Gresham College Lectures

When Net Zero? The Climate Braking Distance

September 28, 2023 Gresham College
Gresham College Lectures
When Net Zero? The Climate Braking Distance
Show Notes Transcript

The accumulation of carbon dioxide in the atmosphere determines what global temperature is reached. So, just like a braking distance, future warming is determined by global emissions today, the year we start emission reductions, and the year we achieve net zero. The goal of climate policy is no longer up for debate: we have to reduce global emissions to net zero. We just need to decide when and how fast.

A lecture by Myles Allen recorded on 26 September 2023 at Barnard's Inn Hall, London

The transcript and downloadable versions of the lecture are available from the Gresham College website:

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Thank you very much. Um, so apparently it's gonna be five years later than we thought it was gonna be. Um, anyway, we'll come on to that. But, uh, it, it is a very, uh, timely lecture. Um, what I was, the way I was gonna frame this course, welcome back to those, uh, who, who, who were watching last year. So we, we talked last year about what it would, you know, why net zero in the sense of what it would take to stop global warming. Um, but we didn't really talk about why we wanted to stop global warming at all. We sort of took that for granted. Um, and this year's lectures are gonna be about the, when, which of course determines just like the braking distance of a car. It determines what, how, how far you go, how fast you stop. And so we're, we're talking, we're gonna be talking, uh, in, in this lecture, uh, about, and, you know, I've rather adapted this, um, uh, um, as they say, events, my dear events have kind of overtaken this lecture. So, um, I, I, I've adapted it rather at the last minute, um, to, to talk about, um, uh, the, the, the discussions that are going on at the moment. Um, but we'll be, we'll be talking about the implications of different levels of warming. Um, and because of course there's a direct relationship between how fast we stop the warming and where we end up, which means, of course, this year's lectures, we'll be looking at the, the impacts of climate change. Um, in the intergovernmental panel on climate change, we divide everything up into science impacts, responses. Um, and the impacts part always tends to be the most depressing. And it is important. And I, I really don't want this year's lectures to turn into a catalog of doom. And it is important to remind ourselves, um, at all times, this is a problem we can solve, and it's a problem we can solve quite quickly if we wanted to. I think I reminded you in, in the, the first of last year's natures, um, that, you know, the amount of money made in 2022 by the global fossil fuel industry would've been enough to stop the products itself from causing global warming. So the fact that global warming is still happening is a choice. It's 'cause we're spending money on other things than stopping the products that cause global warming from doing so. So, um, it, it's, it's important and particularly, you know, particularly young people get very anxious about climate change. Um, and it is a big and, and important and, and anxiety inducing, um, issue, but it's just important to remind us it's also fixable. Um, and, uh, uh, that's, that's a, that's a sort of something to, to keep with us in the course of these lectures. Um, but, uh, obviously I'm gonna start. I, uh, it's the elephant in the corner at the moment. I, I can't ignore the fact that, uh, we had a, uh, uh, uh, a, it was a big news, uh, week, last week for Net Zero. Um, our Prime Minister, um, gave, gave a speech, I think a few days before he intended to give it, um, explaining how, um, we were going to, uh, uh, revise our, our net zero strategy. And, uh, it's, you know, there's been a lot of, uh, judging from the sort of immediate reaction and some quick polls, it seems certainly a lot of commentators and maybe even the majority of the public think, uh, he was right to do that. Um, and since the opposition has said very firmly that they're not going to go in the direction he was setting out, it seems like it's now gonna be shaping up to be, uh, an issue at next year's election. So it'll be the first time in Britain we've actually had climate as an election issue. Um, I'm in very much two minds about this. Um, on the one hand, I think we haven't, I'll be explaining to you, and I've emphasized last year, I don't think we've had enough discussion about how we get to net zero, net zero in the political, uh, debate. I think we've, far too many decisions have just been made by default. So in some, in a sense, we need to welcome the fact that it's entering the political discourse. Um, that what's worrying is, uh, what we'll be arguing over. And that's what I want to be talking about a bit in this, um, in this lecture, um, the sort of big headline, I mean, as, as ever with election issues or potential election issues, um, there's rather less in it than meets the eye. Um, the, the headline which everybody took away from them from about the Prime Minister's speech was putting back the commitment to phase out, uh, pure petrol and diesel cars. Um, and this is just a, a graphic from the Department of Transport Department for transports about new car sales in the uk. And of course, that ban only affected new car sales. And so you'll notice, um, several really striking things about this figure. Um, diesel sales went off a cliff in 2016 when they discovered that they weren't quite as good for the environment as everybody thought. Um, and they've, they've really dropped to a, a pretty low level now in a still heading downwards. Remember why 2030s, probably at sort of, at the edge of the, of, of the screen here, um, petrol cells dropped a lot, um, in sort of 2019 to 20. Um, and they, well, they may be leveling off a bit, but the main increase that is, or the main trend you're seeing here is the wholesale replacement of petrol with, um, other fuel types, which includes both battery electric and um, hybrid vehicles. Um, and so the green, um, the, the green line won't be affected by the, the ban. Um, which of course means that, you know, from the point of view of consumers, it's not very clear what the ban was going to do anyway, since it looks like if just current trends had continued, we probably wouldn't have been buying very many, um, of the, uh, pure petrol and pure diesel cars by 2030 anyway. Um, it's also from the point of view of the environment, it's very that not that big a deal either. And that's because that other fuel types actually contains both pure battery electric cars and plugin hybrids. And, um, for anybody goes and digs it up. Full disclosure, I drive a plugin hybrid. Um, it's for the kind of life we lead. We can drive it around on the battery pretty much all the time, but only if we plug it in religiously every time we come back to the house, which is easy for us 'cause we've got a driveway and all the rest of it. I can imagine if I was living in, in a, in a house without a driveway, I think most evenings I might just not get around to plugging it in. And so I'd end up just driving it on, on the petrol. And I've noticed when we do do a long journey, the reason we got it was because we had a kid, the other end of the country at university. So we needed something which could both do the long journeys and the short journeys around town. If we, and the, the consumption, to be honest, when we get onto, I won't tell you the brand for Fiona gonna get sued, but, um, the, the consumption, um, once we get onto the motorways is really no better than the, the old diesel we had, which