North Atlantic temperature and salinity changes are driven by external forcing, underestimated by CMIP6 models

Abstract The Atlantic Meridional Overturning Circulation (AMOC) is projected to weaken in the 21st century, although evidence of this trend in the observational record is limited and conflicting. Here we utilize the growing set of in-situ observations from Argo floats and Earth System Models, to detect and attribute North Atlantic (NA) climate change signals in temperature and salinity fields. We show that observed changes over the past 65 years are significantly different from expected natural variability and can be attributed to anthropogenic greenhouse gas emissions. Distinct NA patterns of heat and salt accumulation around 40°N and freshening and cooling around 55°N are detectable in both modeled and observational datasets, consistent with the theorized weakening of the AMOC upper cell. Importantly, our results suggest that CMIP6 models underestimate the present-day observed changes in NA ocean temperature and salinity. This is worrisome, given the potentially devastating and irreversible impacts of the AMOC slowdown.