Arctic Amplification through Inter-seasonal Feedback Effect in Past Interglacials

Past interglacials allow investigating the climatic processes and associated feedbacks during warm periods, which are characterized by different combinations of climatic forcing such as solar radiation, GHGs, and ice sheets. Arctic warming amplification, a common phenomenon between past interglacials and present warming, has seasonality in its feedback mechanism, and detailed study of these internal feedbacks is still lacking despite its global impact. In this study, the simulation experiments under conditions close to the past interglacial periods (MIS1; Holocene, MIS5e; Last Interglacial, and MIS11) are conducted using a coupled atmosphere-ocean-vegetation model MIROC (4m) AOVGCM, particularly focusing on the role of ice sheets and Arctic sea ice. Climate responses to inputs and conditions are compared to examine the seasonal effects of atmosphere-ocean-ice feedbacks on Northern hemisphere high-latitudes temperature. Ice sheet distribution is set as a boundary condition in addition to the orbital elements, land cover, and GHGs to account the effect of remaining ice sheets at the timing of peak insolation. Feedback Analysis is also conducted to quantify the contribution of each feedback element to the surface temperature change. It is demonstrated that an inter-seasonal effect of air-sea-ice-vegetation feedbacks contributes to Arctic warming amplification, where heat gained in summer is used for sea ice melting and ocean absorption, and is released in autumn and winter, resulting in annual warming. This process is amplified when considering vegetation feedbacks and seen commonly in MIS1, 5e, and 11. In periods when ice sheets remain, Arctic sea ice keeps a high degree of concentration in summer, and annual mean temperatures at Northern high latitudes are lower than would be expected from insolation intensity. These results imply that the presence of Northern hemisphere ice sheet has a significant effect on Arctic climate response to insolation intensity by suppressing feedbacks that contribute to Arctic amplification through the reduced melt of summer sea ice.