of course, the old diesel had other problems, I'm sure. But, uh, but the point is therefore, if it's a wholesale shift from, um, I mean, there's quite a lot of battery electrics going into that other fuel types, but I think most people who wouldn't have been in a position to buy a, a battery electric because it didn't suit them, uh, would've been buying a, a plugin hybrid. So the impact on the environment of that, of, of, of that ban wasn't gonna be that great anyway. So, um, there we are. It's sort of probably not gonna affect, and the only people, I think there are some people are grumbling that it'll affect the secondhand market. But if you look at this figure, you realize, you know, you'd be struggling to buy a, a secondhand diesel more than, um, 15, that's less than 15 years old by 2030 anyway. And I was sort of thinking, why would you want to buy a diesel car in 2030 that's 15 years old? And I was thinking, well, the only reason you might is if you wanna stand to the council and complain that you're affected by the les. Um, but, uh, anyway, so no doubt there will be people in that category. But, um, okay, so, so I'm, I'm stressing this is, although this is what lots of people took away as a big headline, um, from the pmcs, it, it, that, that probably wasn't the main, the main impact of the speech. And there was a lot in the speech that was actually really encouraging. I mean, you know, the Prime Minister acknowledged, um, that we're seeing in the floods in Libya extreme heat that we saw in Europe this summer. Um, climate change is real and it's happening, okay, I mean, 10 years ago we might not have had that clear acknowledgement, um, from, uh, all of our politicians, um, of what's going on. Um, he was very clear, we must reduce our emissions, and he insisted that we will still meet our international commitments and hit net zero. I'm just quoting directly from his speech here and hit net zero by 2050. And so that's sort of encouraging. And he also, um, insisted that we're now gonna have a better, more honest debate about how we get there. And encouragingly it was how, not how fast or whether we're gonna bother at all. Um, so, you know, and that's something that those of you coming to last year's lectures will be aware, something I've been calling for, for some time. I think we do need a conversation about how we get to net zero, um, because big decisions are getting made and, you know, politicians and commentators and so on should be getting involved because these decisions are gonna affect us all. Um, and so he introduced a specific commitment that when parliament votes on carbon budgets in the future, um, it should be with the plan as well as just the budgets, rather than just saying, we're going to reduce emissions by x by X date. Um, we actually discuss how we're gonna do it, um, which is probably also a good thing. Um, so that was all, that's all positive, that's all encouraging and reassuring. Um, there was lots of other stuff that was kind of irrelevant in the Prime Minister's speech. Um, and one of them was, he really dwelled on the fact that, um, we've already reduced our emissions a lot. Um, and, uh, we're down almost 50% since 1990. I mean, he could have said, actually, were the, the only advanced economy that has lower emissions than it did in the 1890s, which is true. Um, but if you remember some of those who came to the final lecture last year, well, remember that movie I showed you of where who was emitting carbon when in the past 200 years? There's a reason why we have lower emissions now than we did in the 1890s. I mean, back in the 19th century, the British economy was the most advanced in the world. We were gushing out carbon dioxide at a rate, you know, comparable to, to modern standards a hundred years before anybody else was not necessarily something to be tremendously proud of. Um, but, uh, anyway, we are down, um, 50% since 1990, and then he's sort of disparaging comparisons with other countries that he felt hadn't done nearly as well. Um, and again, this trope of our share of global emissions is less than 1%. Whenever somebody says that, I wanna say, Hmm, my taxes are a very small fraction of the take of the ex checker. So can I just not bother? It won't make any difference. See what Ishak makes of that anyway, but how could it be? Right? The British consumers are now being told to sacrifice even more than others. This is, this is really disingenuous. I mean, the reason our emissions have come down are not because of sacrifices made on behalf of the British by the British consumer on behalf of the climate sacrifices were made. Um, this is a big reason our emissions came down. We had a wholesale transition from coal to gas for reasons. Well, I mean, sacrifices were made by, by miners. Um, and, uh, but I think, um, Mrs. Thatcher's enthusiasm for switching from coal to gas would've been no, nonetheless, um, had the climate issue not been there less well known actually, is that a big chunk of that 50% reduction in emissions that we've achieved, um, before, before 2010 or so. So, so the, the initial reductions that the UK managed was due to the reduction of methane emissions, mostly due to us maintaining our landfill sites better and managing our, our waste streams rather better than we used to. And the trigger for that, again, was nothing to do with the climate. Um, older members of, of the audience may remember this appalling incident in, in 1986 when a bungalow, this, this was this, a bungalow blew up because of methane leaking out of a, um, amazingly no one was killed. Uh, three people were badly injured. Um, but this, this bungalow suddenly exploded because of methane leaking out of a nearby landfill site because we'd been throwing all our rubbish, including all the food into the same landfill. And of course, the food was decaying underground, and methane was leaking up, and that was a big chunk of the UK's emissions. You know, once bungalows start blowing up, it didn't take much incentive to, for people to say, okay, we've gotta fix our landfills. And we did. And we've, we've done a much better job. We, we now, it's, it's now a bit gross to put food into the general waste, and I think most people have grasped that it's not a huge sacrifice. Um, and, uh, uh, we manage the waste stream so that we're not, um, you know, blowing up houses in the vicinity of landfills anymore, touch wood. So, um, you know, uh, after 2010 or so, I think you probably could make an argument that climate policy was starting to help reduce UK emissions. So we could perhaps take credit for some of that 50% reduction, but a lot of it came for free. So the sort of suggestion here that were lot so much better than everybody else we can afford to take our, our foot off the pedal, um, is, is, is, is really disingenuous. Um, where I, I found that Prime Minister's speech rather intriguing was when he got onto the other big headline, uh, sort of takeaway that people had, uh, when he started talking about heat pumps, he said very firmly, we'll never force anyone to rip out their existing boiler and replace it with a heat pump. Um, okay, heat pumps driven by electricity. So you can run a, a, a, a heat pump, or you can heat your home with a heat pump, uh, without if, if the electricity itself is renewable, you can do so without causing any greenhouse gas emissions. Um, and the policy was to sort of phase out heat pumps in the early 2030s. It wasn't. And, and the, the, um, it, it, it, to be honest, the policy wasn't entirely clear before the speech. But anyway, it's clear that it's, um, it's, he's, it's clear what he's saying now is that, um, he's not gonna require anybody to, uh, remove their existing boiler. That was never the policy