Quantification of the cascading tipping probability from the AMOC to the Amazon rainforest

TL;DR

This study models the probability of a cascade effect where an AMOC weakening influences Amazon rainforest degradation, revealing low likelihood of rapid transition but highlighting potential for severe impacts following AMOC collapse.

Contribution

It introduces a coupled conceptual model and a rare-event sampling method to quantify the probability and mechanisms of the AMOC-to-Amazon tipping cascade.

Findings

Amazon transition within 200 years is very unlikely without AMOC collapse.

AMOC collapse significantly increases the risk of Amazon degradation.

Severe wildfires may follow after AMOC weakening in the region.

Abstract

The Amazon rainforest and the AMOC are considered to be tipping elements: they are important components of the Earth system, but may collapse under climate change. Moreover, an AMOC collapse may favor the transition of the rainforest to a degraded forest by influencing the precipitation patterns over the Amazon. This phenomenon is known as tipping cascade and better understanding it is key to anticipating the impact of tipping events. Here, we investigate in a coupled conceptual AMOC-Amazon model the probability that an AMOC weakening affects tree cover loss in two regions of the rainforest. To get more insight into the mechanisms behind the tipping cascade, we also analyze the dynamics of both systems and their evolution during the Amazon transition. Namely, we track the transition probability and the transition time of the Amazon, and reconstruct the distribution of AMOC strength at every stage of this transition. These tasks require a large ensemble simulation, containing in particular a large number of transitions. Since such events may be too rare to be sampled by direct numerical simulation, the collapse of both systems is studied using TAMS, a "rare-event" algorithm designed to efficiently sample rare transitions. We find that, in the northwest of Brazil, a transition of the Amazon rainforest to a degraded forest within 200 years is very unlikely. However, in this region, such transition can only occur after an AMOC collapse, which would have a large drying effect that favors the development of extreme wildfires.