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Debrief from Cheltenham

I’m at home, groggy but happy after our Cheltenham Science Festival event yesterday, “Can we trust climate models?”. It was exhausting, fun, exciting, and long…

I’ll write about the content of the event in future posts, but I wanted to jot down my impressions about its atmosphere, which I think was unique for an event of this kind.

I’d been nervous in the morning and early afternoon. My relaxed day of preparation was steadily eroded by things going slightly wrong, such as realising after my laptop battery ran out that I’d left my charger the other side of Bristol after Bright Club. I had a long list of papers I wanted to skim, notes I wanted to make, an introductory talk to write. Taking the train with my friend and colleague Jonty, I was too stressed to speak and had a sense of humour failure when he gently teased me about leaving my adapter somewhere (again, he said, though I can’t think which other time *cough* times he was thinking of…).

Arriving at the Science Festival site I felt more at ease. It’s like home. In the previous two years I’d come as a punter, had huge fun, loved the events and met extremely wonderful people. This was my first year as an event organiser, and as the time approached I became less nervous, in part because I couldn’t do any more preparation. It helped to take some time out for a gentle, fun radio interview by (the extremely wonderful) Timandra Harkness.

The event itself was an hour long, with introductory talks from the panel – myself, “climate agnostic” Jonathan Jones, professor of physics at the University of Oxford, and Claire Craig, science advisor in the UK government – followed by a few questions from chair Mark Lythgoe and many from the audience. The venue holds 2-300, depending on seating arrangements, and was almost sold out. After the main event we continued at the “Talking Point”, a small tent with informal seating, with around 50-70 of the audience. We took questions for, I think, another hour.

I spent more time battling with the chair than the other panel members! Mark repeatedly accused me of waffling and not answering the question. I told him I didn’t like his questions when they were ill-defined or about policy (I don’t make public statements about preferred policy options). Some of the audience questions were also a little heated, on both sides: those worrying about climate change, and those worrying about climate scientists.

Listening to @flimsin in talking point tent, sending a big virtual hug to her as she keeps getting interrupted mid explanation. #stressful –Amanda Woodman-Hardy (Cabot Institute)

But despite this, the mood of the event was absolutely wonderful throughout. Almost all the “battles” were respectfully teasing, filled with humour. We laughed a lot, which must be a first for a discussion about climate change, scepticism and policy! I put this down to the warm and respectful relationships between the panel members (even though Claire and Jonathan had only just met), to our joyfully provocative chair, and to the audience who quickly created the serious and light atmosphere we hoped for. It was a privilege to have such an interested and supportive audience, such thoughtful, interesting and honest co-members of the panel, and a fun chair who dug into us to make us react and think more deeply about our answers.

At the end of the event, Mark stepped back from his aim of provoking us for theatre and entertainment. He thanked us very sweetly for trying so hard to answer so many questions, and said we were the bravest panel he’d ever seen. And he sent a wonderful tweet afterwards:

Best panel on climate models yet thanks to star cast fab @flimsin articulate @nmrqip wise Claire Craig #cheltscifest brave and entertaining — Mark Lythgoe (chair)

It was an enormous pleasure to put on this event, and I learned a lot. Thank you to the Cabot InstituteBristol Environmental Risk Research Centre (BRISK)ice2sea and my department (School of Geographical Sciences at the University of Bristol) for sponsoring it, thank you to the Centre for Public Engagement for supporting me (including giving me an award! hurrah!), thank you to my panel members and chair for saying yes and working so hard, and thank you to all that came.

  1. Tamsin,

    I attended the event to which you refer, and I was the one who spoke about a model which includes solar cycle lengths as well as CO2 – and on which no panellist responded to my question about non-primary effects of the sun.

    Anyway, herein I merely wish to mention two of your statements which seemed to be slightly in error. The first was to call GCMs “Global Climate Models”; it may seem trivial to point it out but I believe most climate scientists use GCM to mean “General Circulation Model”. The latter require some clever physics to implement, whereas the former could mean anything.

