Tomorrow is Earth Day, and I expect we will hear lots of warnings about potential environmental disasters. We don’t want to discount all of these predictions, but we should also exercise some discernment when we hear these warnings.

When I was in college, a report by the Club of Rome warned of impending environmental disasters. It said we would run out of various essential minerals by the 1980s and would run out of petroleum and natural gas by the early 1990s. That didn’t take place and illustrates the need to view many of these warnings with a few grains of salt.

Walter Williams talked about some of these wild predictions in one of his columns. He pointed out that Stanford professor Paul Ehrlich predicted there would be a major food shortage in the U.S. and that “hundreds of millions of people are going to starve to death” in the 1970s. He went on to forecast that 65 million Americans would die of starvation between 1980 and 1989. He had even gloomier predictions for England. He said: “If I were a gambler, I would take even money that England will not exist in the year 2000.”

He was not alone in his warnings. In 1975, the Environmental Fund took out full-page ads warning, “The World as we know it will likely be ruined by year 2000.” And Harvard professor George Wald in 1970 warned, “Civilization will end within 15 or 30 years unless immediate action is taken against problems facing mankind.”

It is also instructive to remember that the fear forty years ago was not global warming but global cooling. Environmentalist Nigel Calder warned at the first Earth Day that: “The threat of a new ice age must now stand alongside nuclear war as a likely source of wholesale death and misery for mankind.” C.C. Wallen of the World Meteorological Organization said: “The cooling since 1940 has been large enough and consistent enough that it will not soon be reversed.”

The next time you hear an environmental warning, remember that many of them just never took place.