As we all prepare to celebrate Earth Day on April 22, let us hearken for a moment to Steven Hayward, who is one of nature’s rare creatures – two parts scholar, one part troublemaker. As author of well-regarded biographies of both Ronald Reagan and Winston Churchill, Hayward is a man always worth hearkening to, even if, like me, you aren’t completely sure what hearken means.

I want you to hearken to Hayward because many people who should be, aren’t. Hearkening, I mean. In addition to his work in historical scholarship, Hayward does research in environmental law under the auspices of the Pacific Research Institute in San Francisco.

For several years now he has been releasing an annual Index of Leading Environmental Indicators. It’s his own way of celebrating Earth Day. And sure enough, for several years now, the leading lights of the environmental movement have been pretending Hayward and his index don’t exist.

Why? Hayward is an optimist. His index of environmental indicators is a collection of good news. And, for the professional pessimists of the green movement, too much good news is bad news.

In last year’s index, for example, Hayward and his colleagues cheerfully noted that levels of ambient air pollution in the U.S. had dropped dramatically, beginning in 1976. By 2002, ozone was down 31%, sulfur dioxide 70% and carbon monoxide 75%. Lead, once one of the deadliest, scariest and most ubiquitous pollutants, had dropped 98%.

U.S. water quality, though much more difficult to measure consistently over so large an area, has also shown steep improvement. According to the Environmental Protection Agency, the percentage of the U.S. population served by community water systems with no reported violations of health-based standards has grown from just under 80% a decade ago to nearly 95% today.

This year, when Hayward releases his new index, the EPA data will be even sunnier: U.S. air quality, measured in levels of particulates, is better than it has been since such measurements were first made.

Environmentalists downplay the happy news for understandable reasons, not all of them cynical. It is true that professional activists of every ideological coloration thrive on trauma and trouble, according to the general principle that a frightened citizenry is a generous citizenry – at least when it comes to offering money to professional activists.

At the same time, a true-believing environmentalist might sincerely worry that overattention to successes in the fight for a clean environment will lead to a risky complacency and false optimism.

Yet, not all optimism is false. Hayward’s optimism is grounded in reason and experience – particularly in his belief that technology, know-how and the entrepreneurial spirit, prompted by the market and urged on by government, will overcome our environmental difficulties. His index suggests he has history on his side.

And here is where the troublemaker comes in. To dramatize his belief that the good environmental news will keep getting better, Hayward has publicly and flamboyantly offered environmental doomsayers a bet.

“Since day one of the Bush administration,” he says, “environmentalists have been saying George W. Bush will be a disaster for the environment: He is gutting the Clean Air Act, pollution will just get worse and worse and so on.

“So I’ve offered anyone who wants it a wager: I’ll bet that levels of particulates and ozone will be lower in 2009, the end of the Bush administration, than they were in 2001, when the administration began.”

Hayward has yet to find any takers. He isn’t surprised. Environmental pessimists have been here before. Hayward has modeled his stunt on a similar wager made in 1980 between Julian Simon, an economist at the University of Maryland, and Paul Ehrlich, the paragon of environmental pessimism.

Ehrlich was already famous for his 1968 bestseller “The Population Explosion,” whose first line reads: “The battle to feed all of humanity is over. In the 1970s the world will undergo famines – hundreds of millions of people are going to starve to death.”

Not a happy camper, this Ehrlich – and also, of course, spectacularly wrong. Population increased after his book was published, but so did food supply. Unluckily for him, the world-wide famine never materialized.

His bad track record didn’t prevent him from publicly betting Simon that within a decade, from 1980 to 1990, scarcity and overpopulation would drive up the price of five vital minerals (copper, chrome, tungsten, nickel and tin) on the world market.

Simon made the bet knowing that the price of natural resources like minerals had been falling for centuries, thanks to technology and human adaptability. And he was right. By 1990, the price of all five minerals had fallen dramatically, even as population rose. Ehrlich paid off the bet gloomily, as is his style.

It was a dramatic victory for environmental optimism, and it should have been seen as a repudiation of the pessimists. Instead, Simon lived out his life in relative obscurity, while Ehrlich has gone on to receive honor upon honor, including a lucrative MacArthur Foundation “genius grant.”

We should hope that Steven Hayward, Simon’s heir, draws more attention (and a genius grant). Every year at Earth Day, we keep hearkening to the wrong people.

Mr. Ferguson is a columnist for Bloomberg News.