Extreme events and anthropogenic emissions

This is a post that I’ve been thinking of writing, but have been somewhat reluctant to start. It’s mostly because it relates to something said by Roger Pielke Jr, so could end up being a bit of same ‘ol same ‘ol, which I’ve become rather tired of. However, it’s an interesting issue, and I’m not entirely sure that I’m right, so I’ll have a go.

As part of Roger’s attempt to withdraw from the public climate debate, he publishes a monthly newsletter. In his most recent one, he discusses extreme weather and climate change and says

Research keeps accumulating that shows that so far at least, the rising costs of weather disasters are not a result of weather extremes that have become more common or intense due to climate changes resulting from the emission of greenhouse gases

Now, I think the above is probably strictly correct. We probably have not been able to definitively demonstrate that the rising cost of weather disasters can be formally attributed to the human emission of greenhouse gases. However, I think this is mostly the wrong way to consider this, and I’ll try to explain why.

Let’s start at the beginning. We’re emitting greenhouse gases into the atmosphere. These greenhouse gases accumulate in the atmosphere. Their increase reduces the outgoing longwavelength flux, producing a planetary energy imbalance. This means that energy accrues in the climate system, causing it to warm.

Now, even if we do observe warming, we can’t necessarily claim that it is due to our emission of greenhouse gases. However, as this Realclimate post explains, we can do attribution studies to determine the most likely causes. However, it’s not as simple as observating that it is indeed warming; it requires some kind of model and also requires considering how what we expect from the different possible causes compares to the actual observations. In particular, the different possible causes produce different spatial, and temporal, patterns of warming, which can then be used to determine the most likely cause of the observed warming. Having now done this type of analysis, we are pretty confident that most of the observed warming is anthropogenic.

What are the consequences of this anthropogenically-driven warming? We obviously expect an increase in the frequency and intensity of extreme heatwaves. We also expect the hydrological cycle to intensify, which essentially means more evaporation and, consequently, more precipitation. In particular, we expect an increase in the frequency and intensity of the most extreme precipitation events. We also expect an increase in the frequency and intensity of some of the more extreme weather events, such as tropical cyclones.

Can we actually formally attribute changes in some of these extreme events to anthropogenic emissions? I think this is actually quite tricky, partly because the events are extreme and, therefore, rare. We don’t therefore have enough suitable data to make formal attribution claims (I may be wrong about this, so happy to be corrected). However, I think we do have evidence for an increase in the frequency and intensity of extreme precipitation events and heatwaves. We also have evidence for an association between increased sea surface temperatures and an increase in the frequency and intensity of tropical cyclones (and an understanding of why). So, the observations appear consistent with what would be expected.

In some cases, climatic events do damage that we can quantify in terms of how much this would cost to repair. Typically, these are the rare extreme events, not all of which do damage, which makes the events that do damage even rarer. Hence, formally attributing this to anthropogenic emissions is very difficult. Furthermore, there are many factors that could influence the scale of this damage. It could increase partly because there are now more valuable assets in the way. On the other hand, it could be lower than it might otherwise be because the infrastructure is now more able to withstand the impact of these events.

However, does this really matter? Do we need a formal attribution study to be quite confident that an increase in the frequency and intensity of extreme precipitation events will likely impact flooding? That increased evaporation and warmer weather will likely impact droughts and wildfires? That increased sea surface temperatures will intensify extreme tropical cyclones and make these more damaging if they impact populated coastal areas?

I don’t really think so; these don’t seem to be a particularly controversial inferences (they probably are, but it’s not clear why). Of course, that we expect our emission of greenhouse gases into the atmosphere to ultimately influence the cost of weather-related disasters doesn’t immediately tell us what we should do. However, recognising this seems more relevant than highlighting that we haven’t yet formally attributed increases in weather related damage costs to our emissions of greenhouse gases, especially since the latter could be true even if anthropogenically-driven warming has indeed lead to an increase in the cost of weather related disasters.

