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Earth's climate exhibits internal modes of variability on various  timescales. Here we investigate multi-decadal variability of the  Atlantic meridional overturning circulation (AMOC), Northern Hemisphere sea-ice extentand global mean temperature (GMT) in an ensemble of CMIP5 models under control conditions.We report an inter-annual GMT variability of about ±0.1° Coriginating solely from natural variability in the model ensemble.By decomposing the GMT variance into contributions of the  AMOC and Northern Hemisphere sea-ice extent using  a graph-theoretical statistical approach, we find the AMOC to  contribute 8% to GMT variability in the ensemble mean. Our  results highlight the importance of AMOC sea-ice feedbacks that  explain 5% of the GMT variance, while the contribution solely  related to the AMOC is found to be about 3%.  As a consequence  of multi-decadal AMOC variability, we report substantial variations  in North Atlantic deep-ocean heat content with trends of up to  0.7 × 10<sup>22</sup> J decade<sup>−1</sup> that are of the order of  observed changes over the last decade and consistent with the  reduced GMT warming trend over this period. Although these  temperature anomalies are largely density-compensated by salinity  changes, we find a robust negative correlation between the AMOC and  North Atlantic deep-ocean density with density lagging the AMOC by 5  to 11 yr in most models. While this would in principle allow  for a self-sustained oscillatory behavior of the coupled AMOC–deep-ocean  system, our results are inconclusive about the role of  this feedback in the model ensemble

The role of the North Atlantic overturning and deep ocean for multi-decadal global-mean-temperature variability