Jens’ Bayesian Models

[W] Hello. How’s everything?

[J] Things are good, thanks 🙂 Busy December, but that’s par for the course. I hope you’re well also.

[W] I have the flu, but hope to survive against all odds. That’s you:

https://oxfordmartin.ox.ac.uk/people/dr-jens-koed-madsen/

[J] Ah, the classic December curse. Yep.

[W] And here’s a video of you

[J] Yeah, it was a book launch a month and a bit ago

[W] Wow, you can talk! Wait – you launched a book?

[J] Yeah, the talk was a presentation of the book.

[W] Ahhhhhhhhhhhhhhhhh. OK. Now, let me get this straight. You published a book in 2019, and what, 88 articles?

[J] Yes – the book was published in 2019. Haha, hardly – I think I published 7 papers in 2019 or so

[W] So, tell me – how many hours does writing an article take you?

[J] How many hours? That depends on the length and technical difficulty of the paper – usually, it probably takes a few days or so to draft it, but with model development, testing, data collection, analyses, revisions, and contributions from co-authors, it can easily take a few months from the initial idea to the submitted paper. But once the legwork is done, usually the draft takes a few days.

[W] Give me a ball park in terms of expectation. I tell you – Jens let’s write a thing, how many hours you need to put aside. Two full weeks?

[J] It entirely depends on this [what you’re going to write] – for example, smaller papers can take 1-2 days while larger papers can take weeks 🙂

[W] So about a full week. You’re good. First article you wrote is this.

[J] Yes, that’s the earliest paper published in 2019, but I’ve been publishing papers since 2012 🙂 I think my first paper was this: Because Hitler did it! Quantitative tests of Bayesian argumentation using ad hominem

[W] Oh, I love ad homs. I know you have tricks, I just want readers to understand they’re obsessing over something that happens in a limited time span.

[J] That makes sense – managing reader expectations is crucial.

[W] I’m working on the practical aspects of fallacy fluff these days. I think people misunderstand them, and that it’s the philosophers’ fault.

[J] Oh cool – there’s a lot of interesting Bayesian papers on fallacies.

[W] You work on Bayesian models, that seem the constant in your research.

[J] Yep – I’ve been working a lot with Bayesian models 🙂

[W] OK, which paper should we look into, your most recent one?

[J] I figured the seepage paper was the one that sparked your interest, yes?

[W] Yes. There is also this one but I must admit that it’s more you that interests me. I want to show a variety of scientists. Here’s the seepage paper:

We present an agent-based model of scientific consensus formation in climate change.

An evidence-resistant minority can prevent the public from acquiring the consensus position.

An evidence-resistant minority can delay, but not prevent, a scientific consensus.

The model matches several aspects of public opinion formation and consensus formation

Love the hightlights.

[J] Thanks 🙂 We felt the model in the paper yielded some interesting perspectives on belief revision and the impact of contrarian interpretation of data

[W] Let’s start with the basics, what’s a Bayesian model?

[J] It’s a probabilistic model that integrates two things: prior beliefs and some new evidence (which can be more or less relevant to the hypothesis under consideration). From these, Bayes’ theorem gives you the posterior degree of belief in the hypothesis given that evidence. Critically, Bayes’ theorem can use subjective probabilities – that is, two people may have different priors and thus arrive at different posterior degrees even when given identical information

[W] Good point. So it’s how people should in principle revise their beliefs based on new evidence. Your model says that contrarians can’t prevent correct beliefs to spread.

[J] Our simulations showed that unbiased agents necessarily acquire belief in the climate-change hypothesis, even when they start from an initial position of extreme skepticism and even when they rely on un- duly short temperature trends.

[W] Wow. But then we’re all biased, no? Even I am biased toward your research.

[J] We use ‘agents’, as we use an agent-based model (‘agents’ are just the individual actors in the simulation). To some degree, we probably all are biased to some extent by our personal experiences.

[W] So contrarians can’t prevent correct beliefs to spread, but you found that some contrarians are unconvinceable, right?

[J] The contrarians in the model are people who transmit biased interpretations of the data to the population. But yes, we show that even the contrarians cannot remain sceptical without biased interpretations of the data.

