Earth System Modelling Group

... at UEA Norwich

Post from Erice

I write this from the 38th session of the International Seminars on Planetary Emergencies in Erice, Sicily. For the second time in as many weeks I am presenting the results of a review of tipping points in the Earth system. One of my co-authors, Stefan Rahmstorf, warned me last week that despite their title the Erice seminars have been, in the past, something of a home for climate sceptics. I am duly wary on arrival, but heartened to find that the first day of meetings of the various climate, energy, and development permanent monitoring panels are dominated by people who accept that human-induced climate change is happening and are concentrating on doing something about it. As we enter the Seminar proper, most of the first two days are devoted to ‘Managing climate change’ followed by the intriguingly titled ‘Theoretical alternatives to climate modelling’. Much of the debate also plays out over long lunches and dinners in splendid Italian style.

My presentation is striking enough to get me an invite to ‘high table’ with the organiser, Professor Antonino Zichichi. Stefan has already warned me that Professor Zichichi is a climate sceptic, and it is clear from the sessions that he holds climate models in low regard. His main argument is a theoretical one; that in his own field of nuclear physics a model (of gauge coupling) comprising three weakly-coupled non-linear differential equations, calibrated on experimental data, made spectacularly wrong predictions, until a previously unrecognised mechanism was included. He notes that in simulating climate dynamics we have much larger systems of strongly coupled, non-linear differential equations, with many free parameters, ergo they have greater scope for getting it spectacularly wrong. Efforts to cite data, or use simple thermodynamic arguments, do not impress him, indeed he seems either unaware or innately suspicious of all data presented.

Zichichi is prone to interrupt the sessions and ask (quite reasonably) how a particular data set is measured and gathered. He seems genuinely surprised when I explain over dinner that a global temperature curve can be constructed from thermometer measurements that have been routinely taken in many meteorological stations for centuries. Then we get onto the rise of carbon dioxide in the atmosphere “why do you say it is due to us?” he asks me, I go through how emissions estimates are collated, and start sketching out the global carbon balance on a napkin. I end up drawing out Ralph Keeling’s elegant geometrical approach to using O2/N2 and CO2 measurements to constrain ocean-atmosphere and land-atmosphere CO2 exchange. Zichichi loves it, and leaves with the napkin. It is clear that once someone explains the subject, he is fascinated and, as you would hope and expect, quite willing to accept reasoned scientific argument.

Over lunch a group of us long-time ‘climate converts’ are mulling over quite what it is that makes certain theoretical physicists and applied mathematicians willing to publicly denigrate a subject they apparently know very little about. I begin to build up a picture of three groups; climate data folk on one side, climate modellers (such as myself) who want to ground truth against data in the middle, and over to the right the ‘pure’ theorists (approaching the subject from other areas of physics or from applied maths). Sadly the data folk are essentially missing here, and I begin to wish that one or two of my colleagues from the Climatic Research Unit were here, so that they could inject the data into the discussion with more authority than my efforts.

Instead we seem to have been set up for an argument between ‘conventional’ climate modellers on the one side and the ‘pure’ theorists, some of whom have little regard for the data, on the other. We can all agree that there are weaknesses in climate models, and there seems to be consensus that key non-linearities are missing or poorly represented. But what is remarkable is that some of the pure theorists appear to be arguing that this is grounds for less concern about what might happen in the future. Having catalogued, from an expert elicitation exercise, and extensive review of the literature, the potential for critical thresholds (‘tipping points’) in at least eight components of the Earth system to be passed this century, I am flabbergasted.

Step in Professor Christopher Essex, the chair of the session on ‘theoretical alternatives to climate modelling’. His main point seems to be that the climate system could undergo regime shifts and exhibit trends in the absence of any ‘external’ forcing, such as rising concentrations of greenhouse gases. I’m pretty sure that most climate modellers would agree, but it does not falsify the proposition that the present forcing is triggering a response. I try framing it as a question to Chris; “the Earth currently has an energy imbalance with an excess of 0.85 Wm-2 coming in, would you expect that to heat the system up?” He does not answer “yes” or “no”, instead he responds with; “are you telling me energy is equivalent to heat?” before launching into; “how is the energy imbalance measured?” So much for thermodynamics! I try to get to the crux of the matter with; “do you deny that climate models have any predictive utility?” His response; “I’m not going to bother answering that, I’m a known climate sceptic”. Clearly Chris is a hard man to get a “yes” or “no” answer out of. I guess he would make a good politician. (Lest you think there was an open fighting match, I actually find myself liking the person behind the climate scepticism.)

Richard Garwin comes out with the most amusing paraphrase of the sceptics’ position regarding climate models; “it may work in practice, but it will never work in theory”. However, with the data that is coming in we should now be well past the point of worrying about the beauty of the theory. Change is underway, and in components such as the Greenland ice sheet and the Arctic sea-ice, the rate of change appears to be increasing. My confrontations with the sceptics remind me how difficult it is not to get emotive about this issue. But then again why shouldn’t I be agitated? As best I understand it, it is my generation’s future (and that of all the generations to follow us) that is at stake.

10/09/07 14:54

Comments

© 2009 all rights reserved.