This critical ocean current is collapsing…. Or is it?

Added: 2026-05-12

[00:00:00]We've seen the film The Day After Tomorrow and also seen some of the relatively dramatic headlines in the news calling back to it. And I think you'd probably be forgiven for being a bit of an anxious wreck right now.

[00:00:13]Several new studies have come out about the Atlantic Meridional Overturning Circulation or AMOC, and I think it's worth digging into. So, let's have a go, shall we? The AMOC is a system of ocean currents is often known as the global conveyor belt, and it's a part of the global interconnected ocean current circulation that transports heat, water, and carbon around the planet. And it's set up by cold, dense, salty water sinking at the poles, descending to depth, and moving at that deep level, and then returning to the surface in the equator region where it's warmer, and then you have this return leg where the warm water is moved by winds and the current and further up back to the poles.

[00:01:01]Now, the theory and some modeling suggest that this kind of closed loop of circulation is weakening because the polar regions are warming up. And this is especially true in the Arctic, which is warming four times faster than the global average because water is entering the ocean, which is meltwater. It's fresh. It's not as salty. And that's kind of diluting this salty, cold water thing, and it's causing the overall circulation to weaken. And this is the same thing that's also happening in Antarctica, but in Antarctica it's happening to much less of a degree. And in Greenland the melting is having a more profound impact. And in fact, we see this kind of called the cold blob, and and it's a cold area in the Atlantic, which is supposedly an indicator of the AMOC weakening.

[00:01:55]Anyway, I'm getting ahead of myself.

[00:01:57]Studies show varying different amounts of weakening in the AMOC, and we've seen an increasing number of them covered in the media. And this is because the collapse, or shutdown, or dramatic slowdown of the AMOC is a tipping point.

[00:02:13]The AMOC is a very important ocean current, very important part of our climate system, and if it was to for all intents and purposes shut off, and there are arbitrary thresholds which are defined in the scientific literature, but essentially become much, much weaker than it is currently, then the consequences of that would be quite bad. And I've got a few quotes here, in fact, to kind of underline how how bad it would be. Um even [clears throat] a slight slowdown in the AMOC can cause Europe change precipitation patterns in parts of Europe, South America, and Africa, affect the timing of the Indian monsoon, and lead the tropical rain belt to shift southwards, resulting in droughts over the African Sahel. That's just one quote. A key consequence of the AMOC slowdown, amongst many others, is the equator would shift of the intertropical convergence zone. That's the precipitation band that's concentrated over the equator, which will lead to the drying out of the Sahel region, and put pressure on its agriculture and food security. And both of those quotes are talking about a slowdown in the AMOC, not a kind of off-the-cliff slowdown, and a kind of collapse would have much larger consequences. You know, that would result in changes all over the world, changes in the Amazon, changes in the Sahel region, changes in Europe, South America, Africa, North America. Um one quote that I particularly care about is that it would result in widespread cessation of arable farming in the UK.

[00:03:38]That's pretty bad, objectively pretty bad. And several new papers have come out that I think warrant a little bit of discussion.

[00:03:48]So, I'm going to show you two particular ones, and then have a brief chat about the implication of this, and also something about the the general coverage of this.

[00:03:58]Now, the first is a paper by Rahmstorf and Caesar. It's a preprint, so it hasn't been through peer review yet, but both of these authors are pretty leading experts in the field of AMOC and tipping point research.

[00:04:10]And they essentially talk about the general consensus in the literature about whether or not the AMOC has weakened over this kind of multi uh century time scale.

[00:04:23]And they talk about the state of the understanding about historical changes in the AMOC. The gold standard when it comes to measuring the AMOC in the present is an array of sensors that stretches across the North Atlantic and measures the volume of water that's transported across it. And this is a a really good way of directly observing the strength of the AMOC. The problem is we've only got about 20 years or so of data, which means that the time series is very short.

