Nine years

WordPress has reminded me that I started this blog 9 years ago today. I feel that I should commemorate that in some way, but I’m not sure how, or really what to say.

As you can tell, the blog has been somewhat quiet, even though I do write posts everyone now and again, mostly when I feel that I have something to say. I don’t suspect this is going to change anytime soon.

I had a quick look at the blog stats, and there have been 1261 posts, of which I’ve written 1191. That seems a reasonable legacy, even if not everyone agrees 🙂

Anyway, it’s been an interesting 9 years, during which I’ve learned a lot, even if I have ended up slightly more confused about some things than I was when I started. Hope it’s also been of interest to some others.

Posted in Personal | Tagged , | 28 Comments


Just before the release of the IPCC’s AR6 WGIII report (Mitigation of Climate Change) Joeri Rogelj had a Carbon Brief guest post on how not to interpret the emission scenarios in the IPCC report. It might have been to try and pre-empt some of the simplistic narratives that some have promoted about emission scenarios, but I can’t be sure about that being the motivation.

The key point being made was that

Scenarios can be thought of as stories of what could happen in the future. What they are not, it is important to note, are forecasts or predictions for the future.

As the article goes on to say, scenarios are essentially “what if” thought experiments that help us to answer some questions about what might happen in the future. They do not, however, encompass all possible futures, and are not predictions of the future.

However, the issue of scenario plausibility has been a bit of a hot topic and is something I’ve been thinking about a bit myself. I haven’t managed to really draw any strong conclusions, but the beauty of a blog is that I can present some ideas that others can challenge/clarify in the comments.

I tend to think that scenarios should be plausible in the sense of not violating some fundamental laws of physics, or the essentials of chemistry. I don’t necessarily think they need to pass some kind of societal plausibility test, at least in the sense of them being what we will probably do. They could be “what ifs”, or “what could have been” or even “what might be”. Of course, I do think the motivations, and assumptions, should be made clear when communicating the results of any analysis based on a particular scenario, but I don’t think they have to pass some kind of societal plausibility test.

However, one of the key talking points about scenarios is whether or not their plausibility should be more explicit. I can see some merit to this, but I can also see why this may not be appropriate. If scenarios are “what if” thought experiments, rather than forecasts or predictions, then we should be cautious of suggesting that they are more the latter than the former.

There’s also the issue of independence. If the point of scenarios is to understand the impact of various possible futures, then assigning something like a probability to a scenario might then influence the outcome. For example, if we claim that a particular scenario is impossible, we may then either give up trying to achieve it, or assume that we no longer need to do anything to avoid it. In a sense, the probability of a scenario emerging in reality could be influenced by the probability assigned to that scenario, which would then undermine the intention of these being policy relevant, rather than policy prescriptive.

A potentially interesting issue, though, is the self-consistency of scenarios. In most cases a scenario is developed and then that scenario is used as input to some kind of model to assess the potential impact of that scenario. However, rarely do these models then include how these impacts might influence the scenario itself.

This can have a number of potential consequences. It could be that the impact of following a particular scenario could be so severe that it essentially precludes anything like that scenario from actually emerging. On the other hand, if we don’t consider how the impacts might influence the scenario itself, we might conclude that everything will still essentially be fine even under some extreme scenarios. So, I think it’s important to make clear that these scenarios are often not really self-consistent.

As usual, this has got rather long. I do think we should mostly treat scenarios as “what ifs” and should let society decide what to do, or not do, given what these scenarios might be suggesting. Of course, I do think we should be very clear about the motivations, and assumptions, behind these scenarios, but – IMO – we should be cautious about explicitly defining the plausibility of these scenarios. However, I would also be interested to know what others think.

Posted in ClimateBall, Philosophy for Bloggers, Policy, The philosophy of science | Tagged , , , , | 38 Comments

Techniques of climate denial

Steve Koonin, who I’ve written about before, had an op-ed in the Wall Street Journal a few months ago claiming that Greenland’s melting ice is no cause for climate-change panic. The article uses a graph of mass loss rate to argue that the rate now is the same as it was in the 1930s, that it has actually been decreasing recently, and that natural influences are much more important than human influences.

I’ve just come across a seminar that was essentially a debate between Steve Koonin and David Romps, who is a Professor of Climate Physics at Berkeley. I’ve posted the video below and it should start when David Romps presents his rebuttal to Steve Koonin’s Wall Street Journal article.

I thought David Romp’s presentation was very interesting, especially given that Steve Koonin was in the room. He didn’t pull any punches. He showed how you could cherry-pick the region you focus on, how you could cherry-pick the data set you use, how you could choose what analysis to present, and how you could then underplay uncertainties, and ignore periods that don’t suit your narrative.

