The Hole Story

The science behind the scare


In early February, scientists with the National Aeronautics and Space Administration ominously warned that a fullblown "ozone hole" rivaling the one over Antarctica might open up over the United States during the spring, zapping Americans with damaging ultraviolet sunlight. Time showcased the story on the front cover of its February 17 issue, warning that "danger is shining through the sky.…No longer is the threat just to our future; the threat is here and now." Sen. Albert Gore (D–Tenn.) thundered, "We have to tell our children that they must redefine their relationship to the sky, and they must begin to think of the sky as a threatening part of their environment."

Spooked by NASA, the Senate hastily passed, 96 to 0, an amendment demanding that President Bush speed up the schedule for phasing out the chemicals implicated in ozone destruction. Stung by the vote, Bush changed the deadline for a complete ban on the refrigerants known as chlorofluorocarbons (CFCs) from the year 2000 to the end of 1995.

Although NASA did not acknowledge it, the "danger" of an ozone hole opening over the Northern Hemisphere had already passed less than a month after the putative crisis was announced. By late February, satellite data showed that levels of ozone-destroying chlorine monoxide had dropped significantly, and scientists could find no evidence of a developing ozone hole over the United States. One NASA atmospheric scientist told me that the agency "really jumped the gun," while another drily commented that "it was perhaps premature for NASA to say that something drastic was about to occur."

Why the rush? Why did NASA bureaucrats and scientists feel they needed to frighten the American public?

The NASA revelations were exquisitely timed to bolster the agency's budget request for its global climate change program, whose funding is slated to double by fiscal year 1993. "This is about money," Melvyn Shapiro, a meteorologist with the National Oceanic and Atmospheric Administration, told Insight magazine. "If there were no dollars attached to this game, you'd see it played in a very different way." One NASA atmospheric scientist even wondered if it was only a coincidence that Gore's new book of apocalyptic environmentalism, Earth in the Balance, was published just days before NASA held its ozone press conference. After all, Gore chairs the Subcommittee on Science, Space, and Technology, which oversees NASA's budget.

And there was another reason for jumping the gun. Environmental activists and their sympathizers in Congress and the bureaucracy were anxious to push President Bush into attending the big United Nations "Earth Summit" in June. Gore likened the alleged ozone crisis to global warming and urged the president to sign the global climate change treaty that is the centerpiece of the Earth Summit.

By now everyone (94 percent of Americans, according to one poll) has heard that Earth's protective ozone shield is wearing thin and even has a hole in it over the South Pole. The looming ozone catastrophe purportedly will bring humanity withered crops, collapsing terrestrial and marine ecosystems, skin-cancer epidemics, and populations with seriously compromised immune systems. The culprits in this drama are a group of industrial chemicals purveyed by greedy corporations to pampered and spoiled consumers. Ozone depletion is the perfect ecological morality play.

In a morality play, unfortunately, there is no place for ambiguity. Yet the impact of CFCs on the ozone layer is a complex question that turns on murky evidence, tentative conclusions, conflicting interpretations, and changing predictions. It's tempting to ignore these complications, abandon critical thinking, and join in the popular call for drastic action now. But we do so only in defiance of reality, for it turns out that ozone depletion is less a crisis than a nuisance, one that can and should be dealt with in a calm, deliberate way.

Ozone, which consists of three oxygen atoms, is produced when ultraviolet sunlight splits an oxygen molecule in two and the resulting single oxygen atoms combine with ordinary, two-atom oxygen molecules. Ozone in the stratosphere, some 12 to 40 kilometers above Earth's surface, is continuously produced and destroyed. This cycle of creation and destruction prevents energetic ultraviolet sunlight (in the 280-to-320-nanometer range) from reaching the surface, where it could damage the delicate proteins and DNA in organisms. Ozone is chiefly produced over the sunlight-drenched tropics, from which global air circulation transports it toward the poles. If all the ozone in the stratosphere were compressed to surface air pressures, it would make up a layer only one-eighth of an inch thick.

The ozone layer first caught the public's attention in the late 1960s, when some scientists claimed that the exhaust gases of a fleet of 500 Supersonic Transports (SSTs) would erode it. Environmental activists leaped to oppose the SST program. Congress eventually killed the program, giving the emerging environmental movement its first major victory. Scientists later found that SSTs posed no great danger to the ozone layer.

