New study flags tipping risks in ocean circulation

08/10/2025

Growing evidence shows that the oceans’ circulation systems can undergo tipping behaviour in a warming climate, according to a new review paper. The evidence is less clear for the monsoon systems – but change of rainfall patterns would impact large populations.

Tipping points are thresholds beyond which a system changes fundamentally. Once critical levels of global warming or deforestation are crossed, amplifying feedbacks can become strong enough to drive self-sustaining changes, such as melting ice sheets, collapsing forest ecosystems, or disrupted ocean circulation. 

These shifts can happen abruptly and may be irreversible. Crossing such tipping points would threaten the stability of the Earth system and, consequently, put billions of people at risk.

In 2022, a paper published in Science described 16 systems that show tipping behaviour. The authors, led by Earth Commission contributor David Armstrong McKay, showed that several of these tipping points might already be crossed at 1.5°C of warming. Additional systems may also be at risk.

“Therefore, it is important to gather all available information about these systems to find out if they can tip, under which circumstances, and how tipping would play out”, said Dr. Sina Loriani, Earth Commission researcher based at Potsdam Institute for Climate Impact Research and lead author of a new paper in the journal Earth System Dynamics.

A growing research field

In this new paper Loriani and colleagues reviewed evidence from geological records, observational data and modelling studies to assess tipping points in the ocean overturning circulations, monsoon systems and global atmospheric circulation. This work can help refine safe boundaries and eventually inform how just boundaries can be set to minimize harm to people. 

The authors found multiple strands of evidence for tipping points when it comes to ocean currents such as the Atlantic Meridional Overturning Circulation (AMOC), which carries warm water north and cold water south. A slowdown or collapse of these circulation systems would have far-reaching consequences for climate, biosphere, and human societies. For example, an AMOC collapse could plunge northwestern Europe into a very cold and hostile climate.

“As we continue to massively interfere with the established biophysical dynamics of the Earth system, the risk for crossing tipping points only increases,” Loriani warned.

Tipping in monsoon systems uncertain

When it comes to circulation systems in the atmosphere, the evidence is less clear for tipping behavior. 

“Abrupt change of the West African monsoon is possible but with low confidence, and the tipping of the South American, East Asian, and Indian monsoons is uncertain,” said Earth Commissioner Govindasamy Bala, a professor at the Indian Institute of Science and a co-author of the paper. “However, we need more research to increase confidence in these assessments.”

Nearly two-thirds of the global population is impacted by tropical monsoons and any abrupt change to their rainfall could have disastrous effects for people.

“Could have calamitous effects”

Fellow Earth Commission co-author Dr. Thejna Tharammal, also at Indian Institute of Science, explained how deeply intertwined economies and livelihoods are with monsoon rainfall. She emphasized even small shifts can have widespread social and economic impacts.

“Potential tipping of the monsoon systems could have calamitous effects on hundreds of millions,” she said. “Even a 10% drop in average rainfall is considered a drought in India, often leading to severe economic losses. While tipping of the Indian and East Asian monsoons remains uncertain, paleoclimate records show these systems have shifted abruptly in the past, underscoring the urgent need to close research gaps.”

In the past few years, tipping points as a field of research has been growing. This has lead to a Global Tipping Points Report with more than 200 co-authors first published in 2023, and a dedicated chapter in the upcoming IPCC Seventh Assessment Report with Earth Commissioners Tim Lenton, Ricarda Winkelmann and Cunde Xiao among the lead authors. Earth Commission is also contributing to the Tipping Points Modelling Intercomparison Project, and a discussion series to advance knowledge of tipping points research.