Steve Koonin, of course, disputed that he’d made any suspicious choices, but that’s hardly a surprise. I don’t know if David Romps’ presentation will convince any of those who find Steve Koonin’s presentation appealing, but it was well done nonetheless.

Posted in Climate change, ClimateBall, Global warming | Tagged , , , , | 89 Comments

Ignoring the Economists?

Andrew Dessler had an article in Rolling Stone suggesting that [t]he first step to saving the planet is ignoring the economists. Stoat has already written about it and, as you might imagine, doesn’t seem to like it. Even if suggesting that we ignore economists is a bit hyperbolic, I think Andrew makes some good points. Or, maybe, points I happen to agree with.

Andrew’s specific focus is economists who assess climate policy on the basis of cost-benefit analyses. The problem with this in the climate context is that we have the potential to substantially change the climate and to do so on geologically fast timescales. It’s extremely difficult to estimate the impact of such changes, and hence cost-benefit analyses are going to be extremely uncertain. They’re also quite simple calculations that don’t even come close, as far as I’m aware, to self-consistently modelling the evolution of the world’s economy in the presence of climate change. They also require many judgements that are clearly not value free.

Also, some of these analyses produce rather strange results. For example, suggesting that the damage will be relatively modest even for very large amounts of global warming, or suggesting that the optimal pathway would be one that leads to about 3.5oC of warming. This is another issue with some of these analyses. A lot of recent work has suggested that we’re currently heading along a pathway that will probably lead to between 2oC and 3oC of warming. How can a recent CBA suggest that the optimal pathway is one that would probably lead to about 3.5oC of warming, when we’re already probably heading for less than 3oC of warming*? The answer is probably that they haven’t properly assessed their no-policy baseline, but it still illustrates a potential issue with these analyses.

So, what could we do instead of a cost-benefit analysis? Well, we could determine what it would it take to achieve a normatively determined warming target. Not only does this also have deep economic roots, it’s essentially what the world’s governments have already agreed to try and do. So, it’s not as if this alternative to a simple cost-benefit approach is somehow an outrageously extreme suggestion, or one that would somehow be wildly at odds with the fundamentals of mainstream economics.

Of course, there also isn’t an objectively correct way to assess the ideal target. However, it seems clear that the more we warm, the greater the impact, and that the changes will probably be irreversible on human timescales. Rather than trying to work out some optimal pathway, why not do our best to limit how much we will eventually warm, with some goal of at least trying to meet some warming target, such as < 2oC? We might not meet the target, but just missing it will probably be a lot better than heading along some kind of optimal pathway and then discovering that the impact is far greater than estimated by these rather simple cost-benefit analyses.


* I realise that there are uncertainties that mean that even though our current trajectory is probably taking us towards somewhere between 2oC and 3oC, we can’t really rule out that it might end up being well above 3oC. However, the same uncertainty applies to the cost-benefit optimal pathway.


The first step towards saving the planet is ignoring the economists – Rolling Stone article by Andrew Dessler.
The flower of poor thinking is to lack influence – Stoat’s post.
The impact of climate change, and the cost of climate policies – one of my earlier posts.
Economics and Values – another of my posts.
Moving beyond benefit-cost analysis of climate change – paper by Jonathan Koomey.

Posted in Carbon tax, economics, Philosophy for Bloggers, Policy | Tagged , , , , | 141 Comments

Moral models

I thought I would highlight a recent video presentation by Eric Winsberg, called Moral Models, Crucial Decisions in the Age of Computer Simulations. Some may remember that Eric co-wrote a post here about extreme weather event attribution.

The theme of Eric’s presentation is the moral significance of models and their influence on society. Eric makes a number of points that I largely agree with. A key point is that science doesn’t make decisions, people do. Models can inform decision making, but can’t define it.

Eric focuses particularly on the models used to understand the spread of the COVID-19 virus. Eric is rather critical of some of the modelling, in particular the influential Imperial College model. Eric highlights that some of the early models didn’t do much in the way of sensitivity tests and didn’t really consider the broader implications of their assumed interventions. I’m aware of an attempt to do a sensitivity analysis of the Imperial College model, but I didn’t think it was particularly useful.

What Eric stresses is that the assumptions that go into these models are not value-free. For example, in the case of COVID modelling, modellers will need to decide which potential interventions to consider, and they can almost certainly not do this in an entirely value-free way. What Eric suggests is that the modellers should have given more thought to how the interventions they chose to consider might influence other sectors of society, in particular those sectors with which the modellers probably have no association.