[00:04:53]That means it's quite hard to figure out whether the changes we're seeing over that 20 years are because of climate heating or because there are just natural ups and downs in the system that are, you know, a product of our very inherently chaotic natural climate. So, often what scientists do is they use different methods to kind of go backwards in time, and that could be using models, it could be using uh what we call proxy data, which is indirect measurements or measurements of something else that can be linked to the strength of the AMOC, something like the temperature of the ocean at the surface, or we can use paleo evidence to go even further back, and that might be something like sediment core or an ice core, for instance. These authors are summarizing the results from various different historical methods to to go back through time, and you can see See in this figure. You can see that there are various different studies which have used different techniques and different sources of data. The strength of AMOC is relatively stable up until around the 19th-20th century, after which point it in all data sets appears to decline very quickly. But there's a lot of noise, there's a lot of ups and downs going on in all of those data sets. What these authors say is that on the balance of evidence we think there's weakening over the long term. And I don't think this is news, this is something that's been spoken about quite a lot in the media as well.

[00:06:19]But I think what's different is this sort of collapse framing. And what we consider collapse is somewhat arbitrary. And it's really difficult to understand what's likely to happen, and lots of papers have tried to look at early warning signals. So, can we use this weakening in the observable period to figure out when the AMOC is going to collapse. And still not really possible, I don't think. And the thinking generally is that although the AMOC is unlikely to collapse, and that means enter a completely new state in 2100 that we might exceed some kind of threshold this century that means collapse would occur sometime next century or perhaps beyond.

[00:07:08]Bit wishy-washy, bit vague.

[00:07:11]Because collapse is defined by a pretty specific but relatively arbitrary threshold in lots of the literature, but people use different definitions. And I don't think it's very helpful in some of the communications.

[00:07:23]We'll get to that though. But I thought it was worth emphasizing this quote from the Rahmstorf and Caesar paper because it's the last sentence, and it's I mean, I highly agree. It's [snorts] therefore high time to stop wavering and to take this evidence seriously.

[00:07:39]And coming from scientists, this is, you know, as direct as it gets. This is like pull your socks up lads and I'm not surprised cuz Stefan Rahmstorf is pretty outspoken when it comes to lots of things and has studied the AMOC for 35 years. He's said that collapse must be avoided at all costs.

[00:08:00]I think we hopefully if you're watching this video you probably agree. And he was saying that even when he thought the chances of the AMOC collapsing were about 5% and now it's much higher than that. So we really don't want to exceed this tipping point. We do not want to see the AMOC collapsing. And this is true of all tipping points, right? This is true of any high impact event even if it's not likely to happen. We want to avoid all catastrophic impacts.

[00:08:27]Because we might be committing ourselves to a future which is not really survivable.

[00:08:34]So >> [laughter] >> what's likely to happen in the future?

[00:08:37]I think this is a a very important and pertinent question.

[00:08:42]The IPCC so the Intergovernmental Panel on Climate Change says that the AMOC is unlikely to collapse before 2100.

[00:08:48]Now the IPCC is often thought of as being relatively conservative in its assessments for a bunch of reasons.

[00:08:56]Other studies in more recent years have tried to dig into this a little bit more.

[00:09:03]And there's one answer that's we might have exceeded the threshold now and the impacts might be about to unfold much later. And this is especially true of like slow moving systems like ice sheets, the AMOC for example. And this idea of committed impacts is something that's kind of only recently emerging. So there's a new paper by Portman et al that's come out which uses model predictions of the next century, this century with different emissions. So different flavors of this century's future. And this in and of itself is not new. This is something that most modeling studies of the future would use. But what is new is that this study is using methods that add extra context from the real world observations and combine that with the model evidence to have a better understanding. So this uses that array of sensors and data from it that goes across the Atlantic and helps us understand directly what's going on with the AMOC.

[00:10:03]And it shows that in all scenarios of the next 75 years or so, the AMOC weakens. The AMOC declines in strength. The only one where this is kind of not true is probably the light blue line which sort of decreases and then increases and this is a scenario that's consistent with 1.5° of warming by the end of the century and is increasingly a pie in the sky.

[00:10:30]So the ones that are probably more consistent with our current trajectory would be the yellow and the red lines and that shows a very dramatic reduction from where it currently is.

[00:10:41]And essentially the overall message of this paper is that the most pessimistic models are probably correct. And it suggests that under moderate emissions, we will likely see a weakening in the AMOC of 43 to 59% so it's put a difference is about 51% by 2100. And this weakening is quite a lot larger than other studies because those studies have used to kind of they've all averaged all the models together whereas this one is taking the observations and they're only really looking at the ones that are accurately representing the present period. So that's that's great great news.

[00:11:18]Something I wanted to talk about is that we see a lot of studies on particular topics and here let's consider the AMOC.

[00:11:28]And it can be a little bit like getting whiplash because sure this study has just come out and it says that weakening may be more than we previously thought. But you kind of backtrack a few months and you'll would you would have seen a study that says, "Oh no, actually AMOC weakening is probably going to be less than we previously thought."

[00:11:47]And [sighs] it's part of this general trend and it's it's not necessarily a criticism of media because I understand how media works.

[00:11:56]The media works on news. It's news It's in the name. Has to be new. And because papers [clears throat] come out from scientists the news hooks onto them and it latches onto them and it pub it talks about them and it talks about each study as if it's the truth.

[00:12:12]And actually science is made up of incremental progress. It's also made up of different studies that show different things and then over time we take a kind of consensus view. We see on the balance of evidence what is the most likely truth.

[00:12:26]Those papers, those articles don't necessarily show us that because it can feel feel very easy to be like Wait, this these people said this thing and then they're saying the opposite now a few months later. Like who should I believe? What should I believe? You're getting whiplash from like being pulled in different directions and that's not really the scientists' fault um nor is it particularly the journalist's fault. I understand what happens and how the news works but it means we're creating this kind of atmosphere of confusion and people don't really know where we stand. And it's really difficult.

[00:13:07]It's really really difficult and I think what's unhelpful is this kind of hysteria about the collapse framing and this like day after tomorrow framing that's objectively not helpful. You know, impacts now on what's already killing people now. That's extreme events. That's extreme heat. That's floods. That's droughts. That's wildfires etc. Tipping points and extreme collapse events are, of course, very, very important.

[00:13:33]They're further in the future, even if we commit ourselves by our actions today to tipping a climate system in 70 years time, say, there's still time to adapt and prepare for it. I'm not saying that makes it any better, but the things that we There's kind of a yes and scenario, right? We have to care about the things that are impacting and killing people right now, and we have to care about those really high-impact, scary tipping point collapses further in the future.

[00:14:01]In the media, we see the kind of whipping up of of hysteria, and this can be counterproductive.

[00:14:07]I guess what I want to say about this is that overall, it doesn't really matter if we don't know 100% what's going to happen with the AMOC yet, because the research will continue and will continue to refine our predictions of the future, and that's, of course, really essential.

[00:14:23]But we should be adapting and planning for futures that are potentially quite different from our current present. And we also need to be very dramatically moving away from fossil fuels and very dramatically curbing our impacts, because every degree of warming, every fraction of a degree of warming, increases the risk of tipping these thresholds. And we do not want, objectively do not want, to cross those lines. Whether we experience it in 75 years time or we experience it today, doesn't matter.

[00:14:57]The consequences of climate change are already catastrophic, and they will only get more catastrophic with every increment of warming. So, we really do need to curb emissions and to adapt to the changes that we're already committed to. The joy of science is that it embraces those differences, those uncertainties, but I don't necessarily think that translates very well into the public communication of that science.

[00:15:22]And there are lots of people doing really amazing work on this. Particular shout-out to Carbon Brief, who did an amazing interactive article that was super comprehensive detailing the historical observations, what's happened to the AMOC over time, what's going on in the present, the kind of consensus, the the differences in the literature, what scientists think about certain different important aspects of the AMOC, and they provided a very balanced and comprehensive overview. So, really do go and check that out. It's sensational science journalism at its finest. I also want to give a shout-out to Climate Adam. He's just released an AMOC video, which is better scripted than this one, [laughter] which is unscripted to hell.

[00:16:07]Um and the reason I actually did this uh video in the first place is because I went on um Carissa Fuca's podcast uh called Over the Top Under the Radar last week, and we spoke about this and the reporting of AMOC in the media, amongst other things. And I'll also stick that in the description, so go check out all of those things if you are interested.

[00:16:28]Now, I like to think that I take a balanced approach on this channel, and I think adding the sort of consensus view and evaluating multiple different studies instead of trying to just hook on to one new thing is where we can add value. And if you agree and you'd like to support that work that I'm doing, then please consider supporting this channel [clears throat] on Patreon.

[00:16:50]Links in the description and also the pinned comment. And I'm really grateful for any support you can ping my way. All of the contributions that my subscribers make go directly into funding this channel, allowing me to spend more time on it and making uh the videos better. So, do support the channel if you can. And if you want to stick around on YouTube, then watch this next video about tipping points in the ice sheets, and I'll catch you next time.