Ocean current system could shut down as early as 2025, leading to climate disaster

News
By Keith Cooper
published

The Atlantic Meridional Overturning Circulation has been weakening – and new predictions suggest it could totally switch off between 2025 and 2095.

An illustration showing a visualization of the gulf stream and how heat flows.
Part of a NASA visualization of the Gulf Stream, showing surface temperatures and flow patterns. (Image credit: NASA/Goddard Space Flight Center Scientific Visualization Studio)

A major system of ocean currents that ferries heat from the tropics to the North Atlantic could shut down far sooner than expected, according to new predictions. Such a collapse would prove catastrophic for Earth's climate.

The system, known as the Atlantic Meridional Overturning Circulation (AMOC) had previously been measured to be dramatically weakening in conjunction with rising ocean temperatures. Despite this, however, the Intergovernmental Panel on Climate Change (IPCC) recently announced that climate scientists don't expect the AMOC to totally switch off within the century. 

But a new study is now challenging that conclusion, raising the specter of a halted AMOC to as early as 2025.

"Shutting down the AMOC can have very serious consequences for Earth’s climate, for example, by changing how heat and precipitation are distributed globally," study leader Peter Ditlevsen, from the Niels Bohr Institute at the University of Copenhagen, said in a statement.

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Finding that direct measurements of the AMOC's strength have only been made for the past 15 years, Ditlevsen's team applied sophisticated statistical tools to ocean temperature data going all the way back to the 1870s for an enhanced dataset. This detailed analysis ultimately suggested significant warning signs of the AMOC shutting down between 2025 and 2095, with a staggering certainty of 95%. More specifically, the team's results evidenced that the most likely time for this collapse would be around 2057.

Still, other climate scientists remain cautious, saying that there are still uncertainties in the data that could affect its accuracy. However, it's worth considering that even the mere possibility of the AMOC shutting down so soon is rather alarming.

The AMOC, which includes the Gulf Stream as part of its system, is our planet's main mode of transporting heat away from the tropics. Without it, the tropics would rapidly increase in temperature while vital tropical rains get disrupted. Such rains are essential for the environments of South America, western Africa as well as in India and other regions of south Asia.

Meanwhile, northern and western Europe would lose their source of warm water from the tropics, leading to more storms and severely cold winters in these areas. The loss of the Gulf Stream in particular would also result in rising sea levels on the US’ eastern seaboard. 

"Our result underscores the importance of reducing global greenhouse gas emissions as soon as possible," Ditlevsen said.

In recent years, we’ve already seen the dangers of human-induced climate warming play out as heatwaves grip much of the northern hemisphere. And although the loss of the AMOC may see northern and western Europe cool, “this shutdown will contribute to an increased warming of the tropics," Ditlevsen said, "where rising temperatures have already given rise to challenging living conditions."

The findings were published on Tuesday (July 25) in the journal Nature Communications.

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Keith Cooper
Keith Cooper
Contributing writer

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.

44 Comments Comment from the forums
  • Jan Steinman
    Woa, this is huge!
    Why haven't I seen anything in the mainstream press?

    History will show — to the next sentient species — that Homo sapiens went extinct from apathy.
    Reply
  • Unclear Engineer
    Well, it was covered to some extent several days ago. Here is one story, which has some nice links to interactive maps. See https://wgntv.com/news/map-shows-which-areas-of-illinois-indiana-will-be-underwater-in-2050/ .

    But, the story typically goes quickly to propaganda about how we must change our ways to limit sea level rise. I say "propaganda" because the amount of sea level rise they are talking about in the next 20 - 30 years is pretty much locked in by the emissions and heating that we have already produced. We are not going to "stop sea level rise" in the next few decades, or probably even change it substantially. What we really need is articles that tell us that and we need to start working on how we are going to deal with it - because we will have to deal with it.

