Angus Ferraro

A tiny soapbox for a climate researcher.


How do we decide whether geoengineering is worth it?

Citation: A J Ferraro, A J Charlton-Perez, E J Highwood (2014) PLOS ONE, doi:10.1371/journal.pone.0088849

Some have proposed we take a different approach to climate change and attempt to stop global warming by reflecting sunlight. We have a new paper out today which asks the question: how do we decide whether such geoengineering would be effective?

Maps of climate model simulations using the risk matrix. The simulation uses stratospheric aerosols to balance the surface warming from a quadrupling of carbon dioxide.

Maps of effectiveness of geoengineering using a risk approach. The simulation uses stratospheric aerosols to balance the surface warming from a quadrupling of carbon dioxide.

Does geoengineering have the potential to reduce climate risk?

One way to exert a cooling influence on the climate would be to pump tiny particles up into the stratosphere, where they would reflect a small amount of the Sun’s energy. Should we consider intentionally modifying our environment in this way in order to affect the climate? Some argue there is a chance of unintended side effects, and that such meddling is too risky. Others argue the opposite: that it is too risky to allow global warming to continue.

What are these risks? A basic way to think about it is that people are adapted to our present climate. They are used to a particular mix of warm and cold, wet and dry. As climate changes, this mix will also change, posing a risk to those not prepared for it. For example, a warmer climate might be seen as a risk for healthcare systems not equipped to deal with medical problems associated with heat waves. A wetter climate might increase the risk of flooding. Risks like this could be costly – which is essentially why climate change could pose a problem.

Could geoengineering be used to help? Geoengineering with stratospheric aerosols might pose risks of its own: reduced rainfall, depletion of the ozone layer. It might also produce benefits: reduced warming and enhanced agricultural productivity. We need a way to compare the risks and benefits of geoengineering with the risks and benefits of not geoengineering (here, we are assuming we don’t do a good job of reducing greenhouse gas emissions).

How do we weigh up different kinds of risk?

Consider this: you are diagnosed with a medical condition which may deteriorate in future and cause you difficulty. You are given the option of a treatment which might stop the symptoms of the disease but may also have other side-effects. Do you take the treatment? You have to weigh up the risks.

A matrix showing the different outcomes of geoengineering. On the horizontal axis is the probability of a big climate change under carbon dioxide. On the vertical axis is the probability of a big change in climate under geoengineering.

A matrix showing the different outcomes of geoengineering. On the horizontal axis is the probability of a big climate change under carbon dioxide. On the vertical axis is the probability of a big change in climate under geoengineering.

In the same way we have to weigh up the risks to decide whether geoengineering is worthwhile. We would want it to reduce climate risk compared to not geoengineering. But there’s another layer of complexity here. Perhaps the reduction in risk happens somewhere that wasn’t actually at high risk of big climate changes in the first place. So perhaps no one cares?

We looked at this by dividing climate risk into four possible outcomes, shown in the diagram on the left. The horizontal axis shows the chance of getting a substantial climate change in the first place from carbon dioxide. The vertical axis shows the chance of getting a substantial change from geoengineering. So, if geoengineering reduces climate risk but there wasn’t much risk to start with (low change of substantial climate change on the horizontal axis). we classify geoengineering as ‘benign’ (it hasn’t really done much). If geoengineering reduces risk where carbon dioxide increases risk we classify geoengineering as ‘effective’. But what if geoengineering increases risk? We classify it as ‘ineffective’ if geoengineering introduces climate risk in a similar manner to carbon dioxide. Finally, if geoengineering introduces climate risk into areas which were not previously at risk from carbon dioxide-driven climate change, we classify geoengineering as ‘damaging’.

This way of looking at things can be used to classify climate changes. The maps in this post give an example: temperature and precipitation from a climate model. The ‘global warming’ case involves a climate with levels of carbon dioxide four times what we have now, and a climate about 4 degrees C warmer. The ‘geoengineering’ case uses stratospheric aerosols to counterbalance this warming. So as expected, if you look at temperature, geoengineering is largely effective. But rainfall looks rather different. Geoengineering is not effective in quite large parts of the globe.


We have made some subjective choices here, and different choices would give quite different results as to the effectiveness of geoengineering. To further complicate things, I would expect different climate models to paint quite different pictures of regional changes.

Geoengineering isn’t necessarily good or bad. It involves a trade-off between risks. These risks are different for different aspects of climate. As these (and many previous) results have shown, it might not be a good idea to use geoengineering to counterbalance all warming, because this would produce large rainfall changes. Approaches like the one described here could be used to find what the optimum level of geoengineering is that would minimise changes in both temperature and rainfall.