in the first place, by the way. But the, the policy was going to be to require that if people are replacing a gas boiler, they'd have to replace it with, with a heat pump. But he said firmly to help those households for whom this will be hardest, um, he wants to introduce an exemption so they'll never have to switch at all away from natural gas boilers in homes, but he's still a hundred percent committed to decarbonizing our homes. So if you combine those two statements, um, I've of course found this intriguing, was the Prime Minister perhaps listening to the speech, the lecture I gave, uh, this time last year when I pointed out to you that the royalties and profits in what we pay for gas would be enough to capture every single molecule of c o two that comes out of the boilers of our homes, recapture it from the atmosphere and stick it back under the North Sea twice over gas prices have come down since then. It's now only one and a half times over, but there's still a lot of money out there that could, if it was so deployed, actually decarbonize home heating in the UK without anybody having to take out a boiler at all. Now, hold on, before anybody sort of tweets that, um, you found a scientist that, um, endorses the prime minister's approach. He didn't actually say he was going to do this. Um, and, uh, uh, it's, uh, important to stress that the cost of decarbonizing gas in this way, um, would be for the nation as a whole, outrageously expensive. Although if the individual consumer, it's four pence per kilowatt hour on natural gas. So that's, um, that's what, $250 per ton of c o two, um, air capture and disposal costs, if you want to, if you capture c o two outta the atmosphere and stick it back underground, that's roughly what it costs you to do that. Um, the reason we know this number is 'cause they're doing it in America for roughly that amount for, for, for that level of subsidies. So, so, uh, it's fairly clear that it is possible. Um, and, you know, if you trans, if you think about what that would mean, um, for a consumer, um, that'd be $500, 500 pounds a year on your bill by 2050, if we were, if we decarbonized gas in this way, um, an increase of 25 pounds a year for the next 20 years or so, um, most people faced with the prospect of that would say, I better get a heat pump. That would be a very irrational thing to do. So, um, it's probably, it would make much more sense if we were, if we were going to do this, um, for the individual consumers to buy heat pumps instead, instead of paying their gas supplier to get rid of their c o two. But this is the kind of, um, open discussion I think we should be having about the climate issue, because this is a sort of big decision. Do we, um, all go electrification or do we require the suppliers of natural gas to decarbonize their product, um, that we perhaps should have been talking about as a country at whatever point over the past few years, we decided we were gonna go the full electrification route. Who decided that? I mean, you know, the Climate change committee thought about it and decided that was probably the best way of doing things. The, um, uh, civil servants in snes, I'm, I'm sure thought it through. Um, but, you know, and as a country that, that they may well be right, but it does mean it's a sort of the kind of decision that you probably should involve consumers in because it's essentially a choice between, you know, short-term hassle replacing your boiler, you know, spending a bit of money on, on, uh, revamping the installation of your house and that sort of thing. Um, but for, for long-term saving that most consumers would probably have a view on. Um, and the, the, of course, the, there is the, the challenge of course is that if we do electrify home heating immediately, we're, we're gonna have to also put a huge amount of investment in, in the grid to just to keep pace with that new demand. Um, and of course, there is the danger, um, that if we don't all go to electrification, you could end up with a, a, a sort of rather ugly death spiral on the gas network where the only people left using gas are the ones who couldn't afford a heat pump. And then they're saddled with the fixed costs of running the gas network and you get fewer and fewer consumers, and they're generally the, they're the ones who couldn't afford to shift away and, and then their bills go spiraling upwards. And it, it's, it, it, I mean, this, this does happen. I mean, this happened with, you know, rural bus services and rural post offices and so on. You, you get fewer and generally well off, you know, the, the, the less well off people keep using the network. And if the well off ones all leave, then the margins, you know, all the profitable customers head off somewhere else. Um, and, and the, the, the, the less, the less well off ones get sort of saddled with the bill. So it probably does make sense. I'm not saying that, that the policy was, was wrong. Um, it probably does make sense to encourage everybody to shift together so you don't end up with a sort of rump consumers, um, stuck with the old system. Um, but I don't recall the ever being much of a public conversation about it. And we probably, you know, we might not be in this pickle we're in now if we'd have had the conversation about it at the time and agreed, yeah, okay. This does make more sense, um, to go the electrification route rather than, um, decarbonizing the supply. Um, and, uh, uh, and, and that's, you know, this is the, and hopefully this new interest from our politicians in, in talking about climate change and, and, and making it a political, um, issue, um, will mean that we'll have more of these conversations and we'll decide collectively how we're going to get to net zero and how the burden's going to be spread between, you know, government, consumers and crucially the, the industry that that, um, provides the products that cause the problem. Um, so, you know, that's, uh, hopefully, um, we'll have more of that kind of conversation and we'll be talking next year when we get onto how Net Zero, which is the, the topic of next year's lectures. We'll be talking about these big decisions that are being made, not just here, but of course around the world as well. And you know, the, how, how different countries are approaching net zero, um, and how countries between them are, are dealing with how to share out the bill. Um, what worries me is, despite the fact that the Prime Minister assured us that he was fully committed to net zero by 2050, and he was only interested in a conversation about how, um, if you look at the actual changes in the bill, what he was specific about, were all going, um, back, uh, you know, relaxing policies. Um, the amount of warming we get as, um, those of you who came to last year's lectures will, I hope remember the amount of warming we get depends on the total amount of carbon dioxide we dump in the atmosphere between now and the time we get to net zero. So if you delay the date at which you start reductions, you continue to drive up temperatures and you commit to more warming in the future, because we're already at the maximum rate that we could possibly reduce emissions. So any delay adds around any, sorry, five year delay adds around a 10th of a degree to peak warming. So by only telling us about things that we were going to put back by five years and not telling us what we were gonna bring forward by five years, um, we were only getting what, what what I hope is only half the story. What I, um, I fear maybe the whole story, um, in, in the government's new approach. And this is why, you know, we need politicians thinking about carbon budgets as they now do, or at least they pretend to about national