[W] But you can’t predict that contrarians won’t cling to their priors. You’re not saying that correct information can win against the staunchest of contrarians.

[J] True – but in the model, we wanted to see what happened when they updated their beliefs. An alternate model could simply have contrarians who only transmit their initial prior without developing or changing their beliefs over time.

[W] That would go against my experience. Contrarians usually move into a matrix. They can also play at what I call the climateball bingo.

[J] The idea of not moving their belief could be integrated within the model – in this paper, however, that wasn’t what we wanted to explore 🙂

[W] For instance: But1940, But2ndLaw, But70s, ButABC, ButAbsoluteTemps, ButAcid, ButActivism, ButAdjustments, ButAdvocacy, ButAl, ButAlarmism, ButAnonymous, ButAntarctica, ButArrhenius. And that’s just for before B. Contrarians move around the talking points.

[J] Do you refer to data cherrypicking? Ah, I see – moving the goal post

[W] There are many ways, yes. You can doubt anything but data, or some dataset, or prefer that other data set, or etc. It never ends. It’s quite subtle, contrarians are quite good actually at ClimateBall bingo.

[J] For cherrypicking, The analysis found that since 1970, any bet against warming—even those involving cherry-picking of short-term cooling trends—would have been unsuccessful in the model that is 🙂

[W] Ah, that’s a good point.

[J] Yes, cherry-picking and moving the goal post is really pernicious. One of the points of the paper is to show that cherry-picking cannot yield denial, but that the contrarian must have some biased interpretation on top of cherry-picking. The model used on a two-pronged propagandistic effort: first, promoting and sharing of independent research that conformed to the industry’s position, and second, funding of additional research with selective publication of the results. This was when we wanted to test the influence of contrarians on public opinion

[W] How would you characterize that influence, e.g. is it worth their time to create FUD, i.e. Fear, Uncertainty, Doubt?

[J] The emotional state of the recipient probably influences their perception of the argument and data, but unfortunately I’m not well-placed to say how, as my research hasn’t been concerned with emotions. However, there’s some excellent research done on emotions and reasoning by people like Isabelle Blanchette and others

[W] Will look. Even from an epistemic standpoint, you’re saying that promoting tendentious research slows down the correct information to spread, but in the end it’s insignificant, right? I’m wondering why one would waste time promoting tendentious research.

[J] It might not be insignificant if contrarians are given a large platform.

[W] And they are.

[J] Also, the contrarians might have different incentives than epistemic accuracy – e.g. lobbyists who argue for a very particular point.

[W] The industries are controlling most media. Just look at how Brexit got covered:

[J] Most media are industries in and of themselves 🙂 Yeah, it’s pretty messy – a large part of my research is concerned with how information spreads on social networks, e.g. how echo chambers emerge.

[W] It’s hard to deny that people got served Corbyn’s antisemitism. Not saying it’s not worth discussing, but I think there are other interesting things we could have discussed.

[J] Yeah, that message seems to have been pretty consistent.

[W] I need to ask you about Brexit. You’re Danish. Will it affect you?

[J] I’ve got settled status, so it probably won’t affect me personally (although, I am of course impacted by the economy if that turns bad). But it’ll leave a lot of people in uncertain positions

[W] Good to hear. People around you?

[J] Yeah, friends and colleagues who don’t know if they can (or want) to continue to live in the UK.

[W] Damn.

[J] I guess that’s to be expected, though.

[W] OK. You have a gig, a book, and papers, and… music? Tell me you like music.

[J] Of course 🙂 who doesn’t like music?

[W] Exactly why I ask. What should I listen to absolutely in the next 48 hours

[J] How about some Tom Waits?

[W] Great

[J] Depends on your mood and tastes, I guess.

[W] Which album?

[J] Real Gone? At least, I like that album 🙂

[W] Good choice, I like Alice. And which Danish artist do you think the world would need to know more.

[J] Malk de Koijn (Danish rap group).

[W] Video?

[J] Their lyrics are hilarious (although, unfortunately in Danish).

