We Now Have Early Warning Signal Of Ocean Current Collapse

0:00We're leaving today and entering a world of Mickey Mouse waving, Princess meeting and greeting. Lightsaber clashing. The Twilight Zone Tower of Terror dropping. Banshee flying. Space Mountain launching. Galaxy rewinding. What's the whole deck with galaxy rewinding? Fireworks igniting. World of Other Worlds. For whatever you love. Infinite worlds await at the most magical place on Earth. Walt Disney World Resort. This week we have news about a much-feared tipping point concerning the Atlantic Meridional Overturning Circulation, AMOC. That's the Atlantic conveyor belt that transports warm water from the tropics northward, and that helps keep Northern Europe temperate.

0:46It's what we've relied on for thousands of years. If this conveyor belt turns off, Northern Europe would be plunged into freezing conditions. It would basically destroy agriculture across most of the continent. it's very bad news. So it's vital that we understand the behaviour of the AMOC and have an early warning of if it's going to collapse so that we could perhaps do something about it. That's what we're getting into on this episode of The World, The Universe and Astronom News Scientist. I'm Dr. Rowan Hooper and I'm joined today by climate journalist Alec Loon. Alec, you've been reporting on a new paper in Nature about the AMOC.

1:21Let's start off by distinguishing between the AMOC and the Gulf Stream. The Gulf Stream is part of the AMOC, is the simplest way to put it. The AMOC is this overturning circulation, this ocean conveyor belt. So it has many different branches, but the overall kind of motion is warm water going north through the Atlantic at the surface, and then diving down as it cools, and then going south deep near the ocean floor, back down south, and as part of this global thermohaline circulation around the oceans. So the Gulf Stream is one branch of that AMOC. It flows up the eastern seaboard of the United States, carrying warm water from the Caribbean.

2:10And then at about halfway up the eastern seaboard, it veers off towards Europe and crosses the Atlantic and brings some of that heat to Europe. But again, it's just part of this bigger ocean circulation, this ocean conveyor belt of which the AMOC is a major part. Yeah. And take us through a bit of the history of why we've started getting worried in like over the last 10 years or so about there being a tipping point that the AMOC might even turn off. Yeah. So the AMOC is largely driven by differences in temperature and salinity of the ocean water. What happens is you get this kind of salty water that's warm going north, bringing heat to Europe.

2:58And then as it gets north and cools off, it's so dense and cold that it sinks to the bottom and starts flowing southward. And that's a big part of what kind of pulls the amok and creates that motion, that circulation. But as Greenland and the Greenland ice sheet is melting, that introduces a lot of fresh water into the North Atlantic. And that can mess with that density driven pull, right? So if you have a bunch of fresh water sitting in the North Atlantic, suddenly the water isn't as dense, it's not sinking as fast, and the AMOC can start to slow down and weaken. And so theoretically, the AMOC will weaken with climate change.

3:40It will weaken as the Greenland ice sheet melts. But the problem is we don't have long enough observations to show that. We have a line of buoys across the North Atlantic that are measuring the AMOC speed, but those have only been in place for about 20 years. So it's not quite long enough to see a statistically significant trend. So what scientists are doing are kind of trying to come up with all these other clever ways to show that the AMOC is weakening, as we expect, or not, but to get at the problem from different ways. By modeling it. So that's one way. So I guess so far the main piece of evidence we have is through what's called reconstructions, where they look at, because we have monitored temperatures in the North Atlantic for a long time, so they look at temperatures in the North Atlantic now, They look at how that corresponds to AMOC speed and strength now.

4:40And then they look at the temperatures years ago and they say, okay, if the temperatures were this much lower, then the AMOC was probably this much faster. And those kind of reconstructions suggest the AMOC has already weakened by about 15%. But that's only one piece of evidence, right? There could be something else going on. That could be a mistake. And so what this new study has done is provided a new piece of evidence that the AMOC is already weakening. And they've done that through modeling. What they did was set up a very high-resolution climate model. And that's important because a lot of climate models are looking at like a grid cell of 100 kilometers, right?

5:20But a lot of these currents that make up the AMOC, of which the Gulf Stream is one, right, are actually much narrower than that. And so when you're looking at kind of this more general picture, the differences in water heights and where the current is kind of gets smeared a bit across this model. And you can't really see the differences or what's going on with the actual paths of the currents. So what these guys did was use a very, very detailed model that goes down to about 10 kilometers, even less. And so that allows them to really zoom in and see as the climate changes in the model, as we go into the future, as the Greenland ice sheet keeps melting, what actually happens to the path of the currents.

