For most Americans, last summer was one of the hottest on record. Some experts said the heat may have been a sign of what to expect from the “greenhouse effect”—the increased levels of carbon dioxide in the atmosphere as the result of burning fossil fuels. The carbon dioxide traps the sun’s infrared radiation close to the planet’s surface and causes the temperature to rise. Other experts said no: last summer’s heat was simply weather.

This debate is not new. In 1896 and 1908, the great Swedish scientist Svante Arrhenius published papers setting forth what we know now as the greenhouse hypothesis. He calculated that if enough coal and oil were burned to double the concentration of carbon dioxide that existed in the atmosphere before the Industrial Revolution, the temperature of the planet would increase between four and six degrees Celsius, or seven to ten degrees Fahrenheit. In the decades that followed, other researchers occasionally touched on his work. Almost fifty years ago, in 1939, G.S. Callender, a British meteorologist, speculated that a warming induced by carbon dioxide was already underway. But most scientists were otherwise occupied and, anyway, the prevailing view held that the oceans, which contain sixty times as much carbon dioxide as the atmosphere, would serve as a convenient dump, soaking up the gas as speedily as people could create it.

Then, in 1957, Roger Revelle and Hans Suess of the Scripps Institute of Oceanography in La Jolla, California, demonstrated that the upper layers of the ocean would not absorb carbon dioxide anywhere near as rapidly as had been assumed. This discovery may someday be remembered as defining the most important limit in an age of limits, the central awkward fact of a hot and constrained life. “Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past, nor be repeated in the future,” wrote Revelle and Suess. “The experiment,” they added with morbid understatement, “if adequately documented, may yield a far-reaching insight into processes determining weather and climate.”

The thirty years since have been spent compiling that adequate documentation—what quickly was dubbed the greenhouse theory became one of the main preoccupations of atmospheric science. The first task, since no one even knew for certain that carbon dioxide was increasing, was to measure its concentration in the atmosphere. In 1958, as a part of the International Geophysical Year, a Scripps scientist established a monitoring station 11,150 feet up the side of Mauna Loa in Hawaii, high enough above civilization for uncontaminated readings. In fairly short order, the data revealed a clear pattern: there was an annual fluctuation, with carbon dioxide decreasing in the springtime as plants wake up and take in carbon dioxide through photosynthesis, and increasing in the fall as leaves die, but this fluctuation peaked at a steadily higher level each year. Carbon dioxide was marching upward—concentrations in the atmosphere were rising at a rate of about one part per million each year. The rate has since increased to 1.5 parts per million annually for a total concentration to reach this year about 350 parts per million. So that, at least, was beyond dispute.

Meanwhile, researchers were working out a model of the greenhouse effect, studying other planets, for instance, to see what effect carbon dioxide had on them. Mars, with only trace amounts of carbon dioxide, reradiates most of its heat straight back to space—its average temperature is only 220 Kelvin (about 64 degrees below zero Fahrenheit), compared with 288 K (59 degrees Fahrenheit) on earth, where the atmosphere is .03 percent carbon dioxide, and 700 K (800 degrees Fahrenheit) on Venus, where carbon dioxide levels approach 97 percent. Without the greenhouse effect, Venus would be approximately the same temperature as the earth.

Other scientists, working backward with the aid of glacial cores, established the pre-industrial concentration of carbon dioxide at about 280 parts per million. And slowly researchers began to redo Arrhenius’s calculations, this time using enormously complicated general climate models to predict the outcome of a doubling of carbon dioxide. In 1979, a team of experts assembled by the National Academy of Science forecast a possible 2–3.5 degree Celsius (approximately three to six degree Fahrenheit) warming, and two years later a similar all-star team decided there were no new results that would “necessitate substantial revision” of the estimates. In 1984, an Environmental Protection Agency report predicted global temperature increases of 3.6 degrees Celsius (6.5 degrees Fahrenheit) by 2040; and a year later, in Villach, Austria, a global colloquium organized by the United Nations Environmental Programme and the World Meteorological Organization concluded, “It is now believed that in the first half of the next century a rise of global mean temperature could occur which is greater than any in man’s history.”

