There is debate about slowing of the Atlantic Meridional Overturning Circulation (AMOC), a key component of the global climate system. Some focus is on the sea surface temperature (SST) slight cooling in parts of the subpolar North Atlantic despite widespread ocean warming. Atlantic SST is influenced by the AMOC, especially on decadal timescales and beyond. The local cooling could thus reflect AMOC slowing and diminishing heat transport, consistent with climate-model responses to rising atmospheric greenhouse-gas concentrations. Here we show from Atlantic SST the prevalence of natural AMOC variability since 1900. This is consistent with historical climate-model simulations 1900-2014 predicting on average AMOC slowing of about 1Sv at 30°N after 1980, which is within the range of internal multidecadal variability derived from the models’ preindustrial control runs. These results highlight the importance of systematic and sustained in-situ monitoring systems that can detect and attribute with high confidence an anthropogenic AMOC signal.
Mojib Latif, Jing Sun, Martin Visbeck, and M. Hadi Bordbar: "Natural variability dominates Atlantic Meridional Overturning since 1900", Nature Climate Change, accepted for publication, 2022.