December 12, 2022: online Ocean Circulation and Climate Dynamics Colloquium

When?  Monday, December 12, 2022 at 11 am (GMT+1)
Where?    ZOOM: https://geomar-de.zoom.us/j/7013744802?pwd=M0NvZWlvZVRuQThXdWdPbjJpYUNHZz09

Meeting Room: 701 374 4802
Kenncode (Passcode): 59KaFp

We have analysed the relationships of global ocean heat uptake, global-mean surface temperature change T and the strength of the Atlantic meridional overturning circulation (AMOC) in experiments with atmosphere-ocean general circulation models (AOGCMs) when atmospheric CO2 increases. The results lead us to formulate a new conceptual model of global ocean heat uptake.  In this model, named "MT2", there are two routes for heat to reach the deep ocean, of comparable magnitude. One route occurs in high latitudes, where heat may enter the ocean along isopycnals nearly as if it were a passive tracer. A fraction of the effective radiative forcing is thereby stored in the deep ocean, without affecting T. The fraction is AOGCM-specific and depends linearly on the AMOC strength in the unperturbed climate, but we argue that the heat uptake is not caused by the AMOC.  The other route for heat uptake is diapycnal and occurs in low latitudes, which have large area, receive most of the forcing, and warm up more. This route is described by the two-layer model of previous work. The MT2 model accounts for the strong correlation of AMOC with ocean heat uptake efficiency previously reported, for the decrease of ocean heat uptake efficiency over time, and it explains why the effective climate sensitivity is a better predictor than the transient climate response for T under high-forcing scenarios.

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