Posted in Climate change, ClimateBall, Global warming, Policy, Roger Pielke Jr, Severe Events | Tagged , , , | 102 Comments

The Paris climate targets

I’m currently in Oxford for a meeting and, having spent most of the train ride working on a book chapter I’m writing, I thought I would now spend some time writing a quick post about the recent Schurer et al. paper Interpretations of the Paris climate target. It’s essentially a response to the Millar et al. paper, that I’ve discussed in a number of recent posts.

Credit: Schurer et al. 2018

The key result is probably illustrated by the figure on the right. It shows how different ways of treating the observations influence how close we might appear to be to a target (in this case 1.5oC). For example, the top panel shows HadCRUT4 and how close it is to 1.5oC based on the standard dataset (blue), a version that corrects for HadCRUT4 being a combination of surface air temperatures (SATs) and sea surface temperatures (SSTs) (green), changing the pre-industrial baseline for the standard HadCRUT4 dataset (yellow), and doing the same but for a case where it is all SATs (purple). The middle panel does the same as the top panel, but corrects for HadCRUT4’s coverage bias (i.e., makes it global). The bottom panel is the same, but for the Cowtan and Way dataset.

Essentially, if we use observational datasets to infer how close we are to a target, it will depend on how that dataset is constructed (SST + SATs, coverage) and on the assumed baseline. There are a number of reasons why it’s important to understand this effect. For example, Millar et al. claimed that we’d warmed less than expected, given how much we’ve emitted. Therefore, we have a larger remaining carbon budget that had been realised. However, this difference was (as I understand it) mostly because the observations were blended (SSTs + SATs) and suffered from coverage bias, while the model used to estimate how much we should have warmed was based on global coverage and SATs. If the comparison had been like-for-like, then the difference would have been much smaller.

Additionally, if you’re going to estimate some warming at which impacts become sufficiently severe that we should aim to keep below that, then the observations used to determine how close we are to that target should be consistent with what was used to determine the target. If the latter was determined using global coverage and SATs, then either an equivalent observational dataset should be used, or the target should be corrected to account for form of the observations (blended and masked, for example).

Ultimately, however, I’m not entirely sure I quite get the fuss. I think this is an interesting scientific puzzle. I think it’s useful to understand why there are these differences. However, whether the target is 1.5oC or 2oC, achieving the target is going to be difficult even if we do have a few tenths of a degree more to go than we had realised. It’s essentially still start reducing emissions as soon possible, and reduce them as fast as we can.

Posted in Climate change, Global warming, Policy, Science | Tagged , , , , | 46 Comments


I noticed another discussion on Twitter about whether or not climate scientists should fly. I have written about this before and the issue of people making personal sacrifices is something I’ve pondered recently. I have a great deal of respect for those who’ve decided to forgo something like flying in order to reduce their personal carbon footprints. However, I don’t think this should be expected of climate scientists, in general, simply because their research happens to be highlighting the risks associated with continuing to emit CO2 into the atmosphere. I would add, though, that those who actively advocate for changes in our lifestyles should practice what they preach.

Something that did surprise me, though, was that emissions from air travel make up only about 2% of global carbon dioxide emissions (about 11% of emissions from transportation). So, emissions from air travel do not currently make up a significant fraction of global emissions. However, it is expected to grow and, if we do reduce emissions from other sources, it could make up a much more significant fraction in the future. It is therefore important to think about emissions from air travel, but right now reducing emissions from air travel will – alone – not significantly dent global emissions.

However, there are many other factors to consider. It can be a significant fraction of an individual’s carbon footprint. A single long-haul flight could be 10% of someone’s annual emissions. So, if someone wanted to reduce their personal emissions, flying less can have a big impact. Similarly, it is one of the most carbon intensive forms of transport. If it is possible to travel via bus, train, or even car, emissions will probably be lower than if travelling by air. I certainly now think much more about how I should travel than I used to; if I can catch the train, rather than flying, I try very hard to do so.

