The role of winter temperatures and polar amplification during peak Interglacial warming

Future warming is expected to be amplified over high latitudes, especially in winter, but large uncertainties exist in the amount of this polar amplification and the role of feedbacks such as the winter Northern Annular Mode (NAM). Higher temperatures than today also occurred during the peak warming of the present and last Interglacial which could provide possible insight into the main process and feedbacks involved. Large-scale climate reconstructions for these periods have previously focussed mainly on summer season temperatures over high latitudes, and we have so far lacked a clear view of temperature changes in winter, and over lower latitudes against which polar amplification needs to be judged. We have compiled a synthesis of quantitative proxy-temperature reconstructions from across the Northern Hemisphere during the present and last Interglacial for both summer and winter. We find that warming was greater in winter than in summer, and was much stronger over high latitudes relative to lower latitudes. The strength of this polar amplification is not reproduced in climate model simulations, nor is the strength and spatial pattern of winter warming, which appears similar to that experienced under a high index Northern Annular Mode (NAM).