The United Nations' Intergovernmental Panel on Climate Change will shortly publish the second part of its latest report, on the likely impact of climate change. Government representatives are meeting with scientists in Japan to sex up—sorry, rewrite—a summary of the scientists' accounts of storms, droughts and diseases to come. But the actual report, known as AR5-WGII, is less frightening than its predecessor seven years ago.

The 2007 report was riddled with errors about Himalayan glaciers, the Amazon rain forest, African agriculture,...