Atlantic circulation lies in the balance

The premise behind the apocalyptic blockbuster “The Day After Tomorrow” has taken on a profound new meaning with European scientists now saying they have evidence the planet’s circulation of ocean water lies in the balance.

Their new paper suggests the results of reaching the tipping point for the Atlantic Meridional Overturning Circulation (AMOC) could be even more severe than scientists thought.

“What surprised us was the rate at which tipping occurs,” said the paper’s lead author, René van Westen, of Utrecht University. “It will be devastating.”

The research has been published in Science Advances.

AMOC takes water from the tropics and moves it up to Greenland and Europe to be cooled, before travelling back down again.

The Southern Hemisphere has two similar systems occurring near New Zealand and the tip of South America.

Global ocean circulation gif
A simplified system of ocean currents. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio (Background)

But this incredible ocean process only works because of salt. The cold, salty water near the poles sinks,  to then travel south along deep currents. But with melting sea ice, the water is no longer as salty, and it no longer sinks.

“Climate change melts these ice caps around Greenland and Antarctica,” said climate and oceans researcher Professor Matthew England from the University of New South Wales.

“That’s why these overturning circulations are at risk of slowing down and eventually collapsing – we’re adding melt water and melt water is very buoyant.”

But this new study found that if we reach the tipping point – or point of no return – we won’t have long before we start to see the effects.

“The results showed that the circulation could fully shut down within a century of hitting the tipping point, and that it’s headed in that direction,” the team write in a piece for The Conversation.  

“If that happened, average temperatures would drop by several degrees in North America, parts of Asia and Europe, and people would see severe and cascading consequences around the world.”

While in a world of rapid warming, this might seem positive, England warns that’s definitely not the case.

“Whilst global warming will offset that cooling effect for Europe, it sets things like the global energy balance,” he told Cosmos. 

“If you disrupt that ocean circulation, you’re disrupting the climate system in a very significant way.”

IPCC reports have suggested that the likelihood of the AMOC tipping point being reached this century is approximately 10%, but researchers like England argue that this could be much higher.

“I would say 30-40%. Almost a toss of a coin, percentage wise,” he said.

“The other important thing to say is that the world doesn’t end in 2100. So, we’re already almost a quarter of the way through the century. I think it’s a bit arbitrary.”

But the report did provide an early warning signal – an amount of freshwater being added into the system – that the researchers suggest will be a few decades away from tipping.

“It’s not science fiction,” van Westen told Inside Climate News.

“We need to show this is not only a Hollywood blockbuster, ‘The Day After Tomorrow’. This is real, this can happen. And I think it’s important and urgent to keep saying to people, okay, we need to really tackle our emissions.”

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