I disagree with the recommendations of the Review because it bases its apocalyptic assessments (Table 5.1) on climate models whose projections, so far, are apparently false. If the questions posed by climate change are about science (they are), then we must address themas scientific questions. The only way to do that is to follow the Galilean empiricist’s royal road.
- Form an hypothesis (the IPCC’s AGW hypothesis, for example);
- Makepredictions based on the hypothesis (the IPCC’s 2007 Assessment Report, for example), and;
- Test the predictions against the facts.
There’s nothing novel about this. It works for simple problems (like geocentrism) and equally well for ‘diabolical’ problems like climate change (Review Report Chapter 1) or quantum mechanics.
The empirical evidence relevant to the IPCC projections appears to show that their hypothesis about global warming is false. The temperature rises that their models project have not happened, despite the higher-than-projected economic growth rates and CO2 emissions to which the Garnaut Report referrs. The data over the period 2001–2008 falls outside (below) the two-standard-deviations range for their model projections. While they are projecting a trend in this decade of 2°/century the trend since the start of their projected period is ‑1.1°/century. This is most clearly illustrated by Lucia Liljegren here although her original work is here.
These results make the case for the IPCC AGW model look very doubtful. The IPCC may still be right that the globe will warm at an alarming rate; but there is now very little reason to be confident in this projection and, accordingly, very little reason to take drastic action that will harm our economy and wealth in response to the IPCC view.
I am sure many people feel unease, or maybe scorn, for the idea that an elaborate ‘scientific consensus’ on AGW, constructed over 20 years, that claims widespread support could be over-turned by a simple statistical procedure. But here’s the nub of the problem: the IPCC case is unusually vulnerable to a statistical weaknesses because it has little other than models and hypotheses drawn from the time-series to offer. Their AGW case turns on a mechanism derived, in their latest (2007) report by subtraction, as Ross Garnaut’s report points out (Section 5.1.5). They say, in essence: “if you remove forcings related to human activity then there’s no warming in our models. So warming must be due to human activity. QED”. Their actual culprit—as the Review Report briefly acknowledges at Section 3.3.1—is not CO2: it’s water-vapour which drives the greenhouse effect in a feedback-looped relationship to CO2. The IPCC does not have physical evidence to demonstrate that this feed-back is sufficiently powerful to be the cause of recent warming. The only evidence they have is their models; which is OK if the model projections are confirmed. But, if the IPCC models aren’t getting it right, then their model-derived mechanism starts to look questionable at best.
I do not say that this means the assertion of global warming is wrong. Every empiricist has to acknowledge that things that happen only 5% of the time (actual temperatures falling outside the 2σ bounds of the IPCC projections) are in fact likely to occur 5% of the time. There is a very small chance that the IPCC’s models are still on track, and even if they weren’t there is no doubt that it’s been warmer recently than, say, in the 1950s. You don’t need a model to tell you that.
But the falsification of the projections by the temperature data only adds to a growing body of publications by scientists with sound reputations that the CO2 story is a crock that may be diverting attention from much more important factors in the climate. I have been especially impressed recently by the data presented in this article by Zbigniew Jaworowski, a researcher with specific experience in the measurement of CO2 in the paleo-climate. But there are many other troubling criticisms of the central AGW theory.
One final point, for now. The Garnaut Review Report appropriately—and at some length—acknowledges both the challenge of managing public policy under uncertainty (Chapter 2) and the overlapping uncertainties in the IPCC AGW theory (Chapter 3). So am I just bellyaching because they don’t come to the same conclusion that I do? My answer is ‘no’. The conviction (whether on faith or on the ‘balance of probabilities’) that the AGW theory of the IPCC is correct pervades the assessments in the report, weakening its consideration of both kinds of uncertainty. In brief:
- The Report, in my view, is so interested in the most extreme predictions of this theory being valid that dread overwhelms the assessment of the appropriate public policy response in Chapter 2. I agree with a lot of things in this chapter, including the conclusion that it is sensible to do something now. But the Report’s assessment is colored, at every point, by the conviction that at one end of the risk distribution is an illimitable disaster of our own making that is really impending. The Report seems incapable of making a cool evaluation of the uncertainty.
- The assessment of the uncertainty about the mechanisms of AGW warming in Section 3.5 (figure 3.9 illustrates) is relevant only if the underlying theory—the basic premiss of dominant human forcings due to the CO2-water vapor cycle—is valid. Just as it doesn’t really matter how Phlogiston is incorporated in combustible materials, so the uncertainty in the AGW mechanisms is moot if the explanation is wrong (which is what the data is now telling us).
For another time: what we should do now to mitigate the risk and what role multilateral agreements will play in that mitigation strategy.