January 29, 2018: FB1 seminar

11:00, lecture hall west, Düsternbrooker Weg 20

Abstract:

The overturning circulation of the Atlantic Ocean (AMOC) has a major impact on climate, yet its evolution over the past hundred years or so is poorly known for lack of direct measurements. We use a high-resolution global climate model to derive a characteristic spatial and seasonal fingerprint of AMOC changes and compare this to the observed linear temperature trend since 1870. Both the model and observations show a remarkably similar pattern of a cooling in the subpolar gyre region (most pronounced for the November to May season) and a warming in the Gulf Stream region which in their combination can only be explained by a reduction in the AMOC. We explain the mechanisms that link the pattern to an AMOC slowdown, and use an ensemble of CMIP5 simulations to calibrate the observed decline. This suggests a weakening of the AMOC by ~ 3 Sv (~ 16%) since the mid-20^th Century. Its recent evolution is consistent with direct measurements in the RAPID project and reaches record low values in recent years.

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