However, there are many positives to flying. We can directly explore other cultures and environments, helping us to appreciate how diverse and amazing this planet can be. Even though many meetings could (and should) be done using videoconferencing facilities, there are occasions where a face-to-face meeting would be far more effective than meeting remotely. Many people’s families are spread around the globe and I think it’s important to be able to see one’s parents, children and siblings.

So, I do think it’s extremely important that we think of ways to reduce our emissions, and I have a great deal of respect for those who are making personal sacrifices so as to do so. I also think we should all be thinking more and more about how we can minimise our carbon footprints. However, I don’t think we should be going around expecting individuals to forgo things simply because their research happens to indicate a risk associated with those activities. Ultimately, global emission reductions is going to require much more than simply some people giving up some carbon intensive activities, and we shouldn’t pretend otherwise.

Posted in ClimateBall, ethics, Personal, Policy, Politics, Research, Scientists | Tagged , , , , | 198 Comments


I don’t particularly like discussing moderation and, in fact, it’s been much less of a problem than it once was. However, for various reasons, I thought I would quickly stress something about how, and why, I run this blog. I don’t have any great interest in comment threads that degenerate into slanging matches, or that simply end up being people complaining/insulting those with whom they mostly disagree. What I really appreciate is that the comment threads here do tend to be mostly thoughtful and informed. One reason for this, I think, is that I’ve had quite a strict moderation policy which either discourages some from commenting, and/or encourages others to comment appropriately.

Even though the comments threads here are mostly quite reasonable (in my view, at least) I do still delete some comments. The reasons can vary. Maybe it’s off topic. Maybe I just regard it as not constructive. Sometimes it can even be quite amusing, but a little ruder than I like. Maybe it’s a topic we’ve covered time and time again and I can’t see any reason to repeat previous discussions that achieved little when they first occurred. Maybe it’s promoting something that is simply wrong that we’ve covered before, and I can’t be bothered debunking it again. Sometimes I even get moderation wrong, but moderation decisions are final.

A key point, though, is I do my best to not make it personal. I have no problem with people trying again, ideally while trying to work out why their comment might have been deleted before. Of course, if it’s off-topic, ideally move on to something that is on-topic. I also don’t mind people contacting me privately if they think there is a problem; I can’t guarantee to resolve it, but I’m normally happy to try. What I really appreciate are those who understand that running, and moderating, a blog isn’t easy and that even if I get things wrong, it’s not intentional. There’s also a limit to how much time I can spend on this; there are other things (such as my actual job and my family) that have to take precedence over something that is essentially only a hobby.

Posted in ClimateBall, Personal | Tagged , , , , | 19 Comments

Ignoring adaptation?

Oren Cass has an article in the Wall Street Journal called Doomsday climate scenarios are a joke. It’s based on a report that he has written for the Manhattan Institute. The Manhattan Institute publishes a magazine called the City Journal which did once have an article by Rupert Darwall, in which he defended Murry Salby, so that doesn’t bode well. However, I don’t think that Oren Cass’s article/report are completely without merit.

His article is actually about economic models, rather than physical climate models. His suggestion is that in some cases the assumptions don’t make sense (they ignore, for example, that we can adapt to some of the changes) while in others what the models imply don’t make sense (some very poor countries today will become – because of warming – much richer than countries that are very rich today). If what he say is correct, then it does seem odd. On the other hand, I’m aware that sometimes modellers make assumptions for reasons that may not be immediately obvious. For example, maybe ignoring adaptation presents a worse case scenario, but also provides some indication of what we would need to do to address this (which is not cost-free). On the other hand, my limited encounters with economists might suggest that sanity checking their model results is not one of their strengths.