budgets. If you're gonna make a spending commitment, you've gotta say where it's gonna come from. If you're gonna say you're gonna spend more on this, you've gotta spend less on that. That's the kind of give and take that we should be, that we should see in our discussion of carbon budgets. And I, and this actually is, I mean, I I, you know, I I wasn't really following politics in the seventies, but apparently in the seventies, nobody really bothered with that. You just made spending commitments and that was it. And, and then it was, you know, the realization that that didn't really work out, um, meant that, you know, politicians at least feel obliged to say where the money's gonna come from when they make a commitment. And likewise, if somebody's gonna say, we're going to allow ourselves five more years before we do this, um, which will commit more carbon dioxide to the atmosphere, then where's it gonna come from? Or what's the alternate policy that was brought forward? Um, one question I got asked a lot last week was, um, or one of, one of the points the Prime Minister made was, well, Europe's, um, uh, put back the ban on, uh, uh, petrol and diesel cars by five years. So we're just, you know, going, falling into line with the rest of Europe, which I thought was something we didn't do these days anyway, but there we are. Um, and, uh, but of course, Europe, at the same time, they brought in a commitment to introduce synthetic fuels, decarbonized fuels, where the, the, the, uh, carbon dioxide associated with that fuel had been taken care of, um, as part of that change. So, but I didn't hear about that from, from our government. So, so, you know, if you're gonna take something away, you've gotta put something else on the table. I think that's the principle we need to hold our politicians to, and that's where actually the speech got a bit worrying. Um, and frankly, a bit weird, um, uh, the proposal for the government to interfere in how many passengers you can have in your car, I've scrapped it. The proposal that you should force that, that we should force you to have seven different bins in your home. I've scrapped it. The proposal to make you change your dires and harm British farmers by taxing meat, or to create new taxes to discourage flying and going, I've scrapped those two. What's weird about this, and therefore what I found really worrying about the Prime Minister's speech, is that none of these policies exist. And I mean, lots of people pointed this out, um, but I think sort of as well as sort of laughing slightly at the fact that, you know, there's a whole, he scrapped a whole lot of policies that don't exist is like, what does this tell you about, you know, the, the prime minister's speech writers who clearly feel this is clever? Um, I mean, sadly, um, there are clearly still some, you know, bright young things in the heart of British government who feel it's cute to equate net zero policy with number of recycling bins, and they know what they're doing because that's, that's in the British psyche. Now, if you mention net zero policy to anybody around the country, one of the, you know, you, you can say, don't mention an elephants, don't, don't mention the seven recycling bins. Oh, they've already thought about seven recycling bins. You know, that's, now that's in there, that's in the discourse. So it was, you know, they know what they're doing, but why would you want to equate net zero policy with requiring people to have seven recycling, a fictitious policy to have seven recycling bins in, in their homes if you, um, didn't actually think climate change is a bit of a joke? I mean, if it's serious, you don't equate it with a joke. And that's what I found really worrying, is there are still clearly, and also from the reaction to the speech, there's a lot of people out there who still struggle to take climate change seriously. And, you know, I don't wanna get too serious, but it is actually a serious problem. So I do think we have to think about why are the still people out there probably educated in Oxford, I'm embarrassed to say, um, in British governments who are still unconvinced that this is actually a serious issue. And I'm sure the government would rapidly assure us, oh, no, no, no, we take it terribly seriously. Well, you know, the proof of the pudding, um, you know, if, if you're making, if you're making it into a joke, you don't take it seriously. So you know it, you can't have it both ways. So let's think about the reasons why people are starting this. And I think it is important for all of us to en to engage on this, to keep engaging on it and keep, um, helping everybody to understand why, you know, we do need to take this issue seriously. And so let's go back over, this is a bit of a sort of trip down memory lane for me back over the reasons over the past 30 years or so that people have found to, um, say no, climate change is a joke. It's not something we're going to worry about. Older members of the audience will remember about, uh, 15, uh, 14 years ago around the time, um, we actually published the, the net zero papers. Um, there was another big development in climate science. Uh, a whole lot of, um, emails were leaked from a server in University of East Lia. And somewhere in, uh, many millions of lines of email, um, somebody found the phrase, uh, a trick to hide the decline, which was interpreted as all those climate scientist clubbing together to actually conceal the fact that global temperatures are actually going down rather than going up. Um, this, it, it, it did have a big impact, um, not just on Coral Phil Jones, um, uh, who's personal friend of mine. Um, and it, it, it certainly ruined his life for many years. Um, but, um, it, it probably did set climate discussion of climate policy back, um, by, by, by quite a few years. Um, by the way, um, the trick in question was, and it's, it's probably far enough, long enough ago that we can kind of more safely talk about it now. Um, it was the decline in question, and the trick to hide the decline was about the mismatch over recent decades between temperatures inferred from tree rings and temperatures observed with thermometers. So the, there was a, you know, within climate science, there was a problem in that the, the tree ring record wasn't as, um, reliable as, um, some people would've liked to think it was. Um, and, uh, as a non tree ring person myself, um, I remember, I, I mean, I, I didn't grumble at the time because they were getting such a hard time from everybody else that, you know, didn't really seem inappropriate for me to pile in. But, um, uh, and there's always a tendency as well, for every sub-discipline of science to big up what it can do. I mean, nobody wants to say, oh yeah, this science I've been doing for the past 20 years, turns out it's a bit rubbish. It doesn't really tell you anything. I mean, it's not gonna do you much good for funding if you were to do that. So, so individual subdisciplines are always trying to sort of g up what their subdiscipline can offer. And there was a bit of tension between the so-called paleo climate community, um, the, the, the, the tree rings and the ice core, um, um, groups and so on, uh, about what they could say about past temperatures, uh, versus the sort of physical modeling, uh, side of, of, of science where we, we were much more focused on the, the recent record. Um, and so there was, there was sort of just enough in the story, there was just enough, you know, debate there for it to keep going for a long time. Um, and, uh, it, as I say it, it did do a lot of damage, but what was, what was, of course, what wasn't there, uh, which of course nobody understood at the time was any hint there was anything wrong