The current ozone "crisis" began in 1974, when chemist Sherwood Rowland and his post-graduate fellow Mario Molina calculated that chlorofluorocarbons had the potential to deplete seriously the sheltering ozone layer. Rowland quipped to his wife, "The work is going well, but it looks like the end of the world."

CFCs are extremely stable, nontoxic compounds widely used as coolants in refrigerators and air conditioners. CFCs escape and waft into the stratosphere, where energetic ultraviolet light breaks them down into the highly reactive elements chlorine and bromine. One chlorine or bromine atom can dismember thousands of ozone molecules. Rowland and Molina predicted that increasing levels of CFCs could lead to a 7-to-13-percent decline in stratospheric ozone during the next 100 years.

In 1978, as the result of an environmentalist campaign, the United States became the first nation in the world to ban the use of CFCs as aerosol propellants. In the meantime, ozone depletion predictions fluctuated wildly as scientists calculated and recalculated what the effect of CFCs might be. In fact, by 1984, the National Academy of Sciences had concluded that total ozone might increase by 1 percent.

Then came the Antarctic "ozone hole." British scientists detected a 50-percent decline in ozone just when spring came to the frigid continent in late September and early October of 1984. Many environmentalists and some scientists believed that the ozone hole was a smoking gun that could be traced directly to CFCs. But chlorine floating free in the atmosphere simply could not destroy ozone fast enough to cause the hole. A mechanism was needed.

Scientists eventually focused on the thin and very cold ice clouds that float above Antarctica. These polar stratospheric clouds of water and nitrogen compounds form only in the months-long and exceedingly cold polar night. Every winter a strong and stable wind pattern called the polar vortex swirls around the outer margins of the Antarctic land mass. Because the air in the vortex is isolated from warmer air, it is chilled to below –80 degrees Celsius.

Nitrogen oxides, which inhibit chlorine chemistry, freeze and drop out of the stratosphere, leaving chlorine and bromine atoms and chlorine monoxides free to attack ozone when the returning sun peeks over the horizon at the beginning of the Antarctic spring in September and October. In effect, the clouds are miniature chemical laboratories where chlorine and bromine reactions powered by sunlight catalytically destroy large quantities of ozone. As summer approaches, the clouds dissipate and the hole is filled with newly produced ozone and ozone flowing down as usual from the tropics. UV levels return to normal.

In 1987, concern about the Antarctic ozone hole led 34 countries to reach an agreement in Montreal to cut world CFC production in half by the end of the century. In March 1988, the day after the U.S. Senate ratified the Montreal Protocol on Ozone, NASA's Ozone Trends Panel issued a report indicating that ozone levels over the Northern Hemisphere had been declining by 0.2 percent per year during the previous 17 years.

Alarmed, the governments of 93 nations agreed in 1990 to phase out the production of most CFCs, halons, and carbon tetrachloride by the end of the century. They also set up a $240-million fund, to which the industrialized nations must contribute, intended to help the developing world adopt new, non-CFC-based refrigeration technologies. The U.S. share will total $40 million to $60 million.

Since 1990, the rate of increase in CFCs in the atmosphere has begun to slacken, and atmospheric chlorine is expected to peak at a little over 4 parts per billion at the turn of the century. The chlorine level is expected to return to 2 parts per billion, the level at which the ozone hole first opened, after the middle of the next century.

Despite these projections, a sense of impending doom pervades discussions of the ozone layer. Alarmists warn that the damage has already been done, and public expectations about the impact of ozone depletion are tinged with panic. Accounts in the mainstream news media ignore several key facts that would help to put the supposed hazards into perspective. For one thing, the ozone layer is not evenly distributed to begin with. Its depth is least over the equator, where UV light is strongest, and greatest over the poles, where UV light is weakest. There is generally twice as much ozone over the high latitudes as at the tropics.

A 5-percent decline in the ozone layer would increase UV exposure about as much as moving a mere 60 miles south—the distance from Palm Beach to Miami, from Seattle to Tacoma. Furthermore, UV light increases at higher elevations, so people who live in mile-high Denver receive much higher UV exposures than do citizens of Philadelphia, which is located at the same latitude. Yet few people factor the risk of UV exposure into their decisions about where to live. Furthermore, Goddard Space Flight Center scientist Arlen Krueger, who is in charge of the Total Ozone Mapping Spectrometer, points out that ozone levels over the United States fluctuate naturally by as much as 50 percent. These periodic wide swings in ozone have no apparent effect on people, plants, or animals.