Eric also criticised the models for not considering the broader implications of the potential interventions. How would closing schools influence school children, and their parents? How would closing sectors of the economy influence those who might not be able to easily work from home? etc. Although these are perfectly valid concerns, this is where I somewhat disagree with Eric.

I think it’s very challenging to self-consistently include these impacts in the models and this may well go beyond what these models are designed to do, or should even try to do. Also, I think these are issues that policy makers should be aware of. They should be getting advice from other experts about the economic, and social, impacts of the various possible strategies. I do think we should be careful of suggesting that it was the responsibility of the modellers to provide this broader perspective.

However, I do think that modellers should be as clear as possible about the limitations of their models. This is partly simply because it’s the right thing to do, but also because it’s key to stress that models only inform decision making, not define it. If I was ever in a position to provide advice to policy makers, I would be pretty worried if I thought their decisions were based only on the information I presented. I would want policy makers to be informed by a broad range of experts. It’s key, in my view, to stress that the responsibility for making decisions lies with them, not with modellers/scientists.

Anyway, as usual I’ve written more than I had intended. Eric’s video presentation is below. Even if you don’t agree with it all, it certainly presents some ideas that are worth thinking about.

Posted in ethics, Policy, Scientists, The philosophy of science | Tagged , , , , | 19 Comments

A coupled climate-social system

I came across an interesting paper by Frances Moore and colleagues that considers [d]eterminants of emissions pathways in the coupled climate–social system. In the context of climate science, models that consider both the climate and society tend to not be coupled. For example, global climate models will use emission, or concentration, pathways as input, but these will be pre-defined and will not be influenced by the resulting climate change. Similarly, economic models might use a simple climate model to estimate damages, or to do some cost-benefit analysis, but the latter essentially determines the optimal pathway, but doesn’t really self-consistently couple the climate-social system.

This new paper seems to be the first, or one of the first, that couples a climate-social system. There are quite a large number of factors, but essentially the model estimates the response to various factors and how that might then infuence emissions, and – consequently – climate change. For example, as alternatives become cheaper, their uptake will increase. Similarly, as social norms change, this might influence people’s behaviour in ways that influence emissions. There could be the implementation of policies and laws that will also have an influence. Additionally, our perception of climate change might also directly influence people’s behaviour and the implemention of new policy/laws.

They then run a large suites of models, sampling the various parameters, to produce a suite of outputs that they then group into categories. The main results are shown in the figure below.

Policy (left-hand panel) and emission trajectories (right-hand panel) from a large suite of runs of a coupled climate-social model. (credit: Moore et al. 2022).

The basic result is that a large fraction of their model runs suggest emissions will peak in about 2030, and then fall sharply, leading to warming of about 2.3oC by 2100. There are also some where emissions fall more sharply and warming is closer to 2oC, and others where emission reductions are delayed and warming is closer to 3oC. Overall, most of their models suggest warming of between 2oC and 3oC, but the overall range is from 1.8oC and 3.6oC.

This, however, doesn’t include the full range of climate sensitivity and other possible climate feedbacks, so it can’t quite rule out warming above 3.6oC. However, this does seem to be another paper suggesting that the most likely trajectories suggest warming of between 2oC and 3oC, but that we can’t yet rule out that warming could be kept below 2oC, or that it might exceed 3oC. In some sense this is positive (we can still limit warming to below 2oC) but also somewhat concerning (we can still follow a trajectory that could lead to > 3oC of warming).

From a modelling perspective, this does seem very interesting. The model may rely on a large number of parameters that may not be easy to precisely define, but it is still good to see that some are trying to develop these coupled models that try to self-consistently determine the evolution of the climate-social system.


Determinants of emissions pathways in the coupled climate–social system, Moore et al. (2022), Nature.

Posted in Climate change, Global warming, Policy, Research | Tagged , , , | 21 Comments

A couple of highlights

Since it has been a bit quiet, I thought I might highlight a couple of things the regulars might find of interest.

Climate blogging in a post-truth era:

Thanks to Stoat, I’ve become aware that Giorgis Zoukas finished his PhD on Climate blogging in a post-truth era: opportunities for action and interaction. Mainstream scientist-produced climate blogs as a climate science communication niche. Some may remember that Giorgis had a guest post here where he invited people to participate in his research project.

The project involved interviewing climate bloggers who were also “mainstream” scientists (this blogger included) and also people who commented on these blogs, including some who are regulars here. I haven’t read it all, but did read some and found it very interesting. It was interesting to read some of my perspectives from a few years ago, which I don’t think have changed all that much.

