ALBERT

Description: Both observations and model simulations reveal that the Arctic warms faster than the Antarctic. Previous studies have emphasized that the weaker warming in the Antarctic is due to the northward energy transport by the Antarctic Circumpolar Circulation (ACC). However, few studies have attempted to consider the asymmetric surface warming between the Arctic and the Antarctic and understand the root of this asymmetric warming. To reveal the role of ACC in the asymmetric warming, we close the Drake Passage (DP) to perturb the ocean circulations in the fully coupled Community Earth System Model. Experiments driven by an abrupt CO2 doubling show that compared to the DP opened case, the asymmetric polar warming amplifies in the DP closed case. The amplified asymmetry partially originates in a climatological warmer Antarctic with less sea ice but a colder Arctic with more sea ice in the DP closed case, resulting from climatological weaker ACC and Atlantic Meridional Overturning Circulation (AMOC). With abrupt double CO2 forcing, reduced cooling in the North Atlantic by the less-weakened AMOC in the DP closed case favors more sea ice melting in the Arctic than in the Antarctic. Both strong ice feedback and increase in water vapor transports in the Arctic amplify the asymmetry. Conversely, the oceanic northward energy transport anomaly due to the ACC cutoff contributes to the asymmetry insignificantly. These results highlight the importance of atmosphere-ocean-ice interactions for the asymmetric warming between the Arctic and the Antarctic.