By Lauren Kirschman, UW News

The Atlantic Meridional Overturning Circulation, or AMOC, is a system of ocean currents that plays a crucial role in regulating Earth’s climate by transporting heat from the Southern to Northern Hemisphere. Confined to the Atlantic basin, the AMOC modulates regional weather — from mild summers in Europe to monsoon seasons in Africa and India.

Climate models have long predicted that global warming will cause the AMOC to weaken, with some projecting what amounts to a near-collapse relative to the AMOC strength in observations today. But a new study from a team of researchers that included the University of Washington shows that the AMOC is likely to weaken to a much lesser extent than current projections suggest. The study was published May 29 in Nature Geoscience.

A severe weakening would have far-reaching consequences, including changes in regional sea level rise, and major shifts in regional climate, such as colder conditions in northern Europe and drier weather in parts of the Amazon and West Africa.

“Our results imply that, rather than a substantial decline, the AMOC is more likely to experience a limited decline over the 21^st century — still some weakening, but less drastic than previous projections suggest,” says David Bonan, lead author of the study and a UW postdoctoral research fellow in the Cooperative Institute for Climate, Ocean and Ecosystem Studies.

The researchers developed a simplified physical model based on fundamental principles of ocean circulation — specifically, how sea water density differences and the depth of the overturning circulation are related — that also incorporates real-world measurements of the ocean current’s strength. The real-world data was collected over 20 years with monitoring arrays and other observations of the Atlantic basin.

Results show that the AMOC will weaken by around 18-43% by the end of the 21^st century. While this represents some weakening, it’s not the near-collapse that more extreme climate model projections suggest.