Atlantic Ocean current might weaken, but not as much as thought

The latest modelling has shown that an Atlantic Ocean current critical for regulating Earth’s climate will weaken due to anthropogenic climate change, but perhaps not to the point of collapse as previously suggested.

The Atlantic Meridional Overturning Circulation (AMOC) transports water and heat from the southern to the northern hemisphere. It also regulates regional weather including the relatively mild summers of Europe and the monsoon seasons in Africa and India.

Previous models have suggested that the greenhouse effect driven by the continued burning of fossil fuels would cause the AMOC to weaken. This would be primarily driven by the increase of freshwater in the North Atlantic from glacier and sea ice melting and warming ocean temperatures.

Some projected that the AMOC would nearly collapse, with far-reaching consequences, including regional sea level rise and major climate shifts such as colder temperatures in northern Europe and drier conditions in the Amazon and West Africa.

A new model suggests that, while AMOC will weaken, it won’t be to the extent warned by some earlier projections.

The findings are published in the journal Nature Geoscience.

The model is a simplified physical simulation which incorporates about 20 years of real-world data of the ocean current’s strength. The researchers found that AMOC will likely weaken by 18 to 43% by the year 2100.

Palaeoclimate records obtained from ocean sediment cores show the AMOC experienced weakening in the past, including about 20,000 years during the last ice age.

The research explains the link between the present-day strength of the AMOC and how it will weaken in future.

Models with a stronger present-day AMOC show greater weakening under climate change. This is because a stronger AMOC extends to greater depths, meaning changes in surface water temperature and salinity penetrate deeper into the ocean and drive greater weakening.

A shallower present-day AMOC still shows weakening under climate change, but to a lesser extent. This is more accurate, according to the study.

“Our results imply that, rather than a substantial decline, the AMOC is more likely to experience a limited decline over the 21st century – still some weakening, but less drastic than previous projections suggest,” says first author Dave Bonan, who recently received his doctorate at the University of Washington in the US.

“There is immense value in doing basic research – it can give us a better indication of what the future might look like, as our study shows,” Bonan adds.