Is The Earth Warming Faster Than We Thought? | Ep276: Peter Cox

Professor Peter Cox

But more and more we're recognising that there are also tipping points in the human realm and oftentimes these are positive tipping points. In other words, that they imply some positive change, and we can see these in the adoption of renewable energy, for example. It's not going to save us from 1.5, it might not save us from 2, but we get close, but you can see an incredible growth. You've probably seen the pictures of especially photovoltaic energy, solar energy over the last few years and it's growing at an alarmingly fast rate. So there are some triggers that occur in human systems and they're generally reinforced by an economic driver like “this is the cheapest way to do it”, and I think we can see those happening. So transitions are happening. It feels like the economics are now pointing us in the right direction to the stage where it wouldn't make any economic sense to go back to the old ways.

Bryony Worthington

Hello, I'm Bryony Worthington and this is Cleaning Up. My guest this week is Professor Peter Cox, Professor of Climate Systems Dynamics at University of Exeter and Director of the Global Systems Institute. Peter's a theoretical physicist and a former lead author of the IPCC climate reports. Peter has been studying the complexity of the climate system for decades and I wanted to ask him about the current situation we're in. How sensitive is the climate? Are things speeding up, and if they are, what can be done about it? Please welcome Peter Cox to Cleaning Up. Well, thank you Peter for joining us on Cleaning Up. I'm really delighted to have this call, I'm sorry not to be with you there in person in London. But I wanted to start us off by asking our first question, which is, could you introduce yourself please, in your own words?

PC
Yeah, hi. So I'm Peter Cox, I'm a professor at the University of Exeter in the UK and my official title is Professor of Climate Systems Dynamics. So I look at the interaction of the climate system, especially the carbon cycle vegetation, particularly the land carbon cycle. So, yeah, so I've been around for a while, worked on three IPCC reports and done quite a lot of research with students and postdocs. And it's sort of on the periphery all the time of policy, which is difficult not to be actually with climate change. Pretty much everything we do is relevant, if you want to not be involved with impact, you don't do climate change research one way or the other.

BW
Yeah. And so you're currently in Exeter, but as you say, you started out your career, though, I mean, you took a mathematical approach to climate change, is that right? You're sort of on the modelling spectrum of the work on climate.

PC
Yeah, I am. I mean, I actually did my degree, undergraduate degrees in physics. And then I did a PhD in plasma physics, actually working on nuclear fusion research, which was the great hope for clean energy in the ‘70s and ‘80s. Then I moved to the Met Office in 1990, which is obviously the weather forecasting service and into the new Hadley Centre, which was the Climate Prediction Centre that's still there when it first started up. And because it was the beginning and they didn't have many trained climate modelling scientists or system models as we call them now, they were able to take me on, even though I wasn't particularly well qualified to do it to start with. You know, I was a physicist, they got me modelling vegetation. But in those days, they would invest that time in someone developing if they thought they had raw material, raw talent. And it was pretty raw with me, I think.

BW
But then you obviously kind of loved this hard math problem of the complexity of the climate system, and you were thrown this kind of question, weren't you? Because back then, the models were quite simple, I imagine, and they were working on the basis of inputting greenhouse gases to a system and trying to work out what would happen. But you were involved in kind of trying to work out, well, hang on, there are some dynamic systems in this that are going to create feedbacks. Is that your first piece of work?

PC
Yeah, I mean, yeah, indeed. I mean, the physical climate model has always been quite complex. They're essentially weather forecast models run for long periods of time, and because they run for long periods of time and they cost a lot computationally, they have to run at lower resolution. So more like in those days, 250 kilometres or 150 miles by 150 mile grid boxes. Now they're down to more like 50 or a bit less, 30 or 25 sometimes. But they were physical climate models in the sense that they, as you said, they looked at how the climate would change in response to a given increase in greenhouse gases, especially carbon dioxide. And what we know is that we've been lucky in the sense that even though we're emitting whatever it is, 11 billion tonnes of carbon a year in forms of fossil fuel, only about half of that shows up in the atmosphere and the rest is all by the land and the ocean. So we've been for a long time just assuming that that buffering would continue, but we also knew from empirical evidence that when the climate changes, those sinks are affected, and that's what I was put on doing. And because I was naive about the problem, I thought this would be easy. And 10 years later, we finally got a model where we coupled the carbon cycle and the climate system together. And we got some interesting results that some of which I doubt, but I think the basic direction of travel was right, which is essentially that if you have climate change, it will suppress the ability of carbon sinks, especially on the land, to take up carbon. And that means more of our emissions will remain in the air and climate change will be faster as a result of that for a given amount of emissions.

BW
And this is basically was it mainly terrestrial land sink, because obviously the ocean is a sink as well, but you were trying to solve for the dynamics of what happens when the planet is hotter and we're getting more droughts and precipitation is changing or big, big weather patterns are shifting. Was that what you're looking at?

PC
Yeah, it is. I mean, I think there were at least in those models of that generation, I think still true now, the ocean sink is more reliable, it's slower, but it's more reliable. The land sink is very much a consequence of two very large fluxes counteracting each other. So photosynthesis, it takes up about roughly globally about 120 billion tonnes of carbon a year, so a lot more than our emissions. And respiration for the soil decomposition, if you like, and from vegetation that returns almost an equal amount. So in equilibrium, before we started to emit CO2, these two things would be balanced on average, but they'd vary from year to year. So, for example, during El Nino, lots more carbon comes out of the tropics.

So what happens is that if you change the climate, you change some of those return fluxes in particular. So, for example, I mean we all know this, if you take food out of the fridge, it will decay faster, and when it's decaying, it's emitting CO2. So actually, one of the main feedbacks is if you warm up the soils, expect carbon to come out more quickly and for there to be a reduced amount of carbon in the soil. The other one is to do with vegetation respiration, which occurs anyway when vegetation grows and just for maintaining itself. And that tends to go out with temperature too. So the effects we saw were global, basically temperature enhancing the loss rates that the respiration fluxes that are the return fluxes to the atmosphere.