In many respects, though, I think Oren Cass’s article/report misses the point. Our options are not simply to adapt, or mitigate. We will have to adapt to some of the changes, but should also be thinking about what to do to avoid some of the potential changes (which will largely require emitting less CO2 into the atmosphere than we otherwise could). Precisely how to do this is not necessarily obvious, but there are presumably two extremes that bound the options. Burning everything will almost certainly lead to changes that will prove very damaging. Similarly, immediately halting all emissions will also be pretty catastrophic. So, it presumably has to be somewhere in between these two extremes and there are indeed analyses that provide policy instruments (a carbon tax, for example) that could lead to some kind of optimal pathway.

There are also, in my view, other things to consider. The changes are probably – without technological intervention – irreversible on human timescales. If they turn out to be more difficult to deal with than Oren Cass appears to suggest, we don’t get to easily go back. Also, stabilising global temperatures will essentially require getting emissions to about zero. However, given that we can’t do this immediately, there will always – in reality – be some amount of committed warming. It would therefore seem sensible to think about reducing emissions before it becomes patently obvious to everyone that we should do so. As someone said on Twitter (Peter Jacobs, maybe) the best time to start emission reductions was 20 years ago. The second best time is now.

I’ll finish with my perspective, mostly due to being a physicist. Our climate is a complex, non-linear system. It has, however, been remarkably stable for quite some time, and we’ve almost certainly benefitted from this quasi-stability. However, we’re now pushing it out of balance. For small perturbations, we’re reasonably confident that the response will be linear and that we understand quite well what will probably happen. We do, however, have the potential to produce a large perturbation and, if we do so, the response becomes much more uncertain. This should really make us more concerned, not less.

Posted in Climate change, economics, GRRRROWTH, physicists, Policy | Tagged , , , , , , , | 167 Comments

Living in Liquid Worlds

I spent yesterday at a workshop – organised by Dominic Hinde – at the Institute for Advanced studies in the Humanities. The title of the workshop was Living in Liquid Worlds. The idea was to bring together scholars from different disciplines to discuss the huge environmental and technological changes at the centre of the human-earth relationship. In this context, liquidity (I think) refers to the idea that society continually evolves/flows and the people are somehow embedded in this flow (at least, I think this is what it is – I may well have this wrong).

The morning session revolved around a presentation by Mark Deuze, Professor of Media Studies at the University of Amsterdam, and author of Media Life. His argument was that we essentially live in media; it’s an integral part of our existence. He presented quite a positive view of media, although it might have been more that it was neither good, nor bad, than it specifically being good.

He discussed many things, but the thing that struck me was the concept of transmedia; telling a story across many different platforms. An example would Marvel, which includes many movies, TV shows, comic books, etc. One aspect is thinking big, but starting small. Additionally, every component tries to stick to the same basic story, but what happens in one can then influence how the story on another platform might have to evolve.

I did wonder if this has some applications in science communication. There is definitely a sense that people have strongs views about how we should undertake science communication. It might be better if we accepted that there are many different ways to contribute to telling this story. Sarah Myhre is comfortable telling some personal stories. Katherine Hayhoe often focuses on engaging with those who are most likely to be dismissive about anthropogenically-driven climate change. Others focus more on presenting the scientific evidence. There are also many on Twitter, for example, who engage in various different ways. Maybe we need to do a better job of recognising that we’re all part of the same storyline; we’re just engaging in different, but complementary, ways.

The afternoon session involved a presentation by Philip Garnett who recently published a paper called Total Systemic Failure (which he discusses in this post). Essentially, in complex systems the failure of one part of that system could lead to a significant change in the overall behaviour of that system, or – potentially – to its total collapse. One example would be the banking crisis, that started in 2008 and which required a large injection of money in order to prevent collapse.

Another potential example would be changes to our climate having knock on effects (on ecosystems, for example) which lead to some kind of global collapse/failure. This possibility was discussed in his paper, and I was surprised that there wasn’t a bigger response from the usual suspects. One issue is that we don’t actually know what changes could then trigger some kind of systemic collapse, or even if this is necessarily likely. I guess we have to hope that the potential loss of summer Arctic sea ice and the Great Barrier Reef doesn’t have significant consequences beyond the local ecosystems.