    The second was your statement that HadCRUT4 measures land temperatures, and so oceanic measurements including heat content need to be added in. In fact HadCRUT4 does include sea surface temperatures.

    Anyway, it was an interesting event. I am still amazed that you and Claire read the data of the last 40 years in the way you do, but it’s a free world.


  2. Hi Richard,

    Thanks for getting in touch – I wondered who it was had mentioned their model.

    I didn’t quite catch everything you said, or what question you were asking me, and I could tell you were getting rather technical for the general audience/scope. So I did say, I think, that we could discuss it afterwards. GCM simulations do include variations in solar forcing, so I would need to hear more of what you meant to be able to answer your question or refer you to someone that can.

    I hesitated as I said Global Climate Model – I *think* I said “usually means..” but if not, I was simplifying slightly to be more accessible. However, I don’t usually/always use that definition for public talks, and I take your point that the circulation is (very) important in the definition.

    I definitely did not say land temperatures, I said *atmospheric* temperatures – but I should have said surface temperatures.


  3. Hi Richard,

    I too was wondering who you were!

    To answer your question, I think that solar influences beyond TSI are a very interesting area to look at, and in particular I think that CLOUD experiments are very important. That said while I have read Svensmark and Calder and found it very interesting I did not find it completely convincing. So for me it’s an area to look at in more detail rather than an area where I am ready to conclude anything.

    As I said I think the next ten years will be very interesting, as many of the competing theories are making quite different predictions about where temperatures will go next.

  4. Tamsin & Jonathan,

    Thank you for responding – I’ll reply to both of you here. Jonathan, I agree with your comments on secondary solar effects, and you have certainly understood what my question was. The difference between you and Tamsin there is interesting in itself. It is as if the, how shall I describe them, warmists, or consensual adults, have a fixed script. That is to say, when considering the sun it is “yes the sunspot cycle affects the TSI, and that goes into our radiative forcing models, so we’ve got it covered, and no there can’t possibly be anything else”. In fact, of course, if solar cycles can modulate clouds, the effect may be primary not secondary, in terms of the change to the radiation budget.

    Both of you, it is kind of you to have wondered “who I was”. Yet knowing my name now, tells you little about me I think, as I have no internet presence, so I am somewhat of a nonentity. But you could visit the University of Exeter and find my 1978 thesis I suppose.

    Tamsin, thanks, I did see you hand signal to talk later. Unfortunately, though I did visit the question tent in the hope of talking to you, I couldn’t stay there forever because I had another event to attend.

    Regarding HadCRUT4, I’ll concede your point – I probably misinterpreted what you said. It brings us to another warmist “meme”, though, which is that Trenberth’s missing heat is hiding in the oceans. But you need to be very careful here, you know, as most attempts to explain away the pause in global warming can be thrown back at you with the sharp end leading. In the case of ocean heating, once you open that box, why cannot I say “Ah, well probably most of the warming from 1975-2000 was caused by the oceans _releasing_ stored heat from non-anthropogenic sources.” This is, after all, how El Nino and La Nina are understood to work on short timescales. And there are insufficient measurements over that era, I think, for us to have any clue whether it is correct or not.

    Thanks again,

  5. P.S. Sorry – I must have clicked the wrong “reply” button, so the above comment is not in the proper sequence.

  6. Hi Tamsin,

    I really enjoyed the discussion last week, and have three questions regarding the “flat” region in the temperature data graph: one about the statistics, one about the model and another about the data.

    1. What is the expected probability, derived from the model ensembles, of a “pause” of the current length occurring and how much longer would it have to continue to be inconsistent with them?

    2. Is there any conceivable mechanism that could be included in the models that could lead to the type of stabilisation such as that suggested and, if so, to what reasonable physical phenomenon could this relate?

    3. If the data shown is only for atmospheric or surface temperatures, what does the full data look like?

  7. Hi Tamsin,
    I see you haven’t commented further, and you are probably busy back at work now. I’d just like to leave you with a parting thought, and then sign off.

