THE ATLANTIC OCEAN’S major current, which influences weather systems worldwide, may have been losing stability over the course of the last century, a new scientific study said today.

The Atlantic Meridional Overturning Circulation (AMOC), to which the Gulf Stream belongs, transports warm water masses from the tropics northward at the ocean surface and cold water southward at the ocean bottom.

This plays a major role in creating the relatively mild temperatures found in Europe, notably in Ireland.

Climate models have shown that the AMOC is at its weakest in more than a 1,000 years. However, previously it has not been known whether the weakening is due to a change in circulation or if it is to do with the loss of stability.

“The difference is crucial”, says Dr Niklas Boers from the Potsdam Institute for Climate Impact Research, “because the loss of dynamical stability would imply that the AMOC has approached its critical threshold, beyond which a substantial and in practice likely irreversible transition to the weak mode could occur.”

As it influences weather systems worldwide, a potential collapse of the current could have severe consequences across the globe.

The study, published in the journal Nature Climate Change, found that the weakening is indeed likely to be associated with a loss of stability.

The researchers came to this conclusion by analysing the sea-surface temperature and salinity patterns of the Atlantic Ocean.

“The findings support the assessment that the AMOC decline is not just a fluctuation or a linear response to increasing temperatures but likely means the approaching of a critical threshold beyond which the circulation system could collapse,” Dr Boers said in a statement.

A number of factors are likely contributing to the weakening of the current. 

These factors include freshwater inflow from the melting of the Greenland ice sheet, melting sea-ice, increasing precipitation and river run-off.

Freshwater is lighter than saltwater and reduces the tendency of the water to sink from the surface to greater depths.

These factors add to the direct effect that the warming of the Atlantic ocean has on its circulation.

The researchers note that, while the respective relevance of the different factors has to be further investigated, they’re all linked to human-related climate change.