6:05And what they found was that as the AMOC weakens, the Gulf Stream, it shifts northward. So it follows the coast of the eastern United States further north before it veers off eastward towards Europe, right? So they say, okay, we have this link between AMOC weakening and a northward shift of the Gulf Stream. And the scary part is we've already seen the Gulf Stream shift northward by about 50 kilometers in the past three decades. So what's happening in the model is already happening in real life, which suggests that the AMOC is already weakening. Okay. And is there any indication of how far we can kind of allow the Gulf Stream to go north before, you know, and it carries on weakening the AMOC, but how far it would need to go north before it actually totally disrupts the AMOC?

6:59So this is the interesting part. They run this climate model a couple hundred years into the future. And as the AMOC gets weaker and weaker, at a certain point, and this is a long time in the future, a couple centuries, but there comes a point where suddenly the Gulf Stream shifts north abruptly, and it basically jumps 200 kilometers north in just a few years. So this kind of gradual shift of the Gulf Stream North suddenly just becomes this abrupt shift. And they found that when that happens in their model, that means you have something like two to three decades until the AMOC collapses. This is interesting because, you know, we don't know exactly when the AMOC might collapse.

7:47And we don't really have a warning, any sort of signal that could tell us when it might be on the brink of collapsing, right? So before now, we have different things that could tell us that the AMOC is collapsing, but that's not much good if it's already collapsing and you get this signal, right? This is the first time that scientists have identified an early warning signal that could say the AMOC is collapsing, but tell you that early enough, a couple decades, where you might actually be able to do something about it. That may not be enough time to avert AMOC collapse. It might already be locked in.

8:27That's another scary thing is, you know, we get the early warning signal and we say, okay, well, now we're going to get our act together and really cut emissions. But it's too late. The collapse. We've crossed the tipping point. We've crossed the tipping point, essentially. It's already locked in. That's a possibility. They're not sure. But what they are sure about is that two to three decades, that is a bit of time to adapt a bit to the sudden drop in temperatures in Europe, especially in wintertime, right? So you could do things like add insulation to houses for the negative 20 degrees Celsius, negative 30 degrees Celsius temperatures in wintertime that you could get in places like the United Kingdom, right?

9:09Or you could shift agriculture and start sourcing your food from somewhere else because, you know, agriculture in Europe is not going to be able to produce nearly as much under those conditions. So on and so forth. Have you heard the latest episode of the New Scientist CoLab podcast? It's a great listen. It's about what happens when the UK's best scientific minds team up with Spain's top researchers while funded by the Horizon Europe Innovation Program. What happens is you get a revolution that's reducing the environmental impact of medicines. sponsored by Horizon Europe Research our New Scientist CoLab team traveled to Barcelona to explore a high-stakes European collaboration to reduce pharmaceutical waste before it starts they also wanted to understand the secrets to the success of this cross-continent research partnership discover what they found by listening to the full episode sponsored by the UK government at newscientist.com eternal pod so this is still we still have time effectively.

10:05Even the models are saying this is still a couple of centuries into the future, but this is when the early warning system might kick in. Yes, but the model shows the mechanism. It shows what we expect to happen. It shows this link between the AMOC and the Gulf Stream shifting northward. But they're very uncertain about the time frame. And it could happen faster, could happen over a longer period. That's one of the things they hope to investigate more is the actual timeframe. They don't want these results to be seen as a prediction of AMOC will collapse at this far in the future. They want this to be seen as this is evidence that AMOC is already weakening.

10:51And this is a link that could possibly tell us we could use in the future to look out for the AMOC collapse when it does come because we don't really know. And you mentioned the mechanism there, and we've got a quote from one of the scientists you spoke to, Rene van Westen, about the mechanism they're proposing for how this might come about with reference to the deep western boundary current. So let's listen to that. What we see with our climate model is that this deep western boundary current, so this southward flowing part of the conveyor belt, that is weakening, and that already starts to shift the Gulf Stream northward, first at a very slow pace, and then of course you are having this very spectacular northward shift of almost 200 kilometers within two years time and that really shows that there is some things are getting different within or at greater depth and that's of course very nice because that is something we don't see directly but the deep currents are of course shaping what is happening near the surface okay so you mentioned the mechanism there that's about the deep western boundary current about how this collapse might come about.