[W] Tack så mycket, Jens

[J] You’re welcome 🙂

Posted in Uncategorized | 9 Comments

Science and Technology Studies podcast – part 2

There’s a post I’ve been thinking of writing, but I thought I might first comment on something else. I wrote a post about a Science and Technology Studies podcast that I’d listened to. This is a topic I find interesting, but my post wasn’t wildly complimentary. Essentially, I felt that their message was a little simplistic, a bit one-sided, and maybe a little arrogant. I do think there is maybe a tendency for scientists to over-simplify the role of science in society, or how science should influence policy making. Similarly, though, I think that some critiques of science, or of scientists, can also misunderstand aspects of the science, the scientific process, and how scientists perceive their role in society, and policy making.

However, I’ve just started listening to the third episode of their podcast, and they started with a brief discussion of their first public critique. Maybe it’s not mine, but since they refer to it as the first, and have linked to it from their website, I think it might be. What was interesting was how they interpreted it. It was apparently framed as them not knowing much about science, as challenging science in unacceptable ways, that they were anti-science, and that it was suggesting that unless someone was a scientist, they don’t have anything interesting to say about science. It seemed to remind them of the science wars.

Of course, maybe this doesn’t refer to my critique, but if it does, it certainly wasn’t what I was going for. I was certainly not trying to suggest that they know nothing about science, that they shouldn’t challenge it, that they’re anti-science, or that they don’t have anything interesting to say. If that is how it seemed, I apologise. I had thought that I had highlighted a few things that I found interesting, and had highlighted how I thought dialogue between physical scientists and social scientists was important, but maybe I didn’t get that across very well. The reason I write about this topic is because I find it interesting and important, not because I’m trying to shut anyone down. If I thought that science and technology studies researchers have nothing interesting to say, I don’t think I’d have listened to the podcast in the first place.

One thing that I found somewhat disappointing about this is the sense that academics who see themselves as in a position to critique another discipline don’t seem to engage all that well with criticism themselves. My perspective, which maybe others disagree with, is that we’re all essentially the same; there isn’t some hierarchy that allows one discipline to have a special position where they get to criticise another discipline, but not face any criticism themself. In a sense, I think we’re all researchers and we should be willing to defend our research when suitably challenged. Of course, I don’t think that people have to defend their ideas against unreasonable challenges, so maybe mine was seen as unreasonable (it was, apparently, sociologically interesting).

It’s of course possible that I misunderstand the role of science in society so badly that I should really just sit back and listen to science and technology studies (STS) researchers and not expect them to engage with anything I have to say. However, having discussed this issue with other colleagues and with other people who engage in public discussions about science, I don’t think I’m alone in being somewhat taken aback by some of the views expressed by STS researchers.

I’ve also found it very difficult to engage in discussions with STS researcher. That could, of course, by an indication of my inability to engage in a suitable way, but it does sometimes seem as though the expectation is that role of STS is to observe and critique science, but not to actually engage with scientists. As I said in my first post about this, I do think that there are some in the physical sciences who do have an overly simplistic view of the role of science in society and that there is a lot that physical scientists could learn from social scientists. However, I also think the reverse is true; that social scientists could also learn a lot from physical scientists.

It is possible that STS researchers have a perfect understanding of the role of science in society, while physical scientists have no understanding whatsoever. However, it would still seem quite important for STS researchers to try to understand why some physical scientists seem to not engage well with what STS research is suggesting. Okay, I’ve just previewed this post, and it’s become extremely long, so I’ll stop there.

Posted in Philosophy for Bloggers, Science, Scientists, The philosophy of science, The scientific method | Tagged , , , , , | 67 Comments

Cruel Crazy Beautiful World

Given the disappointing news of the last day or so, I thought I would highlight a song that I find suitably reflective.

You’ve got to wash with the crocodile in the river
You’ve got to swim with the sharks in the sea
You’ve got to live with the crooked politician
Trust those things that you can never see
.
.
You’ve got to trust your lover when you go away
Keep on believing tomorrow brings a better day
Sometimes you smile when you’re crying inside
Just once you’ll turn away while the truth be shinin’ bright
.
.
It’s a cruel, crazy, beautiful world
Every day you wake up I hope it’s under a blue sky

Posted in Personal | Tagged , , | 42 Comments

Different perspectives

I’ve been reflecting a little on some of the recent discussions I’ve had, mostly on Twitter, with those who have more expertise in emission scenarios, and energy systems, than in physical climate science specifically. I’ve found it a somewhat frustrating experience, but it seems that there’s also frustration on the other side too, specifically with the use of RCP8.5, which many seem to think is unrealistic.

