Deep learning reconstruction of Atlantic Meridional Overturning Circulation strength validates ongoig twenty-first century decline.

Abstract The response of the Atlantic Meridional Overturning Circulation (AMOC) – an important ocean system transporting heat and salt across the Atlantic Ocean1,2 – to anthropogenic greenhouse gas emissions is crucial in projections of future climate change3. For Earth System Model (ESM) validation, the short range covered by AMOC observations4-8, inconsistent paleoclimate records9,10, and scattered hydrographic data11 are insufficient. A well-established sea surface temperature (SST) proxy index of the AMOC strength suggests that the AMOC has decreased substantially since the late ninetieth century12 but has received extensive scientific criticism13-21. Here, we use a deep learning method to provide a novel SST-based reconstruction of the twentieth century AMOC strength and show that it has declined by -0.151 Sv/decade since 1900, with the largest contribution in recent decades. In contrast to the earlier SST-based AMOC reconstruction12, the new one is in good agreement with direct 21st century AMOC measurements4 and historical ESM results22. In this way, the new AMOC reconstruction allows for new avenues for ESM calibration3,19 and contributes to a larger confidence in 21st century AMOC decline projections23.