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Impact of geoengineering on rainfall could be greater than we thought

Citation: A J Ferraro, E J Highwood, A J Charlton-Perez (2014) Environ. Res. Lett. 9 014001 doi:10.1088/1748-9326/9/1/014001

Aerosol layer (grey stripe in centre) produced by the 1991 eruption of Mt. Pinatubo.

I have a paper out today (with my PhD supervisors Ellie Highwood and Andrew Charlton-Perez) which suggests that the impact of geoengineering on rainfall in the tropics could be greater than we thought.

Geoengineering is a proposed response to climate warming driven by greenhouse gases. Basically, the idea is to mimic the effects of a large volcanic eruption on the Earth’s climate by injecting tiny particles called aerosols into the stratosphere. These particles would reflect a small amount of the energy coming from the Sun, cooling the planet. The basic idea makes sense, and from observing the climate following volcanic eruptions we know it could provide some cooling.

It’s also well understood that using geoengineering to counteract the warming effects of greenhouse gases and bring the surface temperature down would reduce global rainfall to levels lower than those we would get if there was no geoengineering or enhanced greenhouse gas levels. This is because the reduction in solar energy reaching the surface means there is less energy available to evaporate water, so the atmosphere has less water available to fall as rain.

Temperature changes from carbon dioxide and geoengineering

Tropical temperature changes from carbon dioxide and geoengineering

But my research suggests there’s another effect stratospheric aerosols have on rainfall, especially in the Tropics. Here, rain is mainly produced by towering convective clouds which transport heat energy up from the surface to the atmosphere.

Our paper shows that aerosols in the stratosphere emit radiation down into the troposphere below, interfering with this convection. Geoengineering aerosols emit energy (in the form of radiation, as shown in the picture above) downwards into the troposphere, which causes the upper troposphere to warm up. In essence, the heating from the aerosol increases the stability of the tropical troposphere.

We don’t see in the increase in stability when geoengineering is represented by just turning down the Sun (right-hand panel in the picture above) because there isn’t any aerosol in the stratosphere to emit radiation downwards*.

This effect could be quite important depending on how strongly aerosols interact with radiation in the way I just described. In my climate model simulations I used one particular type of sulphate aerosol with specific radiative properties. However, it’s possible that aerosols in the real atmosphere could behave rather differently. This research shows its important to get the aerosol properties right if you want to correctly predict the effects of stratospheric aerosol geoengineering on the climate.

It’s very difficult to know what the properties of geoengineering aerosols in the real atmosphere might be. It’s not clear how much the aerosols would ‘clump’ together, which would increase their size and increase the amount of energy emitted into the troposphere. This is important because the more energy emitted down into the troposphere, the weaker tropical convection (and rainfall) becomes.

Geoengineering isn’t a ‘quick fix’ to the problem of greenhouse-gas-driven climate change. We’ve know that for a long time. This research shows that there are some important side-effects of geoengineering which should be taken into account when thinking about whether or not it’s a viable option. How important these sides effects are depends on the size and properties of the aerosol, which, as I’ve said, we don’t really know. In order to work how what geoengineering does and doesn’t do, we’d have to crack the tricky problem of understanding how the aerosols behave in the atmosphere.

* EDIT: This is important. Solar dimming geoengineering to counterbalance increasing CO2 concentrations decreases rainfall from pre-industrial levels, but globally this is smaller than the increase that would happen from CO2 alone. So in that sense solar dimming geoengineering gets us closer to the pre-industrial ‘baseline’. Including the aerosol effect on tropical rainfall, however, shows that the reduction in rainfall from aerosol geoengineering to counterbalance increasing CO2 concentrations is about the same size as the increase that would happen from CO2 alone. So sulphate aerosol geoengineering to counteract CO2 takes us about as far from the ‘baseline’ as CO2 alone does.

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Paper review: On the misinterpretation of the North Atlantic Oscillation in CMIP5 models

Citation: Davini, P. & Cagnazzo, C. (2013),  On the misinterpretation of the North Atlantic Oscillation in CMIP5 models, Clim. Dyn. doi:10.1007/s00382-013-1970-y.

The North Atlantic Oscillation (NAO) is a big hitter in the world of atmospheric dynamics. It’s everywhere, and it (or its close relations the Arctic Oscillation and Northern Annular Mode) invoked in pretty much every explanation of why midlatitude countries get the weather they do. But what is it?

