Scientists warn of “irreversible change” in ocean currents that could quickly freeze parts of North America

A major system of ocean currents in the Atlantic, including the Gulf Stream, has been disrupted by climate change, scientists report in a new study published Thursday. If this system were to collapse, it would lead to dramatic changes in weather patterns around the world.

The Atlantic Meridional Circulation, or AMOC, carries warm, salty water from the tropics north near the ocean surface and cold water south near the ocean floor.

“The Atlantic Meridional Circulation is really one of our planet’s key circulation systems,” said study author Niklas Boers of the Potsdam Institute for Climate Impact Research in Germany.

The findings of a similar 2018 study prompted comparisons to the 2004 disaster movie “The Day After Tomorrow,” which used a similar stoppage of the ocean current as its premise. At the time, the authors of the study said it was at least decades away from collapse, but it would be catastrophic.

The potential collapse of this system of ocean currents would have serious consequences for the entire globe, say the authors of the new study.

If this circulation stops, it could lead to extreme cold in Europe and parts of North America, rising sea levels along the U.S. East Coast, and disruption of the seasonal monsoons that provide water for much of the world.

It would also threaten the Amazon rainforest and Antarctic ice sheets.

Researchers studying ancient climate change have also found evidence that the AMOC could shut down abruptly, causing temperature spikes and other dramatic changes in global weather systems.

The study was published Thursday in the peer-reviewed British journal Nature Climate Change.

Climate models showed that AMOC is at its weakest level in more than 1,000 years. But it is not known whether the weakening is due to a change in circulation or a loss of stability.

“The difference is crucial,” Burs said, “because the loss of dynamic stability means that the AMOC has approached its critical threshold beyond which a significant and, in practice, probably irreversible transition to a weak regime could occur.

After examining the underlying AMOC data, the scientists determined that the recent weakening is likely related to a loss of stability. “The results support the assessment that the AMOC decline is not simply a fluctuation or a linear response to rising temperatures, but likely means that it is approaching a critical threshold beyond which the circulation system could collapse,” Boers said.

The study said a number of factors – factors that add to the direct effects of Atlantic Ocean warming on its circulation – are likely important to the disruption of the AMOC. These include freshwater inflows from the melting of the Greenland Ice Sheet, melting sea ice, increased precipitation and river runoff.

Fresh water is lighter than salt water and reduces the tendency of water to sink from the surface to greater depths, which is one of the driving forces behind tipping.

Levke Caesar of the University of Mainoat in Ireland, who was not involved in the study, said, “The method of investigation cannot give us an exact timeline for a possible collapse, but the analysis presents evidence that the AMOC has already lost stability, which I take as a warning that we may be closer to a tipping of the AMOC than we think.”

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