Or, Timmy in the Torygraph. Its a bit broken I’m afraid, though it manages to get some obvious things right. But before I start on the actual matter, we need to sweep away some of the dross.
It starts Perhaps we can sit down and discuss this climate change thing like the adults we are? Put the Delingpoles over here, the vilenesses that are Greenpeace… and the problem – repeated elsewhere – is the pretence of equal treatment of the two “extremes” whilst actually clearly favouring one side. The bias continues in the treatment of climate sensitivity, though for something appearing in the Torygraph it isn’t bad.
The problem is the continuation: Timmy tells us that the IPCC range is 2-4.5 oC, that there are entirely honest and reasonable scientists… out there arguing that this range is either too high or too low (dubious, but we don’t need to worry about that for now) and that It is this “we don’t know” that leads to needing to do something. Economists call this uncertainty, and the correct and reasonable reaction to uncertainty is insurance. This is a broken variation on something I’ll call “mt’s argument”, because as far as I know mt is the person who has been making the (correct, unbroken) version of the argument for longest.
mt’s argument is that uncertainty does not help the cause for inaction, although it is frequently used as such by denialists and the lite. The idea that we don’t know enough climate science, or we don’t know enough about climate sensitivity to pin down its value, and therefore we should do nothing, is twaddle. And this is for two [*] reasons: the first and most obvious is that if there is uncertainty in climate sensitivity, then to first order it is as much on the high side as on the low side, so the mean damage is sort-of the same; so even at the idiot-argument level, it doesn’t work. But the other is that damage is non-linear in sensitivity, in the bad way, increasing faster than linear; so for symmetrical uncertainty about the mean, the more uncertainty, the higher the mean expected damage.
But that isn’t what Timmy is saying. Timmy is asserting that only uncertainty makes action necessary. That if we knew, for certain, that climate sensitivity were 4 oC we would need to do nothing. This, of course, makes no sense at all. Fortunately, this doesn’t much matter, because the uncertainty is much less than Timmy thinks; as any fule kno, climate sensitivity is 3 oC.
The rest of the article argues for a carbon tax, and of course I agree, though I don’t agree that Stern is a good source for the correct numbers.
[*] Oh all right 3: because the distribution of climate sensitivity is limited below (effectively by 0.7 oC, unless you’re a nutter, definitely by 0, unless you’re a true wacko) then “uncertainty” about an expected value implies (to first order) more uncertainty above than below.