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New research led by IIASA reveals a surprising link between two major climate-tipping elements: the Southern Amazon rainforest and the Atlantic Meridional Overturning Circulation (AMOC). While the study finds that a weakening AMOC may buffer dry season rainfall loss in the Amazon, it also highlights the urgent need to reduce emissions as broader climate risks continue to escalate.

The Southern Amazon rainforest, one of Earth's most vital ecosystems, faces intensifying threats from climate change and deforestation. Meanwhile, the AMOC鈥攁 system of ocean currents crucial for regulating global climate鈥攊s weakening. Both are considered climate tipping elements, which may undergo abrupt and potentially irreversible shifts in response to global warming, with potentially devastating consequences.

A new study led by IIASA researcher Annika H枚gner in collaboration with colleagues from the Potsdam Institute for Climate Impact Research (PIK) and the Center for Critical Computational Studies (C3S) in Frankfurt, has now identified a link between them.

Published in , the study is the first to identify a causal pathway from the AMOC to the Southern Amazon from reanalysis and observational data. A weakening AMOC leads to a cooling of North Atlantic Sea surface temperatures, and this causes increased rainfall in the Southern Amazon during the dry season.

Using advanced causal analysis methods spanning 1982 to 2022, the researchers show that for every 1 million cubic meters per second of AMOC weakening, annual dry season rainfall in the Southern Amazon increases by roughly 4.8%.

"The dry season is the most vulnerable time for the Amazon rainforest," explains H枚gner. "Our findings reveal that a weakening AMOC contributes to increased rainfall in the Southern Amazon during this time."

According to the analysis, this previously unknown climate teleconnection may have offset up to 17% of the dry season rainfall decline in the Southern Amazon since 1982. While this sounds like good news, the authors urge caution.

The Amazon is still receiving less rainfall, with dry seasons becoming longer and more intense鈥攁nd although buffering this drying trend, further AMOC weakening would have severe adverse impacts across the globe.

"The Amazon is still drying," notes study co-author Nico Wunderling, a professor at C3S and scientist at PIK.

"The stabilizing interaction we found from the AMOC onto the Southern Amazon competes with other effects like those arising from deforestation and increasing temperatures, which would cause continued Amazon drying that the interaction will not be able to compensate for long-term. To accurately estimate future risks, we need to understand these complex interactions. Our study adds an important piece to this puzzle."

The authors emphasize that this discovery reinforces the importance of integrating tipping element interactions into climate risk assessments. It also underlines the urgency of reducing greenhouse gas emissions to prevent pushing vulnerable systems past critical thresholds.

"Interactions between climate-tipping elements are not just theoretical鈥攖hey are happening now," says H枚gner.

"Even though some tipping element interactions are stabilizing, the majority are not鈥攔ather the opposite. We cannot count on the Earth system to continue absorbing the damage we cause. The only reliable way forward is to drastically reduce greenhouse gas emissions and limit warming."