And the other thing we saw, which was regional, was that in this particular model, climate change was associated with drying and warming in Amazonia. And essentially, we predicted or projected because it was not one particular prediction, but that the Amazon forest would dieback and release a lot of carbon to the atmosphere. So that was the first time someone had used a very complex model or complex for the time and found these very abrupt feedbacks and now called tipping points like in this case, Amazon forest dieback.

BW
And this was taking into account sort of the natural effect of temperature, but was it also looking at things like forest fires? Because well again, it can be an equilibrium, right? A forest can regenerate and in that regeneration absorb CO2, but super intense fires on top of droughts can lead to complete forest death, right? And there is no more forest to come back. Was that included then?

PC
No, it wasn't. Those models didn't have any fires in them, and the latest models do. In fact, when we look at the latest models, the so-called CMIP6 models, sixth generation models, they have dieback in the Amazon primarily because of increased fire frequency like you said. If it gets warmer and drier in the models and you get more fire. But that didn't, so that strong feedback we got was just conditions becoming unfavourable for forests to continue to survive. And therefore, they actually release their carbon through respiration, believe it or not, so it was a bit like a proxy for fire, but it wasn't fire. Fire is much faster, obviously.

BW
Yeah. And fire seems to be happening, you know, places that we perhaps didn't expect. Like I can remember maybe a few years ago now when the Siberian forest started to burn, and I didn't have that on my bingo card of impacts to be worried about in my lifetime. And the models keeping track of that distribution of the fires, as well as the intensity?

PC
They're trying to, yeah. I mean, so the fire models are really tricky because they are, just empirically, it's either on fire or it's not, so it's a very abrupt process locally. And those fires depend on things like the amount of litter you got on the ground, obviously moisture content, the atmospheric moisture content, the temperature, the ignition source, which is often human but sometimes is lightning, all those things feed into it. So I guess the latest models are probably a little bit over keen to have fire compared to the real world. But they do show a tendency for fire to go up in certain regions that are drying and getting drier and warmer, which is quite a lot of the subtropics actually in the future.

BW
And then what about the thorny question of permafrost and methane releases? Before you left, was that also being thought about? I know that's also an uncertain bit of science, right?

PC
Yeah, I mean, we've been thinking about it in modelling for a long time. Relatively, little modelling work's been done, so some work's been done, all models have some ability to freeze soil. So something like permafrost and for that soil to melt and therefore to release carbon through for heterotrophic respiration, soil respiration. But I think in terms of the process that represented, they're still quite deficient and it's basically because we're still dealing with grid boxes that are, you know, tens of kilometres at least and the process that occur in permafrost is on a really small scale. So one of the issues is how do you do that? It's the modelling problem. how do you represent subgrid scale processes in a model that will only ever be able to resolve sort of tens of kilometres?

And we might get down to it, but we're probably always going to be short of the metre levels, that metre level heterogeneity that you see in permafrost. And there were two parts of that actually, that concern, one was the melting of the permafrost and the release of carbon that was stored in the soil profile. And the other was this issue of hydrates, you know, essentially methane molecules that are locked up in ice under pressure and low temperature and whether they could be released. And I think that latter one, there's less concern than there was basically because we don't see strong evidence of them coming out already, you can't see. There's an isotopic signature, which we cannot see very clearly, so it's not as large as we might have feared but I think it's still a concern. It's gone down the list of fast feedbacks, if you know what I mean, of things that could get us in the next century.

BW
Maybe because other things have just risen up, right?

PC
Yeah, probably, probably.

BW
But the Arctic is a sort of concern, right? Because it's a hard region to model. It's got its own regional dynamics, it's warming at three to four times the rate of the global average?

PC
Yeah, if you go far enough north, indeed.

BW
Yeah, you've got a very shallow sea that's taken a lot of material from the continent, right? Flowing off Siberia into that very shallow sea, currently cold and under a lot of pressure. But there's a lot of vegetation down there that could presumably be released if temperatures reach up. That does feel like it could be an abrupt tipping point.

PC
Yeah, so I mean, so the equivalent of permafrost hydrates, but much larger quantity is marine hydrates underneath in the sediments, and the Arctic Ocean is one place where they will probably be. So there is warming, really, that would do it. And weirdly, there's a counteracting impact that you get more pressure if you melt an ice sheet, which will increase the pressure and make them more stable. So the issue comes down to which gets them first, really, whether you get more stable or less stable. I still think that's a concern because there's a lot there. You know, thousands of billions of tonnes of carbon probably locked up in hydrates. Only a fraction of that is probably susceptible to being destabilised but we, you know, we keep an eye on it is the truth, because there's a lot of unknowns in that.

BW
But I hope we keep an eye on it atmospherically through observations, but I've read that there's not that many resources going into the measurement of these observations on the ground because you're dealing with such a hostile part of the world. Most of the coastline is Russian, not a great time to be collaborating with Russia, so how have we got eyes on the problem? Have we got sufficient eyes on the problem I suppose is the question.

PC
Oh, I think there's always a question about that with all the climate problem really is whether we've got enough measurements for it. We've got remote sensing now and sometimes proxies for things like methane fluxes. But methane is harder because it's very patchy and also is shorter lived, so because it's shorter lived you can see the influence of where the methane is being released on the atmospheric concentration, whereas you can't with CO2 because CO2 is in the atmosphere for decades, centuries, so it all gets well mixed. So you can't see very well, you can see a bit, but with methane, you can see more. So I think remote sensing is going to be one way we might do it. And I think it will also show up in the isotopic signature of the methane that comes out because of the nature of the very ancient carbon that's involved.

BW
And how, not to get too political, but how reliant are we on US efforts to collect all this data? Because I think quite a lot of methane analysis gets done in a lab, right, or a number of labs, but are you worried that just at the time when we should be putting more sensors out into the field, we might be losing capacity, like we might be some of our warning lights might be disappearing?

PC
Yeah, I think also that's true of the satellite record, the CERES satellite record that is revealing so much about what the system is doing at the moment, what the climate system is doing, what the energy and balances are. That's also at risk because of the Trump administration. So we are waking up to the fact that we've got rather dependent on the US being fully engaged in this, and I'm guessing that the rest, I hope the rest of the world is thinking we need to be more resilient than that. Because if you're reliant on any one partner to do that, things can change and you can be vulnerable to that in terms of measurement. So I think that's a general issue at the moment.