    On the other hand, I look at some of these predictions for ocean circulation affecting continental weather patterns, and wonder what that means in terms of the the climate cycles that the Earth has been undergoing in the way of ice ages and short interglacial periods. If Europe gets colder, what does that do to Arctic ice accumulation? We don't yet seem to understand how the Earth's climate has managed to shift between glaciation and melt periods. Yes, we know the Milankovitch Cycles, but they don't give us a direct reaction to climate just by the insolation values in the northern and southern hemispheres - there apparently is a lot more to it than just average heat input from the Sun.

    And, there are still geological surprises about climate changes in the past. For instance, it was recently determined that the Greenland ice sheet mostly or completely melted in the interglacial period about 416,000 years ago. See https://phys.org/news/2023-07-greenland-years-high-sea-today.html . That article states:

    "{The location of the ice core samples} is 138 miles inland from the coast and only 800 miles from the North Pole; the new Science study shows that the region entirely melted and was covered with vegetation during Marine Isotope Stage 11, a long interglacial with temperatures similar to or slightly warmer than today. With this information, the team's models show that, during that period, the ice sheet melted enough to cause at least five feet, and perhaps as much as 20 feet, of sea-level rise."

    And, that was without any human inputs to the warming processes. So, sea level is definitely coming up, and the question is not so much where it will stop as it is how fast will it rise and how do we cope with that on the time frame we are going to get?

    But, it doesn't look like the climate is going to lead to extinction of all life on Earth, or even to the extinction of humans. However, I would not be surprised if climate change, coupled with the human overpopulation, leads to a collapse of our technological society as migrations lead to conflicts along with famines and pandemics. In previous climate cycles, humans were hunter-gatherers and likely migrated to suitable areas when the ones they were is became inhospitable. There was probably some conflict even then, as evidenced by modern humans completely replacing Neanderthals and Denisovans in Europe and Asia. But, the social systems in those days did not depend on the level of technology that we need to maintain today to support 9 billion humans. If our technological capabilities crash, so will human population. There would be plenty of misery and death, but probably not complete extinction. But, still something to avoid if at all possible.
    Reply
  • stigster
    If this is even remotely true, then we should obviously all quit the BS measures to stem climate change aka The 4 seasons that have occurred throughout entire history, since there is nothing we as humans can do to stop that from happening.
    Live it up, we'll all be dead in 2 years.
    Thank you !
    Reply
  • Unclear Engineer
    Humans seem to be making climate changes, and we could stop doing so much of that, but probably not all of it that is due to us.

    But, we really do need to recognize and accept that there are climate cycles that we do not have the ability to control, and we need to learn to live with them. Human history is just a brief part of a long natural history, and a part that seems to have been pretty stable, compared to some of the past. We benefited from that stability as we developed a lot of technological infrastructure. But, much of that infrastructure would not survive even the natural cycles of Earth's climate - so we need to keep adapting to what we will get.

    But that does not mean that we should not care how much of a mess we make of our planet. We can definitely make things worse for ourselves than the natural cycles would create if undisturbed.
    Reply
  • Climate Scientist
    Unclear Engineer said:
    Humans seem to be making climate changes, and we could stop doing so much of that, but probably not all of it that is due to us.

    But, we really do need to recognize and accept that there are climate cycles that we do not have the ability to control, and we need to learn to live with them. Human history is just a brief part of a long natural history, and a part that seems to have been pretty stable, compared to some of the past. We benefited from that stability as we developed a lot of technological infrastructure. But, much of that infrastructure would not survive even the natural cycles of Earth's climate - so we need to keep adapting to what we will get.

    But that does not mean that we should not care how much of a mess we make of our planet. We can definitely make things worse for ourselves than the natural cycles would create if undisturbed.
    100% of the warming of the planet and all sea level rise today is caused by humans. We would be in a cooling period without human activity.

    https://www.carbonbrief.org/analysis-why-scientists-think-100-of-global-warming-is-due-to-humans/#:~:text=The%20best%20estimate%20of%20the,fraction%20of%20modern%20global%20warming.

    https://www.quantamagazine.org/how-earths-climate-changes-naturally-and-why-things-are-different-now-20200721/
    Reply
  • Jan Steinman
    Unclear Engineer said:
    … we need to keep adapting to what we will get.
    I've been working on that for seventeen years, and I'm getting tired.

