'We are approaching the tipping point': Marker for the collapse of key Atlantic current discovered

An image of an open oceans surface with crashing waves and a stormy sky.

The tipping point for the collapse of a key Atlantic Ocean current may have been discovered by scientists. (Image credit: HadelProductions/Getty Images)

Scientists have discovered a key warning sign before a crucial Atlantic current collapses and plunges the Northern Hemisphere into climate chaos.

The Atlantic Meridional Overturning Circulation (AMOC) carries warm water north from the Southern Hemisphere, where it releases heat and freezes. The freezing process concentrates salt in the non-frozen portion of the ocean water; this extra-saline water sinks, travels back south and picks up heat again, restarting the conveyor belt. (The Gulf Stream is part of this belt.)

This release of heat helps keep Europe, and to some extent North America, balmier than it otherwise would be. But sediment records over the past 100,000 years suggest that, at times, the AMOC has shut down abruptly, leading to major climate shifts over mere decades.

Scientists believe we could be veering towards this scenario once again — potentially as early as 2025 — as a result of climate change. However, until now researchers had no way of telling if the current is on the path toward one of these tipping points.

In a new study, published today (Feb. 9) in the journal Science Advances, scientists found that the flow of fresh water into the Atlantic Ocean at a latitude of 34 degrees south (the latitude where South Africa sits) may indicate a key warning sign for an impending AMOC collapse. The team found that about 25 years before the AMOC collapses, this flow reaches a minimum).

Scientists don't have a long enough record of observations of freshwater flow at this spot to predict how far away the AMOC is from a tipping point right now. However, they do know that this flow has been declining.

"We are approaching the tipping point, but we cannot deduce the distance to the tipping point," study first author René M. van Westen, a postdoctoral researcher in marine and atmospheric science at Utrecht University, told Live Science.

Because the rising and sinking of the AMOC depends on the salinity of the water, this circulation is very sensitive to influxes of fresh water, van Westen said. As the climate warms and precipitation patterns change, the patterns of freshwater flow into the ocean change, too.

Illustration of the Earth demonstrating the movement of warm water and cold water. — The AMOC transports warm water from the Southern Hemisphere to the north, helping to keep Europe and other regions warm. (Image credit: National Oceanic and Atmospheric Administration (NOAA).)

It's difficult to predict the outcomes, though, and finding the AMOC's tipping point requires simulating a gradual increase in freshwater flow in the northern Atlantic over more than 2,000 years, van Westen said. This is a long and computationally expensive process, but trying to cut corners by simulating large freshwater pulses is not as realistic or precise.

The researchers modeled this gradual freshwater increase using state-of-the-art climate models. They found a long negative trend in freshwater flow at 34 degrees south — the southern border of the Atlantic Ocean — reaching a minimum about 25 years before the AMOC collapses. The minimum is not tied to a specific salinity value, but rather is relative to the patterns that came before, so researchers aren't sure how these conditions compare to today's. The AMOC collapse led to a complete lack of circulation and a loss of about 75% of the heat transport from south to north.

If the AMOC were to collapse in the near future, the consequences would be dire. Without the AMOC, the Northern Hemisphere would get colder, and the southern hemisphere would get warmer, though by a lesser degree . The effects vary by region, but Europe would be hard hit, van Westen said, cooling between 9 and 18 degrees Fahrenheit (5 to 10 degrees Celsius) within a century. That's a huge swing, even compared with the current level of climate change, which is already having impacts.

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"On average, the global climate warms by about 0.2 degrees C [0.36 F] per decade," van Westen said.

The collapse of the AMOC would also lead to changes in precipitation around the globe. For example, the wet and dry seasons in the Amazon rainforest would swap places, leading to major ecological impacts, the researchers wrote in the paper.

"We know under climate change that this AMOC will gradually weaken and this [freshwater] parameter will become more negative, so it will destabilize the AMOC further," van Westen says. The message, he added, is that the need to halt climate change is urgent: "We need to stop emitting as a global society."

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: community@space.com.

Stephanie Pappas is a contributing writer for Space.com sister site Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.

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2 Comments Comment from the forums

Unclear Engineer

I am still waiting for a global climate model to be able to backcast the ice age history as found in geological evidences.

Articles like this one seem to say that the "tipping point" is heading towards massive cooling of the northern hemisphere. Which sounds a lot like the beginning of an ice age, not the global climate "melt-down" of insufferably high temperatures everywhere that are the angst of "global warming" activists.

