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Part I

The Present

A New Atmosphere

Nature, we believe, takes forever. It moves with infinite slowness through the many periods of its history, whose names we dimly recall from high school biology—the Devonian, the Triassic, the Cretaceous, the Pleistocene. Ever since Darwin, nature writers have taken pains to stress the incomprehensible length of this path. “So slowly, oh, so slowly have the great changes been brought about,” wrote John Burroughs at the turn of the century. “The Orientals try to get a hint of eternity by saying that when the Himalayas have been ground to powder by allowing a gauze veil to float against them once in a thousand years, eternity will only just have begun. Our mountains have been pulverized by a process almost as slow.” We have been told that man’s tenure is as a minute to the earth’s day, but it is that vast day which has lodged in our minds. The age of the trilobites began some 600 million years ago. The dinosaurs lived for nearly 140 million years. Since even a million years is utterly unfathomable, the message is: Nothing happens quickly. Change takes unimaginable—“geologic”—time.

This idea about time is essentially mistaken. Muddled though they are scientifically, the creationists, believing in the sudden appearance of the earth some seven thousand years ago, may intuitively understand more about the progress of time than the rest of us. For the world as we know it—that is, the world with human beings formed into some sort of civilization, the world in which North America, Europe, and much of the rest of the planet are warm enough to support large human populations—is of quite comprehensible duration. People began to collect in a rudimentary society in the north of Mesopotamia some ten or twelve thousand years ago. Using thirty years as a generation, that is three hundred and thirty to four hundred generations ago. Sitting here at my desk, I can think back five generations in my family—I have seen photos of four. That is, I can think back nearly one-sixtieth of the way to the start of civilization. A skilled genealogist might get me one-thirtieth of the distance back. And I can conceive of how most of those forebears lived. From the work of archaeologists and from accounts like those in the Bible I have some sense of daily life at least as far back as the time of the pharaohs, which is more than a third of the way. Two hundred and sixty-five generations ago Jericho was a walled city of three thousand souls. Two hundred and sixty-five is a large number, but not in the way that six hundred million is a large number—not inscrutably large.

Or look at it this way: There are plants on this earth as old as civilization. Not species—individual plants. The General Sherman tree in California’s Sequoia National Park may be a third as old, about four thousand years. Certain Antarctic lichens date back ten thousand years. A specific creosote plant in the southwestern desert was estimated recently to be 11,700 years of age.

And within that ten or twelve thousand years of civilization, of course, time is not uniform. The world as we really know it dates back perhaps to the Renaissance. The world as we really, really know it dates back to the Industrial Revolution. The world we actually feel comfortable in dates back to perhaps 1945. It was not until after World War II, for instance, that plastics came into widespread use.

In other words, our reassuring sense of a timeless future, which is drawn from that apparently bottomless well of the past, is a delusion. True, evolution, grinding on ever so slowly, has taken billions of years to create us from slime, but that does not mean that time always moves so ponderously. Events, enormous events, can happen quickly. We’ve known this to be true since Hiroshima, of course, but I don’t mean that quickly. I mean that over a year or a decade or a lifetime big and impersonal and dramatic changes can take place. We’re now comfortable with the bizarre idea that continents can drift over eons, or that continents can die in an atomic second; even so, normal time seems to us immune from such huge changes. It isn’t, though. In the last three decades, for example, the amount of carbon dioxide in the atmosphere has increased more than 10 percent, from about 315 to more than 350 parts per million. In the last decade, an immense “hole” in the ozone layer has opened above the South Pole. In the last half-decade, the percentage of West German forests damaged by acid rain has risen from less than 10 to more than 50. According to the Worldwatch Institute, in 1988—for the first time since that starved Pilgrim—America ate more food than it grew. Burroughs again: “One summer day, while I was walking along the country road on the farm where I was born, a section of the stone wall opposite me, and not more than three or four yards distant, suddenly fell down. Amid the general stillness and immobility about me the effect was quite startling.… It was the sudden summing up of half a century or more of atomic changes in the material of the wall. A grain or two of sand yielded to the pressure of long years, and gravity did the rest.” In much the same comforting way that we think of time as imponderably long, we consider the earth to be inconceivably large. Although with the advent of spaceflight it became fashionable to picture the planet as a small orb of life and light in a dark, cold vastness, that image never really sank in. To any one of us, the earth is enormous, “infinite to our senses.” Or, at least, it is if we think about it in the usual horizontal dimensions: even the frequent flier with the most bonus miles has seen only a tiny fraction of the earth’s terrain; even the most intrepid mariner cuts a single furrow across the ocean field. There are vast spaces between my house, in the Adirondack Mountains of upstate New York, and Manhattan—it’s a five-hour drive through one state in one country of one continent. But from my house to the post office at the end of the road is a trip of six and a half miles. On a bicycle it takes about twenty-five minutes, in a car eight or nine. I’ve walked it in an hour and a half. If you turned that trip on its end, the twenty-five-minute pedal past Bateman’s sandpit and the graveyard and the waterfall and Allen Hill would take me a mile beyond the height of Mt. Everest, past the point where the air is too thin to breathe without artificial assistance. Into that tight space, and the layer of ozone just above it, is crammed all that is life and all that maintains life.

