Gradual changes in the 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 traceable region of cooling in the northern Atlantic. From 1990 the AMOC seems to have partly recovered. 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. Possible contributions of the melting of the Greenland Ice Sheet to the slowdown have been studied. Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event. Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC.