{"version":"1.0.0","segments":[{"startTime":4.755,"endTime":8.565,"body":"This is the 10th, uh, lecture in our series on net zero."},{"startTime":9.145,"endTime":14.533,"body":"Um, and I have to confess, it's the lecture I didn't want to give, um,"},{"startTime":14.533,"endTime":18.485,"body":"because it's the lecture kind of, everybody tends to lead with."},{"startTime":19.665,"endTime":26.165,"body":"And I worry, I mean, about the whole tipping point discussion around climate."},{"startTime":27.645,"endTime":31.932,"body":"The Gresham College lecture that you're listening to right now is giving you knowledge and"},{"startTime":31.932,"endTime":36.219,"body":"insight from one of the world's leading academic experts, making it takes a lot of"},{"startTime":36.219,"endTime":36.505,"body":"time."},{"startTime":37.085,"endTime":40.366,"body":"But because we want to encourage a love of learning, we think it's well worth"},{"startTime":40.366,"endTime":40.585,"body":"it."},{"startTime":41.565,"endTime":44.705,"body":"We never make you pay for lectures, although donations are needed."},{"startTime":45.205,"endTime":46.545,"body":"All we ask in return is this."},{"startTime":47.095,"endTime":49.385,"body":"Send a link to this lecture to someone you think would benefit."},{"startTime":49.765,"endTime":53.415,"body":"And if you haven't already, click the follow or subscribe button from wherever you are"},{"startTime":53.415,"endTime":54.145,"body":"listening right now."},{"startTime":55.325,"endTime":57.105,"body":"Now, let's get back to the lecture."},{"startTime":59.825,"endTime":64.8,"body":"It tends to be when I tell somebody I'm working on climate, if the next"},{"startTime":64.8,"endTime":69.775,"body":"thing they say isn't about low traffic neighborhoods, which it quite often is, um, it's"},{"startTime":69.775,"endTime":74.751,"body":"often about, you know, is it true that some tipping point is about to happen"},{"startTime":74.751,"endTime":77.405,"body":"or is already happened and we're all doomed?"},{"startTime":77.825,"endTime":80.725,"body":"Um, and you know, this is one of the reasons."},{"startTime":81.085,"endTime":84.845,"body":"I mean, there's an obvious reason why tipping points are dangerous."},{"startTime":84.845,"endTime":90.816,"body":"It's a very bad idea, um, to push our planet over a tipping point into"},{"startTime":90.816,"endTime":93.205,"body":"some, uh, completely unexplored climate regime."},{"startTime":93.265,"endTime":97.067,"body":"So I'm not s you know, I don't, the the reason I was sort of"},{"startTime":97.067,"endTime":100.87,"body":"hesitant about giving this lecture is I absolutely don't want to give you the message"},{"startTime":100.87,"endTime":101.885,"body":"none to see here."},{"startTime":102.035,"endTime":103.965,"body":"There's, there's no, there are no tipping points."},{"startTime":104.225,"endTime":105.765,"body":"Um, don't, don't worry about it."},{"startTime":106.385,"endTime":111.952,"body":"But at the same time, there's a very unhelpful narrative around tipping points that I"},{"startTime":111.952,"endTime":117.52,"body":"think is, is out there in the climate conversation, which I, so it's quite a"},{"startTime":117.52,"endTime":119.005,"body":"difficult one to balance."},{"startTime":119.105,"endTime":123.593,"body":"We have to take them seriously on the one hand, while at the same time"},{"startTime":123.593,"endTime":126.885,"body":"not allowing ourselves to be sort of blinded in the headlights."},{"startTime":127.065,"endTime":131.517,"body":"Um, which is the other sort of, part of the, um, of, of, of the,"},{"startTime":131.517,"endTime":134.485,"body":"the other danger with thinking about, about climate tipping points."},{"startTime":135.265,"endTime":138.165,"body":"Um, I'll give you some examples and we'll do some maths."},{"startTime":138.325,"endTime":141.245,"body":"I am a physics professor, as, as, as you know."},{"startTime":141.305,"endTime":144.64,"body":"So there will be, there will be, there will be equations, um, there are for"},{"startTime":144.64,"endTime":145.085,"body":"the newcomers."},{"startTime":145.505,"endTime":151.645,"body":"Um, I'm afraid there won't be any, um, equations done with hydraulic, uh, models."},{"startTime":152.125,"endTime":155.378,"body":"Although if you wanna see our hydraulic model, particularly when it went wrong as well,"},{"startTime":155.378,"endTime":157.765,"body":"and I start swearing on screen, it's all there on YouTube."},{"startTime":158.345,"endTime":163.115,"body":"Um, and, uh, uh, but, and, and I'll, you know, finish up by talking about"},{"startTime":163.115,"endTime":167.885,"body":"how we, how we should get our response to the danger of tipping points, right?"},{"startTime":168.185,"endTime":174.307,"body":"But I wanted to start with the, the danger of tipping points that people don't"},{"startTime":174.307,"endTime":177.165,"body":"normally talk about or don't perhaps appreciate."},{"startTime":177.785,"endTime":185.056,"body":"And, um, kickoff unconventionally, therefore, for a lecture on tipping points with, uh, Dana Nellis,"},{"startTime":185.056,"endTime":187.965,"body":"I hope I pronounced that right."},{"startTime":188.145,"endTime":192.84,"body":"Uh, columnist in the Guardian, um, who a few years ago came up with the"},{"startTime":192.84,"endTime":194.405,"body":"five stages of climate denial."},{"startTime":195.025,"endTime":200.787,"body":"And in the opening lectures of this Gresham series, we've addressed, you know, the, the"},{"startTime":200.787,"endTime":204.245,"body":"challenge of people saying that there is no problem."},{"startTime":204.585,"endTime":208.245,"body":"Yes, there is a problem, um, denying that we're the cause."},{"startTime":208.835,"endTime":213.46,"body":"Yeah, the, I've explained in earlier lectures, pretty clear evidence that we are the cause"},{"startTime":213.46,"endTime":218.086,"body":"of what's going on in the last lecture where we talked about the impact of"},{"startTime":218.086,"endTime":222.712,"body":"climate change on weather, particularly in our part of the world, um, we were addressing"},{"startTime":222.712,"endTime":227.337,"body":"the in increasingly prevalent view among some in the political classes that, yes, climate change"},{"startTime":227.337,"endTime":229.805,"body":"is happening, but don't worry, it'll be fine."},{"startTime":230.145,"endTime":233.257,"body":"And actually, you know, all the things we might want to do about it are"},{"startTime":233.257,"endTime":235.125,"body":"gonna be so expensive, it's really not worth it."},{"startTime":236.505,"endTime":241.165,"body":"Um, the next stage, um, is, uh, denying we can solve it."},{"startTime":241.365,"endTime":245.846,"body":"I mean, here's a headline I found just looking around, I'm sure, um, Tessa slasher,"},{"startTime":245.846,"endTime":250.327,"body":"she's an authoress, and so I'm sure she'd be delighted for me to publicize what"},{"startTime":250.327,"endTime":250.925,"body":"she writes."},{"startTime":250.925,"endTime":255.285,"body":"But I mean, this is the kind of headline that is really, really unhelpful."},{"startTime":255.395,"endTime":257.765,"body":"It's too late to stop climate change now."},{"startTime":257.765,"endTime":261.084,"body":"We must decide what we can save and how we can save it."},{"startTime":261.505,"endTime":266.483,"body":"That's, I hope you'll realize those of you who've been to these lectures, the kind"},{"startTime":266.483,"endTime":271.461,"body":"of headline that really grinds my gears, because, you know, what is, is she sponsored"},{"startTime":271.461,"endTime":272.125,"body":"by Exxon?"},{"startTime":272.325,"endTime":273.525,"body":"I mean, what, what's going on here?"},{"startTime":273.785,"endTime":276.005,"body":"Uh, I mean, you can see who, who benefits."},{"startTime":276.425,"endTime":281.085,"body":"Ask yourself when you see a headline like that, who really benefits from this headline."},{"startTime":281.705,"endTime":286.028,"body":"Um, and, uh, you know, obviously it's attention grabbing, it, it, it gets retweeted and"},{"startTime":286.028,"endTime":286.605,"body":"so on."},{"startTime":286.945,"endTime":290.725,"body":"Um, but, um, it's, it's obviously unhelpful."},{"startTime":291.385,"endTime":295.981,"body":"But finally, there's, you know, another headline, uh, this sort of, it's too Late headline,"},{"startTime":295.981,"endTime":299.965,"body":"which brings us to the tipping point, um, uh, theme of this lecture."},{"startTime":300.545,"endTime":304.965,"body":"Um, here's a headline, Tony Blair, Blair Warns of Climate Change Tipping Points."},{"startTime":305.475,"endTime":310.794,"body":"Tony Blair will warn today that the world will reach catastrophic tipping points of climate"},{"startTime":310.794,"endTime":315.405,"body":"change within 15 years unless serious action is taken to tackle global warming."},{"startTime":316.345,"endTime":322.605,"body":"Anyone, any idea, anyone any idea when this, uh, uh, well, uh, it's, uh, yep."},{"startTime":322.635,"endTime":324.405,"body":"This article is a yellow label on it."},{"startTime":324.405,"endTime":326.205,"body":"This article is more than 17 years old."},{"startTime":326.465,"endTime":327.965,"body":"So that was from 2006."},{"startTime":329.745,"endTime":334.079,"body":"And that's the danger, you know, you, you, you can't say this that often, um,"},{"startTime":334.079,"endTime":338.125,"body":"before everybody starts going, oh, wait a minute, they've said this before, haven't they?"},{"startTime":339.495,"endTime":344.903,"body":"So, um, the first point to make in a lecture about climate tipping points is,"},{"startTime":344.903,"endTime":350.311,"body":"and I'm, I should stress this lecture is about global tipping points, the kind of"},{"startTime":350.311,"endTime":355.719,"body":"tipping points that really grab the headlines that would affect everybody all over the world,"},{"startTime":355.719,"endTime":359.325,"body":"um, which affect the entire planet were they to happen."},{"startTime":360.075,"endTime":364.617,"body":"Obviously, there are other tipping points, you know, local tipping points, you know, a a"},{"startTime":364.617,"endTime":367.645,"body":"a, a river bank being breached, that's a tipping point."},{"startTime":367.645,"endTime":369.325,"body":"Classic case of a tipping like that could be."},{"startTime":369.325,"endTime":372.638,"body":"If it happens to be the bank that keeps the river as of your living"},{"startTime":372.638,"endTime":374.405,"body":"room, then obviously that's very important for you."},{"startTime":374.405,"endTime":375.485,"body":"But it's not global."},{"startTime":376.025,"endTime":381.571,"body":"So I'm not talking about local tipping points or, or, or thresholds being exceeded, for"},{"startTime":381.571,"endTime":387.118,"body":"example, in coral reefs and so on, which have a important impact for globally relevant,"},{"startTime":387.118,"endTime":391.925,"body":"globally important species, but not necessarily a global impact on the entire planet."},{"startTime":391.945,"endTime":393.445,"body":"So I'm talking about global tumor here."},{"startTime":393.825,"endTime":400.751,"body":"And so the first thing I wanna stress is, so far, there's no evidence of"},{"startTime":400.751,"endTime":407.677,"body":"these things happening yet, and I stress the word yet, that climate change has been"},{"startTime":407.677,"endTime":409.525,"body":"really quite surprisingly predictable."},{"startTime":410.345,"endTime":415.335,"body":"And this is a figure from a, uh, uh, a report by William Northouse, the"},{"startTime":415.335,"endTime":420.326,"body":"Economist who won the, uh, Nobel Prize for his work on climate change economics a"},{"startTime":420.326,"endTime":421.325,"body":"few years ago."},{"startTime":421.905,"endTime":427.605,"body":"Um, this was, uh, published in 77, and you'll see here, um, that line, which"},{"startTime":427.605,"endTime":432.925,"body":"I'm sure he drew by hand, um, shows global temperatures up to that point."},{"startTime":432.925,"endTime":434.125,"body":"They were going down at the time."},{"startTime":434.185,"endTime":439.227,"body":"In fact, the summer, uh, time Magazine had a cover about the oncoming Ice Age"},{"startTime":439.227,"endTime":441.245,"body":"People magazine, maybe one of them."},{"startTime":441.745,"endTime":445.213,"body":"Um, and then, but he, but they did know the carbon dioxide concentrations were going"},{"startTime":445.213,"endTime":445.445,"body":"up."},{"startTime":445.905,"endTime":450.157,"body":"And thanks to the work of Sinabi and Klaus Hassman and others, they knew what"},{"startTime":450.157,"endTime":450.725,"body":"that meant."},{"startTime":450.785,"endTime":453.405,"body":"And, you know, we've gone through in these lectures what that does mean."},{"startTime":453.905,"endTime":458.85,"body":"And so he was able to solve, and this was the first time anybody had"},{"startTime":458.85,"endTime":463.795,"body":"actually attempted to make a prediction of the time evolution of the coupled climate economy"},{"startTime":463.795,"endTime":464.125,"body":"system."},{"startTime":464.745,"endTime":468.518,"body":"And I'm sure he used a room, you know, computer the size of a room,"},{"startTime":468.518,"endTime":469.525,"body":"um, to do this."},{"startTime":469.555,"endTime":471.805,"body":"This was back in the mid 1970s."},{"startTime":472.265,"endTime":477.725,"body":"Um, and he calculated the dash line there, and, um, that's what he predicted."},{"startTime":478.385,"endTime":479.845,"body":"And this is what's happened."},{"startTime":479.845,"endTime":481.205,"body":"It, it needs updating here."},{"startTime":481.205,"endTime":483.205,"body":"This is only goes to a couple of years ago."},{"startTime":483.705,"endTime":489.031,"body":"Um, but, um, if I, uh, so, so the, the blue, the blue temperatures are"},{"startTime":489.031,"endTime":494.358,"body":"what Bill Northouse conceivably could have known about, but in fact, he didn't because we"},{"startTime":494.358,"endTime":499.685,"body":"didn't observe global temperatures nearly as well then as, as we have done, uh, since."},{"startTime":499.985,"endTime":503.325,"body":"And the red, of course, is after he actually published his paper."},{"startTime":503.785,"endTime":506.83,"body":"And if we sort of use the magic apart PowerPoint to slide it over, you"},{"startTime":506.83,"endTime":507.845,"body":"can see he nailed it."},{"startTime":508.145,"endTime":512.164,"body":"He predicted we'd get to one degree in this past decade, is exactly what happened."},{"startTime":512.385,"endTime":516.298,"body":"You'll also notice, by the way, that he predicts it accelerates around now, and that"},{"startTime":516.298,"endTime":518.125,"body":"we get to two degrees around mid-century."},{"startTime":518.825,"endTime":524.516,"body":"But to reassure you, this was a prediction made by Bill Northouse, assuming that the"},{"startTime":524.516,"endTime":530.207,"body":"world economy and the world population, um, grew in the way they were projected to"},{"startTime":530.207,"endTime":531.725,"body":"grow in the 1970s."},{"startTime":531.825,"endTime":535.312,"body":"And you, you may recall one of, one of the things I remember as a"},{"startTime":535.312,"endTime":538.8,"body":"teenager, lots of articles about, uh, you know, the population boom and the fact that"},{"startTime":538.8,"endTime":541.125,"body":"we were gonna be, you know, 10 billion by whenever."},{"startTime":541.225,"endTime":544.564,"body":"And, and, uh, so, um, of course one of the great good news stories of"},{"startTime":544.564,"endTime":547.903,"body":"the past 30 or 40 years has been the fact that the world population is"},{"startTime":547.903,"endTime":549.685,"body":"not growing in the way that it was."},{"startTime":550.225,"endTime":556.467,"body":"Um, and of course, we have made perhaps some progress on decarbonization as well, so"},{"startTime":556.467,"endTime":558.965,"body":"we're not predicting that rapid acceleration."},{"startTime":558.985,"endTime":563.388,"body":"But, you know, in other than that, so, but that was, that's the future prediction"},{"startTime":563.388,"endTime":567.205,"body":"from its, you know, the world has warmed pretty much exactly as expected."},{"startTime":567.585,"endTime":573.724,"body":"And interestingly, perhaps, surprisingly, um, in the standard models that we use for predicting climate"},{"startTime":573.724,"endTime":579.045,"body":"change, these are the models used by the intergovernmental panel on climate change."},{"startTime":580.035,"endTime":582.365,"body":"It's actually surprisingly linear."},{"startTime":582.545,"endTime":584.285,"body":"We call, it's a straight line response."},{"startTime":584.285,"endTime":589.018,"body":"If you, if you crank up greenhouse gas concentrations, you can see the yellow lines"},{"startTime":589.018,"endTime":592.805,"body":"there all the way up to four degrees, five degrees and beyond."},{"startTime":593.465,"endTime":598.565,"body":"The, the temperature is just following rising greenhouse gas concentrations."},{"startTime":599.225,"endTime":601.205,"body":"So it's a very, very simple prediction."},{"startTime":602.425,"endTime":607.395,"body":"And in the blue lines, which are a, a, a, a scenario in which we"},{"startTime":607.395,"endTime":612.365,"body":"manage to stabilize, um, greenhouse gas concentrations and start 'em declining again, you can see"},{"startTime":612.365,"endTime":614.685,"body":"that they, they respond again, very predictably."},{"startTime":615.225,"endTime":620.933,"body":"So there's no evidence in these models of anything that you would associate with a,"},{"startTime":620.933,"endTime":626.641,"body":"a, a tipping point like the, the planet sort of going up like this, then"},{"startTime":626.641,"endTime":628.925,"body":"suddenly lurching into a new state."},{"startTime":630.705,"endTime":635.925,"body":"But, you know, are these models, these models miss a lot of the physics."},{"startTime":636.155,"endTime":637.885,"body":"They, they're quite COE resolution."},{"startTime":637.915,"endTime":642.685,"body":"They, they, they, they don't have nearly enough variability of small scales in them."},{"startTime":642.865,"endTime":644.605,"body":"So there's plenty they could be missing."},{"startTime":645.225,"endTime":649.2,"body":"And there is a question we have to ask ourselves is, you know, are they"},{"startTime":649.2,"endTime":650.525,"body":"overly, are they too reassuring?"},{"startTime":651.025,"endTime":654.885,"body":"And plenty of thinkers in this space strongly believe that they are."},{"startTime":655.705,"endTime":661.316,"body":"Um, and this is the kind of tipping point narrative that many of my colleagues"},{"startTime":661.316,"endTime":665.805,"body":"in academia do talk about a lot and worry about a lot."},{"startTime":666.545,"endTime":671.48,"body":"Um, and this is the idea that, you know, we are, and this is a,"},{"startTime":671.48,"endTime":676.416,"body":"a, a nice figure from, um, a, a paper by Will Stefan, um, but, uh,"},{"startTime":676.416,"endTime":680.365,"body":"um, which, which contains a lot of very sensible thoughts in it."},{"startTime":680.585,"endTime":684.765,"body":"But a lot of it is around how do we avoid these tipping points?"},{"startTime":684.865,"endTime":689.617,"body":"How do we navigate the next few decades to avoid, you know, pitfalls here, pitfalls"},{"startTime":689.617,"endTime":690.885,"body":"there, and so on."},{"startTime":691.105,"endTime":696.488,"body":"And clearly the sort of choice they're sketching out here is that, you know, we"},{"startTime":696.488,"endTime":701.871,"body":"have to get on this earth system stewardship pathway, um, it to avoid, um, going"},{"startTime":701.871,"endTime":707.255,"body":"over some planetary threshold and having, um, the, the world run away from us into"},{"startTime":707.255,"endTime":710.485,"body":"this hot house earth that they're, they're worried about."},{"startTime":711.185,"endTime":718.22,"body":"So, um, there's plenty there and there's plenty of, um, processes that are not well"},{"startTime":718.22,"endTime":725.255,"body":"represented in our current models that could result in tipping point globally, significant tipping point"},{"startTime":725.255,"endTime":725.725,"body":"behavior."},{"startTime":726.665,"endTime":733.325,"body":"Uh, there's, here's again, a figure from there article, which highlights the main tipping elements."},{"startTime":733.325,"endTime":738.065,"body":"These are parts of the climate system that could tip over, could, um, suddenly, I"},{"startTime":738.065,"endTime":742.805,"body":"suppose I should have started off by saying what I mean by a tipping point."},{"startTime":742.925,"endTime":745.525,"body":"'cause I'm just kind of assuming everybody kind of knows what I'm talking about."},{"startTime":746.065,"endTime":749.576,"body":"But, um, so when you are, um, uh, Tim Lenton who does a lot of"},{"startTime":749.576,"endTime":753.087,"body":"work in this space, he uses the analogy of a chair if you're sort of"},{"startTime":753.087,"endTime":756.365,"body":"tipping a chair over, and eventually it'll reach a point where it'll fall over."},{"startTime":756.635,"endTime":756.925,"body":"Okay?"},{"startTime":757.065,"endTime":759.965,"body":"So, so that's the analogy people have in their heads."},{"startTime":760.425,"endTime":765.771,"body":"Um, it's, it's not the same as sometimes people talk about a system reaching a"},{"startTime":765.771,"endTime":770.405,"body":"tipping point, just meaning it's accelerating, and that that's not what I mean."},{"startTime":770.525,"endTime":772.445,"body":"I mean, i, I, it's, it's something much more."},{"startTime":772.705,"endTime":776.32,"body":"And, and I'll explain in a bit more detail what we mean in, in by"},{"startTime":776.32,"endTime":777.285,"body":"this sort of behavior."},{"startTime":777.305,"endTime":781.861,"body":"In, in physics, a an acceleration is not an indication of, of, of a tipping"},{"startTime":781.861,"endTime":782.165,"body":"point."},{"startTime":782.165,"endTime":783.525,"body":"It depends what's driving the acceleration."},{"startTime":783.525,"endTime":785.445,"body":"It depends on the nature of what's happening."},{"startTime":785.445,"endTime":790.395,"body":"So, for example, the world is warming at its fastest rates ever at the moment,"},{"startTime":790.395,"endTime":793.365,"body":"as we emphasized in a couple of lectures ago."},{"startTime":793.945,"endTime":798.404,"body":"But the reason for that is because the combination of greenhouse gas concentrations in the"},{"startTime":798.404,"endTime":802.863,"body":"atmosphere that we're putting in is going up if you add up carbon dioxide, methane,"},{"startTime":802.863,"endTime":807.322,"body":"and also the progress we're making on reducing, um, other forms of pollution, which we're"},{"startTime":807.322,"endTime":811.485,"body":"keeping the planet cool, if you add all that up, it's driving that warming."},{"startTime":811.515,"endTime":816.251,"body":"It's not that the system has crossed some boundary and is suddenly moving into a"},{"startTime":816.251,"endTime":819.725,"body":"new behavior, um, it's just that we're pushing it really hard."},{"startTime":819.825,"endTime":822.085,"body":"So that's why it's, it's going going fast at the moment."},{"startTime":822.785,"endTime":828.47,"body":"But these are the parts of the system which we worry about, um, which could,"},{"startTime":828.47,"endTime":834.155,"body":"um, dis display this threshold behavior where you push the system along and then it,"},{"startTime":834.155,"endTime":838.325,"body":"it falls over and, and goes into a completely different state."},{"startTime":838.945,"endTime":844.205,"body":"Um, one will talk about, first is the thermohaline circulation."},{"startTime":844.225,"endTime":849.664,"body":"That's the global overturning ocean overturning circulation, um, often associated with the Gulf Stream, but"},{"startTime":849.664,"endTime":852.565,"body":"it's not the same as the Gulf Stream."},{"startTime":852.565,"endTime":857.478,"body":"The Gulf Stream is a, a surface current in the Atlantic, which moves temperature around,"},{"startTime":857.478,"endTime":862.392,"body":"uh, of the surface, uh, in the surface waters of the ocean, moves heat around"},{"startTime":862.392,"endTime":864.685,"body":"in the surface, waters of the ocean."},{"startTime":865.225,"endTime":870.846,"body":"But beneath it, there's a, a much bigger current, which is the entire ocean, this"},{"startTime":870.846,"endTime":876.467,"body":"conveyor belt carrying water northwards through the Atlantic, sinking in the Arctic, and returning at"},{"startTime":876.467,"endTime":880.965,"body":"depth, which also, which both have an enormous impact on our climate."},{"startTime":881.425,"endTime":884.439,"body":"Um, and it's the thermal headline circulation that, that I'll be talking about when we"},{"startTime":884.439,"endTime":885.645,"body":"come to talk about tipping points."},{"startTime":886.225,"endTime":891.955,"body":"Um, we'll also talk about the ice sheets, the West Antarctic ice shelf and the"},{"startTime":891.955,"endTime":897.686,"body":"Greenland ice streets, which again, are one of the systems in our planet that we"},{"startTime":897.686,"endTime":901.125,"body":"are monitoring and concerned about crossing some irreversible threshold."},{"startTime":901.345,"endTime":906.63,"body":"And finally, the Amazon rainforest, again, which is another big, big part of our planet"},{"startTime":906.63,"endTime":911.915,"body":"that we are monitoring and concerned about the possibility of it being pushed over a,"},{"startTime":911.915,"endTime":913.325,"body":"an irreversible, um, point."},{"startTime":913.385,"endTime":917.966,"body":"But we'll start by talking about the thermohaline circulation, which is the one, uh, the,"},{"startTime":917.966,"endTime":922.547,"body":"it was probably the first big tipping point to be discussed, um, uh, extensively in"},{"startTime":922.547,"endTime":924.685,"body":"the, uh, in, in the climate community."},{"startTime":924.685,"endTime":927.76,"body":"It's also the one, it's also the one where I'm most familiar with the processes"},{"startTime":927.76,"endTime":927.965,"body":"involved."},{"startTime":928.185,"endTime":930.285,"body":"So I'm sort of most comfortable talking about it."},{"startTime":930.745,"endTime":935.487,"body":"And it also gives me a chance to, um, remind those of you who were"},{"startTime":935.487,"endTime":938.965,"body":"at my earlier lectures, um, of things you've already heard about."},{"startTime":939.545,"endTime":944.024,"body":"Um, so I can ask you, I, I won't, I won't, um, I won't call"},{"startTime":944.024,"endTime":948.504,"body":"out the audience here, but, but if you were at, um, my, uh, third lecture"},{"startTime":948.504,"endTime":952.983,"body":"last year, uh, where we talked about the ocean physics behind net zero, there's a"},{"startTime":952.983,"endTime":957.165,"body":"few people looking slightly nervous, you know, is he gonna pick us out here?"},{"startTime":957.465,"endTime":961.557,"body":"Um, um, and, and I was trying to, I was, I was, uh, spent quite"},{"startTime":961.557,"endTime":965.65,"body":"a lot of time in that lecture talking about why the deep ocean is so"},{"startTime":965.65,"endTime":968.925,"body":"cold, why we have this very constant temperature in the deep ocean."},{"startTime":969.705,"endTime":974.788,"body":"And, um, the, the answer I explained to you was because the water that gets"},{"startTime":974.788,"endTime":979.871,"body":"into our deep oceans gets there from very cold places, um, in over most of"},{"startTime":979.871,"endTime":984.955,"body":"the ocean surface, the surface, um, waters are too warm to mix with the waters"},{"startTime":984.955,"endTime":988.005,"body":"beneath them because they're, they're warmed by the sun."},{"startTime":988.005,"endTime":992.525,"body":"They're, they're level less dense than the water underneath them, so they can't mix."},{"startTime":992.915,"endTime":996.445,"body":"They just slide around over the, the abyssal waters."},{"startTime":997.065,"endTime":1003.286,"body":"And the only way water can get from the surface layer down into the deep"},{"startTime":1003.286,"endTime":1009.507,"body":"ocean is through these relatively isolated regions of, so-called deep water formation, uh, which are"},{"startTime":1009.507,"endTime":1014.485,"body":"highlighted in this graphic, um, near Antarctica and in the North Atlantic."},{"startTime":1015.585,"endTime":1020.652,"body":"And the reason the, the water can only sink down to ocean depths in these"},{"startTime":1020.652,"endTime":1025.719,"body":"regions is because of the, of the reason water can sink down, uh, to the"},{"startTime":1025.719,"endTime":1030.786,"body":"ocean depths in these regions is because of the peculiar equation of state, the, the,"},{"startTime":1030.786,"endTime":1034.165,"body":"the, the, the equation that determines the density of seawater."},{"startTime":1034.825,"endTime":1038.929,"body":"And the fact that as you cool water down, it gets denser and denser and"},{"startTime":1038.929,"endTime":1040.845,"body":"denser, but then it stops getting dense."},{"startTime":1041.305,"endTime":1045.805,"body":"You remember, we, we emphasize this as you're cooling water towards zero, eventually it stops"},{"startTime":1045.805,"endTime":1046.405,"body":"getting dense."},{"startTime":1046.405,"endTime":1049.581,"body":"And of course, when it freezes, the ice floats so it sort of becomes less"},{"startTime":1049.581,"endTime":1050.005,"body":"dense again."},{"startTime":1050.265,"endTime":1055.783,"body":"So, so there is a point at which, um, uh, water is no longer the"},{"startTime":1055.783,"endTime":1061.301,"body":"density of water is, is no longer as sensitive to its temperature and becomes sensitive"},{"startTime":1061.301,"endTime":1062.405,"body":"to other things."},{"startTime":1063.105,"endTime":1068.231,"body":"And it's in particular the salt content of water that determines how much, how it,"},{"startTime":1068.231,"endTime":1070.965,"body":"how it escapes down into the ocean depths."},{"startTime":1071.505,"endTime":1076.788,"body":"So crucial to this story, therefore, now we're gonna in that, in that lecture in"},{"startTime":1076.788,"endTime":1082.071,"body":"the ocean physics foundation, net zero, we kind of just mentioned this as something going"},{"startTime":1082.071,"endTime":1087.354,"body":"on, which determined what, which it helped us explain why there were two times scales"},{"startTime":1087.354,"endTime":1090.525,"body":"in the, um, planet's response to rising greenhouse gases."},{"startTime":1090.525,"endTime":1095.311,"body":"We had the sort of surface warming, and then this very gradual warming of the"},{"startTime":1095.311,"endTime":1100.097,"body":"ocean depth, but we kind of took this ocean conveyor as granted, as just something"},{"startTime":1100.097,"endTime":1104.565,"body":"that was happening and, and determined how the system responded to rising greenhouse gases."},{"startTime":1105.225,"endTime":1110.239,"body":"But now we're gonna ask ourselves a bit more about what drives it, what controls"},{"startTime":1110.239,"endTime":1115.253,"body":"it, and, and could the conveyor itself be disturbed by what's going on in, in"},{"startTime":1115.253,"endTime":1116.925,"body":"our, in our surface climate."},{"startTime":1118.225,"endTime":1119.125,"body":"So here's the question."},{"startTime":1119.315,"endTime":1126.805,"body":"What are the controls of that great ocean overturning circulation, the thermohaline conveyor?"},{"startTime":1127.585,"endTime":1133.336,"body":"And on the one hand, we've got accelerators, things that make it go faster, um,"},{"startTime":1133.336,"endTime":1139.087,"body":"which is, um, for example, the fact that polar waters are colder than equatorial waters,"},{"startTime":1139.087,"endTime":1141.005,"body":"um, which makes them denser."},{"startTime":1141.805,"endTime":1145.005,"body":"I mean, even so, so because electorial water are much warmer."},{"startTime":1145.185,"endTime":1149.525,"body":"So, so that temperature does matter at those tempera at the surface."},{"startTime":1150.025,"endTime":1154.35,"body":"And so you have the, the cooling of polar water, the, the fact that the"},{"startTime":1154.35,"endTime":1158.676,"body":"poles are colder than the equator is essential for this overturning circulation to be set"},{"startTime":1158.676,"endTime":1158.965,"body":"up."},{"startTime":1159.705,"endTime":1165.671,"body":"Um, we also had, and I emphasized this in the ocean physics lecture, that evaporation,"},{"startTime":1165.671,"endTime":1171.638,"body":"um, and, uh, ice formation in these cold regions makes water saltier, and therefore, that"},{"startTime":1171.638,"endTime":1177.605,"body":"also makes the water denser and allows it to escape down into the ocean depths."},{"startTime":1178.865,"endTime":1184.325,"body":"But on the other hand, there are breaks on this overturning circulation."},{"startTime":1185.105,"endTime":1189.725,"body":"And the most obvious one is just as it were, friction."},{"startTime":1189.725,"endTime":1193.165,"body":"Like any conveyor belt, you know, it's gotta overcome friction."},{"startTime":1193.705,"endTime":1198.722,"body":"Um, the friction we're talking about here, because it's a fluid and it's on very"},{"startTime":1198.722,"endTime":1203.405,"body":"large scales, uh, it's actually really mostly the role of eddies in the system."},{"startTime":1203.985,"endTime":1209.709,"body":"Um, and, uh, so, so interestingly, when you try and model the behavior of the"},{"startTime":1209.709,"endTime":1215.433,"body":"ocean on very large scales, you have to model it almost as quite a, a"},{"startTime":1215.433,"endTime":1221.158,"body":"sort of sticky syrup substance, um, because you're not resolving all the little eddies that"},{"startTime":1221.158,"endTime":1222.685,"body":"actually slow it down."},{"startTime":1223.985,"endTime":1227.085,"body":"We digress slightly here, but you've probably noticed this."},{"startTime":1227.505,"endTime":1232.149,"body":"If you are, um, if you're trying to suck water through a straw, if you"},{"startTime":1232.149,"endTime":1235.245,"body":"suck it slowly, you don't have to suck very hard."},{"startTime":1235.585,"endTime":1239.362,"body":"But if you try and suck really quickly, you'll notice suddenly it becomes much harder"},{"startTime":1239.362,"endTime":1241.125,"body":"to get the water through the straw."},{"startTime":1241.555,"endTime":1241.845,"body":"Okay?"},{"startTime":1242.345,"endTime":1242.765,"body":"Do try."},{"startTime":1242.765,"endTime":1244.005,"body":"Don't choke yourself doing this."},{"startTime":1244.025,"endTime":1249.072,"body":"But, um, but, but, um, uh, what you're seeing there is the fact that as"},{"startTime":1249.072,"endTime":1254.12,"body":"soon as the flow through the straw becomes turbulent, it, it's actually the, the resistance"},{"startTime":1254.12,"endTime":1257.485,"body":"to the flow goes up a lot very, very rapidly."},{"startTime":1258.225,"endTime":1266.605,"body":"And so, um, turbulence in the ocean, um, slows, slows down this overturning circulation."},{"startTime":1266.705,"endTime":1271.005,"body":"So, so that's one thing that one sort of break we've got on this overturning."},{"startTime":1271.145,"endTime":1275.045,"body":"But the other really important one is the fact that it's not just evaporation and"},{"startTime":1275.045,"endTime":1277.645,"body":"ice formation that I talked about in the last lecture."},{"startTime":1277.645,"endTime":1281.845,"body":"That's the lecture that in the, in the ocean's lecture that matters in these polar"},{"startTime":1281.845,"endTime":1282.125,"body":"regions."},{"startTime":1282.225,"endTime":1283.445,"body":"We also have precipitation."},{"startTime":1283.445,"endTime":1288.578,"body":"We have rain snowfall and so on, which is fresh water being added to, um,"},{"startTime":1288.578,"endTime":1289.605,"body":"our arctic oceans."},{"startTime":1290.025,"endTime":1291.845,"body":"And of course, ice melts as well."},{"startTime":1292.225,"endTime":1297.325,"body":"Uh, both, um, sea ice sand, also ice, uh, on ice shelves and ice caps."},{"startTime":1297.585,"endTime":1303.81,"body":"And that injects fresh water into the polar regions, making it fresher and therefore making"},{"startTime":1303.81,"endTime":1309.205,"body":"it less dense and therefore, um, slowing down the formation of deep water."},{"startTime":1309.265,"endTime":1314.33,"body":"So you can see this, this, this, it's the balance between these two things that"},{"startTime":1314.33,"endTime":1318.045,"body":"determines how, um, uh, how strong the ocean overturning circulation is."},{"startTime":1318.345,"endTime":1323.777,"body":"And I've highlighted the precipitation one because that's the one where we believe things may"},{"startTime":1323.777,"endTime":1328.485,"body":"be happening, which may be affecting the strength of the global overturning circulation."},{"startTime":1329.045,"endTime":1333.638,"body":"'cause if we look in those climate models, and these are the same climate models"},{"startTime":1333.638,"endTime":1338.232,"body":"that gave us that very linear, boring warming response to rising greenhouse gases that I"},{"startTime":1338.232,"endTime":1338.845,"body":"showed you."},{"startTime":1339.115,"endTime":1342.245,"body":"This is what happens to precipitation in those models."},{"startTime":1342.865,"endTime":1348.475,"body":"And you'll notice that in the southern ocean, in these regions where, uh, there are"},{"startTime":1348.475,"endTime":1354.085,"body":"important deepwater formation regions around Antarctica, precipitation is predicted to increase a bit 10, 20%"},{"startTime":1354.085,"endTime":1359.695,"body":"or so, and that there's no sort of, um, hatching there, which means the models"},{"startTime":1359.695,"endTime":1361.565,"body":"are pretty much in agreement."},{"startTime":1362.065,"endTime":1364.325,"body":"80% of models agree as it were."},{"startTime":1364.745,"endTime":1369.691,"body":"Um, that most, that the, that there will be an increase in, in rainfall in"},{"startTime":1369.691,"endTime":1374.638,"body":"those regions in the North Atlantic, you'll notice, um, the colors are a bit washed"},{"startTime":1374.638,"endTime":1379.585,"body":"out, so it's kind of a round zero, but you'll also notice there's lots of"},{"startTime":1379.585,"endTime":1380.245,"body":"diagonal lines."},{"startTime":1380.265,"endTime":1385.015,"body":"So we really don't know what's gonna happen in the long term to precipitation in"},{"startTime":1385.015,"endTime":1385.965,"body":"the North Atlantic."},{"startTime":1387.465,"endTime":1393.533,"body":"Um, uh, by the way, because somebody's bound to be wondering, you'll notice that the"},{"startTime":1393.533,"endTime":1396.365,"body":"UK is, um, blue and there isn't."},{"startTime":1396.665,"endTime":1401.093,"body":"So, I'm sorry, the, the consensus is pretty clear in the models that the UK"},{"startTime":1401.093,"endTime":1404.045,"body":"is gonna get a bit more wet and miserable anyway."},{"startTime":1404.345,"endTime":1407.525,"body":"Um, but we're talking about the global, um, uh, picture here."},{"startTime":1408.225,"endTime":1415.176,"body":"And, um, a long time ago, Henry Stommel, um, introduced a, a model of this"},{"startTime":1415.176,"endTime":1422.127,"body":"process that the overturning circulation and how it might depend on these external drivers that"},{"startTime":1422.127,"endTime":1429.078,"body":"actually captures the essential sort of conceptual ideas of the whole tipping point, ocean tipping"},{"startTime":1429.078,"endTime":1430.005,"body":"point discussion."},{"startTime":1430.545,"endTime":1432.205,"body":"Um, Henry Stonewell was very, very interesting."},{"startTime":1432.265,"endTime":1438.352,"body":"Um, uh, he, he died, um, I think in the 1980s or nine maybe, but,"},{"startTime":1438.352,"endTime":1444.439,"body":"um, uh, uh, so, but he was one of the great oceanographers of the 20th"},{"startTime":1444.439,"endTime":1444.845,"body":"century."},{"startTime":1445.345,"endTime":1448.09,"body":"Um, and, and one of the last ones, he, he never had a, he never"},{"startTime":1448.09,"endTime":1449.005,"body":"took a, did a doctorate."},{"startTime":1449.065,"endTime":1453.106,"body":"Um, he went, he basically, he was a, he was a craftsman, uh, craftsman of"},{"startTime":1453.106,"endTime":1453.645,"body":"the oceans."},{"startTime":1454.305,"endTime":1456.885,"body":"Um, and he really, he understood the oceans."},{"startTime":1456.885,"endTime":1457.125,"body":"He did."},{"startTime":1457.145,"endTime":1462.692,"body":"He was, he was, he did a lot of, um, very, very fundamental work, um,"},{"startTime":1462.692,"endTime":1468.24,"body":"on, on the basic processes that govern our ocean circulation, um, is probably most well"},{"startTime":1468.24,"endTime":1473.787,"body":"known for explaining the abyssal circulation, the sort of circulation of the deep oceans, which"},{"startTime":1473.787,"endTime":1479.335,"body":"of course we were only learning about from, um, very deep, um, uh, uh, uh,"},{"startTime":1479.335,"endTime":1480.445,"body":"long line observations."},{"startTime":1480.445,"endTime":1484.285,"body":"And of course the, the submarine, um, movements and so on."},{"startTime":1484.455,"endTime":1487.558,"body":"After the second World War, we were sort of discovering about our, our, our de"},{"startTime":1487.558,"endTime":1487.765,"body":"patients."},{"startTime":1487.905,"endTime":1492.158,"body":"The work of his, which I wanted to talk to you about today, was his"},{"startTime":1492.158,"endTime":1495.845,"body":"idea of a, a very simple model of the oat global overturning circulation."},{"startTime":1495.845,"endTime":1500.957,"body":"So he just imagine the world is just two boxes, an equatorial sort of rest"},{"startTime":1500.957,"endTime":1504.365,"body":"of the world box, and a relatively small polar box."},{"startTime":1505.785,"endTime":1511.567,"body":"And you've got a, an overturning that's driven by the density difference between the, the"},{"startTime":1511.567,"endTime":1516.965,"body":"water in the polar box and the water in the rest of the world."},{"startTime":1518.025,"endTime":1523.437,"body":"So, um, the water in the polar box is, it's less, it's, it's, uh, less"},{"startTime":1523.437,"endTime":1527.045,"body":"salty than the water in, in the, uh, equatorial box."},{"startTime":1527.245,"endTime":1531.681,"body":"'cause you know, in, in the, uh, the equator, there's lots of sun, lots of"},{"startTime":1531.681,"endTime":1536.117,"body":"evaporation, water's relatively salty, um, in the polar box, uh, lots of rain, lots of"},{"startTime":1536.117,"endTime":1537.005,"body":"fresh water input."},{"startTime":1537.005,"endTime":1539.525,"body":"So it's less salty, but it's also colder."},{"startTime":1540.065,"endTime":1541.245,"body":"Put these two things together."},{"startTime":1541.785,"endTime":1548.022,"body":"Um, the water there is on average denser than it is in the equatorial box,"},{"startTime":1548.022,"endTime":1553.845,"body":"and therefore you have an overturning circulation, and it's steady because there's some friction."},{"startTime":1553.865,"endTime":1558.188,"body":"It doesn't keep, it doesn't just keep accelerating, um, as it would if there were"},{"startTime":1558.188,"endTime":1558.765,"body":"no friction."},{"startTime":1558.765,"endTime":1562.525,"body":"But you've got those important eddies doing the, doing the work to, to control it."},{"startTime":1563.065,"endTime":1569.713,"body":"Now suppose, um, we, if, if imagine the overturning strengthened, um, that would carry more"},{"startTime":1569.713,"endTime":1576.362,"body":"water into the polar box faster, and if the amount of rain that was raining"},{"startTime":1576.362,"endTime":1582.125,"body":"in the polar box stays the same, then the polar box gets saltier."},{"startTime":1582.755,"endTime":1583.045,"body":"Yeah."},{"startTime":1584.065,"endTime":1589.485,"body":"Um, and, um, that actually reduces the, um, difference."},{"startTime":1589.825,"endTime":1591.325,"body":"So you have sort of higher salt."},{"startTime":1592.105,"endTime":1599.067,"body":"Um, and, and, uh, so it reduces the difference of salinity reduces that, um, uh,"},{"startTime":1599.067,"endTime":1603.245,"body":"resistance to the overturning that's introduced by the salinity."},{"startTime":1603.625,"endTime":1609.527,"body":"So the salinity in this, in the sort of starting picture temperatures driving the overturning"},{"startTime":1609.527,"endTime":1615.43,"body":"and the salinity contrast the sort content contrast in the polar box and the rest"},{"startTime":1615.43,"endTime":1619.365,"body":"of the world is actually acting in the opposite direction."},{"startTime":1620.285,"endTime":1623.645,"body":"'cause the sort content here is lower than the salt content here."},{"startTime":1624.185,"endTime":1628.735,"body":"Um, so it's, it, it's actually, uh, acting as a break on, on the, on"},{"startTime":1628.735,"endTime":1629.645,"body":"the overturning circulation."},{"startTime":1630.225,"endTime":1636.445,"body":"But as you, if you strengthen the overturning circulation, you weaken the salinity break."},{"startTime":1637.545,"endTime":1641.875,"body":"Yeah, because you actually add more salt to this region."},{"startTime":1642.655,"endTime":1646.399,"body":"So you don't necessarily, it doesn't mean that, you know, it all falls to bits"},{"startTime":1646.399,"endTime":1649.395,"body":"immediately, but you can see immediately there's, oh, there's something interesting there."},{"startTime":1649.755,"endTime":1655.288,"body":"'cause there's a feedback between what any change in the circulation affects the thing that's"},{"startTime":1655.288,"endTime":1656.395,"body":"also driving it."},{"startTime":1656.625,"endTime":1662.064,"body":"This is the sort of hallmark of a, a non-linear system where a change actually"},{"startTime":1662.064,"endTime":1663.515,"body":"feeds back on itself."},{"startTime":1664.495,"endTime":1665.635,"body":"So there's a feedback there."},{"startTime":1666.135,"endTime":1670.818,"body":"Um, and of course, if you have weaker overturning, you then have more fresh water"},{"startTime":1670.818,"endTime":1671.755,"body":"getting into this."},{"startTime":1671.895,"endTime":1677.326,"body":"So the balance between, um, water flowing in from the equator and water coming in"},{"startTime":1677.326,"endTime":1682.395,"body":"from the rain is such that it ends up fresher, um, therefore less dense."},{"startTime":1682.855,"endTime":1684.915,"body":"And that, that has the, the opposite effect."},{"startTime":1686.215,"endTime":1692.192,"body":"Um, and of course, if you reverse the overturn, this is crucial in, um, uh,"},{"startTime":1692.192,"endTime":1698.17,"body":"staal's, uh, model, is that if you reverse this whole overturning, then you have exactly"},{"startTime":1698.17,"endTime":1702.155,"body":"the same, um, flow of salt into the polar box."},{"startTime":1702.155,"endTime":1703.035,"body":"You have the same setup."},{"startTime":1703.775,"endTime":1708.955,"body":"Um, and, but you have even lower salt there because this is much weaker circulation."},{"startTime":1708.975,"endTime":1715.256,"body":"So let's sort of think about what this model means with a few very simple"},{"startTime":1715.256,"endTime":1715.675,"body":"equations."},{"startTime":1716.295,"endTime":1721.856,"body":"So we'll call the overturning strength q, that's the flow of the flow of water"},{"startTime":1721.856,"endTime":1727.418,"body":"measured in something called a spare drop, which is an, in a, a spare drop"},{"startTime":1727.418,"endTime":1730.755,"body":"is a square kilometer of water moving a meter."},{"startTime":1731.615,"endTime":1735.286,"body":"So it's a way of, it's a way of, it's a unit for a flow"},{"startTime":1735.286,"endTime":1736.755,"body":"of rather a lot of water."},{"startTime":1737.415,"endTime":1740.875,"body":"So, you know, if you have, you did this in liters per second, it would"},{"startTime":1740.875,"endTime":1743.875,"body":"be, you know, but, so spare drops is a better unit to use."},{"startTime":1745.045,"endTime":1751.037,"body":"We've got the temperature contrast, delta TI use deltas to indicate temperature differences here, and"},{"startTime":1751.037,"endTime":1753.035,"body":"it's from low to high."},{"startTime":1753.135,"endTime":1754.555,"body":"So delta T is positive."},{"startTime":1755.025,"endTime":1755.315,"body":"Yeah."},{"startTime":1755.935,"endTime":1760.435,"body":"So that's the difference in temperature between pole and equator or Poland tropics."},{"startTime":1760.655,"endTime":1762.395,"body":"And then we have the salt contrast as well."},{"startTime":1762.715,"endTime":1768.475,"body":"Remember we've got it, you're starting off from conditions where the poles are always less"},{"startTime":1768.475,"endTime":1772.315,"body":"salty than the equator, that that's not predicted to change."},{"startTime":1772.735,"endTime":1775.235,"body":"So delta S is always positive as well."},{"startTime":1775.525,"endTime":1778.867,"body":"Again, we're sort of measur we're, we're using, we're setting this up so that all"},{"startTime":1778.867,"endTime":1781.765,"body":"the, the symbols are positive to make it easy for you to follow."},{"startTime":1782.385,"endTime":1785.765,"body":"So, couple of equations, but bear with me."},{"startTime":1786.195,"endTime":1787.365,"body":"They're very simple ones."},{"startTime":1787.625,"endTime":1793.041,"body":"The rate of overturning, if it's driven by the density is proportional to, so these"},{"startTime":1793.041,"endTime":1794.125,"body":"are just constants."},{"startTime":1794.165,"endTime":1800.915,"body":"A and B, there's numbers, it's proportional to, um, one term, which is depends on"},{"startTime":1800.915,"endTime":1806.765,"body":"the, the temperature difference, which is positive, that's driving it, driving the overturning."},{"startTime":1807.185,"endTime":1810.525,"body":"And another term, which is negative, which depends on the sort content difference."},{"startTime":1810.525,"endTime":1811.645,"body":"So that's slowing it down."},{"startTime":1811.825,"endTime":1815.965,"body":"So it's the balance between these two, which gives you the strength of the overturning."},{"startTime":1818.295,"endTime":1821.245,"body":"We've also got what determines the salt content."},{"startTime":1821.715,"endTime":1828.347,"body":"Well, we've got this continuous freshwater input, uh, called e There's an extra extra, um,"},{"startTime":1828.347,"endTime":1834.979,"body":"freshwater going in, and that's balancing the salt that's being carried in from the equatorial"},{"startTime":1834.979,"endTime":1840.285,"body":"box, which obviously depends on the te on the salt content difference."},{"startTime":1840.755,"endTime":1846.402,"body":"That difference was zero, then the overturning wouldn't change, the salt content wouldn't transport salt"},{"startTime":1846.402,"endTime":1848.285,"body":"into the polar box, okay?"},{"startTime":1848.285,"endTime":1851.045,"body":"Because there's always a difference between the equator and the pole."},{"startTime":1851.065,"endTime":1856.005,"body":"The stronger the overturning, the, the, the more salt it carries into the pole."