I should also add that Giorgis first contacted me when I was still blogging anonymously. It gave me a bit of a start at the time because he was a PhD student at my university and I initially thought that maybe he’d contacted me because he knew who I was. He didn’t, but we did then meet in person.

Anyway, I thought others who have been involved in climate blogging, or commenting on climate blogs, may also be interested in looking through Giorgis’ thesis.

Short- and long-lived GHGs

Since I’ve written a number of posts about methane, I thought I would also highlight a recent paper arguing that we should [i]ndicate separate contributions of long-lived and short-lived greenhouse gases in emission targets. It’s partly interesting because the list of co-authors is quite extensive and includes some who haven’t (from what I’ve seen) always agreed about how to incorporate short-lived and long-lived GHGs into emission targets.

If you’ve read some of my earlier posts you’ll know that I largely agree with the suggestion in this paper. Short-lived and long-lived GHGs do behave differently and the association between emissions and warming is different for short- and long-lived GHGs. Combining them to produce a single emission target can hide a lot of complexity. For example, Zeke Hausfather points out that net-zero all GHGs (based on CO2-equivalence) probably implies net-negative actual CO2 because it’s probably impossible to remove all emissions for some species.

So, treating these different species separately makes these differences clear and allows us to better understand what is actually required in order to achieve some of our stated targets.

Posted in ClimateBall, Philosophy for Bloggers, Scientists | Tagged , , , , | 47 Comments

An international solar geoengineering non-use agreement

I wrote about Solar Radiation Managment, or solar geoengineering, earlier this year. It’s become a rather contentious topic, with some regarding it as worth exploring, and others almost seeming to regard it as something we should avoid at all costs. The latest saga involves a group of scholars signing a letter arguing for an international solar geoengineering non-use agreement, which is partly based on this paper. Their main reason for proposing this is that they regard it as being virtually impossible to develop a suitable governance framework.

As a result of this, I ended up in a brief Twitter discussion with Dan Miller, who then asked me to join their clubhouse discussion that took place yesterday evening. It was an interesting discussion, but a little tricky as I was there to partly defend the call for a non-use agreement, which I hadn’t signed and don’t completely agree with. I do, however, share many of their concerns.

On the other hand, Dan and his colleagues, Stacey and Ely, seem fairly convinced that there is a high risk of us crossing a tipping point soon and that this means that we should be seriously considering actually implementing some kind of solar radiation management now.

Although I don’t completely agree with all of what seems to be being proposed in the call for a non-use agreement, I do not think that we should be seriously considering the use of solar geoengineering. One reason is that even though I agree that there are risks of us crossing some tipping points, I think these become much more likely if we warm beyond 2oC. Consequently, I think our focus should be on limiting emissions so that we give ourselves a good chance of keeping warming below 2oC, rather than implementing some kind of solar geoengineering.

The other reason is because of the risk of what is called a termination shock. If we were to implement solar geoengineering now so as to keep global warming close to today’s level while continuing to emit CO2 into the atmosphere, solar geoengineering could end up masking quite a lot of unrealised warming. If for some reason we were unable to sustain this solar geoengineering, this unrealised warming could then materialise on a timescale of a few years, which could have catastrophic consequences.

So, I do think we should be very cautious of actively implementing such technology. In fact, I would suggest that we really shouldn’t be aiming to implement anything like this at the moment, or any time soon. I also think the governance issues highlighted in the letter are valid concerns, and there may well be no easy way to overcome them. On the other hand, I think it’s probably still worth understanding this option, even if it is something we never actually want to use. In some sense, the cat is already out of the bag (we know that there are ways to artificially cool the planet) so it’s probably better to be informed, than not.


Solar geoengineering non-use agreement
Solar geoengineering: The case for an international non-use agreement, paper by Biermann et al.


As highlighted by Alastair McIntosh on Twitter, solar geoengineering also doesn’t directly address ocean acidification, which is another reason for focussing on emission reductions, rather than implementing something like solar radiation management.

Posted in Climate change, Global warming, Policy, Uncategorized | Tagged , , , , | 69 Comments

The tragedy of climate change science?

Since my last post was about how scientists failed the pandemic test, I thought I might comment on another paper highlighting the tragedy of climate change science. The basic premise of the article is that society has failed to take effective action on climate change and that, consequently, the science-society contract is broken and that the time has come for scientists to agree to a moratorium on climate change research as a means to first expose, then renegotiate, the broken science-society contract.

I have sympathy with the frustration, but I think the basic argument is simply wrong. I don’t think the general description of the social contract is quite right. As Andrew Dessler pointed out, the social contract is simply that [t]hey pay us to do research and we provide them with the results. There is no obligation that policy makers take the results and make decisions that the researchers agree with.