BW
Yeah, I've just been in China actually and I was fortunate enough to meet with the Chinese Meteorological Agency. And we spoke about their new satellite capabilities, I think it's called FY-3 and that is comparable to CERES. I don't think the culture is as embedded Chinese data being used as routinely. It is being used by researchers, but I guess that's a sign that we've at least got two hegemons who have got the capability to put satellites up and do that very detailed work. So just switching gears then from this sort of modelling, which is often focused on a kind of quite a long time horizon, the models are usually sort of running to try and predict over up to 100 years in some cases. But really, what strikes me at this point in the climate debate is how we're seeing observational changes now today that were once predicted. And it would seem to be going through something of an acceleration, is that correct? Is there an acceleration at the moment in the warming?

PC
Depends how you view it. So many models have actually got projections of change that are higher than the ones we're seeing. But I think it's true that the energy imbalance of the system, which we can measure from things like CERES and the fact that the planet is getting darker, is indicative of either additional forcing factors and we could talk about those in a minute, or stronger feedbacks than we thought. So I don't think the models are underestimating the warming in general. I think they have sort of overestimated it, but we may be seeing something else emerge in the system at the moment which is only partially captured by the models. So the models may be warming at the right rate, but they I suspect for the wrong reason.

BW
OK, let's unpack some of that. First of all though, so scientists use forcing and feedback. And for lay people, what that really means is forcing is human contribution to the problem, am I right, this is the net effect of our greenhouse gases into the atmosphere. And then the feedbacks are natural processes that then are kicked off or dynamic.

PC
Yeah, so those can be amplifying, which we weirdly call positive feedbacks, even though they have negative consequences.

BW
They're very negative, exactly.

PC
And negative feedbacks, which often suppress the warming. And most of the things we worry about are positive feedbacks for obvious reasons, they're the things that drive us to higher climate change and higher global warming. So yeah, that's basically it. And so there's this notion of you prodding the system with a forcing and it responding with a feedback, and the overall impact being the sum of these two things, basically. That's what leads to global warming.

BW
And then you mentioned the Earth energy imbalance, which I have become mildly obsessed by, because that is the measure of how much heat is accumulating in the system. So it's the net of how much sunlight reaches us and then how much of that sunlight is trapped and how much it's blocked from being able to, I recently learned about the Planck effect, which is that the world would try and share excess heat through the Planck wave effect but if those long waves are trapped, that's another way in which heat accumulates. So all of that gets captured in a metric, the Earth energy imbalance. And the bad news, I guess, for now is that is quite high, the imbalance is increasing.

PC
Yeah, it is indeed, it is. So yeah, you're absolutely right. So what happens is in terms of the planetary energy balance, the sun is shining down on the Earth. Some of that sunlight is reflected back by clouds, especially clouds, which are really important, but also by bright surfaces like ice and snow. And then it warms up the planet like anybody warms up when it's got energy on it, and then it increases the amount of infrared radiation that goes out to space and that creates a balance. When you put in greenhouse gases, you make a blanket thicker and less of that cooling radiation, infrared radiation can get out. So the planet has to warm up to rebalance and that's basically the greenhouse effect. So, yeah, we've basically got this thing going on where the system is forced by things we do like CO2 increase and methane increase, which produces a sort of initial energy imbalance.

The planet then tries to modify its temperature to come back to equilibrium. And generally, if the forcing is positive, the planet will get warmer. And the thing that relates how much the planet compensates for the increased forcing is essentially we call it the feedback factor. And that is larger when your climate sensitivity is lower. So the climate sensitivity is how much the planet will warm if you double carbon dioxide and wait. Yeah, so the climate modelling problem is really how large is the feedback factor? So the human problem is how do we change our forcing? And the climate problem is what does the system do with the given forcing? And that's still quite uncertain, actually, so within the factor of at least two, maybe three.

BW
So let's pause. So climate sensitivity is currently being looked at in more detail because we're actually now in the era of consequences right, we're actually watching this experiment now in real time. It's not something we need to project forward to 2050, we're on a decadal average temperature increase. We're very close to that 1.5 degree that we were warned about. But now the question is why has it sped up quite so significantly and how sensitive is the climate? But am I right that we're going to be able to look into that now in more detail than perhaps we thought we might?

PC
Yeah, I mean, it's a really interesting thing. In fact, in my research group, we call this the paradox of the darkening planet. So if you look at models in general climate models and you compare them to the rate of global warming, the models with a high climate sensitivity, in other words, that have a lot of warming for a given amount of CO2 tend to overestimate the warming certainly since about 1980 onwards. But if you look at the darkening record, for the CERES record of the planet getting darker, the opposite is true, so that the high sensitivity models look more like a CERES record and the low sensitivity models look more like the global warming record. And it's like, well, this can't both be true, right. So there is a bit of a paradox here that we're trying to resolve. And that's I think that's a fundamental thing for climate science at the moment is to grasp that mettle, because the CERES record is trying to tell us something that we probably just need to listen.

BW
And let's just talk about that darkening a bit more, because I for one I'm sort of slightly embarrassed, I’ve been in climate for so long and it was really only a year ago or two years ago that a scientist said to me, well of course, the planet's a lot darker and that's also not helping. And I was like, really, no one's had that handed to me on a briefing paper. And the darkening was a result, some of it is feedback as we discussed, losing ice sheets. But part of it is we've stripped out all of the sulphurous gases that were so co-emitted with the CO2 when we burn coal or when we burn heavy fuel oil and the particulate matter, which were acting as a kind of sunshade. And so we were pumping greenhouse gases out, but we're also pumping out reflective materials, right. And in the last two to three decades, we've sort of stopped doing that more or less. I mean, we've basically tried to clean the air, stop all that acid rain causing sulphur and all the air quality problems of the particulates. And that's unmasked warming, right?

