Polls show that roughly one person in two is concerned about manmade global warming. Why? Because vivid, alarming forecasts, even those based on weak foundations, are persuasive. For a while at least.

We’ve seen this many times before. Take the alarm over mercury in fish: in 2004, an Environmental Protection Agency employee warned that 630,000 babies per year were born at risk of brain and nervous system damage due to “unsafe” levels of mercury in their mothers’ blood. Expectant mothers were discouraged from eating fish.

Japan consumes a lot of fish, and the supposedly unsafe levels cited by the EPA are exceeded by 74% of women of childbearing age there. Yet there is no evidence that their children are mentally deficient. In fact, only benefits have been reported from high levels of fish consumption, including good brain function and improved intelligence at age four.

The alarming forecast of harm from mercury in fish was derived by extrapolating known bad effects from high doses of mercury to incorrectly predict toxic effects from even very low levels — without bothering to check for evidence. This poorly founded forecast resulted in mothers and their children avoiding a healthy food, to their detriment.

Working with Professor J. Scott Armstrong of the University of Pennsylvania and others, Dr. Kesten Green identified 26 previous alarms that are analogous to the dangerous manmade global warming scare. Besides the alarm over mercury, the 26 alarms include familiar ones like electromagnetic fields (EMF) and cancer, and DDT and cancer.

A 1979 American Journal of Epidemiology article linked exposure to weak EMF from electrical wiring with childhood leukemia. Media and scientists followed, making shrill claims of widespread and diverse harm including headaches and depression. In response, the U.S. government adopted exposure limits and other regulations that World Health Organization researchers estimated impose a $1 billion annual cost on the economy.

But the authors of the journal article that raised the alarm did not actually measure exposure to EMF. Tens of thousands of articles have been published since, and the conclusion is that there is no link between weak EMF and human health.

Rachel Carson raised alarm over the insecticide DDT in her 1962 book Silent Spring, claiming that it caused cancer. There was no good evidence for this assertion, and there still isn’t. The EPA nevertheless banned DDT in 1972, and Europe and Africa, under pressure from international agencies, followed. The main consequence of the ban is that millions of people have died needlessly from mosquito-borne diseases such as malaria.

All of the analogous 26 alarms analyzed by Green and Armstrong turned out to be false, either completely or to such an extent that actions intended to be remedial caused greater harm than the supposed problem. See www.PublicPolicyForecasting.com for descriptions of some of the other 26 analogies: because media report alarms enthusiastically but not their demise, many readers will be surprised to find that alarms they still believe to be true have now been debunked.