"There is no question that terrestrial life is adapted to UV," says Alan Teramura, a professor of botany at the University of Maryland and probably the world's leading expert on the effects of UV on terrestrial plants. He adds, "Even at a 20-percent decline in ozone we are not going to burn up all the plants on the surface of the Earth or kill all of the people. We wouldn't see plants wilting or fruits dropping unripened from their vines."

What would occur would be "subtle shifts" among plants: Those less sensitive to UV would outcompete the more sensitive species. More UV would lead to a gradual shift in the plant communities we would see around us. The impact on plants, if any, of a 5-percent decline in ozone would be masked by the greater effects of other climate factors, such as drought, pests, and frosts.

Some crop varieties are sensitive to UV, so lower yields could result. For example, Teramura found a 25-percent reduction in yield after exposing one very sensitive variety of soybeans to a UV level corresponding to a 16-percent decrease in ozone. Apocalyptic environmentalists repeat this finding endlessly as evidence of the dire effects we can expect from a thinner ozone layer. But they fail to mention that Teramura also found several types of soybeans that actually boosted their yields under increased UV, while others were unaffected.

Teramura has discovered large variations in UV sensitivity among different types (cultivars) of soybeans, corn, rice, and wheat. He tested 100 cultivars, including 40 types of soybeans, and found that 41 were unaffected by or tolerant of UV. Teramura tested his plants at UV levels corresponding to 16-percent and 25-percent reductions in ozone—decreases that no responsible scientist predicts. Teramura's results mean that, in the unlikely event that a thinning ozone layer ever becomes a real problem, crop yields could be maintained by selecting UV-tolerant varieties. Famine would not result from reduced ozone.

This conclusion is bolstered by the fact that in Minnesota UV levels are half those of Georgia and Florida, yet corn and soybean yields in the South generally exceed those in the North. The U.S. breadbasket is not on the verge of being blasted out of existence by UV leaking through a newly porous ozone layer. In fact, corn, wheat, rice, and oats all grow in a wide variety of UV environments now.

Teramura's bottom line: "I would start getting concerned at a 10-percent decline in ozone." Concerned, but not panicked. And he means a sustained 10-percent reduction, not transient fluctuations.

So a small decline in the ozone layer poses no great problems for the world's ecosystems. But what about the Antarctic ozone hole that we hear so much about? Isn't UV frying the penguins and the phytoplankton, bringing the ecosystem of the Southern Hemisphere to the verge of collapse? Marine ecologist Susan Weiler testified in 1991 at a hearing held by Sen. Gore that scientists had measured phytoplankton growth-rate reductions of 6 percent to 12 percent around Antarctica.

Marine ecologist Osmond Holm-Hansen of the Scripps Institution of Oceanography gently dismisses Weiler as "more of a politician than a scientist." Since 1988, Holm-Hansen has been intensively studying the effects of UV on phytoplankton, the tiny marine plants at the base of Antarctica's food chain. He found that increased UV may reduce total phytoplankton growth in the full water column by 5 percent at most. He adds that even if there were reductions of 6 percent to 12 percent in phytoplankton growth rates, this would mean a 2-to-4-percent overall reduction in the course of a year, which is well within natural variations in the Antarctic ecosystem.

Holm-Hansen also points out that Antarctic phytoplankton naturally tolerate similar levels of UV during the Antarctic summer and that phytoplankton are able to adapt to higher UV levels. "Unlike the scare stories you hear some scientists spreading, the Antarctic ecosystem is absolutely not on the verge of collapsing due to increased ultraviolet light," he insists. Even oceanographer Raymond Smith, who reported the 6-to-12-percent growth-rate declines, acknowledges that "the whole ecosystem does not appear to be collapsing."

Ecological apocalyptics also predict that reduced global ozone will mean massive increases in skin-cancer rates. Most light-skinned people are painfully familiar with the damage that UV light can cause—namely, sunburns. The incidence of non-melanoma skin cancer is strongly correlated with exposure to UV light. The U.S. Environmental Protection Agency predicts that every 1-percent reduction in the ozone layer will cause a 3-percent increase in non-melanoma skin cancers.