Another disparity in this particular article is "sediment records over the past 100,000 years suggest that, at times, the AMOC has shut down abruptly, leading to major climate shifts over mere decades." But the last 100,000 years was the last "ice age", at least up to about 20,000 years ago. So, if this happens during ice ages, is it really a "global warming" issue? And, if it has happened before, why is it something that we can "prevent" by changing our emissions?

For some time, there has been a "snow blitz" theory for the beginning of ice ages that has enhanced snowfalls in the northern latitudes change the albedo sufficiently to initiate a new ice age by reflecting much of the summer insolation back into space, keeping the northern summers very cold. The theory originally was counting on the Arctic Ocean to become ice-free, so that it could provide moisture for the massive snow production. Since the Arctic ice does seem to be melting away, combining that with the cooling due to the Atlantic Meridional Overturning Circulation stopping would seem to be a good reason to suspect the onset of a new ice age. Is that what has been happening repeatedly over the last few million years? Will more CO2 in the atmosphere change this cycle - and if so, in what ways?

Humans will suffer no matter how the climate and sea level and rainfall patterns change, because we have so much expensive infrastructure built around the existing conditions, and such a high global population that there is no room to just move to a better place when one place becomes less hospitable while others become more hospitable.

But, my expectation is that we will see some pretty massive changes, no matter what we do. Even without contributions from human activities, sea levels have reached higher values in the previous interglacial periods - 25 feet higher than today about 120,000 years ago, and even higher in prior interglacial periods. We need to expect sea level to rise, and rise a lot. The only question is how fast, and how high. And, I have read that the Gulf Stream stopping would raise sea level by about 5 feet where I live, which would make my own home flood on every high tide. This article seems to say that could happen fast enough that a lot of people on the east coast of the U.S. could be flooded out in the next decade.
Reply
Atlan0001

Unclear Engineer said:
I am still waiting for a global climate model to be able to backcast the ice age history as found in geological evidences.

Articles like this one seem to say that the "tipping point" is heading towards massive cooling of the northern hemisphere. Which sounds a lot like the beginning of an ice age, not the global climate "melt-down" of insufferably high temperatures everywhere that are the angst of "global warming" activists.

Another disparity in this particular article is "sediment records over the past 100,000 years suggest that, at times, the AMOC has shut down abruptly, leading to major climate shifts over mere decades." But the last 100,000 years was the last "ice age", at least up to about 20,000 years ago. So, if this happens during ice ages, is it really a "global warming" issue? And, if it has happened before, why is it something that we can "prevent" by changing our emissions?

For some time, there has been a "snow blitz" theory for the beginning of ice ages that has enhanced snowfalls in the northern latitudes change the albedo sufficiently to initiate a new ice age by reflecting much of the summer insolation back into space, keeping the northern summers very cold. The theory originally was counting on the Arctic Ocean to become ice-free, so that it could provide moisture for the massive snow production. Since the Arctic ice does seem to be melting away, combining that with the cooling due to the Atlantic Meridional Overturning Circulation stopping would seem to be a good reason to suspect the onset of a new ice age. Is that what has been happening repeatedly over the last few million years? Will more CO2 in the atmosphere change this cycle - and if so, in what ways?

Humans will suffer no matter how the climate and sea level and rainfall patterns change, because we have so much expensive infrastructure built around the existing conditions, and such a high global population that there is no room to just move to a better place when one place becomes less hospitable while others become more hospitable.

But, my expectation is that we will see some pretty massive changes, no matter what we do. Even without contributions from human activities, sea levels have reached higher values in the previous interglacial periods - 25 feet higher than today about 120,000 years ago, and even higher in prior interglacial periods. We need to expect sea level to rise, and rise a lot. The only question is how fast, and how high. And, I have read that the Gulf Stream stopping would raise sea level by about 5 feet where I live, which would make my own home flood on every high tide. This article seems to say that could happen fast enough that a lot of people on the east coast of the U.S. could be flooded out in the next decade.
It isn't going to rise in salt sea water but in freshening salt freeing fresh waters which will turn to ice masses quickly unlike the salt seas. It is the more salt free -- though not salt free as such -- freshening waters that will block up the warm Atlantic current and roll pretty fast into the next fresh water 'Ice Age'. The almost cosmic 'colding' of the Earth over millions of years has become the norm of Earth with only lucky interludes of global warming due to our salt seas and, to some degree, tectonic plate movements. The salty oceans only turning slowly back to salty oceans melting the blockage of the Atlantic current flow enough to re-begin global warming. And there are other things, other possibilities including cosmic possibilities from outside Earth, for life on Earth to worry about during the 80,000 to 120,000 years of a real 'Ice Age' (not a 500 year long 'Little (half an...) Ice Age').
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