Remember the Alar scare of 1989, when Meryl Streep went before Congress to warn of a pesticide used on apples? There was much concern at the time, but it didn't pan out. An official with the National Cancer Institute eventually concluded the cancer risk from eating apples treated with Alar was "nonexistent."
How about silicone breast implants? The Food and Drug Administration took them off the market in 1992, but for no good reason: In 1999, the Institute of Medicine said they didn't cause breast cancer or other serious diseases.
There was acid rain, which allegedly was a catastrophe for lakes and forests in the East. The director of an exhaustive federally funded assessment, however, announced in 1990 that "the amount of damage is less than we once thought, and it's much less than some of the characterizations we sometimes hear."
Over and over, we saw a pattern. Environmental and public health groups with a leftward bent said the sky was falling; conservatives and libertarians (me included) asked for scientific evidence; and the science sooner or later debunked the fears.
Back then, those skeptical about environmental warnings deferred to learned people who knew the subject best. Alarmists stoutly ignored them while scrounging up a few experts who would take their side.
But that was another century. Today, it's scientists who agree on the validity of a major environmental peril -- climate change caused by human activity. It's liberals and environmentalists who can point to a broad scholarly consensus for their claims. And it's the skeptics who now revile the scientists as stooges and liars.
Texas Gov. Rick Perry is right in step with many conservative advocacy groups and commentators when he derides global warming as "all one contrived phony mess that is falling apart under its own weight." The conservative magazine National Review regularly heaps scorn on climate-change worries.
So does the editorial page of The Wall Street Journal, which depicts it as an urban legend singlehandedly fabricated by Al Gore. Fox News ... well, I'll let you guess.
This naysaying has had its intended effect. A Pew Research Center poll last year found that 53 percent of Republicans don't believe the earth is getting warmer, and 58 percent think scientists actually agree with them.
That is known as living in a fool's paradise. The consensus among experts, in fact, happens to be virtually unanimous on the other side. A survey of climate scientists who have published research in the field found that 97 to 98 percent believe people are causing the planet to heat up.
Every major scientific group concurs. The National Academy of Sciences published a report last year reaching a firm conclusion: "Climate change is occurring, is caused largely by human activities, and poses significant risks for -- and in many cases is already affecting -- a broad range of human and natural systems."
Groups such as the American Geophysical Union, the American Meteorological Society and the American Association for the Advancement of Science agree. So does the Intergovernmental Panel on Climate Change, made up of scientists from around the world. At this point, disagreeing is like saying Willie Mays has no business in the Hall of Fame.
There are, of course, some scientists who express doubts about global warming. But what would environmental skeptics say if 97 percent of scientists solemnly announced that climate change is a massive pile of horsefeathers?
We don't have to ask, because we know from the past scares. In those instances, a solid scientific consensus was enough to settle the issue in their minds. This time, however, those who once urged opponents to defer to the experts are doing exactly the opposite.
They arrive at their position by reasoning backward: They reach a conclusion and snatch at any shred of evidence that justifies it. The climate change deniers don't like the idea of governments restricting greenhouse gas emissions, so they insist that these emissions are nothing to worry about, that scientists are corrupt and that it's all part of a socialist power grab.
They used to uphold respect for science. Now they prefer magical thinking.