PC
Yes. And indeed, so sulphur dioxide does two things, which burning sulphurous coal for example, or other sulphurous fossil fuels produces sulphur dioxide and they produce sulphur aerosols in the atmosphere. And they can provide nuclei around which clouds droplets can form. And if you have a cloud that's got more droplets, then it will be brighter. And if it's brighter, it will make the planet brighter from space and less radiation will reach the surface. So they provide a kind of accidental protection of climate change for some of the climate change.

And of course, we started to clean them up in the late ‘70s, I guess, so that the peak in global SO2 emissions, sulphur dioxide emissions was ‘79 and it's been coming down since. And then there was another change when in 2019 there was a decision to also take sulphur out of shipping fuel. And there's still a question of whether that's had an impact, for example, on how warm the shipping lanes are in the North Atlantic and North Pacific. We're not sure, circumstantially it looks significant, but when you do the numbers, it doesn't look like it should be big, so that's one of those things. So essentially, what's been going on is we until ‘79, we hit a lot of the global warming with accidental cooling from sulphur aerosol. And then we start to take it out for air quality reasons, as you said, and as a result, we started to see an increase in the rate of warming.

In fact, global warming was sort of flat between the end of the Second World War and 1979/1980, when the CO2 started to come down and now it's gone up. So we're revealing the warming from greenhouse gases, but we also got reduced cooling from sulphur aerosol. And I think that's going on at the moment too, and it'd be one reason why the planet would be getting darker, because basically previously it was unnaturally brighter by virtue of sulphur dioxide brightening clouds, for example. And now we're taking that out, and there's good reason to do it but it's worth knowing why. We occasionally get hit in the face when you do the right thing.

BW
Well, I mean, again, from my recent trip to China, I've just seen how effectively they've cleaned up their coal producing regions. So I was in Shanxi province, the home of the deep coal mining, it's where the coal came from that built the Chinese development, that rapid economic development. But the coal stations are now as clean as nuclear stations almost, you could eat your dinner off them. There's these lovely kind of Dr. Seuss coloured chimneys in the landscape, which have got these little wispy white clouds coming out of them, you know, almost nothing to be worried about here. But it's actually doubly worrying that they're using energy to strip out the sulphur. And this is not unique to China, where we know the US started this and Europe did it, too, in response to acid rain. And China's done it for air quality reasons and for basically this desire to clean up the obvious industrial problems of pollution. But what we are left now with is this kind of innocent looking, but not innocent, emission of CO2 and that loss of quite a substantial regional sunshade really, which has been removed from the system.

PC
Yeah. And I think that's one of the ironies of climate change is that I guess we always like to get political action on things that have an immediate and regional impact, like air quality and it's easier to take out SO2 from our societies than it is to take out CO2. So that has happened. But also SO2 is shorter lived in the atmosphere, it only lives days in the lower atmosphere. So basically, as soon as you stop emitting, you pretty much have the SO2 go down. That's not true with CO2. So we've been in this fortunate situation where the two pollutants were cancelling out. Unfortunate in the sense that had a bad impact on air quality, but fortunate from a global warming perspective. And now we've done the right thing and taken that SO2 pollution out.

But we are therefore getting accelerated warming as a result. And I think that's been known for a while, the issue is how big it is, you know, whether that in particular, the regional effects of SO2 coming out of shipping fuels across the oceans is having an impact. I don't think we know yet, I think that's still an open question.

BW
Yeah, there have been some papers published and I'm sure this is an active area of research, partly because those shipping lanes. I mean, the argument in favour of pollution at sea was actually much less, right. You can see why you'd want clean fuels in ports, and it's been a source of horrible pollution for local people when you have a ship come in burning this lowest bottom of the barrel oil that's hideous. So I can see why you'd want to clean it up. But actually, out at sea, it was probably not doing that much but it was making clouds. And given that the ocean is absorbing so much of the heat, not just the CO2, but also the heat is being absorbed in the ocean, the loss of clouds in the sort of northern hemisphere oceans must be having an effect, right? And is that in the models, will it kind of be added to the models?

PC
It is sort of in the models. Yeah, they have reducing cloud cover in certain regions under climate change, increasing other regions. I think what's happening, at least from the CERES record, is not so much that cloud cover is reducing, but rather the clouds there are less bright than they were. So at least in the global sense, it looks like the cloud cover isn't changing much. I think regional patterns are changing a bit. But the main thing is the clouds are not as bright as they were and that would be consistent with the so-called indirect aerosophic. The fact that these sulphate particles can make clouds have more droplets and therefore be brighter, is reducing.

But it's a really critical question because that darkening, if it's all feedback, in other words it is the Earth system responding to global warming by reducing its cloud cover, we are in a lot of trouble because the climate sensitivity would be extremely high. If it's all forcing, then we will have and I don't think it can be either of these two limits, by the way, but if it was all forcing, we will have a temporary acceleration of warming that might take us over, it would certainly take us at 1.5 (degrees), might take us over 2 (degrees). And there'll be a question about whether you temporarily offset that or not. We've got to hope, I think, most of it is forcing rather than the feedback.

BW
Yeah, meaning that we've still got agency over it. And I guess that's the critical thing, that there's only so much SO2 in particular matter we were emitting. So there's a limit to how much it can be removed, which means it's bounded, you know, it's a bounded problem. And I understand that still quite a reasonable amount of traditional pollutants still being emitted in Southeast Asia, in particular in India, which hasn't achieved the same cleanup rates that China has and Europe has. But that's bounded rate. But what's not bounded, I suppose, is what you were saying, which is this feedback, which if we're unlucky, if things fall badly, we've stripped out the cooling sinks, the sunshade, just at the time when warming is reaching a point where it takes us over some thresholds. Those thresholds release feedback mechanisms, which means we're then potentially into sort of not run away, but it could become, you know, it could keep accelerating because those natural feedbacks. But if it falls the other way, we just have this temporary increase in temperature which we can monitor and understand and then things get back to a more linear path. Is that is that roughly right?