},{"startTime":1856.505,"endTime":1861.485,"body":"Um, but, and it, but it's the, these vertical lines here mean it doesn't matter"},{"startTime":1861.485,"endTime":1864.805,"body":"what the sign of the overturning is, that's always positive."},{"startTime":1865.025,"endTime":1866.925,"body":"So what we call modular sign, okay?"},{"startTime":1867.425,"endTime":1872.555,"body":"And that means that it doesn't matter whether it's mixing it that way or mixing"},{"startTime":1872.555,"endTime":1877.686,"body":"it that way, it's the amount of overturning that determines that the size of this"},{"startTime":1877.686,"endTime":1880.765,"body":"mixing in, of, uh, salty water into the poles."},{"startTime":1881.785,"endTime":1883.365,"body":"So those are our two equations."},{"startTime":1883.365,"endTime":1887.285,"body":"They're the only two equations, uh, in this, uh, uh, in this lecture."},{"startTime":1887.465,"endTime":1891.008,"body":"So if you hate equations, you know, you've, you've made it, um, we've got past"},{"startTime":1891.008,"endTime":1891.245,"body":"them."},{"startTime":1891.705,"endTime":1896.946,"body":"Um, and we can now talk about what they, what they mean if we just"},{"startTime":1896.946,"endTime":1897.645,"body":"rearrange things."},{"startTime":1898.395,"endTime":1900.045,"body":"This is the same equation, okay?"},{"startTime":1900.045,"endTime":1903.345,"body":"Just before, in case you get suspicious of me, ah, he said there was only"},{"startTime":1903.345,"endTime":1906.645,"body":"two, but no, this is, I, I, I have actually feel stuck with the promise."},{"startTime":1906.795,"endTime":1911.603,"body":"Hopefully you can see that that's just, I'm just taking this equation and plugging it"},{"startTime":1911.603,"endTime":1912.565,"body":"into that one."},{"startTime":1912.905,"endTime":1917.572,"body":"And I say that the rate of overturning is just some constant, that's the, uh,"},{"startTime":1917.572,"endTime":1922.239,"body":"the, the overturning we would get if the salt wasn't doing anything at all miners"},{"startTime":1922.239,"endTime":1926.285,"body":"this term, which is proportional to one over the rate of overturning itself."},{"startTime":1927.465,"endTime":1931.23,"body":"And, you know, if you go away and somebody's shaking their heads as if I,"},{"startTime":1931.23,"endTime":1934.995,"body":"oh, he's trying to bamboozle me, but, but you know, you can arrange, you can"},{"startTime":1934.995,"endTime":1938.76,"body":"rearrange this equation and get to that equation fairly, uh, straightforwardly and encourage you to"},{"startTime":1938.76,"endTime":1939.765,"body":"go and do this."},{"startTime":1940.145,"endTime":1941.685,"body":"Uh, we can simplify it even further."},{"startTime":1941.905,"endTime":1947.217,"body":"And again, I'm just rearranging here, you can see I'm just dividing by QN and"},{"startTime":1947.217,"endTime":1952.53,"body":"introducing a new little symbol delta, which is just, you know, a combination of these"},{"startTime":1952.53,"endTime":1952.885,"body":"constants."},{"startTime":1953.105,"endTime":1959.542,"body":"And this makes, this boils the thing down into a single, very, very simple equation"},{"startTime":1959.542,"endTime":1965.979,"body":"relating Q to something, which is one mins a constant divided by the size of"},{"startTime":1965.979,"endTime":1968.125,"body":"Q, the modulus of Q."},{"startTime":1968.985,"endTime":1974.371,"body":"So I'm saying if the, if the, if the overturning is in equilibrium, that's what"},{"startTime":1974.371,"endTime":1976.885,"body":"determines that it, it satisfies that equation."},{"startTime":1978.065,"endTime":1982.433,"body":"And as I hope you can all remember, if you've got an equation which relates"},{"startTime":1982.433,"endTime":1986.802,"body":"sort of one thing and another thing, you can draw a graph and you can"},{"startTime":1986.802,"endTime":1991.171,"body":"see that the po you've got, this is, this is straight line, here is Q"},{"startTime":1991.171,"endTime":1992.045,"body":"on Q note."},{"startTime":1992.045,"endTime":1996.695,"body":"That gives you a straight line because as as you go, it's just proportional to"},{"startTime":1996.695,"endTime":1997.005,"body":"Q."},{"startTime":1997.825,"endTime":2003.096,"body":"And then these dotted lines here are proportional to one minus delta on mod on"},{"startTime":2003.096,"endTime":2005.205,"body":"on the absolute value of Q."},{"startTime":2006.705,"endTime":2010.605,"body":"And so one over Q gets big when Q is zero."},{"startTime":2011.155,"endTime":2011.445,"body":"Yeah."},{"startTime":2011.665,"endTime":2015.285,"body":"So one minus one over Q disappears into the floor."},{"startTime":2015.435,"endTime":2017.085,"body":"Yeah, that becomes infinite."},{"startTime":2017.155,"endTime":2018.165,"body":"When, when, when."},{"startTime":2019.425,"endTime":2023.708,"body":"And so you can sort of see why the dotted lines are the shape they"},{"startTime":2023.708,"endTime":2024.565,"body":"are, I hope."},{"startTime":2025.185,"endTime":2028.645,"body":"And the fact that it's symmetric is because this is the modular side."},{"startTime":2028.645,"endTime":2031.999,"body":"It doesn't matter whether the Q is positive or negative, the the dotted lines are"},{"startTime":2031.999,"endTime":2033.565,"body":"the same on both sides of zero."},{"startTime":2035.185,"endTime":2036.565,"body":"So that's where we are now."},{"startTime":2036.585,"endTime":2041.589,"body":"So I hope you'll realize it was worth it going through this equation because it"},{"startTime":2041.589,"endTime":2044.925,"body":"helps us understand the whole principle of tipping points here."},{"startTime":2045.995,"endTime":2050.066,"body":"This is where we are Now, if the dotted line, um, I haven't left myself"},{"startTime":2050.066,"endTime":2053.324,"body":"enough time to explain in detail why, you'll be pleased to hear."},{"startTime":2053.585,"endTime":2058.799,"body":"Um, so if the dotted lines above the solid line, so if we disturb where"},{"startTime":2058.799,"endTime":2064.013,"body":"we are now, if the dotted line above the solid line, it's pushed upwards, it's"},{"startTime":2064.013,"endTime":2069.226,"body":"pushed towards higher q and if the dotted line's below the solid line, the system"},{"startTime":2069.226,"endTime":2070.965,"body":"is pushed towards lower queue."},{"startTime":2071.385,"endTime":2075.107,"body":"So where we are now, if it sort of wobbles around a bit, it's sort"},{"startTime":2075.107,"endTime":2076.844,"body":"of pushed back to where it started."},{"startTime":2076.955,"endTime":2077.245,"body":"Yeah."},{"startTime":2077.344,"endTime":2078.364,"body":"So it's, it's stable."},{"startTime":2079.895,"endTime":2081.385,"body":"Took me a lot of PowerPoint to do that."},{"startTime":2081.605,"endTime":2086.145,"body":"So \u003claugh\u003e, okay, but what if it rains more?"},{"startTime":2086.935,"endTime":2091.84,"body":"What if, you know, those models are saying it's gonna get wetter in the polar"},{"startTime":2091.84,"endTime":2094.784,"body":"regions and that, so that freshwater input goes up."},{"startTime":2095.045,"endTime":2100.061,"body":"And if you remember this delta term, one of the things feeding into it was"},{"startTime":2100.061,"endTime":2101.065,"body":"that freshwater input."},{"startTime":2101.165,"endTime":2104.359,"body":"It was, uh, it was a combination of various variables, but one of them was"},{"startTime":2104.359,"endTime":2104.785,"body":"the freshwater."},{"startTime":2105.165,"endTime":2107.905,"body":"So suppose delta is increased."},{"startTime":2108.685,"endTime":2111.595,"body":"So I'm gonna go for, oh, whoops."},{"startTime":2111.695,"endTime":2112.715,"body":"Oh, it was so good."},{"startTime":2112.725,"endTime":2113.435,"body":"Let's see it again."},{"startTime":2113.905,"endTime":2114.195,"body":"Okay."},{"startTime":2114.535,"endTime":2118.155,"body":"Um, now, but in, so that was just, those were just random variations."},{"startTime":2118.215,"endTime":2121.937,"body":"So at the moment, it's stable, you know, it's not as if a simple fluctuation"},{"startTime":2121.937,"endTime":2124.915,"body":"from year to year is gonna suddenly send the whole thing haywire."},{"startTime":2125.375,"endTime":2130.115,"body":"But suppose we had a systematic increase, um, in precipitation."},{"startTime":2130.625,"endTime":2130.915,"body":"Okay?"},{"startTime":2131.015,"endTime":2133.955,"body":"So you can see I've increased delta from three to four."},{"startTime":2134.455,"endTime":2137.035,"body":"You can see that the dotted lines move downwards."},{"startTime":2137.915,"endTime":2143.455,"body":"Yeah, because, um, delta increased."},{"startTime":2144.205,"endTime":2144.495,"body":"Okay?"},{"startTime":2145.195,"endTime":2150.611,"body":"And then eventually you're gonna get to a point where the only way it can"},{"startTime":2150.611,"endTime":2151.695,"body":"go is down."},{"startTime":2151.995,"endTime":2158.935,"body":"So as we increase the precipitation, we're pushing down the dotted line."},{"startTime":2159.165,"endTime":2162.935,"body":"Yeah, it's one minus delta over cube, uh, over mod Q."},{"startTime":2163.075,"endTime":2165.535,"body":"So as you make delta bigger, it's pushing it downwards."},{"startTime":2166.275,"endTime":2172.261,"body":"And as I push it downwards, you can see the blue it weak, the overturning"},{"startTime":2172.261,"endTime":2175.055,"body":"weakens, you know, moves towards zero, okay?"},{"startTime":2175.515,"endTime":2181.265,"body":"And eventually you get to this critical point where the dotted line only just touches"},{"startTime":2181.265,"endTime":2182.415,"body":"the solid line."},{"startTime":2183.155,"endTime":2189.08,"body":"And remember, if the, if you're in, if, if your blue.is on a place where"},{"startTime":2189.08,"endTime":2194.215,"body":"the solid line is above the dotted line, it moves to the left."},{"startTime":2195.685,"endTime":2200.735,"body":"And so if we go just one tiny bit further than that, it can't stay"},{"startTime":2200.735,"endTime":2201.745,"body":"there at all."},{"startTime":2201.765,"endTime":2203.825,"body":"And it has to drift all the way off down."},{"startTime":2203.825,"endTime":2209.55,"body":"It has to very suddenly transition off down to this other side of the, uh,"},{"startTime":2209.55,"endTime":2212.985,"body":"of, of the, of the, uh, uh, the regime."},{"startTime":2213.285,"endTime":2219.305,"body":"We call it the, this other, uh, ocean state where the overturning is now negative."},{"startTime":2219.525,"endTime":2222.945,"body":"So it's reversed and it's much, much weaker."},{"startTime":2223.175,"endTime":2229.22,"body":"It's a, it's a small weak negative overturning, and we have a completely different climate"},{"startTime":2229.22,"endTime":2235.265,"body":"state, and that would have very dramatic imp consequences for climate, certainly in Northwest Europe."},{"startTime":2235.645,"endTime":2240.093,"body":"Um, so these are the amount, um, in a recent study, um, uh, led by"},{"startTime":2240.093,"endTime":2244.541,"body":"a a Dutch group, um, looking at the implications of this, um, they found that"},{"startTime":2244.541,"endTime":2248.989,"body":"certainly in the vicinity of Bergen, you could have a reduction of over 15 degrees,"},{"startTime":2248.989,"endTime":2251.065,"body":"um, in the course of a century."},{"startTime":2251.685,"endTime":2255.945,"body":"Um, and, uh, so here we are here showing in various, um, cities."},{"startTime":2256.285,"endTime":2261.172,"body":"Uh, Bergen you can see is the, the pale blue one, which drops very rapidly"},{"startTime":2261.172,"endTime":2264.105,"body":"at the point that where the thermohaline circulation collapses."},{"startTime":2265.165,"endTime":2270.465,"body":"Um, and of course this gives you q um, dramatic film scripts."},{"startTime":2270.645,"endTime":2274.338,"body":"Um, we could digress on all the physics they got wrong in the day after"},{"startTime":2274.338,"endTime":2274.585,"body":"tomorrow."},{"startTime":2274.645,"endTime":2278.332,"body":"But the basic sort of the, the basic, um, premise of the film was that"},{"startTime":2278.332,"endTime":2280.545,"body":"this happened and, and therefore you suddenly had this."},{"startTime":2281.125,"endTime":2286.276,"body":"Now it's important that in the, in those models that I showed you, the sort"},{"startTime":2286.276,"endTime":2291.427,"body":"of standard climate models, we do see a weakening of the overturning circulation, but it's"},{"startTime":2291.427,"endTime":2293.145,"body":"not in none of them."},{"startTime":2293.145,"endTime":2296.185,"body":"Does it look like this over a cliff scenario?"},{"startTime":2296.325,"endTime":2299.465,"body":"The, the, the overturning circulations getting weaker?"