    You are in a precious stage of your career now, and it is within your grasp to make a bold choice. I can see that you appear to be open-minded and caring for the environment, and in that light my challenge to you is to become the British Judith Curry. Professor Curry, as I expect you are aware, is a respected climate scientist who still does research into whether global warming has made or will make strong hurricanes more prevalent. But she has also put up her hand against the worst excesses of the Hockey Team, is in favour of properly scrutinizing global warming claims, and is now a “luke warmer” who states that some warming has occurred but she is doubtful about the balance of attribution. Above all she aims to pursue scientific principles.

    If you were to do such a thing, and paid a little bit of attention to solar climate research, then suddenly you wouldn’t find yourself being accused of waffling. Because you would then have different and more plausible answers to questions about how our climate is currently changing. You could say “CO2 is continuing to edge up, but the warming we expected from it hasn’t occurred; on the other hand the sun is in its quietest cycle for 200 years (or 100 years depending on which measurements you use), and with a 5 to 10 year lag this abrupt change allows us to see that, for now at least, it is a stronger force than CO2”. This would be hugely empowering to you. In 10 years’ time you might even see it as an epiphany which transformed your career.

    Can you be that person?
    Best regards, Richard.

  8. A further question, not relating to the plateaux this time:

    4. To what extent do future projections of temperature and carbon dioxide levels against time include anthropic feedbacks?

    For example: heating and cooling in buildings and cities account for a large proportion of total energy consumption. Warmer temperatures would lead to a shift from heating loads in Winter to cooling loads in Summer. This in turn would alter emissions, and so on in a feedback loop. While this would not impact on the modelled climate sensitivity, it could potentially alter the expected climate trajectory given by the projections.

    Thanks again for answering these in an open forum rather than over a drink!

  9. Richard,

    I’m a civil engineer in the U.S. who provides services in the area of water resources planning. If, when and how to adapt to climate change is a big concern of many of my clients, who manage water supply systems in the arid American southwest. I read this blog for some insight and, frankly, sometimes for entertainment.

    Some feedback: Maybe I’m dense, but I’m not following your arguments, except that you might be claiming that the Sun did it. Or, maybe your position is that CO2 (etc.) is changing the energy budget of the planet, but the solar cycle is now offsetting that effect (a horrifying prospect since the nature of a cycle is to, well, cycle.) And, what’s wrong or inadequate about including solar cycles in the model forcings? Do you think there is a process that’s missing in these simulations? If so, what is it.

    One more thing: you sound a bit evangelical. That makes _me_ skeptical and it becomes even more important that you explain yourself clearly.

  10. Ben,

    I’ll respond to your comments with # lines below.

    (Ben)I’m a civil engineer in the U.S. who provides services in the area of water resources planning. If, when and how to adapt to climate change is a big concern of many of my clients, who manage water supply systems in the arid American southwest. I read this blog for some insight and, frankly, sometimes for entertainment.

    # That sounds like a difficult job, but someone’s got to do it! I don’t really think that global warming theory is going to provide you much insight, because the GCMs have shown no skill AFAIK in reconstructing local climates. But the American SW is reckoned, as I expect you know, to be influenced by ENSO. So for good water supply you really want a lot of El Ninos, and that correlates with global warming (1975-2005 was weighted to El Nino and was a warming period). But there is a significant risk that we are now in a La Nina dominating period, and that would predict difficulties for your water supply.

    (Ben)Some feedback: Maybe I’m dense, but I’m not following your arguments, except that you might be claiming that the Sun did it. Or, maybe your position is that CO2 (etc.) is changing the energy budget of the planet, but the solar cycle is now offsetting that effect (a horrifying prospect since the nature of a cycle is to, well, cycle.)

    # I haven’t really stated here my position as I did at the science festival. It is: I have a model which combines solar cycle lengths and CO2 to predict global temperature, fitting about as well as more standard radiative models; because Cycle 23 was the longest for nearly 200 years, it predicts a mild cooling of up to 0.2K in the present decade; and it predicts warming of 0.9K (over 1996-2006) by the end of the century. Some physicists believe the sun is heading towards a new Maunder Minimum (which occurred at the depth of the Little Ice Age). Some physicists believe a new Maunder will have scant effect on the climate; I am not one of those.