PC
Yeah, that's basically I mean, I think it's quite difficult, if it was all feedback and the climate sensitivity is very high, I think we would have seen more global warming even than we've had to date, so it would have to be a time dependent thing, something that was changing through time. That could be happening, but it's not normally the way we view the system, it’s that there's a kind of climate sensitivity that's a property of the system and is ready to force things that are changing through time and together they create global warming and climate change. But yeah, you're right, of course, that the darkening is so significant. It's about 2.5 watts per metre squared reduction over the CERES record from 2001 to now in the amount of sunlight that's reflected back to space on the Earth. So from 100 to about 97.5. And that might not sound like a lot, but it's about as much as the radiative forcing we have due to greenhouse gases since the pre-industrial. So it's a big number and it therefore is significant in the system.

BW
Yeah, let's just unpack that. So the Earth energy imbalance we talked about earlier is measured in watts per metre squared. And what you're saying is that the reduction in that cooling effect so that the more sunlight reaching us is contributing to warming to roughly half of the warming we're experiencing today, did you say that?

PC
It depends on the period you look at. So I think it's probably about half over the period of the CERES record when the SO2 is dropping and when the darkening is most clear. We're not sure what happened before. What most models suggest, because the CERES only started in 2001, models suggest that the Earth's planetary albedo sort of peaked when sulphur dioxide emissions peaked globally in about 1980 and have been dropping down ever since. And so you've got this interesting thing that we've got a global warming record that goes right back to 1850 and we've got a top of the atmosphere record from CERES that starts in 2001. And it's kind of trying to work out what these two pieces of information imply about the system in its entirety. And at the moment, I think there's many possible answers and we need to look probably at the patterns of the darkening of the planet and compare them to the patterns of sulphur dioxide emission reductions to find out what the balance is between forcing and feedback basically.

BW
What do you mean by patterns? Do you mean regional distribution?

PC
Yeah, so with CERES, we're talking about the global figures at the moment, but CERES will have a reflected shortwave, an outgoing shortwave at the top of the atmosphere for every point on the globe pretty much. And so we can look at that independently and then look at how that compares to where we know sulphur dioxide was being emitted and where it isn't being emitted anymore and make a comparison and find out hopefully how much of this darkening is due to the forcing and therefore how much must be due to the feedback, which is the other part of the problem. And not quite there yet, but it feels like it's a doable problem. And the longer we got the CERES record the better, because it is revealing something about the system that we hadn't seen before.

BW
Yeah, and we can measure it. It's not a projected mathematical model, it's an observational, it's an exercise in observing.

PC
And as you said earlier, it is. And this is more and more the case with climate science. So when I started out in 1990, climate models were using models as an alternative to having observations of the future, right? We were making predictions of how much the globe would warm. Sometimes we forget that the globe has done that and therefore it gives us clues about the system that we didn't have before. And we can begin to piece together what models say the relationships are between observable things and the things you want to know, that are climate sensitive in future climate change and what the real world is saying. And there's a whole technique in that now that is quite powerful for doing that because we've got models and we've got data that's already showing trends. I mean, it is now so clear that it feels like we can rule out some possible futures one way or the other.

BW
Yeah, which is gonna be both a good and a bad thing, right? We're gonna be ruling out the, oh, we're gonna keep temperatures to below 1.5 (degrees), but we might also be able to rule out hopefully some of the more extreme, 7 degrees warming, average global warming. So we'll narrow the range of uncertainties hopefully. And what's encouraging is that we have got this new set of tools to apply. It's not just mathematical models based on whether it's now these Earth energy imbalance satellites are specifically able to measure that flux, aren't they? So we've got more intelligence and more data than we've ever had and hopefully that will speed up our analysis of the problem.

PC
Yeah, but it's the combination of the two I think is really critical, is that we've got the observations, especially the satellite observations is necessarily quite short. We've got 25 years is good, but it's not as long as a global warming record. And we've got models that predict the future for different levels of CO2 emissions, but also simulate that same period. So it's using that overlap period as a way to constrain the possible futures and that's quite exciting. And I think as time goes on with things like the energy imbalance, we'll get a better idea of how the system operates by doing that. That's a comparison between models and data really, where the models are used to tell you how to interpret the data in terms of the real world, if that makes any sort of sense. In the model, there's something like the CERES energy imbalance. And in that model, it's related to a certain future and you can sort of use that to interpret the CERES record itself. That's probably as clear as mud.

BW
Yeah, that wasn't very clear, but also as you were talking, I was just thinking, oh God, we're gonna get dragged into a conversation about climate scenarios here. And the avid listeners of this programme will know that we've had debates about the dreaded RCP8.5, I'm proposing we don't go there today, mainly because in looking into this, I've concluded that the way we do those physical models and the socioeconomic models is fundamentally broken. And it's kind of, the two things are not talking to each other correctly and it's beyond my capacity to try and fix that. But am I wrong? Should we spend a beat talking about this?

PC
I mean, I think there's different views on whether SSP5-85 should have been excluded or not.

BW
Hang on, don't use acronyms like that, because I used RCP8.5, but tell us what that is.

PC
Okay, yeah, sorry. So that's the very fossil fuel intensive scenario that we think we're not on anymore, hopefully. But those scenarios were developed as you suggest in a rather peculiar way in order to give possible ranges for models to be tested over, they weren't intended as equally likely futures. They weren't given probabilities, relative likelihoods, but they were seen as a way to span the range and the range is still alive as far as I can tell. The issue that you talk about though is a good one, which is that we still, in this chain of doing projections, we say we need a range of scenarios to test our models on and the integrated assessment models that do all the socioeconomics and policy related stuff, come up with some socioeconomics scenarios that would lead to those range of futures and come up with some storylines related to that.

And the weird thing about that is it in general ignores the fact that socioeconomics itself is going to be affected by climate change. Economic growth is gonna be affected by climate change. And so it's not done consistently in that way of doing things to the point where you could imagine, for example for these high emission scenarios, the RCP8.5, you have large economic growth but as far as we can tell, the climate change would not allow large economic growth. So there's immediately an inconsistency in there. So I think we have got an issue that we don't yet treat human socioeconomics and the climate system as in a single system. And I sometimes bang on about this to my colleagues, but I think we still have humans outside of the climate system acting like gods or devils or whatever in changing the system but not being impacted by it and that's not the way it is. We can already see that now, climate change is occurring, they're affecting people, it will affect economic growth, will affect socioeconomic factors that affect populations. And it feels like we're still a bit short of that in that chain of doing things, which is to separate human forces from frankly impacts on humanity of climate change.