12:01Can you talk us through a bit about what happens there? Yeah. So as we were talking about, the AMOC is largely warm water flowing north at the surface and then cold water flowing south deep under the ocean. One of the branches that it goes into on that return leg deep under the ocean is the deep western boundary current. So that's kind of like the underbelly of the Gulf Stream. The Gulf Stream is moving north on top on the surface, and then the deep western boundary current is bringing cold water south deep underneath it. And so that's what they think is going on here. They think that the interaction between the deep western boundary current and the Gulf Stream is what's driving this change.

12:47And so essentially, as the AMOC weakens, you have that lower part of the AMOC weakening and getting slower, the deep western boundary current weakening and getting slower. And that means that that southward flowing water is kind of pulling less on the Gulf Stream. So if you think about the deep western boundary current, you know, going south at the depths, it's kind of pulling the Gulf Stream southward so that the Gulf Stream veers off eastward from the United States. at a more southerly point. And if that deep western boundary current gets weaker, then the Gulf Stream is free to kind of flow north further before it veers off into the Atlantic.

13:29So that vorticity, that pull between those two currents that are going in opposite directions at different levels of the water column is what they think is happening. That's how the AMOC weakening is allowing the Gulf Stream to kind of shift north. And again, the Gulf Stream continues to function. The Gulf Stream weakens a little bit, but it continues to function. It's just following a different path. And that's what's so interesting here is that for the first time, we have this kind of, at the surface, we have this current that's showing us what's going on with the AMOC. Yeah. So we didn't have that before, that sort of signal.

14:11There's been so much talk about what we can really say about the AMOC weakening and a lot of worry, clearly worrying about it. But this at least gives us a way of saying this is how it's weakening because it shifted what 50 kilometers north already the Gulf Stream has. Has that surprised people that it's jumped 50 kilometers north already? People have been studying the Gulf Stream for a long time, especially in the United States. And that shift has been documented in previous research. But what's new here is linking that shift to a weakening, showing that that shift is linked in the climate models to a weakening of the AMOC.

14:49Because like I said, the previously climate models did not look at this in great enough resolution, in great enough detail, to actually see that the Gulf Stream shift was linked to and would be continuing with AMOC weakening. So the link is new. The connecting those two together is new. So basically, yeah, we knew the Gulf Stream was shifting northward. We didn't know what significance that had or what that meant in terms of AMOC weakening. And I think people are welcoming this research, but they're also skeptical at the same time because this is a completely new link. This is a completely new piece of evidence suggesting AMOC weakening.

15:33And so I think people are a little bit skeptical that something else might be causing this as well, right? The ocean is an extremely complex system. There are so many different currents. There are so many different isotherms and pycnoclines and all sorts of differences in temperature and density and salinity that can be driving all sorts of processes. So you can't say for sure that it is AMOC weakening that is causing this northward shift in the Gulf Stream. But these researchers who did this study say that in their models, nothing else can account for this northward shift in the Gulf Stream. Yeah.

16:11I mean, as a precautionary principle, we should start really worrying more. I mean, policymakers should really worry more about the consequences of the AMOC collapse. perhaps we hear climate scientists talk about it a lot we talk about it a lot as a tipping point but I don't think it's transferred over to part of the sort of policy talk about yet another reason why we have to get emissions down but I was a bit surprised to hear the talk about adaptation because surely this is something you can't really you I mean if it was going to happen and we had 20 years warning we would try to adapt right but that is the worst still the worst case scenario, we cannot let this happen because it's going to be a disaster.

16:57Any adaptation would be just to take the edge or perhaps the edge off an absolute catastrophe, right? So it's a bit, I found it a bit odd that they talked about adaptation. Yeah. So this is possibly the only early warning we'd have of AMOC collapse. So that's a big deal. And it's possibly the only chance we could have to do any adaptation with a set timeframe, right? You know, it's one thing to go to a politician and say the AMOC is collapsing or the AMOC is going to collapse at some point in the future. People are worried about the next election. They don't think a century down the road. It's a much different thing to come to a politician and say the AMOC is going to collapse and it's going to do it in 20 to 30 years.

17:44So I just think that would be a powerful and more actionable piece of information than what we've had so far, which is just that the best science suggests the AMOC is already weakening. We know that the physics and the theory suggests that the AMOC will continue to weaken. We know that the AMOC, if it gets weak enough, it could collapse at some point. That's scary and that's important science, but it doesn't translate, like you mentioned, as well to policymakers who are concerned about the more immediate here and now. And we actually, we have something from René van Westen on adaptation as well.

