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Wednesday, March 25, 2015

Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation, Nature Climate Change 2015, Stefan Rahmstorf, Jason Box, Georg Feulner, Michael Mann, A. Robinson, S. Rutherford, E.J. Schaffernicht; doi: 10.1038/NCLIMATE2554

Nature Climate Change (23 March 2015); doi: 10.1038/NCLIMATE2554

by Stefan Rahmstorf et al.


Possible changes in Atlantic meridional overturning circulation (AMOC) provide a key source of uncertainty regarding future climate change. Maps of temperature trends over the twentieth century show a conspicuous region of cooling in the northern Atlantic. Here we present multiple lines of evidence suggesting that this cooling may be due to a reduction in the AMOC over the twentieth century and particularly after 1970. Since 1990 the AMOC seems to have partly recovered. This time evolution is consistently suggested by an AMOC index based on sea surface temperatures, by the hemispheric temperature difference, by coral-based proxies and by oceanic measurements. We discuss a possible contribution of the melting of the Greenland Ice Sheet to the slowdown. Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event in the past millennium (p > 0.99). Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC.

At a glance


  1. Linear trends of surface temperature since AD 1901.
    Figure 1
  2. Connection between the AMOC stream function and the temperature-based AMOC index in a global warming scenario (RCP8.5).
    Figure 2
  3. Surface temperature time series for different regions.
    Figure 3
  4. Spectral analysisof the proxy-based AMOC index shown in Fig. 3b.

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