As agreement on the general outlines emerged, more specific forecasts began to appear. The heat would increase the most at the poles (perhaps as much as fifteen degrees Fahrenheit). The temperature could top 100 degrees seventy-eight days each year in Dallas, up from nineteen days at the present. Droughts would become more likely across the grain belt, and forest and brush fires would increase. Scientists began to work out the consequences of these changes. Some were hard to imagine. The sea level could rise a meter or more, because of glacial and perhaps polar melting, and because of the thermal expansion of a warmer ocean. As a result half or more of America’s coastal wetlands, such as those in Louisiana, would be inundated. Wheat might grow in the north of Russia (as a recent report by a UN-sponsored research group argues).* Horrendous trouble would occur in places like Bangladesh, where much of the population lives on flood plains. Some consequences were immediately understandable—New York City’s street bumps, called hummocks, increase dramatically with sustained temperatures above 90 degrees, according to the city’s Bureau of Highway Operations. The draft EPA report on the effects of a warming in America—the most extensive report of its type so far—includes various projections on everything from mosquito-borne cattle disease to Great Lakes shipping.


Meanwhile, still other theorists were finding more causes for alarm. A variety of gases existing in much smaller concentrations than carbon dioxide—including nitrous oxides, methane, and the chlorofluorocarbons (already blamed for destroying the earth’s ozone layer)—were found to act like carbon dioxide in the atmosphere. In fact, some researchers said, these gases—particularly methane, the flammable ingredient of natural gas—could be contributing nearly as much as carbon dioxide to the warming trend.

That is about where affairs stood at this time last year. Carbon dioxide was increasing and the scientific community had reached a consensus (though not, as we shall see, without some doubters) that the greenhouse effect was real, and that therefore the temperature was destined to increase dramatically in the near future. But “destined,” “future,” “projected,” “predicted,” “forecast,” “expected”—these are the words that land a topic on Nova, not the Evening News. From a scientific point of view, the question of whether the warming had actually begun was only one of several necessary tests of the greenhouse theories. From a political point of view, actual onset of the heat was a precondition for a serious discussion of the theories.

The search for what greenhouse theoreticians called the “warming signal” had been underway for some time, but it was not an easy task. We have had reliable temperature records for less than 150 years, so establishing a baseline from which to record any deviation has been difficult. Two enormous studies, however—one by researchers at East Anglia University, the other led by James Hansen of NASA’s Goddard Institute in Manhattan—took the millions and millions of temperature readings available from the last hundred years and attempted to plot them. Each group, to make a very long story short, concluded that global temperatures rose about 0.6 degrees Celsius during the last century (about one degree Fahrenheit), a figure “consistent with” though slightly lower than the greenhouse models predicted. Hansen’s group concluded that three of the four hottest years on record took place in the first half of the 1980s. The question was: Was this proof of a warming or a matter of mere natural climatic variability? Was it signal or was it “noise,” the random fluctuation that marks climate?

Then came the spring and summer of 1988. By midsummer Hansen could say that, barring an extremely cold fall, it would be the hottest twelve months on record for the globe. The awesome drought, which destroyed one third of the country’s harvest, had everyone slightly on edge even before the heat took hold in the East. But was it the greenhouse effect? On June 23, testifying before the Senate Committee on Energy and Natural Resources, Hansen was quoted as saying that it was. Actually, Hansen’s conclusion that the warming “signal” had become apparent was not based on 1988. In addition to the hundred-year finding of a 0.6 degree Celsius increase, Hansen had figured the increase over the last thirty years to be about 0.4 degrees Celsius (0.7 degrees Fahrenheit). In both cases the observed changes were about three times the standard deviation. “When we’re talking about that degree of deviation,” he said in a recent interview, “we have to feel it’s pretty unlikely to be chance fluctuation. There’s no point at which it automatically switches over, but when you get to three times the standard deviation, you’re at a level where it’s unlikely to be an accidental warming.”

This was not the same thing as saying that last summer’s heat was the result of the greenhouse effect—in fact, Hansen’s calculations showed that it would likely take until about 1990 for the effects to be felt locally. But reporters were correct in a larger sense when they said Hansen thought the warming had begun. He would have thought the same thing if it had been a cold, wet summer—but if it had been a cold, wet summer he wouldn’t have made the papers, much less the front page. “I would say there was not a sharp change in my assessment—there was more of a sharp change in the attention, which had a lot to do with the temperature the day I testified,” he said.


Hansen’s proclamation seems to have had the effect of convincing people in the street that there may be trouble in the sky—complete oblivion has turned to a nervous fretfulness, but not an all-out conversion to the greenhouse theory. Which is understandable—other dire predictions have failed to materialize in the past, after all. (There is too much oil at present, not too little as so many feared during the 1970s.) And even among the scientists committed to the greenhouse theory, there is debate about whether the warming has actually shown up, or if 1988 was a freak. Stephen Schneider, of the National Center for Atmospheric Research in Boulder, Colorado, told the Senate in August:

A stiff “I told you so” to scientific doubters and policy delayers might offer some measure of personal satisfaction to those of us who have been advocating a global response to atmospheric change for the past fifteen years. However, scientific caution constrains me to respond instead: “I told you so—almost.”