},{"startTime":2299.965,"endTime":2304.305,"body":"Uh, it does have some climate impact, but it's not showing this tipping point behavior."},{"startTime":2305.965,"endTime":2307.025,"body":"But that's those models."},{"startTime":2307.525,"endTime":2313.746,"body":"And, you know, there are cases if you, with the right experimental setup, um, if"},{"startTime":2313.746,"endTime":2319.968,"body":"you deliberately dump lots of fresh water into the North Atlantic, you can eventually drive"},{"startTime":2319.968,"endTime":2326.19,"body":"one of these models to go over a cliff and transition to a completely different"},{"startTime":2326.19,"endTime":2326.605,"body":"state."},{"startTime":2326.665,"endTime":2330.991,"body":"So this is a case where you can see the Thermo Hill line circulation is"},{"startTime":2330.991,"endTime":2334.165,"body":"trundling along, um, and then they start pumping in fresh water."},{"startTime":2334.665,"endTime":2338.858,"body":"And after a few hundred model years, um, it suddenly goes over a cliff and"},{"startTime":2338.858,"endTime":2343.051,"body":"you get that, um, uh, and you get that sudden transition behavior and what's happening"},{"startTime":2343.051,"endTime":2347.245,"body":"in this model, this is a very complicated model of the whole earth, uh, system."},{"startTime":2347.505,"endTime":2352.839,"body":"But the essential physics of it are pretty much the physics I explained to you,"},{"startTime":2352.839,"endTime":2355.685,"body":"um, from the, the, the, the Stommel model."},{"startTime":2355.685,"endTime":2357.885,"body":"That's essentially what's going on there now."},{"startTime":2357.885,"endTime":2361.125,"body":"And there is some evidence that this has happened in the past."},{"startTime":2361.905,"endTime":2368.355,"body":"So, um, sorry, time, uh, the paleo climate community, the ice core community loved to"},{"startTime":2368.355,"endTime":2369.645,"body":"plot time backwards."},{"startTime":2370.505,"endTime":2375.355,"body":"Um, so, uh, so, so older is over here, and younger is over here, so"},{"startTime":2375.355,"endTime":2376.325,"body":"sorry about that."},{"startTime":2376.465,"endTime":2378.645,"body":"Um, but imagine flip this round in your head."},{"startTime":2378.905,"endTime":2383.845,"body":"So moving outta the last ice age, you can see that temperatures were warming."},{"startTime":2384.265,"endTime":2391.059,"body":"The pink line is temperature in Greenland, temperatures were warming, and then very suddenly dramatically"},{"startTime":2391.059,"endTime":2391.965,"body":"fell off."},{"startTime":2391.965,"endTime":2397.381,"body":"Well, on a couple of occasions, fell very rapidly down back down to ice age"},{"startTime":2397.381,"endTime":2402.798,"body":"conditions, and then even more suddenly recovered and popped outta the ice age again, as"},{"startTime":2402.798,"endTime":2404.965,"body":"it's called the Younger Dryers event."},{"startTime":2405.625,"endTime":2412.48,"body":"Um, and there's a pretty good theory, um, I'm sorry to say that Paleoclimatologists don't"},{"startTime":2412.48,"endTime":2414.765,"body":"seem to agree on much."},{"startTime":2414.945,"endTime":2418.5,"body":"So, uh, although I think it's a great theory, there's plenty of people who still"},{"startTime":2418.5,"endTime":2419.685,"body":"sort of grumble about it."},{"startTime":2419.985,"endTime":2424.901,"body":"Um, but it comes from, uh, Wally Broker, another of the greats of, of 20th"},{"startTime":2424.901,"endTime":2425.885,"body":"century climate science."},{"startTime":2426.585,"endTime":2432.168,"body":"And he pointed out that, um, as the Lauren Tide ice sheet, this ice sheet"},{"startTime":2432.168,"endTime":2437.752,"body":"that covered North America was retreating, um, it created just the presence of the ice,"},{"startTime":2437.752,"endTime":2443.335,"body":"created a massive lake called Lake Azis, which no longer exists, um, but it was"},{"startTime":2443.335,"endTime":2448.919,"body":"a bigger lake than all of the Great Lakes combined, um, trapped by the ice"},{"startTime":2448.919,"endTime":2451.525,"body":"sheet, as the ice sheet was retreating."},{"startTime":2451.785,"endTime":2454.125,"body":"And at some point, of course, the inevitable happened."},{"startTime":2454.665,"endTime":2458.707,"body":"The, the dam burst, the ice dam burst, and all of the water in Lake"},{"startTime":2458.707,"endTime":2460.325,"body":"Azis drained out down the St."},{"startTime":2460.405,"endTime":2462.205,"body":"Lawrence Seaway into the North Atlantic."},{"startTime":2462.585,"endTime":2469.002,"body":"And that would give you the kind of very sudden influx of fresh water that"},{"startTime":2469.002,"endTime":2474.565,"body":"you would need to potentially suddenly shut down the O Ocean overturning circulation."},{"startTime":2475.545,"endTime":2480.466,"body":"Um, so this is the theory, uh, uh, broker Atal in 1989, and it's been"},{"startTime":2480.466,"endTime":2485.388,"body":"sort of confirmed in a few other papers since, uh, of why that young address"},{"startTime":2485.388,"endTime":2486.045,"body":"event occurred."},{"startTime":2486.625,"endTime":2489.9,"body":"Um, there's lots of other papers, every time somebody published a papers saying there's evidence"},{"startTime":2489.9,"endTime":2493.175,"body":"for this, somebody else published a paper a few months later saying, yeah, but their"},{"startTime":2493.175,"endTime":2494.485,"body":"dates aren't quite right or whatever."},{"startTime":2494.485,"endTime":2495.645,"body":"Anyway, but they argue about it."},{"startTime":2495.645,"endTime":2498.765,"body":"But it's a great theory and it's, it's quite a plausible theory as well."},{"startTime":2500.025,"endTime":2501.125,"body":"So here's the question."},{"startTime":2501.795,"endTime":2502.485,"body":"What do you see?"},{"startTime":2502.705,"endTime":2507.936,"body":"That's the Atlantic Meridian overturning circulation, that's the state of the ocean conveyor at the"},{"startTime":2507.936,"endTime":2508.285,"body":"moment."},{"startTime":2508.945,"endTime":2510.005,"body":"Yes, it's gone down."},{"startTime":2511.065,"endTime":2513.845,"body":"Um, and it's gone down significantly in this period."},{"startTime":2513.855,"endTime":2516.165,"body":"We've been observing it over the past 30 years or so."},{"startTime":2517.945,"endTime":2519.205,"body":"Is it heading for a tipping point?"},{"startTime":2519.425,"endTime":2520.605,"body":"I'm afraid, I can't tell you."},{"startTime":2520.825,"endTime":2525.08,"body":"Um, but it's, it's moving in the direction that we would expect it to move"},{"startTime":2525.08,"endTime":2529.335,"body":"in response to, um, freshening of the North Atlantic and so on, all the things"},{"startTime":2529.335,"endTime":2531.605,"body":"which we, which we are believe going on."},{"startTime":2531.825,"endTime":2536.261,"body":"So that's the situation we're on that I'll just skate over a couple of other"},{"startTime":2536.261,"endTime":2537.445,"body":"examples of tipping points."},{"startTime":2537.525,"endTime":2541.536,"body":"I won't, you know, that's, that gives you a, i I wanted to go into"},{"startTime":2541.536,"endTime":2545.548,"body":"detail on one of them says to give you a gist of how it actually"},{"startTime":2545.548,"endTime":2549.56,"body":"works, um, but just sort of for, for, for, for completeness, um, there's the, uh,"},{"startTime":2549.56,"endTime":2551.165,"body":"ice sheets in Greenland and Antarctica."},{"startTime":2551.585,"endTime":2557.565,"body":"Um, these of course, um, uh, can, uh, there's, there's scope for instability in the"},{"startTime":2557.565,"endTime":2563.545,"body":"Greenland and has the ice sheets because I mean, I dunno if you know this,"},{"startTime":2563.545,"endTime":2569.525,"body":"but much of the altitude of Greenland and Antarctica is provided by the ice itself."},{"startTime":2569.865,"endTime":2572.485,"body":"And in fact, if I take away the ice, that's what they would look like."},{"startTime":2573.425,"endTime":2579.464,"body":"Um, so you can see that in particular West Antarctica and central Greenland without the"},{"startTime":2579.464,"endTime":2582.685,"body":"ice would be sea level, below sea level."},{"startTime":2583.385,"endTime":2586.72,"body":"And so one thing you could be sure about is if the ice were gone,"},{"startTime":2586.72,"endTime":2587.165,"body":"it's gone."},{"startTime":2587.315,"endTime":2592.199,"body":"It's, it's not, it, it, it can't grow back because it would take, you know,"},{"startTime":2592.199,"endTime":2594.805,"body":"another ice age to for it to reform."},{"startTime":2594.915,"endTime":2599.618,"body":"Because once you've removed the ice, you've removed, you've actually lowered the surface of the"},{"startTime":2599.618,"endTime":2604.322,"body":"earth in effect as far as the, um, ice, uh, as far as the atmosphere"},{"startTime":2604.322,"endTime":2608.085,"body":"is concerned, um, and, and made, um, surface conditions that much warmer."},{"startTime":2608.625,"endTime":2612.445,"body":"So there's obviously scope for, uh, a tipping point there."},{"startTime":2612.625,"endTime":2619.075,"body":"And, you know, we are seeing very importantly, um, significant loss of ice in both"},{"startTime":2619.075,"endTime":2620.365,"body":"Greenland and Antarctica."},{"startTime":2620.625,"endTime":2626.325,"body":"And this is from gravity measurements, um, that NASA's been performing ever since 2004."},{"startTime":2626.745,"endTime":2630.931,"body":"Um, and we can actually see the weight of the ice sheet from, from the,"},{"startTime":2630.931,"endTime":2633.165,"body":"from the gravity measurements they make with satellites."},{"startTime":2633.465,"endTime":2638.885,"body":"We can see the massive ice changing in both Greenland and in particular in the"},{"startTime":2638.885,"endTime":2644.305,"body":"West Antarctic ice sheet, which is, again, one which we're, um, tracking closely because of"},{"startTime":2644.305,"endTime":2649.725,"body":"course, these are the points where the, the, the ice sheets are potentially most unstable."},{"startTime":2650.105,"endTime":2657.692,"body":"So, um, Greenland is losing about 250 billion tons of ice per year, um, while"},{"startTime":2657.692,"endTime":2662.245,"body":"Antarctica is losing about 150 billion tons of ice."},{"startTime":2662.415,"endTime":2664.925,"body":"Those sound like extraordinarily large numbers."},{"startTime":2664.995,"endTime":2665.485,"body":"They are."},{"startTime":2666.145,"endTime":2670.241,"body":"And again, I wouldn't want to belittle the importance of what's going on here, but"},{"startTime":2670.241,"endTime":2673.245,"body":"I think it's also important to get these numbers into context."},{"startTime":2674.265,"endTime":2679.965,"body":"So 270 billion tons from Greenland, 150 billion tons per year from Antarctica."},{"startTime":2680.345,"endTime":2683.165,"body":"That's in the context of total mass."},{"startTime":2683.905,"endTime":2691.547,"body":"So, so these numbers often people don't put together, um, total mass of ice in"},{"startTime":2691.547,"endTime":2694.605,"body":"Greenland, 2.7 million billion tons, okay?"},{"startTime":2694.605,"endTime":2698.805,"body":"Total mass of ice in Antarctica, 24 million billion tons."},{"startTime":2699.785,"endTime":2705.148,"body":"So if it carries on at the current rate, Greenland will be gone in 10,000"},{"startTime":2705.148,"endTime":2710.155,"body":"years and Antarctica will be gone in, Antarctica will be gone in 160,000 years."},{"startTime":2710.175,"endTime":2714.443,"body":"Now, look, of course, we're worried not about it carrying on at the current rate,"},{"startTime":2714.443,"endTime":2716.435,"body":"but about the possibility of it accelerating."},{"startTime":2716.575,"endTime":2721.063,"body":"But at the same time, when you see the headlines about the speed of melting"},{"startTime":2721.063,"endTime":2724.355,"body":"of Greenland anica, it is important to put those into economies."},{"startTime":2724.355,"endTime":2725.355,"body":"There's a lot of ice there."},{"startTime":2726.135,"endTime":2730.92,"body":"And so we are aware of the possibility of pushing the system over a tipping"},{"startTime":2730.92,"endTime":2732.515,"body":"point, um, in the cryosphere."},{"startTime":2732.895,"endTime":2736.435,"body":"Um, and of course the big danger with pushing the system over."},{"startTime":2736.855,"endTime":2740.235,"body":"So the cryosphere is our name for the, the ice systems of the world."},{"startTime":2740.655,"endTime":2744.952,"body":"Um, and the danger of course of once you've pushed the ice systems of the"},{"startTime":2744.952,"endTime":2749.25,"body":"world over a tipping point, it it, it'll take a very long time, but you"},{"startTime":2749.25,"endTime":2753.548,"body":"wouldn't be able to get it back again because, you know, ice dynamics is so"},{"startTime":2753.548,"endTime":2753.835,"body":"slow."