Quantifying the Impact of Wind and Surface Humidity-Induced Surface Heat Exchange on the Circulation Shift in Response to Increased CO2

We extend the locking technique to separate the poleward shift of the atmospheric circulation in response to quadrupled CO(2)into contributions from (1) CO(2)increase, (2) cloud radiative effects, and (3) wind and surface humidity-induced surface heat exchange. In aquaplanet simulations, wind and surface humidity-induced surface heat exchange accounts for 30-60% of the Hadley cell edge and midlatitude eddy-driven jet shift. The increase of surface specific humidity dominates and mostly follows global mean warming. Consistent with previous work the remaining shift is attributed to cloud radiative effects. Across CMIP5 models the intermodel variance in the austral winter circulation shift in response to quadrupled CO(2)is significantly correlated with the response of the subtropical-subpolar difference of surface heat exchange. The results highlight the dominant role of surface heat exchange for future circulation changes.