This doesn’t mean that researchers can’t, or shouldn’t, disagree with the decisions that are made. As citizens, they’re perfectly entitled to do so. However, researchers don’t have some special right to decide how their research results are used. They, of course, have the right to decide not to do some research if they think it will be used in ways that they regard as unethical, but that seems a somewhat different issue to what is being proposed in this paper.

I also thought that the paper exaggerated the level of failure. The world’s governments now virtually all agree that we need to tackle climate change, even if their actions don’t yet match their words. In some sense, this is a remarkable success of science communication. Also, even though we haven’t yet bent the Keeling curve down, global emissions have probably been lower than they might otherwise have been. There’s been a shift from coal to natural gas and a growth in the use of renewables. There’s much more that needs to be done, but I do think there has been some progress.

I do think there are also reasons to be disappointed; we should probably have acted sooner to reduce emissions and there are still those who seem reluctant to take serious action. However, there are also reasons to be optimistic; outright climate denial is far less prominent than it once was and it does seems as though the more extreme scenarios are far less likely than they once were.

As some often point out, we’re not going to solve this by doing more science. However, I think the reverse also applies; we’re not going to solve it by doing less. Policy makers have largely accepted the scientific evidence and the lack of effective action is probably more to do with political roadblocks than with how much, or how little, science is now done.

There may be merit in changing the IPCC reports so that there is much more focus on WG2 (Impacts, adaptation and vulnerability) and WG3 (mitigation) research, than on WG1 (physical science) research. However, I don’t think this means that physical scientists should change the focus of their work, or stop doing their research. The Earth’s climate is still an interesting system to study and we do still want to continually update our understanding so as to better inform mitigation and adaptation efforts. Ultimately, the failure is a failure of policy making, not a failure of science communication, and I think we should be cautious of suggesting otherwise.

Posted in Carbon tax, Climate change, Research, Scientists, The philosophy of science | Tagged , , , | 128 Comments

How scientists failed the pandemic test

Philip Ball has an interesting article about UK science advice called [q]uiet, uncritical, obedient: how the UK’s scientists failed the pandemic test. It make some good points about there appearing to have been collusion between the science advisors and the government, that scientists seemed reluctant to present certain options given the likely biases of the government, and how they failed to speak out when there was an apparent disconnect between the government’s actions and their words.

Although I think there are many reasons to criticise the science advice that was given, there was a framing in the article that I largely disagreed with. For example, we keep getting told that there isn’t some linear relationship between scientific advice and decision making; there are many other factors that play important roles. If so, how can we then judge the scientific advice on the basis of the decisions that were made? What about all the other factors that will have influenced the decision making?

The article also implied that the scientific community needs to wake up, and that [a] policy of appeasement, normalisation and objective detachment has not worked. One problem is that the scientific advisors are not really representatives of the scientific community. They are mostly individuals who have either volunteered to sit on a committee, or have been appointed to what is essentially a political role. There were plenty of scientists who were speaking out and challenging the government’s decisions.

Also, if the government wants advice from those who will speak truth to power and will challenge them, then they can aim to appoint such people and can encourage them to do so. Of course, people in those positions can choose to speak out, but if they’re discouraged from doing so, then it seems likely that these positions will be filled by those who are pre-disposed to not do so.

I do agree with the article that how science advice has faired during the pandemic bodes ill for the climate crisis. What I don’t quite agree with is the suggestion that somehow the scientific community needs to work out how to fix this. The article itself highlights that we have a libertarian, populist government who will be pre-disposed to prefer certain options. I don’t think it’s the job of the scientific community to work out how to counter the biases of the government that we’ve, collectively, chosen to elect.

I also agree with the article that scientists should be careful of how they might be used by the government. As suggested in the article, scientists will be blamed if necessary. This is why we should be careful of “follow the science” type of rhetoric. We should be clear that the scientific advice is information that can be used by the government to make decisions. However, it’s not the only relevant information and the responsibility for making these decisions lies with the government, not with the scientific advisors.

If we want scientists to speak truth to power and to challenge the government, we should support those who do, we should put pressure on the government to appoint advisors who will do so, and we should feel free to vote for those who we think will aim to be properly informed when making important decisions. Of course scientists have a responsibility to provide reliable information, but they’re not responsible for the decisions that are then made and I think we should be careful of suggesting otherwise.

Posted in Climate change, Policy, Science, Scientists, The philosophy of science, The scientific method | Tagged , , , , | 57 Comments