Positive phase of the NAO (image from Columbia University)

In the simplest terms, the North Atlantic Oscillation is an expression of the location of the jet stream, a band of strong winds which circles the globe at a latitude of about 45 degrees. Weather systems form on the jet stream and are steered along with it. The jet stream wobbles north and south (like most fluids, it forms eddies), and depending on its latitude it might send a storm into the Mediterranean or to the United Kingdom.

The NAO is often used as a neat way to summarise the behaviour of the jet stream. In the real atmosphere it describes a specific pattern of variation in its position, but as this paper (and others) shows, this pattern isn’t exactly the same in climate models.

An aside before we begin. It’s not really correct to say the NAO explains why the jet stream and weather systems are where they are. The NAO must be a certain way if the jet stream is where it is. It’s just a description, like saying, ‘we got a storm because we are at the latitude where the storm was’. The reasons for the way the jet shifts north and south are complex and really not obvious, and we’re learning more about it all the time.

So that’s what the NAO is in general terms. When we analyse atmospheric data we give it a mathematical form. This involves a tricky but really rather clever analysis technical called Empirical Orthogonal Function analysis (or Principal Components analysis). I won’t go into it here but it’s basically a way to pull out a pattern according to which something varies. If you think of the pattern of variation of a swinging pendulum, it’s main variation pattern is a back and forth swing. For the jet stream, the main variation is a north and south wobble – the NAO.

Negative phase of the NAO (image from Columbia University)

The convention is, when the NAO is in a negative phase the jet is shifted southward, and when it is in a positive phase it is shifted northward. Generally, it’s also wavier in its negative phase than its positive phase, and more waviness means more ‘blocking’, which is when we get big meanders, producing high pressure systems which hang around for a week or so and give stable, calm weather.

But some climate models don’t have an NAO that behaves like this. For some of them, the main variability includes too much northward wobbling and not enough southward wobbling. Another group has variability which is more like a pulsing of the speed, going from fast to slow and back again, without any wobbling. For some the north-south wobbling is simply too weak.

This paper shows the weakness of the mathematical definition of the NAO – it’s not the same between different models! The examples above represent different physical processes so it’s meaningless to lump them together like this. But, importantly, all the models do have something like the real-world NAO – that is, the north-south wobbling. It’s just that the standard mathematical definition doesn’t always pick that out. This is the peril of using a mathematical construction with no physical basis to define variations in the jet latitude which are the result of specific physical processes.

Obviously it’s better to think of things, if we can, in terms of the physical processes involved rather than this rather obscure mathematical idea. Davini and Cagnazzo end their paper with this recommendation:

…since climate models represent a slightly different world with respect to the real one, special caution must be applied…when the NAO is studied. We conclude suggesting that instead of using the NAO to study the North Atlantic variability it would be better to adopt diagnostics based on jet stream position and strength

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Don’t be Such a Scientist by Randy Olson

Near the start of my PhD I began hearing a lot of buzz around a book by a guy called Randy Olson called Don’t Be Such a Scientist. First off, what a great title! It grabbed me immediately. I find myself saying that exact phrase in my head (sometimes to others, and sometimes to myself!). Time to investigate, then.

Second thing – this guy, who I had never heard of before, has had a pretty unique career. Starting off in academia and gaining a professorship in marine biology, he gradually transferred to Hollywood where he threw himself way out of his comfort zone, took acting classes and ended up making some rather successful films. Surprisingly, I hadn’t actually heard of any of them before reading this book, but now I’ll be sure to check them out.

Somehow the book sat on my ‘to read’ list for a long time. Finally, now I’m wrapping up my PhD work and my brain is a little less frazzled, I’m doing some more reading for pleasure. So I picked up a copy of Don’t Be Such a Scientist from my university library.

What’s it all about?

It’s not immediately obvious what it’s about, actually. Its subtitle, ‘talking substance in an age of style’, drops some clues, but for reasons I’ll come on to I think it’s rather misleading. The back of my edition lacks a blurb – it has a short author biography and some rave-review quotations from various eminent people.

I see the book as a dose of perspective for those who have been closeted in their own intellectual community for so long they believe that’s all there is. It argues that, for scientists to successfully communicate with other intellectual communities, they must learn to speak their languages, and, in short, not be such scientists.

He expresses his position particularly vividly in relation to scientists’ default mode of suspicion and criticism:

You meet scientists who have lost control of this negating approach and seem to sit and stew in their overly critical, festering juices of negativity, which can reduce down to a thick, gooey paste of cynicism.

