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

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A vital Atlantic current that includes the Gulf Stream and keeps our climate in check may be giving off a warning sign of collapse.

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. 

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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.

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"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. 

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." 

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Stephanie Pappas
Stephanie Pappas
Live Science Contributor

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. 

6 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').
    Reply
  • Shalamanezer
    The "Global Warming" term was initiated before we knew as much earth science as we know now (and there is still so much to learn as this article suggests. So let's avoid fifty years of pedantry and just say "Climate Chaos".
    Not knowing when an AMOC event in the massively complex, interlocking system we call Earth is going to occur does not equate to it's not going to happen. It is evident 25 times in the Greenland ice cores that span around 800 thousand years.
    So it will happen at some point, whether it's before or after we've managed or failed to reduce carbon and related atmospheric emissions.
    Reply
  • Questioner
    My thought is like the 'little ice age' Europe may get a slight reprieve for the earlier stages of global warming. Over the long run (if we don't enact major counter measures) is Europe will cook, broil, steam along with the rest of the planet.

    I don't know if human caused GW is sufficient to cause a bio-terminal (ala Venus) feedback loop,
    But is scarier than mere human extinction.
    Reply
  • Unclear Engineer
    If Europe gets anything like the beginning of an ice age, it will really complicate the politics of conversion from fossil fuels to renewable energy sources.

    Unless the climate forecasters are able to predict the onset and subsequent progression of the temperature declines, there will be no confidence left in the climate projections for any later warming.

    As I stated in a previous post, the article's statement that the current has stopped multiple times during the last ice age tends to make it seem that it is not going to change the long-term trend. But, climate is probably mathematically "chaotic" in the same way that short term weather is chaotic, so it may take a coincident combination of various climate-affecting parameters to "flip" from overall warming to overall cooling and vice versa. Just looking at the Milankovitch cycles would suggest that ice ages should come and go on a frequency of twenty-something thousand years, not 100,000 years or 50,000 years, as the geological evidence indicates that they have after and before about 900,000 years ago.

    I hope the climate modelers can get a reasonably accurate handle on what really causes ice ages to come and go, so that they will be able to retain some credibility when some of that chaotic behavior manifests itself in the present.
    Reply
  • Atlan0001
    The "Little Ice Age" struck fast . . . within less than a century! Geologists have found that some of the largest, longest, Ice Ages encompassed large sections of the Earth within just two short centuries of their beginning . . . and lasted better than a hundred thousand, to a hundred and twenty thousand, and more years apiece before interludes of a few tens of thousands of years of global warming. We are overdue for the start of the next one . . . Earth normal condition now (Ice Age), short the short interlude periods of global warming.
    Reply