with the actual evidence for human influence on global climate, which wasn't based on tree rings at all. It was based on the thermometer records. So, so the, the, the issue was with a discrepancy between a bit of information we weren't using anyway, and the information we were using. Um, so it was, it, it made no difference whatsoever, um, to, to our actual conclusions about human influence on global climate. In fact, I, I remember in the 2001, uh, I P C C report, um, I, you know, at the time, I, I was involved in the attribution chapter there, and we, we didn't really use tree ring data. Um, the tree ring records were just emerging at the time. Um, and I, they didn't really tell us anything we didn't know already. So it didn't seem to make any difference to our conclusions. So I remember feeling a little aggrieved at the time that they were getting so much airtime, but there we are. Um, but, so I'm starting to sound a bit sad now, aren't I? Um, so let's move on, um, to the other, sort of the next sort of objection people make, uh, which is that scientists can't prove human activity is actually causing the observed warming. I, I get this pretty regularly still to this day. I get somebody emails me saying about once a week, somebody emails me, hello, um, uh, if you're watching, um, and to say, can you prove it's due to human influence? Ha, you can't. So therefore, you know, and, and so I, I will talk a bit more about that in, in, in the last 10 minutes, uh, of this lecture. Um, because I think it is important for everybody to understand, you know, why it is, we do know that what's happening is because of human influence, um, the next sort of stage people might take, um, in, in arguing, we don't need to do anything about climate changes.'cause the impacts won't be nearly as bad as scientists claim. We're gonna be looking at that in the next, uh, three lectures, uh, of this series, what the implications are of different levels of warming and what the impacts are, and indeed what the impacts are of the level of warming we're already seeing. We're already at one and a quarter degrees of warming. Um, and, uh, we're starting to see plenty of impacts of that already on, on weather and ecosystems around the world. Um, there's a sort of sub subset of this claim, um, which interestingly seems to be held by the same people. Um, were totally doomed anyway, so there's not much point in doing anything about it. Um, and, uh, again, I think, you know, as I stressed at the beginning, no, this is a fixable problem. If we were to reduce emissions to net zero by mid-century, we would limit future warming, all future warming to not much more. Than's already happened this century. So if we did that, you know, no, yes, we would still have plenty of problems. Um, but, you know, that's, that's, that's not a, uh, uh, uh, extinction level event, um, by any manner of means. That's a manageable ecological challenge. Finally, there's this one, uh, bill Gates is gonna fix it all by turning down the power of the, the sun. The idea that that some techno fix will be brought in in the future, um, to solve the whole problem in this, in many ways, I think is, is the most dangerous line of all. Um, not because it's not possible, but because of the implications of anyone deciding they're gonna take charge of the world's weather for, um, geopolitical instability. I think one, if we've learned nothing else in the past couple of years, it's that we're, we're much more likely to kill ourselves directly, um, with, with bombs and things, um, than, uh, kill ourselves indirectly by changing the climate, by the time the climate changes enough to actually kill us all, we'll have already done the job for it. So I think you do therefore need to look at climate policies very much through a lens of what will this policy do to geopolitics? And that's something which I've decided to really focus on this year, is to ask, you know, of the climate policy of the, and, and we'll be talking about this more next year of the, of the various approaches to climate policy, which ones are the most destabilizing, and which ones are the least destabilizing. Because I do think it's really important that we look at climate policy through that lens, um, because as I say, you know, our, our big problems are, are the Vladimir Putin of this world. But just, um, so that you get a little bit, you know, I'm a scientist. I've, I've talked, I haven't talked any science tool in this later. I've gotta give you a little bit. Um, so I just thought I'd focus in on bullet two here, just to remind you of what it means for the scientific community to say that we are confident that human activity is the cause of the observed warming. And, and, and, because for a lot of people, you know, the, the, the, you know, I, I sort of was put on the spot to do this. I mean, I guess this was last, really a big issue when the Trump administration came in, uh, and you may, um, there was a, an exchange, um, with the then head of the Environmental Protection Agency in the us. Um, the presenter asked them, do you believe it's been proven that carbon dioxide is the primary control knob for climate? If ever there was a sort of low ball question for somebody in his position, that was it.'cause even I would say, well, you know, I'd have to be quite careful about answering that question. Yes, because proven primary control knob, there's plenty of, but no, he, he actually went out of his way to say, no, I would not agree. It's a primary contributor to the global warming. We see. And and many people respond to this, and I think this is the wrong response by saying, well, don't be silly. 97% of scientists think it is. So shut up that, that is often the response to that kind. And I think as a scientist, I don't like that response because science doesn't work by voting. Um, it draws attention to the 3% instantly. So, oh, that's intriguing. What are the 3%? Um, uh, what do they, what do they know that the rest of the scientists don't know? In fact, I got, I got caught out in precisely this way. Um, when the I P C fifth assessment report came out, I was on, um, I was the BBC's sort of talking head in the studio, and the presenter who knew perfectly well what it actually meant. Um, when the sort of light went on, and I knew I was on National Italians, I couldn't afford to sort of say anything too stupid. Um, he turned and sort of twinkle in his eye, said, so scientists are 95% confident that most of the warmings due to human influence. Now what do the other 5% of scientists think? Okay, so, well, it was an opportunity to explain statistical significance, um, on, on national television. So I, I did my best. Um, so, but I'm gonna do my best with you now. Um, so it's, it's not about a vote. It's not about the fraction of scientists that think that think something. Um, it's about the way we assess the evidence and reject the null hypothesis of no human influence or small human influence on global warming. And lots of science works this way. So I'm gonna take you through, forgive me, a brief foray into null hypothesis testing. Um, please don't leave. Um, this is really important. Um, okay, we, we start with the data and we've got past the high, the decline argument. Everybody sees the warming. Yeah, the world is warming. The argument is about why, um, and everybody understands and accepts how different drivers are affecting the global energy balance. Um, the orange line here, human activity driving temperatures up the spikes, for example, being volcanoes temporarily driving temperatures down. This is the, these are the disturbances to the global energy budget that we went through in some detail last year about how they work and how these different