As you can see, Olson also makes an effort to be provocative, because that sets up tension, and maintains interest, and that’s a crucial part of good communications.

Tensions, tensions everywhere

Talking of tensions, the book repeatedly bumps into the tension between substance and style. Olson argues it’s very difficult to have both. An engaging film generally has to be lighter on information. For this reason, film is more of an engagement tool and a motivational medium than one that’s directly educational. Real learning requires repetition, detail and focus, none of which are particularly entertaining. Scientists generally find it difficult to reduce information content. I have lost count of the number of times I have heard scientists say that they are struggling to condense a talk down to the required time, or to keep a publication below a page limit. A key lesson from the book, then, is to think carefully about what the audience really needs to know, and impose some self-discipline.

This is why I find the subtitle of the book misleading. It claims to be about substance, but really it’s all about the style. I found it never really touched on ways to craft writing or film in such a way to keep maximise actual useful information while retaining the audience.

Making headway in the attention economy

I had one other major problem with the book. If I were to take up all its suggestions it would feel to me a little like admitting defeat. Olson talks about how style of communication completely defines our age because humans are so overloaded with stimuli. There are so many media sources clamouring for attention. He describes an ‘attention economy’ which works on these terms. In the attention economy we must scrabble to glean a few moments of attention and we can’t waste that by imparting information. We can only afford to give off a general impression and hope it sticks.

It left me wondering: when Olson talks about science communication, what is he communicating? His goal is to catch the person’s attention for a moment and implant a seed in their brain that makes them want to know more. That’s the initial ‘hump’ to get over with communication – arousing interest.

This is excellent practical advice, but it made me a little sad. Personally I think the ‘attention economy’ is troubling. I feel like some communications barely communicate anything at all and are just stimuli devoid of meaning. I feel like the search for attention amidst fading attention spans favours a simplistic approach which doesn’t reflect the nuances of the real world. We see this every time a politician says…well…anything. I do my best not to fall into the trap of the attention economy, but feel it every day. Often at work I find it difficult to concentrate because the Internet is luring me in: Twitter, Facebook, superficial arguments on online fora, YouTube videos, banal rolling news…for me, it’s a bad thing which encourages lazy thinking. In that sense, I think non-scientists would benefit from a little scientific thinking. Or at least some scepticism when it comes to the claims of those in powerful positions in our society. But making the public think like scientists is a harder task than making scientists think like the public.

It’s not a manual, it’s a demonstration

In the end, that’s what the book is about. It makes a case for scientists learning how other people think. It does so in a light way focusing on a simple message delivered in an engaging style. One might be able to make the case by reviewing the sociological literature on sub-cultures with different psychologies and linguistics, and impeded communications between isolated intellectual communities. Olson does it rather more succinctly with wit, storytelling and occasional overgeneralisation.

I don’t know anything about communications strategy and I’m sure there are all sorts opaque, technical ways to learn about it. Olson sees this and uses this book as a real-life example of communicating technical ideas in an engaging and motivational way. Writing this blog post has helped me understand this. In short, I didn’t realise how much I was learning.

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My thesis: friend or foe?

Bound and ready to submit!

Bound and ready to submit!

Last Monday I submitted my PhD thesis. I walked over to the Examinations Office in the centre of campus, up a few flights of stairs, handed a big old pile of paper over to the secretary there, signed a form, and that was it. I started my PhD in October 2010, and according to my notebook I wrote the first few tentative words of my thesis in June 2012.

I have heard others tell tales of the looming monstrosity their thesis became in their life, constantly bearing down on them. The folk wisdom of the PhD student is that your thesis is your enemy, and that every day you have to do battle with it, to subjugate it and wrestle it into some kind of coherent shape. To be honest, it never felt that way to me. I followed the standard routine chapter by chapter: outline, concept map, make figures, write text, proofread and edit, send to supervisors, revise. When I started blogging I had planned to use it to describe the process of writing a thesis as it happened: a ‘stop-motion’ thesis, as I called it then. It turns out that the process is a largely uneventful one, churning through the routine described above.

Occasionally this process broke down. There were times when I felt mentally and physically sluggish, so I took a short break – an afternoon off, perhaps – to refocus. It helped that I was still doing little bits of analysis quite late into my PhD. I had done enough to be content, but had a few extra things that were worth doing since I had some spare time. These tasks were pleasant distractions and allowed me to keep my mind active without stressing it out with major pieces of work with real and imminent deadlines. My thesis was never my friend, but it wasn’t my enemy either.