But Temple University dermatologist Dr. Frederick Urbach, a consultant to the U.N. panel on ozone depletion, says the EPA's extrapolations are not very reliable. "You can crunch numbers in a computer and get whatever result you want to come out," Urbach says. He notes that skin-cancer rates have been going up dramatically in recent decades but adds that "the increases are due to people spending more time outside, not more UV." Moreover, the death rate for non-melanoma skin cancer is negligible, less than 1 percent. "It takes real talent for someone to die of non-melanoma skin cancer," Urbach says. "You basically have to ignore a hole in your skin for years."

The weak evidence that UV may slightly lower the body's immunological defenses (after all, sunburn damages the body's largest organ, the skin) has also been greatly exaggerated. Gore and environmentalist Paul Ehrlich even hint that increased UV may make the AIDS epidemic more virulent. By contrast, Johns Hopkins University dermatologist Dr. Warwick Morison says the evidence for UV immunosuppression in human beings is "very incomplete."

Apocalyptics are also fanning fears of UV-induced epidemics. But the United Nations Environmental Program says "it should be stressed that the activation of viruses by UV is unlikely to result in an increased rate of infection." In other words, no epidemics due to thinning ozone.

In any case, it's not even clear that global ozone is really declining. University of Virginia environmental scientist S. Fred Singer notes that extracting tiny trends from the data is fraught with difficulty because the "natural variability [in ozone levels] is hundreds of times larger than the alleged steady change." In the 1960s the ozone layer "thickened" by 5 percent over the United States. The "thinning" in the 1980s just about brings ozone down to earlier levels, which were not thought to be harmful at the time.

In March, meteorologist Dirk De Mure and his colleagues at the Belgian Meteorological Institute published a study showing that the instruments used to measure ozone have probably mistaken reductions in atmospheric sulfur dioxide (due to air-pollution controls) for declines in global ozone. The reduced sulfur dioxide, they wrote, "has induced a fictitious Dobson total ozone trend of –1.69% per decade." The researchers found that, once the sulfur-dioxide trends are taken into account, there appears to be a small upward trend in global ozone.

If ozone has declined globally, scientists should be able to measure an increase in ultraviolet light at the surface. Yet there is no evidence of increased UV reaching the surface in the Northern Hemisphere. In fact, National Oceanic and Atmospheric Administration scientist John Delouisi reports that the network of Robertson-Berger meters that measure UV showed "an average surface ultraviolet radiation trend of –8 percent from 1974 to 1985 using RB-meter data from eight stations located in mainland United States."

Furthermore, UV flux in the rural midlatitude Northern Hemisphere (the United States) has declined by between 5 percent and 18 percent during this century, according to NOAA scientist Shaw Liu. He attributes the lessened UV to an increase in clouds and low-level haze resulting from industrial activities. University of Virginia meteorologist Patrick Michaels points out that if we were somehow to eliminate the haze, "the increase in skin cancer would far outweigh anything caused by what we may have done to the midlatitude stratosphere."

Moreover, it's wrong to draw conclusions about what might happen to the stratosphere over the United States based on the Antarctic ozone hole. "It's a purely localized phenomenon," says Guy Brasseur at the National Center for Atmospheric Research in Boulder, Colorado. The polar vortex limits its size. Brasseur expects the hole to disappear when chlorine levels drop below 2 parts per billion in the next century.

Conditions are less conducive to ozone destruction at the North Pole than at the South Pole. In contrast to Antarctica, the Arctic polar vortex tends to break up before sunlight can reach it, owing to atmospheric turbulence caused by the more variable geography of the Northern Hemisphere. And the North Polar stratosphere warms up quickly in the spring, so whatever chlorine monoxide forms is broken down and bound up in nitrogen compounds that inhibit its ability to destroy ozone.

So why the furor over a possible ozone hole in the Northern Hemisphere earlier this year? The chief reason is that atmospheric scientists detected elevated levels (1.5 parts per billion) of ozone-destroying chlorine monoxide. Despite the crisis atmosphere generated by NASA's publicity in February, scientists had been predicting since last summer that ozone might decline substantially in 1992.