factors affect the flow of energy into and out of our planet from our, in, from the sun and out back into space. And we also know the climate system conserves energy. There's nobody's arguing with that. So therefore, if we take these disturbances to the global energy budget, we can, we can, we can, we can predict how we would expect the climate system to respond to them. And you'll notice that, you know, between the, the per the perturbations to the global energy budget and the expected temperature responses, the big change is the fact that we've smoothed out the volcanoes a bit. Yeah. Because that's, if you've got a system that conserves energy, you can't instantaneously drop the temperature and ra raise it again. It takes a little time for the heating to have an impact. Okay? So these are sort of all things that are accepted, but what we don't know is how large the responses to these different drivers are. So when we're assessing the evidence for human influence on global climate, the first thing we do is to assume lots of, you know, assume complete lack of knowledge. This isn't some, this is the way hypothesis testing works. We assume, we have no idea how much these natural drivers might have actually inflated or deflated global temperatures. So sort of, you know, between that one and that one, we sort of inflated the long-term solar variability signal here by a factor of 10. And you can see that if you do that, just I'll go to single line. So you can see if we assume no human influence and just allow the natural drivers to, um, fit the data as best they can, you can see that up to about 1990 or so, it's not a bad fit. In fact, if you sort of, if you squint a bit and you lose, um, after, you know, lose the dip just before that dip at the beginning of the nineties, you could say that's sort of more or less capturing, um, the overall record. And there was, in fact, there was a paper published, um, in 1990 by, uh, frisk Christensen and Lassen, which, um, hypothesized that most of the warming up until then was driven by variations in the, um, cosmic reflux resulting from this low frequency variability in the sun. And it, and, you know, it was quite impressive the fit they got. Um, they were lucky because of course, if they published it even a year or two later, it probably wouldn't have looked nearly as good. Um, and of course what's happened since then is, is the solar solar output has gone down. So the sort of, everything's rather gone into reverse, um, whereas the warming temperatures have have carried on up. But what we do, and also if we, you know, that's the, that's the sort of best fit to the observed warming we can get, even with all the data to present, um, allowing for any amount of amplification of these natural drivers. And if we take the data we've got here, and then we just plot the residual, this is what goes on when scientists are assessing this kind of evidence. You look at the residual and you ask, does that residual look suspiciously? Like the thing you've left out? And it obviously rather obviously does, you don't need a statistical test to tell you that you know, what's left over there looks rather like that orange line you remember before, which was the expected response to human influence on climate. So what we do is we introduce a new unit, um, at the time I introduced the Pruitt, which means one 10th of a degree of human induced warming, c o two induced warming, and we increase the number of pruitts. Okay? So cranking them up here until, so we've gone a little bit too far there. So you see now it's sort of going down a bit. So, so you can sort of adjust it around. And we find the best explanation, best in the sense of there's no leftover residual suspiciously correlated with the thing we've left out is with about 80% of the observed warming being due to carbon dioxide emissions. Um, and, uh, the remaining 20% overwhelming, but due to, due to, um, other greenhouse gas emissions, methane and nitrous oxide. So that's the, um, the best fit we get with about an eighth of a degree of c o two induced warming in 2017. Um, and it's up to about one degree now. So now we are the, um, um, it's up to about 0.9 degrees now, just to get that right. Um, so the best explanation of the observed record is that carbon dioxide emissions have contributed 80% of the observed warming since 1870. And any attempt to explain what we're seeing by natural factors alone allowing for any amount of unknown amplification mechanism for these natural drivers leaves that residual that just looks just like the thing you've left out. And if that's what you find, then you've, you are, you are driven by the data, by the evidence to conclude that what you've left out actually is playing a role in, um, in, in, uh, driving the warming. And this is, I, I just thought you might be interested to see how the intergovernmental panel and climate change has the, how the statements on this con with of confidence that we, um, that we are seeing human influence and global climate change has evolved over time. Back in 1995, it was the balance of evidence suggests a discernible human influence on global climate. Nothing more. 2001. Um, uh, this was my, I cut my teeth on this one. Um, this is my first involvement. Most of the observed warning over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations that made page three of the Guardian, um, 2007, most of the observing is very likely, so they increased the confidence level and they got the Nobel Prize. Um, oh yeah, I'm only a little bit bitter. Um, and, uh, and both 2013, to be fair, I was involved in 2007 as well. Um, and it's extremely likely, this is all sort of tightening up the confidence with which we can be, uh, sure that, um, what we're seeing is, uh, in, and also, um, introducing a, a new element in 2013 is to point out how the size of the observed warming the fact that the, our best estimate of the human induced warming was the same as the total warming we were observing. Finally, in 2018, in the special reports on 1.5 degrees, we actually started using some numbers, which I think we probably might have perhaps should have done many, many years earlier. Um, because, you know, you've got a, the, the, the really interesting piece of information for people is how much of the warming, what's the number, how much of the warming is due to human influence? What's the range of uncertainty on that? And there we are in, in the latest, it's unequivocal that human influence has warmed the atmosphere, ocean and land. That's the, and the latest, uh, I P C C report in 2021. And to bring this all bang up to date, uh, paper published by Piers Forster, uh, and, and many co-authors, including myself earlier this year, to, to bring all these indicators up to date. And if you want to find out where we're at, there's a, a nice website, climate change, uh, which will tell you that, you know, when we get to 2022, we, we've already passed one and a quarter degrees of warming and warming at almost a quarter of a degree per decade. So you don't need to be a, uh, uh, you don't really need to be a climate scientist to realize we haven't got long to turn things around if we actually want to limit warming to way close to the goals of the Paris Agreement. And I think the impacts of climate change that we're seeing around the world already is plenty of motivation enough, even if the Paris Agreement itself wasn't enough, um, to justify doing that. So when net zero every five years delay, um, adds another 10th of a degree, more than a 10th of a degree, two peak warming, because we're already at the point where we, you know, we won't be able to reduce emissions by delaying now. We're not gonna be able to reduce emissions faster