BW
It's just as we spoke about at the start of the programme, there are feedbacks that had to be included into the physical models that we had to take into account the dynamism of the system and the complexity of the system in the physical models. But in the socio-economic models, they're very static. And maybe I'm misinterpreting this, but they are not taking into account the complexity that we've required of the physical models. So it feels like, yes, they were asked to come up with a scenario, but the levers they could pull to get us to that scenario were fairly blunt, right? So yes, it came in for a lot of criticism.

PC
Yeah, I mean, some of them are fairly sophisticated, but they make various assumptions about the way economics works, which I'm not in a position to criticise, but they do. I think the issue is the one that you put your finger on earlier, which is that it's not so much the weakness of the integrated assessment models or the climate models as the fact that they're two separate things. And I don't think we're gonna solve this problem properly unless we start to see ourselves as inside the earth system, not outside it. And that way of doing things sort of is as if humans just have choice about what they do, and that choice is not affected by what each choice does in terms of feedback on the human wellbeing and the social and economic so I think we're still short of that. And I think the way we do traditional climate modelling if you want to call it that, or I have called it that so let's do that, is to separate them out almost in a chain, just because we have a seven year cycle for the IPCC and we have to get one bit started before we can do the other bit. At some point, we're gonna need to develop models where humans are inside models, as it were, inside the earth system. And the moment they're not really, we are not really.

BW
Yeah, I wonder if the integration of that would reveal a much more rich picture and it would allow us to understand the agency that we have. The human agency is present not just in the causing of the greenhouse gases and the concentrations, but also in the reduction of reflectivity. And if the IAMs, the economic models are not sufficiently taking into account the degree of agency that we have over the physical system and then the physical systems agency over us or its impact on us, it's sort of predicting the number, predicting the future with some numbers which are kind of divorced from reality, that's what I worry about.

Michael Liebreich

Cleaning Up is proud to be supported by its Leadership Circle. The members are Actis, Alcazar Energy, Arup, Climate Imperative Foundation, Copenhagen Infrastructure Partners, Cygnum Capital, Davidson Kempner, EcoPragma Capital, EDP, Eurelectric, KKR, Mitsubishi Heavy Industries, National Grid, Octopus Energy, Quadrature Climate Foundation, Schneider Electric, SDCL and Wärtsilä. For more information on the Leadership Circle, please visit cleaningup.live. To keep up with all that's going on in the Cleaning Up universe, make sure you subscribe to our newsletter. Written and edited by my longtime New Energy Finance and Bloomberg NEF colleague, Angus McCrone, it comes out every second Monday. Angus provides the latest on the episodes we're recording, the events we're hosting, stories we're watching and what Bryony Worthington and I are up to. To sign up for the Cleaning Up newsletter, visit cleaningup.live.

BW
We are just switching from diagnosing the problem, what we do about it is currently under debate, right? And some people don't want to do anything because they think it's a hoax, others are trying to get into the weeds of where do we have the maximum leverage over this problem? And to give us a bit of hope, apart from solving the analytics, which I think we are more capable now doing an effort before with the data that we have and the satellite capability and the advent of AI and super intelligence, but on the doing something about it side of things, where do you derive your hope from that we can slightly change our fate?

PC
Yeah, we work on tipping points at the University of Exeter where I am and originally we started out concerned about things like the AMOC, the Atlantic Meridional Overturning Circulation collapsing, or the Amazonian forest dying back. But more and more, we're recognising that there are also tipping points in the human realm and oftentimes these are positive tipping points, in other words, that they imply some positive change. And we can see these in adoption of renewable energy, for example. It’s not going to save us from 1.5 degrees, it might not save us from 2 degrees, but we'll get close but you can see an incredible growth. You've probably seen the pictures of especially photovoltaic energy, solar energy over the last few years and it's growing at an alarmingly fast rate. So there are some triggers that occur in human systems and they're generally reinforced by an economic driver, like this is the cheapest way to do it, and I think we can see those happening. So transitions are happening.

We had these targets, I guess, they're fairly arbitrary targets really, 1.5 and 2, because they were a kind of balance between wanting to minimise the amount of global warming we have, which would be damaging and what was feasible and they’re round numbers so that people have nice targets. So maybe we shouldn't get too worried about the 1.5 and 2. But what I would say is that the transition needs to occur even faster, but it is happening anyway, to the point where it feels like the economics are now pointing us in the right direction to the stage where it wouldn't make any economic sense to go back to the old ways frankly, even though there might be some attempts particularly to prop up the old way of doing things. I think the transition's underway and we're on a slope to reduce decarbonising the economy, the global economy. So that is a bit of good news.

BW
Yeah, that is good news. I think it's more apparent in the Eastern Hemisphere than the Western Hemisphere, meaning where I am currently in America, where there is a very dogged narrative around fossil fuels being the future. It's counter-cultural to most of the rest of the world, but the Americas are very powerful.

PC
But isn't there also strong evidence that despite that rhetoric, the adoption of solar energy is going on at a pace in places like Texas, where there's an extraordinary amount of PV?

BW
Yeah, there's definitely where it makes money. There's still money going in and batteries has been the big unlock, actually. But the problem is that the US hasn't invested in the supply chain. So there's this pushback against dependency on imports and it coming from China. And it's still happening because making money is the biggest driver of everything here, but you've also got the US being the largest exporter of fossil fuels in the world now, and with huge reserves that it can still draw on, geographically quite blessed in terms of its ability to use fossil fuels. And the data is showing a return to CO2 from coal last year because of relaxation and because of gas prices rising, because America is now exporting so much gas to the rest of the world. So it isn't looking great. We may have Tesla and Rivian, but most people are driving big, nice petrol trucks around and there's no sign of that slowing, unfortunately, yet.

