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Reto Knutti
and
Thomas F. Stocker

Abstract

A zonally averaged three-basin ocean–atmosphere model is used to investigate mean steric sea level rise in global warming scenarios. It is shown that if the North Atlantic deep water formation stops due to global warming, steric sea level rise is much larger for the same global mean atmospheric temperature increase than if the thermohaline circulation remains near the present state. In the equilibrium, global mean steric sea level rise depends linearly on the global mean atmospheric temperature increase. The influence of different subgrid-scale ocean mixing parameterizations on steric sea level rise is investigated.

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M. Latif
,
E. Roeckner
,
U. Mikolajewicz
, and
R. Voss

Abstract

Most global climate models simulate a weakening of the North Atlantic thermohaline circulation (THC) in response to enhanced greenhouse warming. Both surface warming and freshening in high latitudes, the so-called sinking region, contribute to the weakening of the THC. Some models even simulate a complete breakdown of the THC at sufficiently strong forcing. Here results are presented from a state-of-the-art global climate model that does not simulate a weakening of the THC in response to greenhouse warming. Large-scale air–sea interactions in the Tropics, similar to those operating during present-day El Niños, lead to anomalously high salinities in the tropical Atlantic. These are advected into the sinking region, thereby increasing the surface density and compensating the effects of the local warming and freshening.

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