Please join us for a special in-person SEAS Colloquium in Climate Science talk on Monday, October 16.

Speaker: Jonathan Gregory, University of Reading, UK

Title: "A new conceptual model of transient climate response and global ocean heat uptake"

Abstract: We formulate a new conceptual model, named "MT2", to describe global ocean heat uptake during climate change as simulated by atmosphere--ocean general circulation models (AOGCMs) forced by increasing atmospheric CO2. MT2 has two routes whereby heat reaches the deep ocean. In low latitudes, whose surface temperature change dominates the global mean, heat uptake is temperature-driven, as represented by the commonly used two-layer model. In high latitudes, heat is taken up nearly like a passive tracer, with little effect on global-mean surface temperature change. The fraction of the radiative forcing absorbed by the latter route, mostly in the Southern Ocean, depends on the unperturbed state of the global ocean, and is correlated with the strength of the Atlantic meridional overturning circulation (AMOC). MT2 can account for several relationships among variables simulated by AOGCMs, some found in this work, others previously reported but unexplained. In particular, the warming due to increasing CO2 is smaller, both in the global mean and worldwide, in AOGCMs with a stronger AMOC in the unperturbed state.