Rapid rise in CO2 levels could threaten key Atlantic Ocean circulation: Study

A rapid increase in atmospheric carbon dioxide levels could threaten the stability of a major Atlantic Ocean circulation system that plays a key role in regulating Europe's climate, according to a new study.

Researchers at Utrecht University in the Netherlands found that the speed at which the climate warms could be crucial in determining whether the Atlantic Meridional Overturning Circulation (AMOC) weakens to the point of collapse, Danish public broadcaster DR reported.

The AMOC transports warm water from the tropics toward the North Atlantic, helping keep northern Europe relatively mild, while colder and saltier water sinks and flows southward through the deep ocean.

Climate change is weakening the system as melting ice and increased rainfall add freshwater to the North Atlantic, while rising ocean temperatures also disrupt the sinking of dense water.

The study, published in the journal Nature Climate Change, suggests the pace of warming, rather than only the eventual temperature increase, could significantly affect the AMOC's stability.

“During slow warming, the entire ocean, from the surface down to its deepest layers, has time to gradually reorganize and adapt to the changing conditions,” said Henk Dijkstra, professor of dynamic oceanography at Utrecht University and a co-author of the study.

“During faster warming, the ocean simply cannot keep up,” he added.

Researchers compared different rates of atmospheric CO2 increase, defining rapid warming as an annual rise of 2.5 parts per million (ppm) and slow warming as 0.5 ppm. The current annual increase is around 3.2 ppm, according to DR.

Under the slower scenario, global temperatures could rise by around 4C (7.2F) or more without triggering an AMOC collapse, the study found. Under rapid warming comparable to the current pace of CO2 increase, however, the circulation could collapse at around 2C (3.6F).

Peter D. Ditlevsen, a climate researcher at the University of Copenhagen, said the findings were concerning.

“If we look at our current CO2 emissions, we should be concerned,” he told DR.

A major AMOC collapse could bring significantly colder winters to northern Europe while making tropical regions warmer and disrupting rainfall patterns, potentially threatening agriculture.

Researchers also warned that the circulation may be difficult to restore once it collapses, even if atmospheric CO2 levels are subsequently reduced.