Does the surface of the Southern Ocean (SO) cool or warm under a sustained increase in the Southern Annular Mode (SAM)? Yavor Kostov shows the answer depends how long you wait! All climate models show an initial cooling; but then some models stay cold for decades, while others warm up within a few years. Where does nature do? Hard to say definitively, but it seems that it may stay cool for a while following a strengthening of SAM. This means that the trend in SAM over recent decades (probably mostly caused by stratospheric ozone depletion) might be the reason for the observed cooling and sea-ice expansion within the SO.
Kostov Y, J Marshall, U Hausmann, KC Armour, DG Ferreira and MM Holland (2016) Fast and slow responses of Southern Ocean sea-surface temperature to SAM in coupled climate models, Climate Dynamics, doi: 10.1007/s00382-016-3162-z