Schneider offered a device for thinking about the problem—imagine a pair of dice with 12,000 sides, he said. Each roll determines the weather. “Most climatologists do agree that the current evidence is strong that human activities are loading the dice with many more warm faces, and perhaps a few dry ones, too,” he said. However, the warm years of the 1980s, or last summer’s drought, are not necessarily “proof” that the dice are loaded, any more than that the dealer drawing four aces “proves” he’s dealing off the bottom of the deck. “Different tastes cause some people to accept the reality of a hypothesized climatic change at a low signal-to-noise ratio, whereas others might not believe in the reality of the change until a large signal has persisted for a very long time,” Schneider told the Senate. “Indeed, such confusing and contradictory statements from experts are frequently found in media accounts of global warming. Quite simply, accepting any particular signal-to-noise ratio as ‘proof’ of global warming reflects the personal judgment of the investigator.” And some scientists who have looked for proof of a signal—Tim Barnett at Scripp’s Institute for instance—say they see no sign so far. Still, disagreements over whether the warming has yet begun are not the same as disagreements about the theory. “No theory in atmospheric science” is as widely accepted as the greenhouse hypothesis, Schneider said recently.

In fact other scientists—a distinct minority—take issue with various parts or all of the greenhouse argument. Some believe that the world is actually cooling, not heating up, and the increased temperatures of the last century reflect only the “urban heat island effect,” the fact that cities full of concrete and exhaust “have grown up around thermometers,” skewing readings. Both the Hansen and East Anglia studies corrected for this effect (without it, says Hansen, the 0.6 degree Celsius rise shows up as more than 0.7 degrees), but critics charge they didn’t go far enough. “The National Weather Service has identified a set of rural stations that are judged suitable for drawing inferences about climate trends. Almost all show markedly lower temperatures since 1940,” said Kenneth E.F. Watt, professor of environmental studies at the University of California at Davis in an August letter to The New York Times. (Watt has elsewhere called the greenhouse effect the “laugh of the century.”) Indeed, recent reports indicate that a tropical “cold event” called La Niña, a still mysterious weather pattern originating in Pacific equatorial waters, could decrease global temperatures next year. “But these are only bumps,” Hansen says.

There are also those who argue that the greenhouse effect will produce “feedbacks” of one sort or another that will ameliorate the temperature rise. S. Fred Singer, a former professor at the University of Virginia and now chief scientist for the Department of Transportation, has taken a part-time job as greenhouse curmudgeon. In a “My Turn” piece in Newsweek and an op-ed essay in The Wall Street Journal, he argued that doomsayers have been wrong before, and that there is an unprecedented need at the moment for skepticism. He suggested that as the earth heats up clouds might form, and that all that white cover will reflect sunlight off the planet before it has a chance to reach the surface, or that some other factor may intervene. Greenhouse scientists, he implies, are jumping to conclusions because they like to “attend delightful international conferences” and testify before Congress.

In fact, the computer models have tried to take increased cloudiness into account. Though Hansen admits the cloud factor may be a weakness in the model, he says most projections show cloud cover increasing the temperature. The models have other weaknesses—their estimates of the patterns of circulation of deep ocean waters remain uncertain and, as a result, it is hard to say how much carbon dioxide and heat the oceans will absorb. But it is worth noting that the feedback effects are as likely to be bad as good. Say a significant area of snow and ice melts—there will be a big patch of brown or dark blue to absorb the sun’s heat. Higher carbon dioxide levels could cause increased plant growth (the US Department of Agriculture has grown what one journalist called “supercucumbers” in a carbon dioxide–enhanced hothouse), but the corresponding higher temperatures and dryness would likely outweigh its benefits.