One simple issue is that I think many climate scientists simply see the representative concentration pathways (RCPs) as bracketing the range of possible concentration pathways that we could follow, without thinking specifically about how we might do so. One reason for the latter is that there isn’t an easy way to determine how we might follow a specific concentration pathway; it will depend on our future energy pathway, how the carbon sinks respond, and on whether or not some carbon cycle feedbacks start to operate.

My impression is that many emission/energy experts think that we should put more focus on considering the impact of following a pathway that is likely, rather than simply considering a small sample of concentration pathways, at least one of which is seen as very unlikely. Climate models are, however, very computationally expensive, and so there is a limit to how many scenarios can be considered. It’s also important to be able to compare different climate models, so using the same basic scenarios can be important for that reason too. It’s also often possible to extrapolate between scenarios to work out how the system might respond if we followed some scenario that hadn’t explicitly been considered by a climate model.

One might think that if the highest concentration pathway isn’t really all that plausible anymore, that there shouldn’t be as much focus on it. There is certainly some merit to this. However, there are also reasons to still consider this scenario. One is that the impact of climate change depends mostly on how much we are likely to warm, which depends on how sensitive the climate is to these radiative perturbations. If you use RCP8.5 with a climate model that has a climate sensitivity near the middle, or lower half, of the range, then this can also represent what might happen if we follow a lower concentration pathway, but climate sensitivity turns out to be higher.

This is essentially my perspective; until someone can rule out the higher levels of warming (by considering both the plausible range of concentrations pathways and the range of climate sensitivity) then I think it is still important to understand the impact of these higher levels of warming.

I also think that this whole basic debate ignores something that I happen to think is key. We’re moving the Earth’s climate into a regime that we have probably never experienced before. We have some idea of what might happen, but we can’t really know for sure. Maybe we’ll be very lucky and find that it evolves smoothly and in ways that we can manage. Maybe, however, we’ll discover that some natural processes have been masking some of the forced warming, and that we have more warming in the pipeline than we expected, or that we’ve crossed some tipping points that lead to substantial, irreversible, changes on a short timescale.

Clearly we can’t avoid some future warming, since we can’t simply stop using fossil fuels overnight. However, rather than arguing about whether or not climate scientists are using the optimal concentration pathways in their models, maybe we should just recognise that we might not want to face too much more future warming and should spend our time finding ways to limit our future emissions. That’s just my view, of course. Other people probably have a different perspective.

Posted in Climate change, Climate sensitivity, ClimateBall, Philosophy for Bloggers, Policy, Scientists, The philosophy of science | Tagged , , , , , | 147 Comments

Stocks and Flows

Sitting at home waiting for a delivery, so just a quick post. There’s been a new narrative, on social media at least, that we may be heading for a plateau in global emissions. The suggestion, then, is that we are on track to follow one of the lower representative concentration pathways (RCP4.5, for example). This would be a good step, if true, but it seems to be based on a single assessment that suggests that emissions in 2040 will be similar to those today. Not only do there appear to be other assessments that disagree, what some seem to be concluding from this appears to confuse stocks and flows.

What will ultimately determine how much we warm will be how much we emit in total. Emissions in a single year might give a clue as to what this would be, but it’s really going to depend on emissions across the whole time period. In particular, for the mid-range RCPs (RCP4.5 and RCP6) most of the emission reductions happen after 2040. So, emissions in 2040 may be a poor guide to how much we are likely to emit in total.

It would, of course, be great if we are starting to see emissions plateauing and, eventually, starting to drop. One concern I have with the current narrative is the suggestion that somehow it is happening without us really having done very much. It’s possible, I guess, but it would seem rather unfortunate if we start to think that we’ve almost solved this problem and then discover that emissions have continued rising. Maybe a better narrative would be one where we highlight how we might be heading for a plateau in emissions and then suggest that we aim for a fall, rather than simply a plateau.