},{"startTime":2754.455,"endTime":2760.167,"body":"Um, so this is, you know, um, this is a, a, an area of, of"},{"startTime":2760.167,"endTime":2765.88,"body":"concern for, I mean, it would, uh, uh, collapses in ice sheets are at the"},{"startTime":2765.88,"endTime":2771.593,"body":"moment in current models not predicted to have a big impact on sea level rise"},{"startTime":2771.593,"endTime":2772.355,"body":"this century."},{"startTime":2772.535,"endTime":2776.897,"body":"But again, it's, we're discovering all the time that the ice, that the ice sheets"},{"startTime":2776.897,"endTime":2779.515,"body":"are more dynamic than perhaps we thought they were."},{"startTime":2780.095,"endTime":2784.595,"body":"Um, and so it's an area also that the scientific community is monitoring very closely."},{"startTime":2785.745,"endTime":2788.915,"body":"Finally, um, uh, tipping points in forests."},{"startTime":2789.455,"endTime":2795.676,"body":"One of the concerns, uh, in Amazonia, um, is that the rainfall in Amazonia is"},{"startTime":2795.676,"endTime":2798.995,"body":"sustained by the presence of the forest itself."},{"startTime":2799.535,"endTime":2804.944,"body":"And so you've got, again, just as we had with the, over the, the overturning"},{"startTime":2804.944,"endTime":2810.353,"body":"circulation where there was an interaction between the circulation itself and the forces that were"},{"startTime":2810.353,"endTime":2811.075,"body":"driving it."},{"startTime":2811.305,"endTime":2815.962,"body":"There's an interaction between the presence of the forest and the rainfall that sustains the"},{"startTime":2815.962,"endTime":2817.515,"body":"forest in the first place."},{"startTime":2817.975,"endTime":2820.275,"body":"And we are seeing drying out."},{"startTime":2820.455,"endTime":2826.167,"body":"So wherever you see red and orange in this, we're seeing, uh, reductions in soil"},{"startTime":2826.167,"endTime":2829.595,"body":"moisture over amazonia over the past, uh, few decades."},{"startTime":2830.295,"endTime":2834.715,"body":"And we're seeing in particular incidents like a drought that occurred just last year."},{"startTime":2834.735,"endTime":2839.103,"body":"So you can see it's the same image, the same location in just a few"},{"startTime":2839.103,"endTime":2839.395,"body":"months."},{"startTime":2839.535,"endTime":2844.666,"body":"You went from that to that, um, when rainfall was essentially ended in la a"},{"startTime":2844.666,"endTime":2846.035,"body":"large chunk of Amazonia."},{"startTime":2846.695,"endTime":2853.005,"body":"So people are worried about the possibility of pushing Amazonia over a, a tipping point."},{"startTime":2853.465,"endTime":2859.334,"body":"Um, but this is the one, this is one of the ones where, uh, when"},{"startTime":2859.334,"endTime":2865.204,"body":"it was initially proposed back in two thousands, it actually had a very unfortunate consequence"},{"startTime":2865.204,"endTime":2871.073,"body":"of many people in Brazil saying, well, if it's all doomed anyway, bring on the"},{"startTime":2871.073,"endTime":2871.465,"body":"chainsaws."},{"startTime":2873.265,"endTime":2875.865,"body":"'cause we may as well make some money outta this while it's still there."},{"startTime":2876.135,"endTime":2876.425,"body":"Okay?"},{"startTime":2876.525,"endTime":2881.07,"body":"So it's very important to emphasize that most of what's happening in Amazonia is nothing"},{"startTime":2881.07,"endTime":2882.585,"body":"to do with climate change."},{"startTime":2882.725,"endTime":2889.097,"body":"Yes, climate change is contributing something to what's going on, but you know, it abso"},{"startTime":2889.097,"endTime":2893.345,"body":"amazonia is, please take note, Amazonia is not already doomed."},{"startTime":2893.885,"endTime":2898.435,"body":"Um, and there's, there's therefore no logic to saying, oh, well, we may as well"},{"startTime":2898.435,"endTime":2902.985,"body":"exploit it while it's there because, um, because it's gonna be gone by mid-century anyway."},{"startTime":2903.285,"endTime":2908.666,"body":"And that's an example of where, you know, talking about tipping points is, can get"},{"startTime":2908.666,"endTime":2909.025,"body":"dangerous."},{"startTime":2909.445,"endTime":2914.003,"body":"Um, and just to sum up, I mean, the things that I'm, I-I-I-I-I, I worry"},{"startTime":2914.003,"endTime":2918.562,"body":"about, you know, the reason I put off talking about tipping points for so long"},{"startTime":2918.562,"endTime":2921.905,"body":"in this lecture course is I feel it can encourage fatalism."},{"startTime":2922.205,"endTime":2926.455,"body":"You know, you can think, oh, well, you know, we're, we're doomed anyway, so, um,"},{"startTime":2926.455,"endTime":2927.305,"body":"what's the point?"},{"startTime":2927.845,"endTime":2931.785,"body":"Um, and you know, we do need, it's not to say tipping what's not important."},{"startTime":2931.785,"endTime":2933.305,"body":"We do need to understand what's happening."},{"startTime":2933.485,"endTime":2936.915,"body":"And of course, the further you stress the system, the more likely it is you're"},{"startTime":2936.915,"endTime":2938.745,"body":"going to encounter one of these tipping points."},{"startTime":2939.245,"endTime":2943.905,"body":"Um, but it's certainly not too late to stop climate change."},{"startTime":2944.005,"endTime":2946.985,"body":"And I cannot emphasize that point more than enough."},{"startTime":2947.325,"endTime":2950.856,"body":"In the next subject, we will talk about some of the more wilder ideas out"},{"startTime":2950.856,"endTime":2952.505,"body":"there about how to stop climate change."},{"startTime":2952.965,"endTime":2955.779,"body":"Um, but when I say it's not too late to stop climate change, it's not"},{"startTime":2955.779,"endTime":2956.905,"body":"too late to stop climate change."},{"startTime":2956.925,"endTime":2960.84,"body":"And it's not too late to stop climate change in a pretty sensible, controlled way"},{"startTime":2960.84,"endTime":2962.145,"body":"without doing anything particularly stupid."},{"startTime":2962.685,"endTime":2967.841,"body":"Um, so, um, that's the, the, the, the main message of this entire, uh, lecture"},{"startTime":2967.841,"endTime":2968.185,"body":"course."},{"startTime":2968.485,"endTime":2969.625,"body":"Anyway, thank you very much."},{"startTime":2973.895,"endTime":2974.505,"body":"Wonderful."},{"startTime":2974.505,"endTime":2975.905,"body":"Thank you for the fascinating talk."},{"startTime":2975.975,"endTime":2976.705,"body":"That was great."},{"startTime":2976.925,"endTime":2981.972,"body":"Um, there's been lots of coverage in the last month or so of dramatically out"},{"startTime":2981.972,"endTime":2984.665,"body":"of the norm temperatures in the, uh, Atlantic."},{"startTime":2985.295,"endTime":2987.065,"body":"What does that mean for these models?"},{"startTime":2987.095,"endTime":2988.305,"body":"Does that tell us anything?"},{"startTime":2988.305,"endTime":2989.865,"body":"What, what did that make you think?"},{"startTime":2990.925,"endTime":2997.162,"body":"Um, they, so, so I I, I don't think anybody knows why this particular mode"},{"startTime":2997.162,"endTime":3000.905,"body":"of warm water in the Atlantic has, has occurred."},{"startTime":3000.935,"endTime":3004.385,"body":"It's a mode of variability that we weren't expecting."},{"startTime":3004.965,"endTime":3009.093,"body":"Um, and, uh, it was, uh, this is all part of the, the, so-called marine"},{"startTime":3009.093,"endTime":3010.745,"body":"heat wave that happened last year."},{"startTime":3010.765,"endTime":3013.865,"body":"So ocean temperatures were extremely warm last year."},{"startTime":3014.535,"endTime":3018.948,"body":"Undoubtedly, climate change will have contributed to that, of course, in other parts of the"},{"startTime":3018.948,"endTime":3023.362,"body":"world, El Nino will have contributed to that, but, um, I don't think we know"},{"startTime":3023.362,"endTime":3027.776,"body":"why, but as the, it's a, it's a part of, but we don't know why"},{"startTime":3027.776,"endTime":3028.365,"body":"it's happen."},{"startTime":3028.465,"endTime":3031.765,"body":"It is a part of the world where there's a lot of ocean variability."},{"startTime":3032.625,"endTime":3038.288,"body":"So, um, it's not inconceivable that this is a natural phenomenon and that that that"},{"startTime":3038.288,"endTime":3043.952,"body":"part, obviously the components of the warming that's baked in from greenhouse gas emissions, that's"},{"startTime":3043.952,"endTime":3045.085,"body":"gonna stick around."},{"startTime":3045.665,"endTime":3049.824,"body":"But I guess we, we probably have to hope that, that this will be, that,"},{"startTime":3049.824,"endTime":3053.984,"body":"that a lot of this, uh, anomalous warming in the North Atlantic is, is a,"},{"startTime":3053.984,"endTime":3058.143,"body":"is is a natural fluctuation, one of these wobbles in the overturning circulation and in"},{"startTime":3058.143,"endTime":3060.085,"body":"the Gulf Stream that happens perfectly naturally."},{"startTime":3060.545,"endTime":3066.114,"body":"Of course, one of the things people do point out is these kind of fluctuations"},{"startTime":3066.114,"endTime":3069.085,"body":"get bigger as you approach a tipping point."},{"startTime":3070.265,"endTime":3073.907,"body":"Um, and that's actually one of the things that people have pointed out is that"},{"startTime":3073.907,"endTime":3077.55,"body":"as you get closer to the tipping point, it becomes less and less stable and"},{"startTime":3077.55,"endTime":3078.765,"body":"eventually sort of tips over."},{"startTime":3079.025,"endTime":3084.968,"body":"And so if we see bigger fluctuations, is it a harbinger of reaching a tipping"},{"startTime":3084.968,"endTime":3085.365,"body":"point?"},{"startTime":3085.365,"endTime":3089.765,"body":"And that has been discussed, um, in, in, in the scientific literature."},{"startTime":3090.185,"endTime":3093.565,"body":"Um, but I, I think the jury's out on that one."},{"startTime":3093.565,"endTime":3096.028,"body":"So I'm sorry, I can't give you a very satisfactory answer to that question 'cause"},{"startTime":3096.028,"endTime":3096.685,"body":"we just don't know."},{"startTime":3098.065,"endTime":3102.227,"body":"Um, uh, I'll, I'll take one, uh, from the online, uh, uh, audience or who"},{"startTime":3102.227,"endTime":3106.39,"body":"may have submitted in the room, um, in, in your opinion, you, you showed, you"},{"startTime":3106.39,"endTime":3109.165,"body":"showed a range of potential tipping points on the slide."},{"startTime":3109.185,"endTime":3113.485,"body":"In your opinion, uh, whi which do you think will affect humans the most?"},{"startTime":3113.985,"endTime":3116.285,"body":"Or will it be a combination of a number of them?"},{"startTime":3118.165,"endTime":3122.39,"body":"I mean, to be honest, the tipping points that I think are gonna affect humans"},{"startTime":3122.39,"endTime":3124.925,"body":"the most are the ones that involve humans directly."},{"startTime":3125.865,"endTime":3130.05,"body":"Um, so, and, and we'll talk a bit about that both in the next lecture"},{"startTime":3130.05,"endTime":3131.445,"body":"and in next year's lectures."},{"startTime":3131.825,"endTime":3136.445,"body":"Um, it's when you, when you stress a society and then everybody changes their mind"},{"startTime":3136.445,"endTime":3141.065,"body":"and goes off in a different direction, that's the kind of tipping point, you know,"},{"startTime":3141.065,"endTime":3145.685,"body":"that that's the kind of tipping point that I think we're going to worry about,"},{"startTime":3145.685,"endTime":3148.765,"body":"uh, well before we have to worry about these ones."},{"startTime":3149.425,"endTime":3153.445,"body":"Um, so, so that's, yeah, that's the tipping point that keeps me awake at night."},{"startTime":3153.825,"endTime":3161.845,"body":"And there's plenty of evidence of societies crossing tipping points and moving in unpredictable directions"},{"startTime":3161.875,"endTime":3162.925,"body":"With our own feedback"},{"startTime":3162.935,"endTime":3165.325,"body":"Loops in the system with our own feedback loops in the system."},{"startTime":3165.475,"endTime":3168.765,"body":"Yeah, you can think about that, you know, that simple model I was showing you."},{"startTime":3168.765,"endTime":3173.365,"body":"You can, you can replace the terms with, you know, voters and things and you"},{"startTime":3173.365,"endTime":3176.125,"body":"can see how well things can happen quite dramatically."},{"startTime":3176.465,"endTime":3176.885,"body":"Thanks."},{"startTime":3177.465,"endTime":3182.438,"body":"You said that the ice and say Greenland, for instance, would disappear in 10,000 years"},{"startTime":3182.438,"endTime":3183.765,"body":"at the current rate."