Roughly one person in two is concerned about man-made global warming. Why? Because vivid, alarming forecasts are persuasive only for a time. We've seen it all before. Take the alarm over mercury in fish.
In 2004, a United States Environmental Protection Agency employee warned that each year 630,000 babies were born at risk of brain and nervous system damage due to ''unsafe'' levels of mercury in their mothers' blood.
It turns out that ''at risk'' meant having concentrations of mercury in the blood that were higher than unjustifiably low levels.
The Japanese consume a lot of fish and those ''at risk'' levels are exceeded by 74 per cent of Japanese women of childbearing age and by centuries-old mummified remains.
Yet, there is no evidence that Japanese are mentally deficient, and only benefits have been reported from high levels of fish consumption, including good brain function and improved intelligence at age four.