It’s time, once again for the Monday Message Board. As usual, civilised discussion and absolutely no coarse language, please.
Anatol Rapoport has died at the age of 95. Among many contributions, perhaps his most widely-known was the Tit-for-Tat rule for repeated games of the Prisoner’s Dilemma, embodied in a four-line program Rapaport successfully entered in a contest run by Robert Axelrod. Rapoport’s program co-operates inititially, and thereafter matches the other player’s last action, defecting in response to a defection, and returning to co-operation if the other player does so. There’s more here from Tom Slee.
The fact that the American Enterprise Institute (currently funded by ExxonMobil, but not for much longer it seems) is offering $10K a pop to scientists and economists willing to attack the IPCC report is all over the press and the blogosphere (a PDF scan of one of the letters has been posted here. I was alerted by David Adamson, who pointed me to this Courier-Mail report citing the Guardian. It’s striking to think that when I started blogging in 2002, the AEI was still widely respected.
Meanwhile Brad DeLong has suggested that he and I should put our hands up for the cash. Since we are closely familiar with all the main denialist arguments, it would be money for jam after all. Sad to say, this appears to be an invitation-only offer and neither Brad nor I is on the list. In any case as radek points out in comments
10K seems like a pretty low amount to pay for a shredded reputation. Unless, I guess, you ain’t got much reputation to begin with. Even market forces, politics and ideology aside, predict that whatever comes out will be of extremely low quality. You get what you pay for.
Of course, this applies equally to anyone willing to hire AEI itself.
In related shenanigans, another recipient of the ExxonMobil cash spigot, the Fraser Institute (whose efforts on this point are headed by the egregious Ross McKitrick) is holding an event on Monday in London, aimed at discrediting the IPCC. The Fraser Institute report has already been leaked and dissected at DeSmogBlog, which suggests that Fraser may be fronting for AEI. Any readers who happen to be in London might want to roll up and join the Rent-a-crowd there. No guarantee that you’ll get paid for attendance only, though.
And on the lighter side, the search engine on the White House website has been rigged to return no results for searches on “global warming”
The much-leaked report of the Intergovernmental Panel on Climate Change will be released today (this evening our time). As everyone knows, it will conclude that it is very likely (more than 90 per cent) that human activity is the main cause of observed global warming. The IPCC best estimate of the impact of business as usual is an increase of around 3 degrees C relative to preindustrial levels by 2100.
There’s still room for debate over the central estimate, particularly regarding the projections of CO2 emissions. For example, the population growth projections used in the estimate are probably too high. On the other hand, I doubt that some feedback effects like bushfires have been fully taken into account. And the climate models themselves are still being refined. Still, it doesn’t seem likely that the estimates are going to be changed much by another 5 years of data and improved modelling, so we can probably take this estimate as settled for the moment.
In many ways, though, the real interest now is in the tails of the distribution. Most of the attention so far has been focused on the lower tail, representing the possibility that global warming will turn out to be modest or non-existent. Denialist arguments that the whole idea of anthropogenic global warming is wrong have received a lot of attention but have been thoroughly refuted by now. On the other hand, if all the questions now in doubt turned out the right way for us (forcings at the low end of estimates, feedbacks from water vapour and so on less positive, historical trends at the low end of the margin of error) and some factors we haven’t yet considered turned out to reduce warming, we could see lower numbers, small enough to make adaption rather than large-scale mitigation the best response (in hindsight).
But all these arguments are symmetrical. If warming could be slower than the best projections, it could also be faster. According to the ABC, the report says gains of up to 6.3 degrees can’t be ruled out, though this figure is from only one model, and does’t fit well with other data.
Although the probability distribution of possible outcomes is essentially symmetrical, however, this doesn’t mean that we can ignore the tails. This is because the costs of climate change grow much more than linearly with the rate of change. Let’s say, for illustrative purposes, that 3 degrees of warming would impose costs equivalent to a 5 per cent reduction in income. Taking account of a small probability (less than 10 per cent) that warming will be very modest, so that costs are zero, doesn’t change the analysis much. By contrast, 6 degrees of warming would be catastrophic – it’s equal to the change since the last Ice Age. Even a small probability of 6 degrees of warming (say 5 per cent)** would greatly increase the expected cost of warming. For plausible levels of risk aversion, the expected cost could be as much as 10 per cent of GDP. So the cost of warming is greatly affected by the probability of these extreme events, and this is an issue that is still unresolved.
** This number isn’t really crucial to the argument, but the lower the number the greater the relative importance of the low-probability tail events. A lot of published estimates, like those of Nordhaus and Tol are lower than this, but (as noted in the previous posts) these estimates impute trivial costs to the severe ecological damage that would inevitably arise with 3 degrees of warming.