The robustness of future changes in Northern Hemisphere blocking: A large ensemble projection with multiple sea surface temperature patterns

Future changes in the frequency of Northern Hemisphere blocking are investigated via large ensemble simulations using a 60km mesh atmospheric general circulation model prescribed with six future sea surface temperature patterns derived from state-of-the-art climate models under a 4K warmer climate. Our simulations depict the frequency of wintertime blocking decreasing from 16.6%0.7% to 13.1%2.1% in the Euro-Atlantic sector and from 17.4%0.7% to 14.8%2.4% in the Pacific sector. This decline in frequency is seen to affect Euro-Atlantic blocking of all durations and Pacific blocking of more than 15days' duration. During summer, our simulations not only exhibit a robust decrease (from 10.7%+/- 0.4% to 7.6%+/- 0.7%) in the Euro-Atlantic blocking frequency but also show that the magnitude of this decrease is smaller for longer-lived blocking. In contrast, the Pacific blocking frequency either does not change or increases slightly, particularly for events of 15-29days' duration.