An initial reaction to Garnaut

Professor Garnaut’s Draft Report has been coming in dribs and drabs, and now we have the biggest chunk of it, nearly 550 pages, with a supplementary report still to come.

It is impossible not to feel sorry for him. He himself writes, in a much quoted phrase, that “climate change is a diabolical policy problem”, and the his anxiety comes through again and again. “Why did I take this on?” must have been a constant mental refrain: “this issue might be too hard for rational policy making” (page 2). There is only a “slender chance” that the world can pull this one off. The first five pages provide much evidence of the mental agony of the Draft Report’s author.

He was not helped by the Terms of Reference, which committed him to the IPCC view of things, a view to which Garnaut refers, all too easily, as “the weight of scientific evidence”. The first term asks him to consider “the likely effect of human induced climate change”. Thereafter, human causation is simply assumed: the subject is simply “climate change”. Professor Garnaut follows the same path. “Climate change” is what he is about, and humans have caused it. His job: find out how to stop them.

But he is too sharp not to know that this is a form of sleight of hand. Climate change occurs everywhere and is a slow natural process. “Human-induced climate change”, or “Anthropogenic Global Warming”(AGW), is something else again. Human beings have to adapt to climate change, whatever causes it, and they do. If human beings actually cause climate to change adversely, then it is possible that they could do something to prevent that change. The sleight of hand is most obvious in his recognition that a substantial body of opinion has it that the onward and upward rise in measured global temperature has faltered since 1998, and that there has been no sustained increase since.

He asked some econometricians to help him out there, and they told him that “the temperatures in most of the last decade lie above the confidence level produced by any model that does not allow for a warming trend”. Setting their constipated prose aside, the issue of course is not the existence of a warming trend (that seems almost universally accepted), but the extent to which it is and has been caused by human activity. Again and again he ducks that question, which is central to the debate. (No, the science is not settled.)

The same econometricians point out (Box 5.1) “that the upward movement [in temperatures] over the last 130-160 years is persistent”, and Professor Garnaut must surely have wondered how much of that century-and-a-half rise was due to human activity. The adjacent Figure 5.1 shows, at least to the untutored eye, that the warming trend from 1910 to 1940 has virtually the same shape as the warming trend from 1975 to 1998, if it is not actually steeper. But of course the great increase in CO2 that so worries the IPCC is the recent one. Let us assume that it did produce the increase in temperatures in the latter part of the 20th century. What then produced an equivalent increase in the earlier part?

That issue must have engaged his attention, for it almost leaps from the graph. But my guess is that finally he simply gave a shrug. “The outsider to climate science,” he writes, “has no rational choice but to accept that, on the balance of probabilities, the mainstream science is right”. And then immediately he covers himself, in case later on it turns out that the mainstream was wrong, as it sometimes is. “There are nevertheless large uncertainties in the science.”

He recognises that there are “sceptics”, but he is only prepared to concede validity to the views of “a small number of climate scientists of professional repute”. It is not clear who they are, and I could not find a sceptic known to me by publication in any of the references save one whose words are used to establish a basic point that no one would disagree with. The others, he says, “hold strongly to the view that the mainstream science is wrong”.

With that out of the way, Professor Garnaut uses the IPCC’s Fourth Assessment report as the source of his science, summarises that for us, and then moves, one imagines much more happily, into the economics of what to do about it. He refers much more than once in the scientific chapters to “uncertainty”, but simply accepts, it seems to me, that the IPCC has dealt with that problem of uncertainty itself, and that he can rest confident that whatever uncertainties exist do not disturb what should be done. The balance of probability, he says a number of times, is that things are so.

In my view this is a most rigid account of what seems to me a most fluid debate. By setting up critics as people who say “the science is wrong” he trivialises what is going on. As I read them, the critics never say that the science is “wrong”, only that the science is not “settled”, and that there are, as Professor Garnaut repeatedly says, “large uncertainties” in what is hypothesised.

The critics then go on to offer whatever course of action they think appropriate to a situation of uncertainty. This critic, interested in data and their measurement, thinks that any educated person can understand the issues, and is puzzled at Professor Garnaut’s decision that it was not his job to “debate the existence or extent of human-induced climate change”. I could accept that the existence of AGW was taken as given by his terms of reference. But its extent? Surely that is the nub of the question. How much has human activity contributed to the warming of the last 50 years, the last 100, the last 200? Isn’t that the question we have to answer before we get on to solutions?

The IPCC doesn’t tell us the answer to those questions in its Fourth Assessment Report, and so of course the Garnaut Draft Report cannot either. It must take as a basic assumption, given the lack of contrary evidence, that global warming since 1975 is entirely, or virtually entirely, caused by the emission of greenhouse gases. But if it does, what are we to assume about the message of Figure 5.1, with its very similar warming from 1910 to 1940?