Posted in advocacy, Carbon tax, Climate change, Global warming, Policy | Tagged , , , , , | 120 Comments

Tipping points/elements

There has been quite lot of discussion recently about climate tipping points, or tipping elements. It’s mostly motivated by a recent Nature comment suggesting that Climate tipping points [are] too risky to bet against. The suggestion is that some the tipping points (West Antarctic Ice Sheet, Greenland Ice Sheet) may triggered sooner than we have anticipated. Hence, we should take this seriously and that international climate action should reflect this. One particular issue would be if there were a cascade of tipping points that, when combined, lead to some new climate state.

However, there do seem to be some who don’t entirely accept this argument, and I can see why. A lot of what is suggested about tipping points is quite speculative; it’s very difficult to quantify the actual likelihood of them being triggered. Also some (like ice sheet retreat) might still be quite slow and may not even be truly irreversible. Hence, I understand why there is some reluctance to make this a major aspect of the narrative.

However, I am starting to think that there is a problem with how we typically discuss this topic; we tend to focus more on what we think will probably happen and not enough on what might happen. Even though what will probably happen could be pretty severe, the low-probability, high-impact outcomes carry the greatest risk. So, I do think we should be talking more about the potential worst-case scenarios, but I’m not entirely sure of how best to do so.

One problem is that the outcome is conditional on what we do in future, and there are a large number of uncertainties associated with that future – what do we do in terms of future emissions, how will our emissions be taken up by the carbon sinks, how will the climate respond to the resulting atmospheric concentration, what will be the impact of this climate response, and how will we then respond to these impacts? In some sense, it’s a continually moving target.

If we fail to limit our emissions, then it becomes more likely that some of the more serious outcomes will materialise. If we start to limit our emissions, then they become less likely. If we have to consider what future pathway we might follow, what will probably happen if we follow that pathway, and also what could happen if we’re unlucky, it all gets rather convoluted. Also, if we do start to limit our emissions, do we stop talking about some of the worst case scenarios that would now be less likely than they had been before, or do we continue to highlight them in case we then start to take emission reductions less seriously?

Also, some of the tipping points/elements are so uncertain that we may have already almost triggered them, or it could still take a fairly substantial amount of additional warming. How should this influence our thinking? Clearly, if we want to avoid them we should aim to limit our emissions, but if we’re not really sure when they’d be triggered, how do we balance this with all the other factors that should influence how we go about reducing our emissions?

As you can probably tell, even though I think it is important to highlight some of the more extreme, worst-case outcomes, I’m still not sure how to do this in a way that accounts for all of the uncertainties, without it becoming so convoluted that it’s difficult to explain clearly. Similarly, how do you avoid simplifying it to the point where it is open to valid criticisms? Maybe other people have some ideas of how to do this. If so, I’d be interested to hear them.

Posted in Climate change, Global warming, Philosophy for Bloggers, Policy, Severe Events | Tagged , , , , , , | 249 Comments

Methane

I’ve always been a little confused as to why so much attention is paid to methane emissions. It’s short-lived, so isn’t it maybe somewhat less important that CO2 emissions, which are long-lived? One reason it is quite prominent is because it is regarded as having a large global warming potential; one tonne of methane is regarded as having about 28 times the impact of one tonne of CO2. The global warming potential (GWP) is defined as the time-intergrated climate forcing due to a one-off pulse of methane when compared to a one-off pulse of CO2 of the same mass.

Credit: Allen et al. (2016)

However, as this paper by Myles Allen, and colleagues, highlights, the actual impact of a pulse of methane is very different to that of a long-lived greenhouse gas like CO2. The figure on the right shows warming due to equivalent pulses of short-lived, and long-lived greenhouse gases. A pulse of a long-lived greenhouse gas like CO2 will lead to sustained warming that will persist for a long time. An equivalent pulse of a short-lived greenhouse gas, like methane, will have a large impact initially and then decay away. After a few decades, the impact will be largely negligible.