in the future. Um, so, so, um, ev ev every, every five years delay is just pushing up the warming we're committed to. We still have to work at explaining that the evidence that climate change is a serious problem, apparently. So, because I'm afraid there are people, maybe not our prime minister, but certainly as speech writers who still think it's worth a bit of a joke about recycling bins. So, um, I hope you've, uh, uh, you can take that with you, um, and, um, go convince these people, um, that this is something worth getting our minds around and worth taking seriously. Thank you. Thank you, Mars. I'm, I'm sure you can predict that many of the questions are intensely political, so I'm just gonna separate some of those out and ask you some more factual ones if I can do it. First of all, is it correct that we don't include shipping, aviation, or imported products into our carbon budget? And so in which case, have we really reduced our emissions by 50%? Uh, when you include shipping, aviation, uh, the, the 50% claim does include, I hope I get that right, but apologies if I don't. I believe the 50% claim does include sort of 50% of the shipping and aviation emissions associated with travel to and from the uk. Um, uh, but, uh, it's true that, and, and, um, uh, as of the past few years, uh, the UK I believe is following Europe in including international aviation emissions, uh, in, in our, uh, commitments. Um, so our, our net 0 20 50 commitment, for example, does include, uh, shipping and aviation, which is important.'cause obviously shipping and aviation is, is a, is a big deal. Um, but, um, it's also there, there, there are two sectors where we probably have the least idea how we're going to get rid of those missions. So, um, it's important that they are included. So, so the answer, short answer, yes, it, yes, they are included. Um, but the, your question is quite right. They're not included very consistently, uh, and across the world, um, there's plenty of, still plenty of, um, scope for wriggling around when it comes to shipping and in aviation and do All countries, or is there significant variation in which the way these things are measured from countries and the way in which therefore pressure is put on politicians? Uh, yes. Yes, emphatically so, um, and, uh, uh, and, and although shipping and aviation is probably the least of our problems, well, it, it's one of our problems. But, but, um, and the, the really big problem in that, how, how different countries, uh, quantify their emissions, um, is the one which, um, hope some of you remember from the carbon cycle lecture from last year, which is how a country counts. Um, its trees growing faster through no action of its own. Um, and, um, I, I heard today, I mean, there's increasing excitement about this sort of trees growing faster approach and, uh, news this week, um, a company in, uh, a Dubai based company has just bought 10% of Liberia for the carbon absorbing capacity of its forest. And if that doesn't worry you, um, it should, um, because, you know, this is the kind of, um, uh, transaction that only makes sense because there's an enormous scope for muddle in that part of our carbon account, Which leads onto another anti-political question, which is, goes back to speech, said, we are only a little country. What we do doesn't matter. So I don't pay very many. I'm not a very wealthy man. So whether I pay taxes doesn't matter. I mean, So the, the question is, why Chuck money at our little country? Why don't we really put more money into other countries where the problem is greater? Uh, if, If the money we're spending was assuredly, um, getting the world on a path to net zero, then I think there's, there's actually a, a, a, a, a strong case for, for both. But I don't think you can do it as an either or, because you can't have every country saying, oh, well, we'll pay somebody else to reduce their emissions after a while. You know, we're gonna run outta people to chase. Um, so, so I, and, and I think the, the other argument, of course, for us moving early, I mean, there's a very strong argument. We were the, we led the world into this. We ought to be leading the world out. Um, and, um, the obvious, um, commercial benefits to actually getting ahead on the transition. I mean, I thought it was very, one of the most interesting things about the Prime Minister speech was just how cross the society for motor manufacturers was, was, um, you know, so, so there's this clear, you know, um, paying other countries to transition and then deciding to be last ourselves. It seemed to be quite, it might be good environmental policy, but it seems quite stupid economic policy. Um, before I open it to the floor, there was, um, was anybody at Ian Mud Way's lecture the other night, um, where he was talking about basically the accumulation of waste? So we have now, he pointed out that we now have exceeded the biomass of the world on accumulated manmade products, and the companies are not being taxed on the production of the waste products. It, it overlaps with your argument about taxing the producer, if you like, causing the producer to pay the bills. Would you like to expand on that to see if there's any overlap between that? I always like to expand on the principle of producer responsibility, as people will recall from last year. Um, but you know, if you are introducing a product into the world economy that has an irrevocable impact, um, I think we should have a principle that you have to fix that impact or not introduce the product. Um, and this could be applied to plastic, it could be applied to carbon. Um, and, and I think this is something we, we should be, we should be talking about, it would make, um, uh, um, un unes destroyable, what's the word? Um, it would make, it would make, um, uh, products that don't, non, non-degradable products are substantially more expensive if the people selling them had an obligation to get rid of the material that they're made of. Um, but eventually, I think that's the only way we're gonna control our waste, our waste streams, because those companies have the agency to do it. The people who buy their products generally don't. Hello, um, Patrick Newman here. Um, what do we mean by we've reduced our emissions? I mean, we're adding to the emissions, the total emissions in the atmosphere every year, and we don't seem to have, we seem to have forgotten what the historical cumulative Emissions are. Yes. That that's a that's a very good point. Sorry, sorry, sorry. No, do do. That was basically what the point I'm trying To make. No, it's, it's a very good point. Um, the UK started emitting a hundred years before anybody else did. So our cumulative emissions, um, in 1990 were enormous. We've reduced the rate at which we emit, um, and that's what politicians love to talk about. Um, but yes, all of that period we've been adding more carbon diox into the atmosphere, continuing to drive up global temperatures, um, and, and, you know, which is why, um, as we'll be emphasizing in the lectures next year, we need to be getting ready, um, to take carbon dioxide back out of the atmosphere in the second half of this century because, um, you know, of all the countries in the world, we've probably got, um, one of the greatest responsibility responsibilities for doing that. Very good point. Um, I wanted to ask you about Bhutan. Uh, is it making a positive contribution to c o two emissions and global warming? Bhutan, Bhutan, Bhutan is one of the countries of the world, which is, uh, which is declared that it's already at net zero. Um, and, um, they, they actually have a, a relatively small fossil fuel economy and a large, uh, forest forestry sector. Um, and, um, it's, it's perfectly, perfectly