So, for me at least, writing a thesis hasn’t been an epic climactic undertaking. It’s been built up bit by bit, and I’ve worked without putting myself under crippling pressure. I think the academic environment here at the Department of Meteorology really helped: my supervisors provided encouragement, advice and calming words when they were needed, while the rich programme of seminars and group meetings reminded me that I was also there to learn, not just to write a big book and plonk it on someone’s desk.

As I walked back to my office after submitting my thesis I did feel noticeably ‘lighter’. Although it hadn’t been a stressful experience, getting rid of it still felt good. I am now free to do things for their own sake, rather than the artificial goal of a document for examination.

On the subject of examination, I still have my viva (or thesis defence) ahead. In the UK this takes the form of an oral examination by two examiners: the main one from another institution and the other from one’s own (who also takes the role of a moderator). The candidate is quizzed on the details of their thesis in order to check whether it really is their own work and whether they have the depth of knowledge befitting a PhD. It doesn’t sound like a pleasant experience but at the same time I’m looking forward to discussing my work with others. Much like the process of writing is pleasurable if one puts aside the fact it’s for a thesis, I hope the process of discussion my work will be pleasurable if I put aside the fact it determines whether or not I get a PhD!

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A year of throwing stuff into the Internet and seeing what bounces back

It’s just over a year since I published my very first blog post, and set up my Twitter account.

When I started blogging I was excited by the novelty of it all and posted about once a week. Sometimes my posts were good, sometimes they weren’t. I wasn’t too bothered. Then I started to slow down. Partly this was the novelty wearing off, but partly it was the realisation that people might just read this stuff. Of course, that’s what we hope, but as I learned more about blogging the more I realised that it was possible to say some rather silly which don’t do one’s reputation much good. This is more likely to happen if you have a big readership (which I don’t), but the beauty of the Internet is even obscure content can be shot to prominence through nothing more than a few re-tweets. As a result I’ve become a bit more cautious about what I say.

Sometimes, though, it’s better to post something rough than not post at all. It’s good to get comments on things, and the only way to do that is to post. Sometimes I do throw stuff out there that’s not particularly good. Sometimes it’s little more than some stream-of-thought opinions given the once-over for spelling and grammar. I hope I make it clear when I’m in this mode – perhaps I should put some sort of disclaimer on these posts!

Twitter has been a very positive experience for me. Yes, it can be a time-sink. Yes, it can be inane. But those aren’t problems associated with Twitter itself, but how you use it. It’s my fault I waste so much time on Twitter. I’m getting better at managing it though. And the inanity can be guarded against by careful choice of who you follow. But the overall conclusions is that there are people (and things) I know now that I wouldn’t have known had I not been on Twitter. Interactions on Twitter can be incredibly useful. I found the EGU 2013 General Assembly to be a revelation. There was this undercurrent of voices on the Internet which enhanced the whole experience for me. I could dip into this current to hear highlights from other sessions, interesting opinions, news I would otherwise have missed, and learn the names of the people doing really awesome science.

I’m going to end with a few of my favourite posts, a couple of my least-favourite (self-criticism is always good) and some goals for the future.


  1. Storms are like cake - this was fun to write. It’s a mixture of quotes from other people are some commentary of my own on the classic analogies used for the difference between weather and climate.
  2. The working day of a PhD student – I took the scientific approach to my work by recording, for one month, what I was doing when I was at work. There was nothing too surprising there, but it was really fun to put together. I suppose the headline conclusion is that you don’t need to be working much more than 9 to 5 to get a PhD!
  3. Tuning the climate of a global model – my first post, so it’s a little significant. I thought it would be a good idea to write occasional layman’s summaries of important or interesting papers. I should do more of this type of post!


I’m only doing one here – I don’t want to whip myself up into some kind of frenzy of self-hate. In ‘Clandestine geoengineering is real’ I tried to pretend I was a proper science news commentator. I don’t think it worked. I mainly have an issue with the title, which is a bit too sensationalistic about an issue which requires more subtlety.

Oh go on then, I’ll have another. Climate policy is a question of values as much as it is a question of science was basically a ‘what I think about…’ post. I gave it quite a bit of thought and stand by most of the stuff I said, but now I cringe a little when I think about this post. I think it’s because I’m conscious of the fact anyone can (and does) spout their opinions on the Internet. I want to offer something a bit more thoughtful and useful than the standard stream-of-consciousness stuff, but I don’t always succeed.