Sustained emission of short-lived greenhouse gases (solid lines) compared to a single pulse of CO2, a long-lived greenhouse gas [Credit: Allen et al. (2016)]

Hence, simply comparing the global warming potentials of short- and long-lived greenhouse gases can be somewhat misleading. However, a sustained emission of a short-lived greenhouse gas can be equivalent to a single pulse of a long-lived greenhouse gas. The figure on the left shows the sustained emission of short-lived greenhouse gases compared a single pulse of long-lived greenhouse gases, with the total emission of the short-lived greenhouse gases over a century being equivalent to the single pulse of the long-lived greenhouse gas.

All of this implies that one should be careful when comparing short-lived and long-lived greenhouse gases. When considering long-lived greenhouse gases, stabilising temperatures requires getting emissions to zero. When considering short-lived greenhouse gases, it requires getting emissions to stabilise. Constant emission of a long-lived greenhouse gas is equivalent to increasing emissions of a short-lived greenhouse gas. Finally, reducing emissions of a long-lived greenhouse gas leads to continued warming until emissions get to zero, while reducing emissions of a short-lived greenhouse gas can lead to cooling. Also, if emissions of short-lived greenhouse gases are reduced to zero, their overall warming impact will eventually become negligible.

As a consequence of this, there are a couple of papers that have suggested a modification to the global warming potential metric, called GWP*. It still uses the original GWP metric, but depends on how the emission rate of the short-lived GHGs changes (essentially because one can relate a single pulse of a long-lived greenhouse gas to an increase in the emission rate of a short-lived greenhouse gas). This allows one to more properly compare changes in the emission of short-lived and long-lived greenhouse gases.

The reason this is important is because if we simply use the original GWP metric, we could end up committing a lot effort to reducing emissions of a short-lived greenhouse gas (that only has a warming impact for decades) at the expense of emission reductions of a long-lived greenhouse gas, that can have a warming impact that lasts for centuries, or longer. Similarly, the original GWP metric would suggest that reducing the emissions of short-lived greenhouse gases should still lead to warming, as it does for long-lived greenhouse gases. This, however, is wrong. Reducing the emissions of short-lived greenhouse gases should lead to cooling. Hence, we could end up over-estimating what we need to do to achieve some target.

On the other hand, because short-lived greenhouse gases have a large impact on decadal timescales, they are still important if we are to achieve some of our near-term targets. So, they certainly can’t be ignored. There are also other factors associated with them that are also important (for example, land use change and excess water use associated with livestock farming).

There are also some potential issues with the new global warming potential metric, as pointed out in this paper. Under the new metric, a region with a high, but constant, level of methane emission, could argue that they’re no longer contributing to global warming and, hence, don’t need to do anything. However, reducing their methane emissions could still account for some of the impacts that they’ve already had, and would clearly make it easier to achieve some of our targets.

It’s clear that this isn’t a simple issue, but it does seem that there is still some confusion about how short-lived greenhouse gases, like methane, compare to long-lived greenhouse gases, like CO2. I hope this post clarifies some of the issues. I hope I have indeed explained things properly. Feel free to correct me if I have got something wrong. I’ve also provided links, below, to the papers I’ve mentioned, plus links to a couple of other articles about this topic, including a very nice Carbon Brief guest post by Michelle Cain (one of the authors of the papers I mentioned). If you want to learn more, I can also recommend this podcast with Michelle Cain.

Links:
New use of global warming potentials to compare cumulative and short-lived climate pollutants – Allen et al., Nature Climate Change, 2016.
A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation – Allen et al., NPJ climate and atmospheric science, 2018.
Improved calculation of warming-equivalent emissions for short-lived climate pollutants – Cain et al., NPJ climate and atmospheric science, 2018.
Unintentional unfairness when applying new greenhouse gas emissions metrics at country level – paper by Joeri Rogelj about an unintentional issue with the new GWP* metric.
Guest post: A new way to assess ‘global warming potential’ of short-lived pollutants – Carbon Brief guest post by Michelle Cain.
Why we’re still so incredibly confused about methane’s role in global warming – Chris Mooney article about this topic.

Posted in Environmental change, Global warming, Policy, Research, Scientists | Tagged , , , , , | 241 Comments