One of the first things I encountered, when I started to learn about anthropogenic global warming, was the charge that humanity was conducting a giant experiment with the planet, and since we only had the one planet, the experiment should stop. There are different versions of this defence of the position that ‘we must combat climate change by curbing greenhouse gas emissions’, and by and large I now take little notice of them.
But I came across one recently that I thought was worth summarising and wrestling with. It was by Steven Mosher, whom I’ve mentioned here as the joint author, with Thomas W. Fuller of an excellent book, Climategate. The Crutape letters. Mosher is a quirky guy, often commenting in terse and sometimes almost incomprehensible fashion about what he sees as errors in other people’s comments. He can receive a taste of his own medicine, too, as was the case here. I always read what he writes, and on the present occasion I thought what he wrote was important, even though I disagree with his position.
It wasn’t about anything substantive, but what he called the structure of the arguments. There is a single temperature time series, he says. It’s all we have — the temperature of thousands of places at thousands of times, over quite a short period. We have earlier proxies for temperatures too, but for a smaller range of places and over a much longer period of time. All of them come with errors of various kinds.
Mosher sets up what he sees as the central sceptical attack on the orthodoxy. In a lab setting we could run an experiment and control and vary these causes and develop a working theory of how things work. But we can’t — there is no lab, and we don’t have a ‘control planet’ to use as a test-bed. Climate science is not a lab science where you run controlled experiments. And some critics (sceptics) point out that the time series is the result of a chaotic system which we cannot understand. So while there are causes for the time series, its trajectory is chaotic and not predictable. Climate science, then, is not ‘real’ or laboratory-based science, where hypotheses are tested experimentally, by observation and measurement. Critics then say we should dismiss the work, because it doesn’t satisfy the ideal of experimental science.
Mosher sees these two objections as misunderstanding the world that climate science lives in, so to speak. As he sees it, sceptics can attack the data, or attack the theory, because the data don’t quite, or effectively, support it, or point out that the theory is incomplete. The criticisms sound persuasive, but Mosher thinks they miss the point. I’ve written this somewhere else: the data are what we’ve got. We need to make the best use we can of them.
How would he do this? Since I cannot control the variables in the real world, the second option is to create a synthetic world where I can: modelling or simulation. In simulation we move from the theory to the observation. In simulation we can flip CO2 on and off and hold volcanos constant. we can hold everything constant and only change the sun. And with simulation we can make predictions or test our hypothesis… simulation makes an observational science more like a lab science.
To which the critics can respond, as follows:
1. These really are not experiments.
2. You can’t model nature perfectly.
3. Your answer isn’t perfect.
4. Even if your answer is perfect, your explanation is still underdetermined; something else could have caused it.
And he goes on: It doesn’t matter what physical system you are simulating — folks will have the same objections. To those outside observational science these objections will always look reasonable. They can appear to be made in good faith. Until you point out that they rely on observational science all the time.
I hope that I have done his argument justice. There is always a risk of my not doing so when I cut, paste and summarise. I think Mosher has made a sensible defence of the position that the data are what we have and that models are the only way we can investigate their meaning and importance. Let me step aside from the climate domain, and consider the Australian economy. It can be argued that governments and the Reserve Bank are conducting experiments with the Australian economy. Governments and central banks have levers, and they manipulate them in the hope of achieving certain outcomes.
But they don’t have an AustraliaB as a control, nor can they really use any other country as a control, for none of them is close to the Australian reality. So they use models. There are a number of models of the Australian economy, owned by Treasury, the RBA and others, and I can remember considering whether or not to recommend funding for an early university version of one in the 1980s. To the best of my knowledge, neither the Treasury nor the Australian Government ever relies wholly on any model output in making recommendations or decisions. Why not? There’s too much at stake.
It is different in the world of climate. To begin, AGW became important not just because scientists said it was, but because there was a mood in the electorate receptive to that message. I wrote about this factor recently. The combination of the early ‘warmists’, like James Hansen and others, and the anxiety in the electorate has proved decisive in the Western economically developed societies.
In consequence, the real debate about ‘climate change’ is not about the science, it is about policy. No one I know in the sceptical and agnostic worlds disputes that the earth has warmed a bit over the past century or so. Nor does anyone argue that adding CO2 to the atmosphere has helped in that warming, and will do so again in the future while we continue to burn fossil fuels. They do argue about whether or not the warming is beneficial to life generally, and they do argue about whether or not the warming could become dangerous.
And this is where the models come in. Because the notion that warming could be dangerous is not based on science, but on assumptions that are plausible, and on their being incorporated into models that produced ‘projections’ about the future. So far the serious tests to which the climate models have been subjected to — the pattern of warming over the last ten years — has shown them to be deficient. Maybe they’ll improve, maybe not.
Now to policy. With the science in this state, how could one support carbon taxes, subsidies on renewable energy sources that require fossil fuel backup, and the great agitation about getting a worldwide agreement in paris at the end of the year? The answer is straightforward: that is about policy and politics, not about science. Mosher is right, I think, but his defence is a defence of a very limited kind — about whether or not the temperature data are any good. I think that the discussion has gone a long way past that.