PC
Maybe we'll see this period where there's a sort of duplicity to it in the sense that you promote the use of fossil fuels because you've got external markets for them, but you actually adopt renewables because it makes sense economically as well as from an environmental perspective. I think that's probably going on in quite a number of places and probably going to go on in the UK soon as well, alas.

BW
I think the UK's transition is doing much better than many, many other countries but I think this is also holding onto your nuclear. The US has a huge slug of nuclear plants that are on the bars today and it'll be a disaster if they close and aren't replaced, because as much as solar is expanding and wind is expanding, it's only really cutting into fossil because you've kept your low carbon hydro and nukes. And if the nuclear starts to decline as those stations age, that's when it gets really hard to bend the curve. But nuclear is getting increasing interest mainly because there's an insatiable demand for energy right now in the US to power all these AI machines and data centres.

PC
Yeah, sure that's the next big challenge, isn't it? Yeah, the energy requirement of that, which we're all getting hooked on so quickly. We spoke about it before about the impact on education but the impact on everything really of AI and the environment is gonna be a footnote unless we're careful in that but it needs to be much more upfront I think, as an issue.

BW
Yeah, definitely. And well, I think AI is almost more pressing to sort out and in the sorting out of it, we might have to rediscover some version of multilateralism. It's such a likely and present threat, and I'm not a doomer that we're all gonna be dead in 10 years, but it is so capable and in the wrong hands can damage so much, either wittingly or unwittingly. And there's gonna have to be some sort of global governance in my view. That'd be hard, it'll take a decade but in the doing of it, we might have to rediscover that we're all on this shared little planet hurtling through space and we do need some sort of way of talking to each other that isn't just nationalism and everyone, winner takes all kind of mentality. And historically, it's been the US that has played that role. So, give it a few years and we might get back to that I hope, that's where I derive my hope from.

But before we leave this topic though and I'll let you go off to the Royal Society for your meeting, I wanted to just talk about another aspect of technological intervention, which is coming back to that reflectivity point, because you and I have spoken about this, it is actually possible, we do have agency over reflectivity. We've had the agency, we've just had a sort of termination shock, if you like, of stopping doing something, and there is now a growing amount of interest and research money going, and it's still tiny, but going into, are there ways in which we could make the clouds brighter, we could put back reflectivity in a less harmful way or a more efficient way? What are your views on this debate?

PC
Yeah, I mean, so this form of geoengineering, which is called solar radiation management, which basically means reflecting more sunlight, is a potentially very powerful way to call the system down. It is essentially doing what we were doing accidentally with the SO2 emissions that came from sulphurous coal burning, but probably by putting it in the stratosphere. And this is what volcanoes do. So when, for example, Mount Pinatubo went off in the Philippines in the early nineties, it threw up sulphur dioxide into the stratosphere, produced sulphur aerosols, there weren't many clouds to affect it there, no stratospheric clouds to speak of, but there were bright particles everywhere. And it cooled down the climate system by an estimated half a degree, which wasn't far short of global warming at the time.

So there was immediately a demonstration that that sort of impact of these particulates being sent, in this case, up into stratosphere, could be quite significant offsetting global warming. There's been concerns about this, well discussion about this actually, since the early reports on climate change in the US and also a Russian scientist, famous Russian climate scientist called Budyko, proposed stratosphere aerosol injection or something like it in 1974, when climate change was beginning to emerge as an issue, so we've known about it for ages. The problem we've ever had is that it's been largely a taboo among climate scientists. And the reason for that is that there was a concern that if you give the impression that we could solve this problem without cutting emissions of CO2, especially in fossil fuels, we would just burn all the CO2 in fossil fuels and two things will happen. The oceans will acidify, and even if we offset it with more reflecting, more sunlight, when we stopped it or if anyone shot down our planes or machines that were doing this, the planet would warm by the amount that it would have done without that but very quickly, and that would be very damaging. It's called termination shock that you alluded to.

So there's a whole issue about this notion of moral hazard, the idea that if you have a safety net, you might just be really dangerous, you might behave in a really crazy way. In this case, it would be burning fossil fuels at an alarming and fast rate. So to cut to the chase, SRM is therefore kind of a no go, has been kind of a no go area for climate scientists like me. And I think it needs not to be because I think there are actors that might do it without research if we don't discuss it. But my colleagues, some of my colleagues differ with me on this, they're very concerned that it is becoming more and more attractive and more and more spoken about. I just think there is huge power in it, potential power in it, not as an alternative to cutting greenhouse gas emissions, but as a sort of emergency measure if things get really bad.

BW
Yeah, I think that's, you've put your finger on it there that it's a kind of break glass, if we need it kind of option. And if we're not allowed to research it, we won't have it. So I feel like allowing the research to carry on is essential if we need that break glass moment, if we ever get to the point where we can coordinate ourselves to do something like that. But the other thing about it strikes me as that it is temporary and that's described as a bad thing. You know, it would reveal the warming very fast, but if you're slowly increasing it, if there are problems and we can observe those problems, we can stop doing it and it's not making a permanent change to the system in the way that CO2 seems to be. I mean, it's not permanent, but it's to all intents purposes because it's so long lasting.

PC
Indeed. And it comes back a bit to the planetary darkening issue we spoke about earlier. So if the darkening is due to our cleaning up the air, so removing sulphur dioxide from the lower atmosphere, then we could argue that we could counteract that bit of global warming with SRM, but deliberately not counteract any greenhouse gas warming because of the issue that it would be a lock-in and we'd end up with other issues like ocean acidification. So there are ways now to think about having an exit strategy from SRM that need not be switched off and suffer abrupt warming by making sure that you don't offset the thing that's going to be staying in the air for a long time, which is mainly CO2, but you offset the thing that's been in the air and is dropping out rapidly, which is tropospheric SO2, pollutants in the air that we breathe. So I think there are ways to frame it.

BW
Yeah, that seems like a very sensible position and one that as long as we understand that the reflectivity is part of the problem, and I feel like that's only just being understood. I don't really feel that beyond conversations like this, every politician in the world is understanding that the world is darker than it was. I don't really feel that's yet the case. So there's a job to be done there to communicate, to diagnose the problem properly, right? We've got this patient, need to know exactly the symptoms, why the symptoms are happening. And then emergency measures might be needed to stabilise things while we address the underlying conditions. That does seem like a fairly sensible position.

