Environmental economist Partha Dasgupt a reviews Cool It: The Skeptical Environmentalist’s Guide to Global Warming, by Bjorn Lomborg in Nature

Unfortunately, Lomborg’s thesis is built on a deep misconception of Earth’s system and of economics when applied to that system. The concentration of CO2 in the atmosphere is now 380 p.p.m., a figure that ice cores in Antarctica have revealed to be in excess of the maximum reached during the past 600,000 years. If there is one truth about Earth we all should know, it’s that the system is driven by interlocking, nonlinear processes running at different speeds. The transition to Lomborg’s recommended concentration of 560 p.p.m. would involve crossing an unknown number of tipping points (or separatrices) in the global climate system. We have no data on the consequences if Earth were to cross those tipping points. They could be good, or they could be disastrous. Even if we did have data, they would probably be of little value because nature’s processes are irreversible. One implication of the Earth system’s deep nonlinearities is that estimates of climatic parameters based on observations from the recent past are unreliable for making forecasts about the state of the world at CO2 concentrations of 560 p.p.m. or higher. Moreover, the nonlinearities mean that doing more of a bad deal (Kyoto) may well be very good.

These truths seem to escape Lomborg. His cost–benefit analysis involves only point estimates of variables (interpreted variously as ‘most likely’, ‘expected’, and so forth), implying that he believes we shouldn’t buy insurance against potentially enormous losses resulting from climate change. His concerns over the prevalence of malaria, undernutrition and HIV in today’s world show that he is an egalitarian. There is, then, an internal contradiction in his value system, because if you are averse to inequality you should also be averse to uncertainty.

The integrated assessment models of Earth’s system on which Lomborg builds his case are arbitrarily bounded on either side of his point estimates. It can be shown that if those bounds are removed (as they ought to be), even a small amount of uncertainty — when allied to only a moderate aversion to uncertainty — would imply that humanity should spend substantial amounts on insurance, even more than the 1–2% of world output that has been advocated. If the uncertainties are not small, standard cost–benefit analysis as applied to the economics of climate change becomes incoherent, even if those uncertainties are judged to be thin-tailed (gaussian, for example); this is because the analysis would say that no matter how much humanity chooses to invest in protecting Earth from passing through those later tipping points, we should invest still more.

Economics helps us to realize what we are able to say about matters that will reveal themselves only in the distant future. Simultaneously, it helps us to realize the limits of what we are able to say. That, too, is worth knowing, for limits on what we are able to say are not a reason for inaction. Lomborg’s seemingly persuasive economic calculations are a case of muddled concreteness.

Australian ecologist Tim Flannery makes some similar points in his review and concludes with the much stronger statement that:

By empathizing with those who are concerned about climate change and poverty, and trying to persuade them to divert their energies, Cool It is a stealth attack on humanity’s future.