The title of this highly readable book has a double meaning: steps should be taken against global warming, but unsupported claims that climate change will lead to global catastrophe and human calamity should be avoided. The book is a plea for a rational discussion of social priorities, persistently invoking cost-benefit comparisons. The Danish statistician Lomborg finds the Kyoto Protocol far too costly for the modest benefits it can bring, even as only a first step. A big concern in the increasingly global dialogue on climate change is that the poorest countries, with the least adaptive capacities, will be the most damaged. Thus issues of equity play a large role in the discussion. Lomborg argues that greatly slowing down climate change is a terribly inefficient way to help poor people, now or in the distant future. Payoffs per dollar spent can be increased many hundredfold by instead seriously attacking HIV/AIDS and malaria, providing safe drinking water and sanitation, and distributing micronutrients. Lomborg also debunks some of the more spectacular claims about climate change -- for example, that it is depleting the global population of polar bears. To mitigate climate change, he suggests taxing emissions of carbon dioxide -- initially at a modest rate of $2 a ton -- and greatly increasing research-and-development expenditures for nonemitting technologies that can provide adequate energy to all.