The Atlantic Ocean's system of currents, which impact the Northern Hemisphere's climate, could be weakening and result in major changes to the world's weather, a new scientific study warned.

In the study, published on Thursday in the journal Nature Climate Change, researchers focused on the Atlantic Meridional Overturning Circulation (AMOC). The large system of ocean currents, which is part of the Gulf Stream, transports warm water from the tropics northwards into the North Atlantic.

It transports that warm water from the tropics near to the ocean's surface, while it pushes cold water southwards and deeper below the surface. As the AMOC redistributes heat, it influences weather patterns globally.

"Significant early-warning signals are found in eight independent AMOC indices, based on observational sea-surface temperature and salinity data from across the Atlantic Ocean basin," researchers wrote in the study's abstract.

"The AMOC may have evolved from relatively stable conditions to a point close to a critical transition," they concluded.

A collapse of the system would substantially cool Europe and have a strong impact on the tropical monsoon systems.

Weaker than 'any time since 1,000 years'

Niklas Boers of the Potsdam Institute for Climate Impact Research (PIK) in Germany, wrote in the journal that the AMOC system was found to be weaker than at any time in the past 1,000 years.

It had not been clear whether the weakening is due to a change in circulation or a loss of stability. Researchers said in the study that the difference matters.

Researchers analyzed the sea-surface temperature and salinity patterns of the Atlantic Ocean. They concluded that the weakening of the last century is likely to be associated with a loss of stability.

"The loss of dynamical stability would imply that the AMOC has approached its critical threshold," Boers wrote, which could lead the circulation system to collapse.

Climate change impacting Gulf Stream change

Among the factors affecting the current are the melting of the Greenland ice sheet, melting of Arctic sea ice, and an overall enhanced precipitation and river runoff.

Climate change is behind these factors, as the atmosphere warms due to increased greenhouse gas emissions, the surface ocean beneath retains more of heat. 

A potential collapse of the AMOC system could have severe consequences for the world's weather systems. But in particular, it would increase cooling of the Northern Hemisphere, sea-level rise in the Atlantic, an overall fall in precipitation over Europe and North America, Britain's Met Office said.

So far, scientists have not predicted a collapse of the AMOC system before 2100.

Correction from August 9, 2021: This article previously included a NASA visualization of currents in the Pacific Ocean, not the Atlantic Ocean. The image has been replaced and we apologize for the error.

jcg/rs (dpa, Reuters)