18:25Let's listen to that. If we would see, for example, such a shift, maybe in the upcoming decades, we would know that we are approaching the tipping point very fast for the aim of tipping. And this could, of course, inform policymakers that we like, you know, need to take real actions because we are now maybe locked in or whatsoever, or you have like this amount of years to really divert the path of ABOB tipping. And that is something what we didn't have before because there are other indicators, early warning indicators, but they are actually confirming like, hey, if this goes off, then you already are at the tipping point.

19:03So you don't have any time to take any action anymore. So it's like a tsunami warning center. So when they measure something, they can like already say to coastal zones like hey please go away from the coast because in two hours from now a tsunami will hit your area it doesn't make any sense like if this warning goes off and there's already a tsunami at your coast right so you don't have any time to flee so this is something nice that there is now a very proper early warning indicator that actually goes off okay so given that what what sort of way we can we translate this research into some sort of actionable policy.

19:41This is something that not only these scientists, but other scientists have been thinking about because like we've been talking about, the science keeps on giving us clearer and clearer indications that the AMOC is weakening. And yet we're going in the exact opposite direction of what we need to do to prevent that carbon dioxide emissions continue to increase each year. And so there's actually another project that I've been reporting on that's led by researchers, including some from the British Antarctic Survey. And they're going to Greenland this summer to begin research that would look at how Greenland's melt is affecting the AMOC, try to figure out exactly how much the AMOC will weaken with exactly how much Greenland melt.

20:25And they're going to be looking at things like sea cliffs collapsing into the ocean, these kind of nonlinear processes, these processes that could cause, you know, sudden spikes in the amount of fresh water going to the North Atlantic. And one of the reasons they're doing that is they're hoping to build a tool that would give a near real-time update of what is going on with the Greenland ice sheet and its effect on AMOC. So essentially what we have now is, you know, every year or two a big study comes out that says, Here's another piece of evidence that the AMOC is weakening, or here's another indication of how bad it would be when the AMOC collapses, so on and so forth.

21:10But it's all, the timelines are uncertain, and it's not very actionable. It's not very translatable into policy. But what they would like to do is have something like a website that would be updated at least yearly, and hopefully they're hoping something like monthly, with the latest science. and the latest measurements showing AMOC weakening so that you could not only think of this kind of in the distant future, but you could go and see right now that, okay, the AMOC is weakening now. It's been weakening. The meltwater coming off of Greenland has been increasing. It is increasing by this much and kind of have a real-time indication, which would, again, be a way to monitor AMOC strength and give us a warning of when AMOC is possibly going to collapse and give us more information on how much time we have to adapt.

22:08When you want your spring break to feel like and your kid's pool day to feel like and your hotel bed to feel like and room service to feel like because at Hilton, hospitality feels like Your cabana's ready. Would you like fresh towels? It matters where you stay. Book now at Hilton.com. Hilton, for this day. Is there any indication about whether we've crossed the tipping point yet and that it's inevitable? Or is that still just a complete blur? I think most scientists would say we haven't crossed the tipping point yet. And there's a lot of disagreement over when we may cross that tipping point.

22:57You know, there was a study that said we could be crossing that we could cross the tipping point with the AMOC, with AMOC collapse within the coming decades. But then there's other research that says it's more like centuries. So it's very uncertain when that happens. One thing we do know is that the AMOC has weakened and it has collapsed in the distant past when there has been influxes of meltwater, of freshwater into the North Atlantic like is gradually happening now. Well, you say gradually, but it's coming off in billions of liters of water coming off Greenland, isn't there? Yeah. As well as the rest of the Arctic coming down from there.

23:37Yeah. Yeah, I forget how many billions of swimming pools, but it's an extreme amount of meltwater coming off of Greenland, and that's very frightening. But in the past, there's also been, for instance, the Laurentide ice sheet. When that broke up, they think it may have released this flood of freshwater into the North Atlantic that kind of shut down the AMOC. So we do have a sense of what happens when you put a bunch of freshwater into the North Atlantic, and it is AMOC weakening and or collapse. Yeah, which is something we don't want to do. Okay, we'll leave it there. Thanks to Alec Loon. Thank you for listening to The World, the Universe, and Us.

24:14I'm Rowan Hooper. Do follow so you don't miss out more from our podcast. Bye for now.

24:37protein into something hearty, satisfying, and built for life on the go. From craveable sauces to satisfying textures, they're designed to keep you going without slowing you down. So put that fork down. Try the new wraps today in app or at order.sweetgreen.com. Available at participating locations only.