Future plans

  1. Paper reviews. They’re useful for me to write and might be useful for others. A no-brainer really!
  2. Stuff about academic life. This was supposed to be a big theme of this blog but I have trouble writing a post about it that isn’t completely banal. Perhaps that tells you all you need to know.
  3. Original science. I want to share some interesting results using this blog. A few things have discouraged me from doing this so far: concern about whether the work is good enough if it’s a casual note, and issues with subsequently publishing the work in a paper if it’s a major piece of science.

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Climate policy is a question of values as much as it is a question of science

There has been a lot of discussion recently about how climate scientists should engage with climate policy, sparked mostly by Tamsin Edwards’ post on the Guardian’s Political Science blog. I didn’t intend on jumping in because I’m not sure I have much new to add, but perhaps I should put it on the record anyway.

Stick to what you know

I would encourage scientists to speak out on what they know (i.e. science). The claims of climate ‘sceptics’ who deny basic greenhouse theory are easy to refute, and we should be doing that. In fact, by and large we are doing that.

But it’s really not clear to me why a climate scientist should use their position of authority to argue for specific policies. Policy is a democratic process. Scientists shouldn’t abuse their position to give their values the loudest voice. Those on the left who call for them to do so might not always like what they hear. What if a climate scientist proposes using natural gas from fracking as a bridge fuel? What if they come out in support of market-driven responses to climate change, like a cap and trade system? These are views they are entitled to have, of course, but they are outside their area of expertise. They are views partly based on values.

The question of what should be done about climate change is a policy question and should be debated as such. Of course, ‘what should be done’ is influenced by what we think we know about future climate, but that is by no means the only influence. The response to climate change encompasses so many other factors, each as important as the physics of the climate system: engineering and technology, spending and taxation choices, international diplomacy, and democratic representation of values and priorities of the population.

A question of values

The fact is, it is not obvious what to do about climate change. Assuming we have a finite pot of money to spend on a range of policies, it’s not obvious that climate change is top of the list. What about improving energy access to the billions without it? Even if we assume climate change is top of the list, how do we go about reducing our emissions? Taxation, perhaps? How should that tax be designed? How progressive should that tax be? What kind of ‘energy mix’ should that taxation system be striving towards?

These are all important questions which have little to do with climate science, and everything to do with value judgements. In an ideal world we decide on a policy through a mix of democratic discussion (including everyone) and expert input (recognising that some people know more about policy options than others). Most climate scientists cannot claim to be policy experts. As citizens it is their right to engage in the discussion about what should be done, but it’s irresponsible to place themselves as experts when they’re not. It helps no-one.

A crystal-clear separation of science and policy would prevent them from hiding behind ‘but the science isn’t settled’ and force dissenters to articulate why they actually object.

Some object because they perceive calls for climate action as a critique of their wasteful, consumption-based way of life, and they simply can’t handle that critique. Some object because they see climate policy as something which can only be driven by the State, which they mistrust. There may be a way to deal with these objections and move forward with good climate policy, but only once we remove the scientific veil and address why they really object.

What kind of world do you want?

For advocacy groups, the science is somewhat irrelevant. They know what kind of world they want to live in already. The Taxpayers’ Alliance knows what kind of world it wants to live in. Greenpeace know what kind of world it wants to live in. Neither of their conceptions of the world is determined by climate science. They will inevitably use scientific conclusions to back up their pre-conceived notions of how the world should be.

For example, an overzealous left might institute climate policy which is inconsistent with the science. Perhaps they assume climate change is reversible (on near-term timescales it just isn’t). Perhaps they waste public money compensating people for extreme weather events despite plenty of scientific uncertainty about the link between climate change and weather extremes. I don’t know what they might do, but it’s important that everyone gets the correct scientific information, because otherwise everyone will just twist what little science they know to fit with how they want the world to be. If scientific errors are highlighted, it is up to the policymaker to justify their choices in other ways. The left could justify by talking about their particular values, but once again, that’s not to do with science.

Policy options are as much a matter of values as ‘good’ and ‘bad’. Scientists aren’t policy experts, and shouldn’t pretend to be. If they pretend, they enable dissenters to set up a strawman and dismiss both the particular policy they are pushing and the generality of the science. If scientists (in their professional capacities) stick to describing the consequences of certain policies their credibility as honest brokers is strengthened. Policymakers can then make policy choices based on credible facts and the values and preferences of the citizenry. Climate scientists are free to hold and express policy views, but in my opinion they should be very careful about doing so when they are speaking in a professional capacity.


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