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Sir, Martin Wolf's attempted defence of the Stern report ("After the arguments, the figures still justify swift climate action", November 15) completely fails to address the single biggest objection to it - the choice of emissions scenario. It is this choice that makes the entire review worthless in policy terms.
The Intergovernmental Panel on Climate Change bases its projections for future temperature rise on a series of scenarios (more properly, "story lines") that suggest how much greenhouse gas will be emitted through the century. These story lines produce rises ranging from 2.5-5.8°C in 2100. Economists as distinguished as Prof David Henderson have pointed out implausibilities and professional errors in the development of these scenarios, which would have been a good place to start any review of the economics.
Yet Sir Nicholas Stern not only took these as read but chose to assess only the effects of the A2 story line, which results in the highest temperature increase. On top of this, he then added extra effects that go beyond the "consensus" science so beloved of global warming alarmists.
A proper review would have looked at all the story lines and, perhaps, have added a scenario in which temperature rises were not as great as the IPCC predicts as well as the "high climate" scenario. Yet it is likely that such an analysis would have shown a range of costs that would not have provided the sensationalist headlines the review sought and got.
The Stern review was only able to reach its conclusions by choosing a worst-case scenario, extending it and then amplifying it. That is no base for an informed review of policy choices. It is no wonder that Richard Tol, one of the acknowledged experts in climate change economics, called the review "alarmist" and "incompetent".