    Started an ecovillage. Then gave it up when my wife got cancer. Then she dumped me.

    So who wants to pool their resources and create what Richard Heinberg called a "lifeboat community?"
    Reply
  • Unclear Engineer
    Climate Scientist said:
    100% of the warming of the planet and all sea level rise today is caused by humans. We would be in a cooling period without human activity.
    I am not buying that as a real fact. The models are not good enough to support that. And the best evidence is not so supportive.

    Geological evidence clearly shows sea levels higher than today in previous interglacial periods, and we really don't have climate models that can "predict" (actually "backcast") those climate histories. Which is really good evidence that we really do not yet understand all of the circulation changes, etc. that are involved, and cannot predict them very well for long periods of time.

    It is normal for modelers to have more confidence in the accuracy of their models than turns out to be warranted. Usually, models drastically underestimate the uncertainty for the accuracy of their model predictions.

    But, that doesn't mean that things will necessarily be better, they can also be worse than predicted. However, the media tends to hype the worst case results, which, when sometimes they don't actually happen, leads a lot of the public to think that models are always too negative.

    If you look at the current situation in the Milankovitch Cycles, yes, it looks like the heat input to the northern hemisphere should be decreasing from its maximum. But, that doesn't mean that the northern hemisphere should immediately get colder. Think about the analog of a yearly cycle. The heat input to the northern hemisphere peaks about June 21st, but the hottest days are usually in July and August, substantially after the peak heat input. In the Milankovitch cycle, the Earth is now closest to the sun about January 4th and very slowly getting later in the year. and the northern hemisphere is tipped most toward the Sun about December 21st. Would you expect the hottest days in a year to have already occurred by the first week in July? Of course not, and you should also not expect the peak temperatures and sea level rise to occur when the perihelion is on Dec 21st or within a couple weeks of that.

    It is the modeling of the behaviors of circulation and thermal reservoirs (ice, deep oceans, etc.) that is needed to translate heat inputs to climate. We are still in the first iteration of doing that, and we need to learn by doing it and comparing our results to what happens. Remember how bad our weather models used to be, and how unreliable they still are today once we get out several days. Well, climate modeling has not yet had the opportunity to do the thousands of predictions and leaning from the errors that our weather models have benefited from. So, we really cannot expect, and certainly cannot prove that they are even as accurate (in their own way) as our weather models have become.

    That does not mean that I think global climate models are useless. But, I wish modelers would stop making such strong statements about their conclusions, because those are the types of statements that can be proven wrong, and that leads to people disregarding the model predictions completely.

    Anyway, my point still stands, that we are not going to be able to stop the sea level from rising another foot no matter whether "100% of the warming today is caused by humans." I doubt we can even slow it down very much if we all left the planet tomorrow. But, we can certainly make things worse if we keep doing what we have been doing.
    Reply
  • malcolm.mellon
    This is exaggerated. Ocean currents are a result of the rotation pf the earth. There are some thermohaline curculations that accompany these coriolis driven currents which may be affected by changes in temperature such as the Atlantic meridional overturning circulation but thus accompanies but does not drive the ocean circulations.

    nice video by respected physicist:

    tnVWUIhQ8dEView: https://youtu.be/tnVWUIhQ8dE
    Reply
  • Unclear Engineer
    Good video explanation.

    But, with respect to sea level rise, the Milankovitch Cycle that has the northern hemisphere now heading for less solar energy input also has the southern hemisphere heading for more solar energy input. And, the ice in the Antarctic is much more extensive than the ice on Greenland. While totally melting Greenland's ice could raise ocean level by about 23 feet, melting all of Antarctica could raise sea level by more like 350 feet. So, slowing the melt at Greenland at the "expense" of increasing the melt in Antarctica isn't exactly great news.

