Here are the conclusions from Richard Tol's The Stern Review of the Economics of Climate Change: A Comment:
In sum, the Stern Review is very selective in the studies it quotes on the impacts of climate change. The selection bias is not random, but emphasizes the most pessimistic studies. In this sense, the Stern Review reminds one of Lomborg (2001). The discount rate used is lower than the official recommendations by HM Treasury. Results are occasionally misinterpreted. The report claims that a cost-benefit analysis was done, but none was carried out. The Stern Review can therefore be dismissed as alarmist and incompetent.
This is not to say that climate change is not a problem, nor that greenhouse gas emissions should not be reduced. There are sound arguments for emission reduction. However, unsound analyses like the Stern Review only provide fodder for those skeptical of climate change and climate policy – and may well further polarize the debate.
Climate policy is for the long-term. It will only be successful if a broad coalition – of countries and of stakeholders within countries – supports climate policy and continues to support climate policy. To my mind, this calls for a sober analysis, rather than hyperbole.