CCSS Meeting #80: Failure to track a stable AMOC state under rapid climate change

This lecture will be held in physical format at the CCSS Living Room (Min. 4.16) with lunch and refreshments provided. The overarching topic of the CCSS Lunch Meetings of the academic year 2025/2026 is Tipping behavior in Natural and Societal Systems.

Speaker Overview
Dr. René van Westen is a climate physicist and researcher who became internationally known in 2024 for his influential study on the Atlantic Meridional Overturning Circulation (AMOC). In that work, he and his co-authors used high-resolution climate models to demonstrate how the AMOC could potentially collapse and explored the far-reaching climatic consequences of such an event. Van Westen studied physics in Amsterdam and went on to complete a PhD focusing on finely resolved climate models, including earlier work on the AMOC. This expertise proved valuable in projects like TiPES (Tipping Points in the Earth System), where he investigated abrupt changes in the climate system. He is now a postdoctoral researcher at Utrecht University, where his research continues into ocean dynamics, climate tipping points, and early warning indicators for critical shifts in Earth’s climate.

Lecture Overview
The Atlantic Meridional Overturning Circulation (AMOC) is a tipping element in the climate system, which has been demonstrated in a hierarchy of climate models under increasing freshwater flux forcing. The AMOC may also become unstable under 21st century climate change, with an increasing risk of AMOC tipping above +1.5C of global warming. By contrast, several studies report stable AMOC states under extreme climate change conditions (4xCO2). Consequently, it remains unclear whether a global warming threshold for AMOC tipping exists.

Here, we reconcile differing perspectives within the AMOC tipping community and demonstrate that the rate of warming controls the risk of AMOC tipping. By analysing state-of-the-art climate model simulations, we identify a robust mechanism that stabilises the AMOC under climate change. Higher sea surface temperature induce net evaporation and reduce the sea-ice cover over the Atlantic Ocean. Both effects contribute to a salinifying Atlantic Ocean that strengthen and stabilise the AMOC. This stabilizing mechanism operates on timescales slower than the present-day radiative forcing rate that destabilises the AMOC, hence the AMOC may collapse when the radiative forcing is large enough.

There will be 45-min lecture from the speaker, followed by a 15-min discussion session.

To attend the lecture, please signup below before 15:00 on Wednesday March 11.