Asymmetric changes of temperature in the Arctic during the Holocene based on a transient run with the CESM

Abstract. 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 °C and -0.61 °C for Atlantic Arctic and 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 Atlantic Arctic and 0.09 °C warming for 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 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, indicating that the orbital modulation of the Pacific Decadal Oscillation, which in turn links to the Arctic dipole pattern, further affects the temperature asymmetry.