Over the last couple of weeks, I’ve seen four major reports (details over the fold) from very different sources, all making the same point: decarbonizing the world economy will involve economic costs that are
(a) small; and
(b) far outweighed by the benefits
And, the empirical evidence so far is strong. The EU and US have both reduced CO2 emissions significantly, at negligible or even negative economic cost. The measures announced by Obama, including vehicle emissions standards and restrictions on coal-fired power stations appear set to achieve further substantial reductions, again while yielding net economic benefits.

Against the expectations of doubters, wind and solar PV are steadily increasing their share of electricity generation, to the point where they constitute the majority of new installations in many countries. Again, the costs have been trivially small: in Australia’s case, made up almost entirely of the reduction in asset value imposed on existing generators.

There is as far as I am aware, no credible analysis to support the opposite claim (call it the economic armageddon hypothesis) that decarbonization will involve economic costs sufficient to greatly reduce living standards, or, for poor countries, prevent catchup to the developed world. (Again, more detailed argument over the fold.

Nevertheless, past experience suggests that lots of people are sufficiently wedded to the economic armageddon hypothesis that neither this, nor any other evidence will change their minds. I have previously analyzed this unwillingness to respond to evidence in terms of Noah Smith’s Bayesian definition of “derp“: “the constant, repetitive reiteration of strong priors”.

But I no longer think this is sufficient. A central concept of Bayesian decision theory is the separation of preferences from beliefs. That is, your subjective belief about the probability that a proposition is true should be independent of whether (because you have bet on it, or for some other reason) you want it to be true. This is the opposite of what is often called “motivated reasoning” or, less politely, “wishful thinking”.

This, I think, is the central distinction between “derp” and “denial”. Both involve the rejection of factual evidence that would (to a person without strong preconceptions) be overwhelmingly strong. This must involve strong prior beliefs. Denial differs from derp in that these factual beliefs derive from preferences, and are unlikely to undergo any updating. If anything, denial may be strengthened by evidence of the proposition being denied.

This in turn suggests different possible cures. Derp may eventually, if very slowly, be overcome by an accumulation of evidence. By contrast, denial can only be addressed by changing the source of wishful thinking; for example, by convincing rightwingers to stop being rightwingers.

As promised above, here are my sources for the proposition:

First, there’s Pathways to Deep Decarbonization an international collaborative project under the auspices of the UN.

Second, the Better Growth Better Climate report from the Global Commission on the Economy and Climate

Third, this report on Green Growth from the Center for American Progress (covers the US only)

And, most strikingly, this report from staffers at the International Monetary Fund, long the guardian of fiscal rectitude has concluded that for most countries, the local side benefits of reducing pollution would be sufficient to offset the costs for carbon prices up to $50/tonne.

On the other side, I haven’t seen anything that comes close to being a credible source for the economic armageddon hypothesis. What I have seen are

* Lawyerly quibbles with evidence, not internally consistent and always supporting one side of the case (these are too numerous to bother linking)
* Attempts to make small numbers look big, for example by converting annual flows into present values
* Amateur exercises by committed non-experts, riddled with errors. Ted Trainer, whom I’ve mentioned here before is probably the archetypal example
* Rectal extraction: confident pronouncements based on nothing whatsoever

All of these are, of course, the standard argumentative practices of climate science denialists, who are entirely consistent in their treatment of economic issues. Unfortunately, there are also many who, like Trainer, regard themselves as being on the environmental side of the debate but give aid and comfort to its enemies by backing their bogus claims of economic armageddon. At these point, it is necessary to extend the denialist label to cover this group as well.