    But, things really aren't even that simple. If Europe gets 5 degrees C colder, would that start glacier and even ice sheet formation again in the northern hemisphere? Would that help stabilize ocean level? Would ocean level not rising as fast make the loss of shelf ice and thus the loss of continental ice in Antarctica slow down, compared to the models that assume continuously rising ocean levels? Could that be the way that interglacial periods have ended in the past? Could that still happen today, given human effects on atmospheric CO2 levels, continental vegetation and surface reflectivity, etc. etc. etc.?

    I am also wondering if climate scientists have addressed the effects of ice sheet changes on the Milankovitch cycle periods. Taking 300 feet of water mostly from oceans at the equator and piling it as ice mostly near the poles probably has a measurable effect on both the speed of rotation of the earth (length of day) and the rate of precession (wobble like a spinning top) of the Earth's rotational axis, which is the main Milankovitch cycle. (However, the ice ages do not follow that cycle, which is about 24,000 years, but instead now last about 4 of those cycles, something around 100,000 years). But, wait, the earth is not a totally rigid piece of rock below the oceans. Ice accumulation actually changes the shape of the Earth, so that its rocky part bulged more at the equator when there was more ice near the poles. But it doesn't shift shape as rapidly as the ice accumulates and melts. Even today, the Earth is still sinking where the ice was not and rising where the ice was 25,000 years ago. Where I live, the ground has sunk about 3 ", and sea level has risen about 3", since my parents built this house in 1980.

    Modeling all of this is not simple, at all.
    Reply
  • Ken Fabian
    Climate Scientist said:
    100% of the warming of the planet and all sea level rise today is caused by humans. We would be in a cooling period without human activity.

    https://www.carbonbrief.org/analysis-why-scientists-think-100-of-global-warming-is-due-to-humans/#:~:text=The%20best%20estimate%20of%20the,fraction%20of%20modern%20global%20warming.

    https://www.quantamagazine.org/how-earths-climate-changes-naturally-and-why-things-are-different-now-20200721/
    Yes, more than 100%. The modeling as well as pre-industrial trends show that without human influences there would be slow cooling. And there is the aerosol cooling effect - about 0.5 C - that has the unfortunate ability to mask the level of warming from enhanced greenhouse, that grows as fossil fuel use grows - with aerosol cooling dependent on the ongoing rate of dirty fuel burning whilst enhanced greenhouse depends on the accumulated total that has been burned. One starts high and stays that way as long as it continues, the other starts at zero and builds over time. One stops quickly when the causal source stops. The other continues long after the source stops.

    "But climate models could be wrong" - in an absolute sense, yes, they are imperfect/wrong, but they not entirely wrong or even that wrong or necessarily wrong only in the direction of less damaging, but it is a convenient argument and justification for doubt, denial and delay.

    And blaming the messenger - attributing their own freely made choice to doubt, deny and delay as an uncontrollable, reflexive reaction to scientists or more often to climate activists, without even bothering to check what scientists say. They were making a point of how bad as well as how likely the climate problem has the potential to be. Claiming "I wouldn't be a climate science denier or oppose climate policies or argue for the most unpopular and expensive options as first choice if they hadn't made so much fuss about it being bad" - neatly squares the circle - it is ALL down to those who say it is real and serious, the existence of a climate problem and opposition to doing anything about it, all despite the modeling and the fundamental understandings they are built on showing that to be the case.

    In my view it hasn't been climate scientists letting us down - or even environmentalists, for reacting to the science like it were true, ie that the problem is serious - it has been mainstream influential voices, by promoting distrust of science and prioritising obstruction of actions to address it, largely on behalf of large parts of commerce and industry that promoted alarmist fear of taking appropriate action. Interests that politicians and parties seek to defend and promote and avoid upsetting, that chose their political stance based on how they see actions to fix it would affect their near term costs, competitiveness and profitability - NOT on the validity of the science or the potential for longer term economic harms.

    Deliberately undermining public trust in that science has been one of the most profoundly irresponsible and dangerous choices people with power, influence holding positions of trust and responsibility have ever made. Except doubling down.
    Reply