Some biologists are terrified that if the temperature climbs anywhere nearly as rapidly as is currently predicted, forests will be trapped out of position—trees that should be in the climate suddenly found in northern Quebec will still be in southern New York, and as a result they will die. Balsam firs in northern Minnesota, for instance, could begin to die quickly with “substantial declines” over just a few decades, the new EPA report to Congress, released in November, estimated. And when they die they will release huge amounts of carbon dioxide into the environment, in a sort of chain reaction. A small-scale analogue to this serial process may have been happening this summer when Yellowstone burned—though there’s much confusion about the factors that caused the vast extent of the devastation, everyone agrees that if the summer had not been dry and hot, Montana would not have been burned so badly. And not only did the fire fill the air with carbon dioxide, but those dead trees won’t be there next spring to suck up their share of the gas. That is to say; one thing can lead to another. In the draft of its report to Congress, the EPA projects possible consequences region by region, as in the accompanying chart for the southeastern states. The outlook seems bleak if only a considerable part of the consequences takes place. The greenhouse temperature estimates, remember, are not “worst-case scenarios.” It is “equally likely,” Schneider told Congress, that the projections are too low as that they are too high.

Still, we are largely dependent on the skill of the experts. This is not like economics, where everyone can extrapolate from his household budget to form an opinion on what’s happening. Most of us don’t know enough chemistry to begin to assess the contending arguments. A series of metaphors, beginning with the “greenhouse,” allow us to understand the bare outlines of the theory, but they do not permit us to criticize it. This was brought home for me by reading the works of John Hamaker, a retired engineer, and a recently published book, The End, by one of his followers, Larry Ephron. Neither is a member of the scientific establishment, and both are skeptical of the warming theories. In fact, they are utterly convinced that increasing carbon dioxide will trigger an Ice Age—trigger it, in fact, within the next two to four years, resulting in mass starvation and the extermination of civilization as we know it by 1995. They argue that, along with the burning of fossil fuels, forests are dying naturally (and giving up their carbon) because the mineral content of the soil has been naturally depleted. The increased carbon dioxide will cause a greenhouse effect, but very quickly that will generate huge masses of clouds, which will cool northern latitudes and dump huge amounts of snow. Shortly, one of these bad winters will carry over into the summer, freezing the entire grain crop and causing general starvation. The warming theories, they charge, are a government cover-up.

My point here is not that they’re correct—the established scientists I talked to dismiss the Hamaker theory. It’s just that, more than in most matters of national policy, we are largely at the mercy of specialists when it comes to the greenhouse problem. (If it’s any comfort, the same steps used to counter a greenhouse warming would also help counter a greenhouse Ice Age, though the Hamaker theory also calls for grinding huge quantities of rock into dust to “remineralize” the soil. In any event, Hamaker declared some years ago that if comprehensive steps weren’t taken by 1985 it would be too late and we’d be in an Ice Age within the decade, so it may be there’s not much to do about it anyway.)

The situation, then, is one of scattered dissent amid general scientific consensus. As this configuration seems likely to persist for at least a while, how should we proceed? If the greenhouse theories are correct, no course of action will prevent some significant warming—all the researchers agree that the amount of carbon dioxide we’ve already pumped into the air condemns us to a significant temperature increase.

But what about the future? Should we wait for absolute scientific certainty, for everyone to agree they’ve heard the signal above the noise? This is pretty much what happened with the controversy over ozone—the fears that industrial chemicals known as chlorofluorocarbons or CFCs and used as aerosol propellants and refrigerants were eroding the layer of ozone that surrounds the earth at altitudes ranging between ten and thirty miles above the planet’s surface. The ozone layer shields the surface of the earth from the sun’s ultraviolet radiation, which can damage cells of living organisms and cause cancer.

The first alarms about chlorofluoro-carbons were heard in the early 1970s, and a graphic vision of a world underarm-deodorizing its way to destruction moved this country to ban aerosol sprays; but the use of the chemicals for other purposes, chiefly refrigeration and automobile air-conditioning, continued to rise. Then, five years ago, a wide “hole” was discovered in the ozone layer above the South Pole, a hole that has grown each year since and seemed to some experts clearly the result of CFCs. At first even this discovery didn’t prompt much action—a few scientists said the hole might be caused by polar winds. Reagan’s secretary of the interior, Donald Hodel, said that since CFC’s were useful to industry, people should use sunglasses and baseball caps as protection against retina damage and skin cancer. But politicians of many nations, gathered in Montreal in 1987, agreed to 50 percent cuts in CFC production, to be replaced by a number of substitute chemicals. In the intervening months, before that treaty has even gone into effect, new evidence has emerged about the effects of CFCs and similar chemicals, and late in September, EPA administrator Lee Thomas called for a total ban on the chemicals. It took scientific unanimity to win even the halfway measures. But since CFCs are far from having a central place in our lives, and there’s plenty of available money for finding substitutes, opposition from industry, though scandalously stiff for a long while, eventually collapsed.

