Quantifying the impact of wind and surface humidity induced surface heat exchange on the circulation shift in response to increased CO2

Abstract:

We extend the locking technique to separate the poleward shift of the atmospheric circulation in response to quadrupled CO₂ to quantify the importance of: 1) CO₂ 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 the CMIP5 models about 60% of the intermodel variance in the austral winter circulation shift under RCP8.5 scenario is accounted for by the response of the subtropical-subpolar contrast in surface heat exchange and longwave cloud radiative effects. The results highlight the dominant role of surface heat exchange and cloud radiative effects for future circulation changes.