Although all the evidence is not yet in, the chlorine-monoxide peak in the Northern Hemisphere appears to be the result of the 20 million tons of sulfur blasted into the atmosphere during the June eruption of the Philippine volcano Mount Pinatubo. In the atmosphere, volcanic sulfur is transformed into sulfuric acid droplets, which act like polar stratospheric clouds by sequestering the nitrogen compounds that inhibit the formation of chlorine monoxide. Linwood Callis, a scientist in the Atmospheric Sciences Divison at NASA's Langley Research Center, found that after the Mexican El Chichon volcano erupted in the early 1980s, ozone was significantly reduced worldwide. David Hofmann, senior scientist in NOAA's Ozone and Aerosols Group, told Insight: "I couldn't understand why NASA didn't come out and say that this could be a very unusual year because of the volcanic eruptions, that maybe what we're seeing is something that we'll never see again."

Despite elevated levels of chlorine monoxide and the attendant NASA hype, scientists found no evidence of an ozone hole opening up over the Northern Hemisphere this past spring. A small Arctic ozone hole could develop during an exceptionally cold, still winter, but it would be a rare and transitory occurrence. A Northern Hemisphere ozone hole, if it ever occurred, would happen in February and early March, when people are generally indoors or are well covered and sunlight is weak.

While the current scientific consensus is that CFCs are responsible for the Antarctic ozone hole, some distinguished scientists still think that it may turn out to be a natural and transitory phenomenon. The University of Virginia's Singer points out that G. M. B. Dobson, the inventor of the machine that measures ozone, reported very low ozone values—only 150 Dobson units—over Halley Bay, Antarctica, in 1956 and 1957. (By contrast, in the 1960s and '70s, the level was more than 300 Dobson units.) Two French scientists recently republished data showing pronounced ozone decreases, down to 120 Dobson units, during the Antarctic spring in 1958. These measurements were taken years before CFCs could have caused any such decline.

NOAA meteorologist Walter Komhyr links both Antarctic and global ozone depletion to sea-surface temperatures in the eastern equatorial Pacific Ocean. Analyzing data from the last 25 years, Komhyr and his colleagues found that when the eastern equatorial Pacific cooled between 1962 and 1975, global ozone increased. Conversely, when temperatures warmed between 1976 and 1988, ozone declined worldwide.

Warm sea-surface temperatures dampen the circulation patterns that replenish ozone supplies at the poles with the huge quantities of ozone produced in the tropics. Warm sea-surface temperatures also retard the winds that break up the circumpolar vortex at the beginning of the Antarctic spring. A stable vortex prevents stratospheric warming that would short-circuit the ozone-destroying chlorine chemistry, which can take place only at temperatures below –80 degrees Celsius. After Komhyr published these data, he says, a number of atmospheric chemists chewed him out because they thought his findings might hurt funding for their CFC projects.

If the Antarctic ozone hole may not be due solely to CFCs, what about global reductions in ozone levels? The U.N.'s 1991 Scientific Assessment of the Stratospheric Ozone acknowledges that "there is not a full accounting of the observed downward trends in global ozone." The panel nevertheless insists on attributing global ozone losses chiefly to chlorine and bromine reactions, apparently because they "are the only ones for which direct evidence exists." In other words, we'll blame CFCs because it's the only explanation we have right now.

As noted earlier, however, NOAA's Komhyr thinks that some of the decline in global ozone is caused by changes in atmosphere circulation. Since the mid-1970s, he explains, weaker tropical winds have failed to transport ozone-enriched air from the equator to the higher latitudes.

Callis, the NASA scientist, analyzes the destructive effects on ozone of highly energetic electrons, the sunspot cycle, volcanic eruptions, the dilution effect from the Antarctic ozone hole, and changing tropical wind patterns. "CFCs come in a very poor last as the cause for lower levels of global ozone," Callis says. He calculates that fully "73 percent of the global O3 [ozone] declines between 1979 and 1985 are due to natural effects related to solar variability." He also points out that global ozone made "a significant recovery between 1985 and May of 1990." Since we passed the solar maximum in 1991, ozone levels will decline naturally until the buildup to the next solar maximum begins later in the decade.

Environmentalists often decry the 14 years supposedly lost to inaction after Rowland and Molina first made their predictions about CFCs and ozone. But it's not as if there was nothing to lose by imposing an immediate ban. Environmentalists tend to discount the real and substantial contribution to human well-being that CFCs have made.

Cheap refrigeration made possible by CFCs has been a tremendous boon. For millennia people died because they could not prevent food from rotting or becoming contaminated with disease organisms. Cheap refrigeration permits fresh and healthy food to be transported by truck, train, and boat to markets thousands of miles from where it is grown and harvested. Primitive methods of long-term food preservation, such as salting and smoking, filled foods with large quantities of potent carcinogens. CFC-based refrigeration saved millions of lives and enabled billions of people to enjoy much better diets of fresh meats, fruits, and vegetables.