},{"startTime":3184.385,"endTime":3186.045,"body":"At the current rate, very important to stress."},{"startTime":3186.045,"endTime":3186.325,"body":"Yeah."},{"startTime":3186.325,"endTime":3190.475,"body":"So I was going to ask is presumably that would slow down at the current"},{"startTime":3190.475,"endTime":3192.965,"body":"temperature rise at the current level of global warming?"},{"startTime":3192.965,"endTime":3199.455,"body":"Would it, and, and the second related temperatures at what rate of global warming would"},{"startTime":3199.455,"endTime":3202.485,"body":"cause guarantee the ice will totally disappear?"},{"startTime":3203.265,"endTime":3205.165,"body":"Yes, that's a, that's a, that's a great question."},{"startTime":3205.345,"endTime":3209.605,"body":"Um, so we, we obviously need, we obviously have to rely on models for this."},{"startTime":3209.605,"endTime":3211.205,"body":"It's not something we can experiment with."},{"startTime":3211.745,"endTime":3217.155,"body":"Um, but um, the current consensus is that if we, if we, if we sustain"},{"startTime":3217.155,"endTime":3222.205,"body":"temperatures over two degrees, we pro eventually we will doom the Greenland ice cap."},{"startTime":3222.845,"endTime":3226.738,"body":"I mean, you could argue the green and ice kept doomed anyway because, you know,"},{"startTime":3226.738,"endTime":3230.632,"body":"on a 10,000 year timescale it was gonna go, I mean, during an interglacial, um,"},{"startTime":3230.632,"endTime":3234.525,"body":"the only thing which will save it is another ice age, if you see what"},{"startTime":3234.525,"endTime":3235.045,"body":"I mean."},{"startTime":3235.465,"endTime":3240.23,"body":"So, um, but it, but on the other hand, if we push temperatures up by"},{"startTime":3240.23,"endTime":3243.725,"body":"two degrees, that's probably enough to to to doom it eventually."},{"startTime":3244.025,"endTime":3248.765,"body":"And the reason is because if you warm surface temperatures, um, the, the, the, the"},{"startTime":3248.765,"endTime":3251.925,"body":"ice, the, the, the surface of the ice itself descends."},{"startTime":3251.925,"endTime":3255.325,"body":"And as I hope you remember from our atmospheric physics behind net zero, uh, lecture,"},{"startTime":3255.325,"endTime":3258.045,"body":"the, the lower you go in the atmosphere, the warmer it gets."},{"startTime":3258.505,"endTime":3262.628,"body":"And so there's a feedback effect there that as the, as the ice gets, um,"},{"startTime":3262.628,"endTime":3266.751,"body":"thinner, uh, the surface temperatures go up and so it, it, it melts faster and,"},{"startTime":3266.751,"endTime":3270.325,"body":"and makes it harder for snow to accumulates to, to, to restore it."},{"startTime":3270.705,"endTime":3276.535,"body":"So, um, yeah, around two degrees, if you, if you held temperatures at two degrees"},{"startTime":3276.535,"endTime":3279.645,"body":"indefinitely, um, it would probably go, um, anyway."},{"startTime":3279.645,"endTime":3283.418,"body":"And, but you know, as I say it, it may be, you know, you may"},{"startTime":3283.418,"endTime":3287.191,"body":"be talking about bringing forward the demise of the green and ice cap by 5,000"},{"startTime":3287.191,"endTime":3290.965,"body":"years or something, but you know, it's still a very long timescale for, uh, process."},{"startTime":3291.385,"endTime":3296.057,"body":"But, but that said, so what we're really worried about is not that kind of"},{"startTime":3296.057,"endTime":3300.73,"body":"rather dull dynamics of just the whole ice sheet sort of, but, but the possibility"},{"startTime":3300.73,"endTime":3303.845,"body":"of large chunks of the ice sheet just going unstable."},{"startTime":3304.305,"endTime":3309.758,"body":"So in particular, those regions, so the West Antarctic ice sheet where the bottom of"},{"startTime":3309.758,"endTime":3315.212,"body":"the ice sheet is well below sea level is if sea water penetrates there, if"},{"startTime":3315.212,"endTime":3318.485,"body":"whole, um, ice sheet itself can, can be destabilized."},{"startTime":3318.545,"endTime":3322.317,"body":"And I mean, it, it, it couldn't happen in one block, but you know, in"},{"startTime":3322.317,"endTime":3326.089,"body":"principle, a lar large chunks of the West Antarctic ice sheet could suddenly start to"},{"startTime":3326.089,"endTime":3329.862,"body":"break off and drift off into the Pacific when at which point they would melt"},{"startTime":3329.862,"endTime":3330.365,"body":"very rapidly."},{"startTime":3331.105,"endTime":3336.017,"body":"So, so that's a, a, a, a serious concern because that would of course drive"},{"startTime":3336.017,"endTime":3340.93,"body":"very rapid, um, sea level rise and, and potentially also dump a lot of fresh"},{"startTime":3340.93,"endTime":3344.205,"body":"water into the southern oceans and affect the overturning circulation."},{"startTime":3344.205,"endTime":3346.792,"body":"So there's, you know, so that's the kind of thing that we, we don't wanna"},{"startTime":3346.792,"endTime":3346.965,"body":"happen."},{"startTime":3347.025,"endTime":3351.405,"body":"And that's the kind of, um, uh, and of course the warmer we make the"},{"startTime":3351.405,"endTime":3354.325,"body":"planet, the, the more likely that sort of process becomes."},{"startTime":3354.825,"endTime":3358.685,"body":"Um, and that's why we're monitoring what's happening in Antarctica very carefully."},{"startTime":3358.705,"endTime":3362.285,"body":"And that's so probably more so than what's going on in Greenland."},{"startTime":3362.325,"endTime":3367.191,"body":"I think the, the news coming out of Antarctica in terms of, um, uh, sort"},{"startTime":3367.191,"endTime":3372.058,"body":"of discovering how, how dynamic, uh, the West Antarctic ice shelf, uh, is in particular"},{"startTime":3372.058,"endTime":3374.005,"body":"is, is, is is pretty worrying."},{"startTime":3375.265,"endTime":3375.465,"body":"Excellent."},{"startTime":3375.605,"endTime":3378.97,"body":"Um, now we've had a couple of questions, actually, we go right back to the"},{"startTime":3378.97,"endTime":3382.336,"body":"beginning of your lecture this evening when talking about the, uh, the phases of climate"},{"startTime":3382.336,"endTime":3382.785,"body":"change denial."},{"startTime":3382.785,"endTime":3383.285,"body":"Yeah, yeah."},{"startTime":3383.465,"endTime":3387.65,"body":"And people have picked up a couple of different phases of that, uh, to ask"},{"startTime":3387.65,"endTime":3389.045,"body":"you about, about the communication."},{"startTime":3389.225,"endTime":3392.445,"body":"So, uh, I, I'll, I'll, I'll chuck in both questions at the same time."},{"startTime":3392.445,"endTime":3394.205,"body":"They're slightly different angles on the same thing."},{"startTime":3394.225,"endTime":3400.28,"body":"So one, one is, um, about, uh, what do you think the, the key problems"},{"startTime":3400.28,"endTime":3405.125,"body":"are of explaining the level of catastrophic risk related to climate change?"},{"startTime":3405.745,"endTime":3410.941,"body":"And the second one is, um, how can the media reduce the kind, the late"},{"startTime":3410.941,"endTime":3414.405,"body":"nature of the climate fatalism of it's too, too late?"},{"startTime":3414.465,"endTime":3416.205,"body":"So one is right at the beginning of the chain."},{"startTime":3416.465,"endTime":3416.685,"body":"Yep."},{"startTime":3416.865,"endTime":3418.165,"body":"How do you address that?"},{"startTime":3418.425,"endTime":3419.925,"body":"And the other is at the end of the chain."},{"startTime":3420.665,"endTime":3421.445,"body":"How do you address that?"},{"startTime":3422.645,"endTime":3428.311,"body":"I think as humans, we seem to be very bad at getting our minds around"},{"startTime":3428.311,"endTime":3429.445,"body":"planetary scale risks."},{"startTime":3429.865,"endTime":3434.365,"body":"People almost seem to like it, it's slightly weird, sort of weird fascination with global,"},{"startTime":3434.365,"endTime":3437.965,"body":"why, why do we watch disaster movies like the day after tomorrow?"},{"startTime":3437.965,"endTime":3443.205,"body":"There's this sort of odd fascination with, with disasters that affect everybody."},{"startTime":3443.965,"endTime":3446.325,"body":"I mean, in a sense, I think we find it almost reassuring."},{"startTime":3446.865,"endTime":3451.365,"body":"In fact, they, they did public surveys of that film in Germany before they, people"},{"startTime":3451.365,"endTime":3455.865,"body":"saw the film and after they saw the film and they found that people actually"},{"startTime":3455.865,"endTime":3458.565,"body":"came outta the film feeling reassured about climate change."},{"startTime":3458.865,"endTime":3461.511,"body":"And, and, and there's two reasons that I guess one of them was people looked"},{"startTime":3461.511,"endTime":3463.805,"body":"at the film and thought, well, if that's what it is, that's ridiculous."},{"startTime":3463.835,"endTime":3464.725,"body":"It's obviously ridiculous."},{"startTime":3464.725,"endTime":3465.925,"body":"I mean, you know, don't worry about that."},{"startTime":3466.105,"endTime":3470.535,"body":"But the other thing is this message that somehow climate change is something that's gonna"},{"startTime":3470.535,"endTime":3474.965,"body":"affect everybody like a World War, in which case somebody else will deal with it."},{"startTime":3475.355,"endTime":3480.382,"body":"It's, it's not, you know, it's not your problem, which is why I emphasize to"},{"startTime":3480.382,"endTime":3485.409,"body":"people that the real problem with climate change is not these kind of massive global"},{"startTime":3485.409,"endTime":3487.085,"body":"changes that affect absolutely everybody."},{"startTime":3487.665,"endTime":3494.565,"body":"Um, but the fact that it exacerbates injustices between countries to the point where it"},{"startTime":3494.565,"endTime":3497.325,"body":"will generate I fear geopolitical conflict."},{"startTime":3497.425,"endTime":3500.815,"body":"And this, of course is the looking forward to the final lecture, um, of, of"},{"startTime":3500.815,"endTime":3504.206,"body":"this series where we talk, where we talk about the, you know, the justice implications"},{"startTime":3504.206,"endTime":3504.885,"body":"of all this."},{"startTime":3505.505,"endTime":3510.291,"body":"So, um, I, I think, um, I, I, you know, I, I don't the, the"},{"startTime":3510.291,"endTime":3515.078,"body":"answer to your question about how should we communicate this sort of global, these global"},{"startTime":3515.078,"endTime":3519.864,"body":"threats, um, I dunno the answer because I just think we, we've got a real"},{"startTime":3519.864,"endTime":3524.651,"body":"cognitive problem with, with even thinking about them somehow as a species, we've not really"},{"startTime":3524.651,"endTime":3526.885,"body":"evolved to be able to comprehend those."},{"startTime":3526.905,"endTime":3530.405,"body":"But I don't think you need to, to understand that we can fix climate change."},{"startTime":3530.425,"endTime":3532.685,"body":"And this is on onto the second question."},{"startTime":3533.025,"endTime":3536.866,"body":"You know, I, I do think it's very important to remind people, you know, for"},{"startTime":3536.866,"endTime":3540.707,"body":"less than, for less than what we paid for gas last year, less than the"},{"startTime":3540.707,"endTime":3543.525,"body":"profits that everybody made from in what we paid for gas."},{"startTime":3543.625,"endTime":3545.882,"body":"You could have captured all the CO2 it generated and put it back on the"},{"startTime":3545.882,"endTime":3546.485,"body":"North Sea twice over."},{"startTime":3546.705,"endTime":3549.765,"body":"So, you know, I keep emphasizing that this is a fixable problem."},{"startTime":3550.385,"endTime":3555.245,"body":"Um, and, and that's why people need to, to, to recognize that because that avoids"},{"startTime":3555.245,"endTime":3558.485,"body":"you getting sort of caught into the spiral of doom."},{"startTime":3558.585,"endTime":3562.445,"body":"Um, that a lot of discussion of tipping points tends to, to generate into,"},{"startTime":3563.585,"endTime":3565.885,"body":"Um, ladies and the, um, good news and bad news."},{"startTime":3565.885,"endTime":3569.295,"body":"The good news is clearly we do still have time to address some of the"},{"startTime":3569.295,"endTime":3570.205,"body":"challenges of climate change."},{"startTime":3570.975,"endTime":3575.765,"body":"Sadly, we don't still have time, uh, to carry on this evening's, uh, questions."},{"startTime":3575.865,"endTime":3579.81,"body":"So I'd be grateful if you could join me for one last time in, uh,"},{"startTime":3579.81,"endTime":3581.125,"body":"thanking our speaker this evening."},{"startTime":3581.425,"endTime":3585.405,"body":"The Gresham College professor of the environment, miles Allen, thank."}]}