This, I realize, is a far from novel observation. I repeat it only to make the same case I made with regard to time. The world is not so large as we intuitively believe—space can be as short as time. For instance, the average American car driven the average American distance—ten thousand miles—in an average American year releases its own weight in carbon into the atmosphere. Imagine each car on a busy freeway pumping a ton of carbon into the atmosphere, and the sky seems less infinitely blue.

Along with our optimistic perceptions of time and space, some comparatively minor misunderstandings distort our sense of the world. Consider the American failure to convert to the metric system. Like all schoolchildren of my vintage, I spent many days listening to teachers explain liters and meters and hectares and all the other logical units of measurement, and promptly forgot it all. We all did, except those of us who became scientists, who always use such units. As a result, if I read there will be an 0.8-degree Celsius rise in the temperature between now and the year 2000, it sounds less ominous than a degree and a half Fahrenheit. Similarly, a ninety-centimeter rise in sea level sounds less ominous than a one-yard rise; and neither of them sounds so ominous until one stops to think that over a beach with a normal slope such a rise would bring the ocean ninety meters (that’s 295 feet) above its current tide line. In somewhat the same way, the logarithmic scale that we use to determine the overall composition of our soils or waters—pH—distorts reality like a fun-house mirror for anyone who doesn’t use it on a daily basis. For instance, “normal” rainwater has a pH of 5.6. But the acidified rain that falls on the Adirondacks has a pH between 4.6 and 4.2—that is, it is ten to fourteen times as acid.

Of all such quirks, though, the most ephemeral may be the most significant. It is an accident of the calendar: we live too close to the year 2000. Forever we have read about the year 2000. It has become a symbol of the bright and distant future, when we will ride in air cars and talk on video phones. The year 2010 still sounds far off, almost unreachably far off, as though it were on the other side of a great body of water. If someone says to me that a very bad thing will happen in 2010, I may feign concern but subconsciously I file it away. So it always shocks me when I realize that 2010 is almost as close as 1970—closer than the breakup of the Beatles—and that the turn of the century is no further in front of us than Ronald Reagan’s election to the presidency is behind. We live in the shadow of a number, and that makes it hard for us to see the future.

Our comforting sense of the permanence of our natural world, our confidence that it will change gradually and imperceptibly if at all, is, then, the result of a subtly warped perspective. Changes that can affect us can happen in our lifetime in our world—not just changes like wars but bigger and more sweeping events. I believe that without recognizing it we have already stepped over the threshold of such a change: that we are at the end of nature.

By the end of nature I do not mean the end of the world. The rain will still fall and the sun shine, though differently than before. When I say “nature,” I mean a certain set of human ideas about the world and our place in it. But the death of those ideas begins with concrete changes in the reality around us—changes that scientists can measure and enumerate. More and more frequently, these changes will clash with our perceptions, until, finally, our sense of nature as eternal and separate is washed away, and we will see all too clearly what we have done.

SVANTE ARRHENIUS took his doctorate in physics at the University of Uppsala in 1884. His thesis earned him the lowest possible grade short of outright refusal. Nineteen years later that thesis, which was on the conductivity of solutions, earned him the Nobel Prize. He subsequently accounted for the initial poor reception this way: “I came to my professor, Cleve, whom I admired very much, and I said, ‘I have a new theory of electrical conductivity as a cause of chemical reactions.’ He said, ‘This is very interesting,’ and then he said, ‘Goodbye.’ He explained to me later that he knew very well that there are so many different theories formed, and that they are almost certain to be wrong, for after a short time they disappeared; and therefore, by using the statistical manner of forming his ideas, he concluded that my theory also would not exist long.” Arrhenius’s understanding of electrolytic conduction was not his only shrug-provoking new idea. As he surveyed the first few decades of the Industrial Revolution he realized that man was burning coal at an unprecedented rate, “evaporating our coal mines into the air.” Scientists already knew that carbon dioxide, a by-product of fossil fuel combustion, trapped infrared radiation that would otherwise have reflected back out to space. Jean-Baptiste Joseph Fourier, who developed the theory of heat conduction (and who was also one of the earliest students of Egyptian archaeology), had speculated about the effect nearly a century before, and, indeed, had even used the hothouse as a metaphor. But it was Arrhenius who, employing measurements of infrared radiation from the full moon, did the first calculations of the possible effects of man’s stepped-up production of carbon dioxide. The average global temperature, he concluded, would rise as much as 9 degrees if the amount of carbon dioxide in the air doubled from its preindustrial level. That is, heat waves in mid-American latitudes would run into the 110s, the 120S, the 130s; the seas would rise many feet; crops would wither in the fields.