Environmentalists can now point to new substitutes for CFCs. But many are toxic and flammable, making them far more dangerous to handle. In addition, the substitutes cost three to five times more. The extra cost will delay the spread of desperately needed refrigeration to the developing world, where food spoilage is a huge problem. It is probably inevitable that many people will continue to go hungry because of the CFC ban.

Aside from the cost of a ban, governments and companies have had to contend with ambiguous data and shifting conclusions about the impact of CFCs on the ozone layer. How many times have theories, put forth in good faith, been shown later to be wrong? In the 1972 Club of Rome report The Limits to Growth, a very distinguished group of scientists, including Jay Forrester and Dennis and Donella Meadows, warned humanity that we would run out of oil in only 20 years. Our government acted on that prediction, making energy conservation the "moral equivalent of war," and ended up wasting billions of dollars on subsidies for synthetic fuel programs.

Or consider the dire predictions of activists like Jeremy Rifkin, who warned that biotechnology would let deadly new microbes run amok and upset the balance of nature. Had we acted on such fears and banned biotechnology in the 1970s, humanity would have forgone the new miracle drugs and agricultural products that now promise to alleviate the suffering of the sick and the hunger of the poor. Today scientists agree that early concerns about the hazards of biotechnology were overblown, and the Bush administration recently moved to speed up approval of drugs produced through genetic manipulation.

There's ample reason to doubt similarly catastrophic warnings about CFCs and the ozone layer. It's instructive to recall that climate alarmists Stephen Schneider and Carl Sagan claimed for years that CFCs were particularly potent greenhouse gases, contributing as much as 25 percent to increased global temperatures. But they failed to take into account the first law of ecology: Everything is connected to everything else. Ozone, too, is a potent greenhouse gas, and so when CFCs destroy it the atmosphere tends to cool. According to NASA, ozone decreases largely offset predicted increases in global temperatures due to CFCs. "What had been thought was a major greenhouse gas turns out to be having a cooling effect," noted EPA Administrator William Reilly.

Nevertheless, despite a great deal of continuing scientific uncertainty, it appears that CFCs do contribute to the creation of the Antarctic ozone hole and perhaps to a tiny amount of global ozone depletion. If CFCs were allowed to build up in the atmosphere during the next century, ozone depletion might eventually entail significant costs. More ultraviolet light reaching the surface would require adaptation—switching to new crop varieties, for example—and it might boost the incidence of nonfatal skin cancer. In light of these costs, it makes sense to phase out the use of CFCs.

But ozone depletion is certainly not the "global emergency" that environmentalists like Friends of the Earth's Elizabeth Cook say it is. The normal processes of science and democratic decision making have proved adequate to correct what might have become a significant problem. In 1990 our national and international institutions hammered out an agreement to control CFCs, the Montreal Protocol, that takes the interests of all affected groups into account (though imperfectly). Calls to abandon a moderate course of action and push up the deadline for the CFC ban are based on exaggerated fears and unrealistic predictions. On the evidence so far, despite the lurid crisis mongering of radical environmentalists, waiting for more information on CFCs and ozone did not cause any great harm to people or to Earth's ecosystems, nor will it.

Radical environmentalists argue that the experience with ozone depletion should teach us to respond swiftly and dramatically to the threat of global warming. Rafe Pomerance of the World Resources Institute says the international negotiations over CFCs were merely the dress rehearsal for drastic reductions in carbon-dioxide emissions aimed at preventing global climate change. While replacing CFCs eventually will cost billions, the price tag for abating carbon dioxide could run as high as $600 billion a year, according to Maurice Strong, secretary-general of the Earth Summit in Rio de Janeiro. He adds that the industrial nations will have to provide $70 billion more in aid to developing countries each year to help them lower carbon-dioxide emissions.

The environmentalists are right to suggest that the example of ozone depletion is relevant to the debate over global warming. But the example indicates that we should be skeptical of environmental "crises." The relevant lesson is not, "He who hesitates is lost," but rather, "Look before you leap."

Contributing Editor Ronald Bailey, producer of the weekly PBS series TechnoPolitics, is writing a book on apocalyptic environmentalism to be published by St. Martin's Press.