    (Ben) And, what’s wrong or inadequate about including solar cycles in the model forcings? Do you think there is a process that’s missing in these simulations?

    # Yes, I think there is a process missing on top of the known effect from Total Solar Irradiance.

    (Ben) If so, what is it.

    # That’s the $64000 question. Modulation of albedo by cloud cover is one possibility. I believe we need some pretty high-powered research into this.

    (Ben) One more thing: you sound a bit evangelical. That makes _me_ skeptical and it becomes even more important that you explain yourself clearly.

    # Which bit was “evangelical”? Do you mean the bit down-thread where I exhort Tamsin to be a Judith Curry? Well, fair enough; that was a bit of a one-off, I won’t be doing it again. The main thing I am passionate about is to see all scientific avenues properly explored and evaluated.


  11. Nick,

    I don’t know if this helps regarding your first question, but…

    As I mentioned in an earlier reply, I work in the area of water resources planning, primarily in the American west. I am a civil engineer, _not_ a climate modeler (not even close). As part of an analysis of projected future streamflows in the Colorado River Basin, my colleagues (Andy Wood and Jim Prairie) and I used the CMIP 3 projection ensemble to force a hydrology model. Among other things, we summarized the temperature projections in a paper. Here is a link to charts of the temperature projections:
    (It’s embarrassing that we managed to introduce a production error in the _final_ edits, so you have to see the complete chart in the corrigendum.)

    This figure shows the evolution of trailing 30-year mean temperature over the entire Colorado River Basin for 112 projections, broken down by GCM. The projection period starts in 2000. By 2030 the means are completely free of the constraints of the overlap period (1950-1999) You can see plateaus and even dips in the 30-year mean temperatures after that time, most often but not exclusively in the B1 emission scenario.

    I can’t help but note (being focused on water resources) that model disagreement about future precipitation in the basin is far greater; projections of the sign of change in precipitation are essentially equivocal in this region. The low-frequency, “internal” or “unforced” variability in precipitation is also much more dramatic than is the case for temperature (in this region) and is a significant component of uncertainty at any particular time from about 2020 through 2099. You can see this by looking at the full paper.

    Ben Harding

  12. A wonderful little blog you’re running in your spare time Tasmine. Please do keep up the excellent work.

    A few reactions to some comments posted here lately:

    1) There have been three well studied reasons for the tropospheric flattening of temperatures over the past decade: cool phase of the PDO, increased aerosols from a series of moderate sized volcanoes, and of course the rather sleepy sun. Any one of these could easily knock a few tenths of a degree off of tropospheric temps. It is actually remarkable the troposphere hasn’t cooled even more– but there still is time. Moreover of course, none of these factors is specifically included, except for backtesting for validation in climate models. They highlight the truth of why the models are always wrong. One would, and can through back testing the models, see what would have happened with the triple-whammy of negative forcings over the past decade if CO2 had been at 280ppm. Brrr….

    2) Regarding the ENSO cycle and Snowpack and thus water supplies in the Western US. It’s more complicated of course than just “El Niños mean more water and La Nina’s mean less”. Some studies suggest a very abnormal (by long term historic standards) general warming and drying of the western US which is not part of the ENSO cycle but seems to be related to some other forcing. See:


    Of course anthropogenic climate change is sited as the likely culprit. It could of course be some other unknown natural multi-decadal cycle.

    3) Regarding ocean heat content and the current lack of tropospheric warming, ARGO data make it pretty clear that down to 2000m the oceans have certainly been storing a lot of energy over the past decade. Some of this certainly is related to the cool PDO, but on a basin by basin analysis, we see the Atlantic and Indian are responsible for more of the increase. From a total Earth system energy perspective, when including ocean heat content and the global reduction in net ice, the last decade has showed an acceleration to the energy imbalance and not any sort of flattening, which is only a tropospheric phenomenon.

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