Substantial Risk of 21st Century AMOC Tipping even under Moderate Climate Change

TL;DR

This study indicates a substantial risk of Atlantic Meridional Overturning Circulation (AMOC) collapse within the 21st century at moderate climate change levels, with a critical threshold around +3°C global warming, posing severe societal impacts.

Contribution

The paper reassesses the critical global warming threshold for AMOC collapse using climate models, observations, and reanalysis, highlighting a higher risk than previously estimated.

Findings

AMOC likely to tip within the 21st century under moderate warming scenarios

Critical global warming threshold for AMOC collapse is around +3°C

AMOC collapse will cause significant societal impacts despite regional warming offset

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the climate system and considered to be a tipping element. There is still a large uncertainty on the critical global warming level at which the AMOC will start to collapse. Here we analyse targeted climate model simulations, together with observations, reanalysis products and a suite of state-of-the-art climate model results to reassess this critical global warming level. We find a critical threshold of +3C global mean surface temperature increase compared to pre-industrial with a lower bound of +2.2C (10%-Cl). Such global mean surface temperature anomalies are expected to be reached after 2050. This means that the AMOC is more likely than not (> 50%) to tip within the 21st century under a middle-of-the-road climate change scenario and very likely (> 90%) to tip under a high emissions scenario. The AMOC collapse induced cooling is shown to be offset by the regional warming over Northwestern Europe during the 21st century, but will still induce severe impacts on society.