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.