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

The response of the Atlantic Meridional Overturning Circulation (AMOC) – an important ocean system transporting heat and salt across the Atlantic Ocean^1,2 – 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 observations^4-8, inconsistent paleoclimate records^9,10, 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 criticism^13-21. 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 calibration^3,19 and contributes to a larger confidence in 21st century AMOC decline projections²³.