Anyway, I’ve said enough. It was interesting day, which has given me lots of things to think about. It was also fascinating to discover that there are people in many different disciplines who are looking at various aspects of environmental change. It would probably be good if this was better known and if there were more links between the different disciplines. This workshop may have been a step in that direction.

Posted in advocacy, Climate change, Environmental change, Global warming, Research | Tagged , , , , | 49 Comments

Talking solutions and motivating action

There’s been a lengthy Twitter discussion about scientists moving away from simply discussing the science of climate change, to talking about solutions and motivating action. I broadly agree with this; I do think that the main discussion should be about the solutions and how we should motivate society to implement these solutions. What I don’t know is what these solutions should be, and what action we should be motivating.

Credit: Glen Peters

While I think about this, I thought I would post a figure that – in my view – largely illustrates the issue. It shows the probability of staying below 1.5oC, 2oC, 2.5oC and 3oC plotted against cumulative emissions, in GtCO2. For example, to have a 66% chance of staying below 2oC we’d have to emit no more than about 3600GtCO2. (Caveat: The result does depend a little on how you define the targets, but it’s probably about right at the ~10% level. However, this article seems to suggest that some of the cumulative emissions numbers are a bit too high.)

A few other relevant numbers. We’ve already emitted about 2000GtCO2 and are currently emitting around 40GtCO2 per year. So, if want want a good chance of staying below 2oC, then no more than about 30 years at current emissions. Similarly, staying below 3oC would require no more than about 70 years at current emissions. If we keep emitting, CO2 will continue to accumulate in the atmosphere, and we will continue to warm; stopping this requires getting net emissions pretty close to zero.

The expectation is that the impacts of climate change and our ability to adapt to the changes depend mostly on how much the temperature changes. It’s also likely that the impacts do not increase linearly with increasing temperature; each extra degree of warming will probably have a much greater impact than the previous degree of warming.

So, if we want to ultimately stop anthropogenically-driven warming we need to get net emissions to essentially zero and – ideally – we should do so before the impacts become so severe that they hamper our ability to adapt – or deal with – the resulting changes. Sooner, rather than later, essentially. Exact timescales are hard to define, but we’re talking decades, rather than centuries.

However, this is where I find it gets complicated. We need emissions to peak and then drop to zero, but how do we do so in a way that fairly takes into account all the various factors? Do we simply rely on a carbon tax and hope that the market really does select the optimal pathway, or do we take a more direct approach and actively influence the direction in which we progress? How do we share the remaining carbon budget in a way that’s fair to those who’ve emitted least, but isn’t punative towards those who’ve emitted most? What about personal responsibilty? Do we hope that the system evolves so that emissions can reduce without us having to do too much individually, or do we insist that individuals should be actively trying to reduce their personal emissions? What about new technologies? Do we hope that we can develop negative emission technologies that allow us to continue using fossil fuels without emitting CO2 into the atmosphere, or do we focus on technologies that we’re more confident can actually be implemented?

There’s almost certainly many more factors that should be considered, and I certainly don’t have any answers to the above questions, most of which are probably too simplistic anyway. I find the basics simple, but the details very complicated. The basics are essentially that it’s our emissions that are driving climate change and that stopping this will require getting net emissions close to zero. The details (what we should do, how we should do it, when we should do it) are, however, what we should probably be focusing on now. I just don’t have a good sense of how to do so. It’s also hard to see how we can move on to talking about the details while there are still substantial numbers disputing the basics. Maybe there’s still a place for scientists who talk more about the science, than talk about solutions and how to motivate action?

Posted in Climate change, Global warming, Policy, Research, Science, Scientists | Tagged , , , , | 492 Comments