Dealing with carbon dioxide, however, will be much harder. Aside from the harm caused by tropical deforestation (burning the rain forests contributes as much as a fifth of the annual human contribution of carbon dioxide to the atmosphere) the problem is that we in the West use too much fossil fuel. At the moment, as the oil crisis gives way to the oil glut, we are going backward. Today’s paper carries the news that Cadillac is stretching the Sedan de Ville’s wheelbase by nine inches for the new model year (making it over seventeen feet long) while Buick is adding eleven inches to the Riviera. There’s no question that we could be going in the other direction—that we could increase energy efficiency by driving smaller cars, insulating houses, and dozens of similar plans, and cut down on carbon emissions.

In State of the World 1988, the Worldwatch Institute’s latest checkup on the globe, it is estimated that while a 1 percent annual increase in the rate of energy efficiency would allow carbon dioxide levels to nearly double (from 346 to 600 parts per million) by 2075, a 2 percent increase in efficiency would keep carbon dioxide levels down to 463 parts per million by that date, allowing a much less catastrophic rise in temperatures. In temperament the Worldwatch Institute is a group much like the League of Women Voters; it tries to deal with calamitous events rationally and constructively, and always offers logical solutions. We should probably be doing all they suggest. But this is unlikely, since it runs counter to the momentum of the last few millennia.

Irving Mintzer, a Washington researcher, has calculated a way to cut the projected warming in half. Along with ending deforestation, he assumes a 1.5 percent annual increase in energy efficiency, stepped up research and development of solar energy, and strong policies that sharply increase coal, oil, and gas prices—in every country in the world. Though Mintzer does not calculate the direct costs of this transition, his estimates allow economic growth to continue at expected levels. Still, the transition will involve a huge effort of will. In return we would be committed to a warming of between 1.4 and 4.2 degrees Celsius (2.5 and 7.5 degrees Fahrenheit) by 2075, as opposed to the rise of as much as 16 degrees Celsius (nearly 30 degrees Fahrenheit) in his worst case projection; but this is still a change unprecedented in all of human history. There will be a strong temptation to agree with Dr. Chauncey Starr, president emeritus of the Electric Power Research Institute, an industry-sponsored enterprise, who pointed out that cutting carbon dioxide emissions from American utilities in half would only set the warming back a few years. “What,” he asked, “would you be willing to pay for that?”

Hard as such changes will be, they will obviously be more severe and thus harder if we wait to shake all uncertainty out of the hypotheses. “It is often said,” Schneider told the Senate committee,

“Won’t ten more years of research provide us with answers?” Indeed, I heard just such an argument from a government official at the outset of my career in the early 1970s, and then again from a Department of Energy official in the early 1980s…. If we choose to wait for more scientific certainty over details before preventive actions are initiated, then this is done at the risk of our having to adapt to a larger, faster-occurring dose of greenhouse gases, acid rain, and ozone depletion.

Mintzer has attempted to calculate the price of pausing: thirty years’ delay in implementing his harsh policies might mean an extra warming of as much as 0.8 degrees Celsius (1.5 degrees Fahrenheit), a considerable amount. And the price might be higher than that. William Ruckelshaus, the former administrator of the EPA and no radical, has said in regard to the greenhouse effect:

The ultimate danger is that by remaining reliant on the “catastrophe theory of planning” in an era producing catastrophes of a magnitude greater than in the past, we can place our institutions in situations where precipitate action is the sole option—and it is then that our institutions themselves can be imperiled and individual rights overrun.

On the other side, there is the aforementioned S. Fred Singer. “We need,” he argues, “an analysis that weighs the risk from a delay in instituting far-reaching controls against the possibility of substantially improving the science so that predictions will become more certain.” (Mr. Singer also noted, last fall, that “some scientists are now beginning to fret about the recently observed Antarctic ‘ozone hole.’… So far the ozone hole has had little effect on skin cancer rates in the United States.”) The Reagan administration has been somewhat more straightforward. Though the greenhouse effect is “cause for serious concern,” undersecretary of energy Donna Fitzpatrick admitted, “significant gaps exist in our knowledge…. These scientific uncertainties must be reduced before we commit the nation’s economic future to drastic and potentially misplaced policy responses.”

The tie will be broken, I suspect, by the weather. Another horribly hot summer and the frightened will overwhelm the skeptics; with an anomalously cool and wet summer (which is entirely possible—La Niña may chill us, and in any event, remember Schneider’s dice), everyone will forget about the greenhouse effect while the warming gains momentum. In the meantime, we seem to be heading for a warming of about the size forecast by Svante Arrhenius.

This Issue

December 8, 1988