processes. Therefore, we confirm the occurrence of the asymmetry of the Arctic temperature changes in un-accelerated simulations using ECBilt-CLIO, IPSL, and in TraCE-21k. [ABSTRACT FROM AUTHOR]