plausible that they are on the way we do our accounting, uh, effectively net zero already. Um, I, I'm not too fussed about Bhutan making that claim. Um, but using the same accounting system, um, Canada could also make the same claim and that would matter. So, um, we, we don't have time to wander off on the, um, problems with greenhouse gas accounting systems at the moment, as you know, I, there's a point, which exercises me, but, but the point is, if you're still burning fossil fuels and you're not sticking c o two back underground, then you are contributing to the problem. And, um, Bhutan is in that category, I'm afraid, very small. They're not the one I would want, I would want to pick on. Um, but, um, it's just, you know, we need to establish the principle that if you're taking it out, you gotta put it back, whatever, whatever's happening to your forests at the time. Thank you. You, you mentioned fake offset, um, such as existing forests. Are we any closer to to, to proper understanding and recognition of, of, of the real, of, of true offsets? I geological net zero and putting it back in the ground. Um, In many ways true. It, it, it's a much simpler problem. We, we know what it takes to get rid of c o two permanently. You've gotta re-inject it under the North Sea and, you know, compress it and so on. And, and that, that's, we know we can do that. We know the industry can do that. It's just a whole lot more expensive than planting trees. Um, so, um, and we haven't done it at the kind scale we're gonna need to do it. So I don't think, I, I don't think it's true that we've really got our minds around what it's gonna take. Um, there's lots of, you know, hand waving about the vast potential about the North Sea as a c o two repository, but until it starts happening, um, I don't think we're going to, we, we, we, we haven't discovered how hard it's gonna be. Maybe it'll be, maybe it'll turn out to be quite easy. Who knows? Let's hope so. Is it even understood that it's needed? It, it, it is understood that it's needed in the sense that we will generate more fossil origin c o two than we can afford to dump in the atmosphere. That's a absolute certainty. Um, and therefore we're gonna have to get rid of it permanently. And right now, the only at scale method of getting rid of c o two permanently is sticking back in the ground. There are some other ideas out there. You can turn c o two back into rock or you can, um, in effectively injected into the earth's oceans by, um, making the oceans more alkaline. Um, again, these are sort of large scale, you know, modifications of our, of that. That's the sort of large scale modification of our planet planetary system. Um, generally speaking, just sticking it back underground where it came from, looks like the safest option to me. Hello? Just, uh, you've not given very many figures, uh, tonight. I understand for you're trying to avoid that, but when I was a student, um, I was, I do remember that being told that the amount of c o two in the atmosphere was about 200 parts per million. Um, what is it at the moment?'cause I was told about above 400 per million was reaching a critical point. Uh, it's about four 20, uh, at the moment. Um, and, uh, I don't think it was two, when was it 200 parts minute? It was three 50 in 1980 or so. Three or 19, 19 90 or so. So it's been going, oh, no, so, so extrapolate backwards. Um, but, um, uh, so, so that's the speed with which it's going up. Um, the impacts are driven by, uh, the temperature, the, the warming. So that's why I've been focusing on the fact that we've got to a certain, because most impacts of climate change scale with the global temperature increase, not with the level of c o two. Um, and that is at one and a course degrees attributable to human influence up from the, the 19th century. Um, and it's going up at a quarter of a degree per decade. Um, yes, I haven't showered you with figures, but those two should be enough. And one last question. Um, Hi. Um, when it comes to net zero, do you think the problem of like climate tipping points are discussed enough?'cause if you're adding 0.1 degrees and you get to a tipping point, it's not something really people are talking about on a political scale. Um, I'm So, scientists certainly worry about it a lot. I mean, lots of us, lots of us do, do little else, um, than than worry about, um, uh, non-linearities, uh, in the system's response, um, in political discourse. Um, what worries me about the discussion of tipping points is the, oh, we're gonna, we've already reached the tipping point, um, which I, I hear quite often, um, which I'm sure sends the message to people, well, that is what's the point? Um, and so I think that's quite dangerous or, or we're certain to cross the tipping point, or we will cross the tipping point if we cross 1.5 degrees. Again, there's no evidence for that. Um, the more I don't want to send the message, therefore doesn't matter, you know, every 10th of a degree does matter. It makes the impact worse, but there's no evidence that something, you know, extraordinary and global happens when you go from 1.5 to 1.55. So, um, and, and, and those kind of messages can be really harmful because we will reach 1.5 degrees. I mean, uh, you know, the rate we're going in, not too, the not too distant future. And the last thing we want is for everybody to think, oh, well, we've got a 1.5 degrees, so that's that. You know, there's nothing we can do about it. So this is a stoppable problem. Um, but of course, the further we get away from pre-industrial, the more we've destabilized, um, the natural, uh, carbon cycle, the natural systems of our planet, the harder it is to stop. Um, and, and yes, of course you can get into a situation where global warming would simply continue without any further emissions. Um, and that is a pretty frightening prospect. Um, we're at the moment, as far as we can tell, quite far away from that. Not not far away, but you know, uh, we, we, we, we, we, if we managed to limit warming to well below two degrees or around two degrees, uh, we're unlikely to get into that regime. But it is a, a, a, a disconcerting pro prospect.'cause of course, that doesn't necessarily mean, again, even then, it wouldn't mean it's too late. The planet's gonna turn into Venus, there's nothing we can do. It would just mean we'd have to spend even more money dragging c o two outta the atmosphere to pull temperatures down again. So the, the tipping point, it, it's actually more about just how is expensive, is it gonna be to fix the problem? Uh, not is it utterly unfixable. I'm gonna leave you with a, a question to an answer next time, which is, what's been the, has there been a measurable impact of the war in Ukraine on c o two production? Uh, gosh, don't have to answer that one. Okay. Yeah, I, I'm, uh, <laugh>. Um, it's certainly been a measurable impact on climate policy. Um, and, and, and, uh, so, and certainly and and level of interest in climate policy and so on. You know, it, it, it's, it, it was depressing how, you know, in, in, in, uh, Glasgow in, in at COP 26, we had all these decisions that we were gonna, um, uh, abandoned. One of the key commitments in Glasgow was we were gonna, um, phase out inefficient fossil fuel subsidies. Um, as soon as gas prices went through the roof, our own government discovered that actually a bit of fossil fuel subsidy was, was quite a good idea. Um, so, um, yeah. Um, as I say, the best, the best policies, uh, don't, don't last first encounter with reality, unfortunately, which is why we have to keep thinking about it. Well, It's, you've clearly got us thinking everybody online thinking big problems. Miles, Allen, thank you very much indeed. Thank You.