Inter-Model Differences in Future Summer Onset Over the Northern High Latitudes

Climate models consistently project a significant advance of summer onset over the Northern high latitude lands in the late 21st century. However, large inter-model differences exist, in particular, over Northwest Russia, Bering Sea region and Northeastern Canada. This study quantifies the influences of background global warming rate and regional snow-albedo feedback on the inter-model spreads in summer onset projections. Linear regression analysis reveals that models' transient climate response (TCR) values explain around 39%-50% of regional inter-model variances, indicating the dominant contribution of models' global warming rate. When removing TCR influences, the summer onset and snow cover exhibit significant inter-model correlations over Bering Sea region and Northeastern Canada, explaining 25%-30% of the inter-model variances. These results suggest that global climate sensitivity as well as regional snow-albedo feedback need to be considered for reliable projection of future summer season timing at regional scales.