PC
Yeah, absolutely. So I think this interpretation of what the CERES record is telling us about and the global warming record telling us about, the reasons for the planetary darkening is critical for the whole debate about whether SRM makes sense or not, because if it turns out it's all feedback, then we've got an issue and you might have to do it forever and we wouldn't want to do that. But if it turns out it's forcing, then we might temporarily offset that warming that we're getting from reducing the cooling of SO2 and the troposphere by doing something else. And it could involve SO2 or something else in the stratosphere, but also brightening clouds by other means, like blowing seasalt into them is one of the suggestions.

BW
Yeah. And in fact, that is something the UK is currently leading the world in researching, which is phenomenal for a tiny little country about the size of Britain. But I suppose that's an indication of how little research is being done, but the UK has at least kicked that off with its ARIA programme. And yeah, it certainly feels that the research should be something we do.

PC
Yeah, I mean, I think the issue with SRM research is that there is stuff going on, but it's not publicly discussed. And I think that's the biggest concern is that if we make it something that respectable people don't talk about, then it won't stop it happening. It will just mean that it goes underground. And so the argument I have with my colleagues is really comes down to, we ought to be studying this and studying it openly to counteract the possibility that someone does it without having done the due diligence, the discussions with the public, especially the regional effects of it. Without having done the research in an open way, that needs to be done. So it feels like we must blow the doors off this now in order to get out in the open to avoid that danger.

BW
Yeah, and also just engage in a conversation about the ethics and the morality of it, which is as much as possible taking into account the relative risks, right? Because I was thinking as you were talking about, what if we find a way to cool the planet, won't we all just become reckless users of fossil fuels? Well, the risk of that is slightly less because as you say, cleaner technologies are now cheap so that's a good thing. But also I seem to remember when seat belts were being introduced into cars, everyone said, oh no, don't do that, everyone will drive really fast and will have loads of deaths. But that wasn't borne out by how we responded. We actually just took the seat belts and died less, you know, it was a good thing to have done.

PC
Was there a period where pedestrians on the pavement were a bit more at risk than they were before? Because people drove a bit more quickly and then I think it adjusted back, maybe speed limits came down as well, but yeah

BW
But we took other measures, right, to traffic calm.

PC
Yeah, indeed.

BW
But you wouldn't argue against the seat belt, that's my point, you know, that it was seen as something that would unlock recklessness but actually just led to less death.

PC
Yeah, and we have a bit of a conundrum in climate science and policy in that we've framed, well, two degrees as the dangerous level of global warming. And I think, as I said, that was a kind of a pragmatic decision to get up something, to have something to aim for that was potentially achievable and would reduce the worst impacts. But if you stick with that and people have the impression it's fine, it's fine, it's fine, and then it's catastrophic, which is not quite how it is, then you are in a situation where it's very illogical to not think about an emergency measure at that point.

And I think that framing is also slightly dangerous because it turns a political target into a sort of drop dead threshold. But there is an inconsistency at the moment in the way climate policy and climate science are interacting, which is still to reinforce the view that two degrees is dangerous and we must avoid it. What if we can't avoid it through conventional mitigation? You could argue we've still got a chance to do that but there's a chance we won't. Then what would we do then? So I think framing it really in terms of the impact of the SO2 reductions in the troposphere is the way to do that, to avoid that. But the debate has to be had really, in a way it hasn't been had.

BW
Yeah, no, absolutely. I think we can agree that there's a broadening of the understanding of the problem and that there has to be a broadening of the conversation about the solutions and the two have to go hand in hand. Well, I know that you as a person who loves complex problems are actually quite excited by this period we're in at the moment where it's live and things are moving and dynamics could be observed, and I think that gives me comfort that there are people really getting into the weeds of this and the next years are gonna reveal more knowledge, more information. So there is reason to have hope, right? Even in the face of adversity.

PC
Yeah, there's a weird kind of dichotomy for people like me in that we're concerned about climate change but we really like to study it. So I'd like it to stop after I've understood it. Well, as soon as I've understood it, you could stop it then, that's fine. But yeah, there's an interest in studying a system in transition. It reveals something about itself that it doesn't when it's in a sort of equilibrium state, so that's really exciting for scientific point of view. But also the things we find will hopefully inform what sort of solutions might be acceptable or not. And that's where the payoff is, I suppose, for non-researchers who just wanna live in a decent place.

BW
Yeah, well we all wanna live in a decent place, that is something that hopefully unites us. Well listen, Peter, I'm gonna let you go, thank you so much for your time with us today and look forward to staying in touch and you'll be publishing papers I hope and more research will be coming out. And actually we'll hopefully get more and more annual stock takes of the climate science because it does feel like whilst the warming is speeding up also ability to track it is increasing in speed too. So look forward to hearing more about what's going on on an annual basis.

PC
Thanks, my pleasure.

BW
So that was Professor Peter Cox, Professor of Climate System Dynamics at the University of Exeter. My thanks to Kendall Smith, our Head of Operations, to Oscar Boyd, our Producer, to Jamie Oliver, our Editor and to the rest of the cleaning up team that make these podcasts possible. And my thanks to the wonderful members of our Leadership Circle and thanks to you for listening. Please join us at the same time next week for another episode of Cleaning Up.

ML
Cleaning Up is proud to be supported by its Leadership Circle. The members are Actis, Alcazar Energy, Arup, Climate Imperative Foundation, Copenhagen Infrastructure Partners, Cygnum Capital, Davidson Kempner, EcoPragma Capital, EDP, Eurelectric, KKR, Mitsubishi Heavy Industries, National Grid, Octopus Energy, Quadrature Climate Foundation, Schneider Electric, SDCL and Wärtsilä. For more information on the Leadership Circle, please visit cleaningup.live. If you're enjoying this episode, please hit like, leave a comment, and also recommend it to friends, family, colleagues, and absolutely everyone. To browse our archive of around 250 past episodes and to subscribe to our free newsletter, visit cleaningup.live.