Causal pathway from AMOC to Southern Amazon Rainforest indicates stabilising interaction between two climate tipping elements

Climate tipping elements like the Atlantic Meridional Overturning Circulation (AMOC) and the Amazon Rainforest (AR) are critical components of the Earth system that currently both show declining trends in their resilience due to anthropogenic climate change and other human disturbances such as deforestation. A shutdown of the AMOC or a large-scale dieback of the AR would have severe impacts on a global scale. Additionally, AMOC and AR are not independent from each other but disturbances from one system can propagate to the other. The sign and strength of this interaction has so far been classified as unknown by recent literature surveys. Using causal discovery and inference methods on observational and reanalysis data, we find that AMOC weakening increases precipitation in the Southern Amazon during the critical dry season. Specifically, a 1 Sv AMOC weakening results in 4.8% additional dry season precipitation, amounting to a 16.5% increase under the current estimated 3.45 Sv AMOC weakening since 1950. These findings, supported by multiple data sources, suggest that the Southern AR drying trend due to global warming and deforestation, which amounts to 4 mm/year since 1982, would be even more severe without concurrent AMOC weakening. Our results demonstrate the potential of causal discovery in the data-driven study of tipping element interactions and contribute to the understanding of coupled AMOC-AR dynamics, with the potential to improve assessments of climate tipping risk under ongoing global warming.