This idea floated in obscurity for a very long time. Now and then a few scientists took it up—the British physicist G. S. Callendar speculated in the 1930s, for instance, that increasing carbon dioxide levels could account for a warming of North America and northern Europe that meteorologists had begun to observe in the 1880s. But that warming seemed to be replaced by a temperature decline around 1940; anyway, most scientists were too busy creating better living through petroleum to be bothered with such long-term speculation. And those few who did consider the problem concluded that the oceans, which hold much more carbon dioxide than the atmosphere, would soak up any excess that man churned out—that the oceans were an infinite sink down which to pour the problem.

Then, in 1957, two scientists at California’s Scripps Institution of Oceanography, Roger Revelle and Hans Suess, published a paper in the journal Tellus on this matter of the oceans. What they found was dismaying. No, more than dismaying—what they found may turn out to be the single most important limit in an age of limits, the central awkward fact of a hot and constrained planet.

What they found was that the conventional wisdom was wrong: the upper layer of the oceans, where air and sea meet and transact their business, would absorb very little of the excess carbon dioxide produced by man.

To be precise, what they demonstrated was that “a rather small change in the amount of free carbon dioxide dissolved in seawater corresponds to a relatively large change in the pressure of carbon dioxide at which the oceans and the atmosphere are at equilibrium.” To be dramatic, what they showed was that most of the carbon dioxide being pumped into the air by millions of smokestacks, furnaces, and car exhausts would stay in the air, where, presumably, it would gradually warm the planet. “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,” they wrote. This experiment, they added with the morbid understatement of true scientists, “if adequately documented, may yield a far-reaching insight into the processes determining weather and climate.” While there are other parts to this story—the depletion of the ozone, acid rain, genetic engineering—the story of the end of nature really begins with that greenhouse experiment, with what will happen to the weather.

WHEN WE DRILL into an oil field, we tap into a vast reservoir of organic matter that has been in storage for millennia. We unbury it. When we burn that oil (or coal or natural gas) we release its carbon into the atmosphere in the form of carbon dioxide. This is not pollution in the normal sense of the word. Carbon monoxide is “pollution,” an unnecessary by-product. A clean-burning engine releases less of it. But when it comes to carbon dioxide, a clean-burning engine is no better than the motor on a Model T. It will emit about 5.6 pounds of carbon in the form of carbon dioxide for every gallon of gasoline it consumes. In the course of about a hundred years, our various engines and fires have released a substantial amount of the carbon that has been buried over time. It is as if someone had scrimped and saved his entire life, and then spent every cent on one fantastic week’s debauch. In this, if nothing else, wrote the great biologist A. J. Lotka, “the present is an eminently atypical epoch.” We are living on our capital, as we began to realize during the gas crises of the 1970s. But it is more than waste, more than a binge. We are spending that capital in such a way as to alter the atmosphere. It is like taking that week’s fling and, in the process, contracting a horrid disease.

There has always been, at least since the start of life, a certain amount of carbon dioxide in the atmosphere, and it has always trapped a certain amount of sunlight to warm the earth. If there were no carbon dioxide, our world might resemble Mars—it would probably be so cold as to be lifeless. A little bit of greenhouse is a good thing, then—the plant that is life thrives in its warmth. The question is: How much? On Venus the atmosphere is 97 percent carbon dioxide. As a result, it traps infrared radiation a hundred times more efficiently than the earth’s atmosphere, and keeps the planet a toasty 700 degrees warmer than the earth. The earth’s atmosphere is mostly nitrogen and oxygen; there’s currently only about .035 percent carbon dioxide, hardly more than a trace. The worries about the greenhouse effect are actually worries about raising that figure from .035 percent to .055 or .06 percent, which is not very much. But plenty, it turns out, to make everything different.

In 1957, when Revelle and Suess wrote their paper, no one even knew for certain that carbon dioxide was increasing. The Scripps Institution hired a young scientist, Charles Keeling, and he set up monitoring stations at the South Pole and 11,150 feet above the Pacific on the side of Mauna Loa in Hawaii. His readings soon confirmed the Revelle-Suess hypothesis: the atmosphere was filling with carbon dioxide. When Keeling took his first readings in 1958, the atmosphere at Mauna Loa contained about 315 parts per million of carbon dioxide. Subsequent readings showed that each year the figure increased, and at a growing rate. Initially the annual increase was about .7 parts per million; now it is at least twice that, or 1.5 parts per million. Admittedly, 1.5 parts per million sounds absurdly small. But by drilling holes into glaciers and testing the air trapped in ancient ice, even by looking at the air sealed in old telescopes, scientists have calculated that the atmosphere prior to the Industrial Revolution contained about 280 parts per million carbon dioxide, and, in fact, that that was as high a level as had been recorded in the past 160,000 years. The current reading is near 360 parts per million. At a rate of 1.5 parts per million per year, pre–Industrial Revolution concentration of carbon dioxide in the atmosphere would be doubled in the next 140 years. And since, as we have seen, carbon dioxide at a very low level helps determine the climate, carbon dioxide at double that very low level, even if it’s still small in absolute terms, could have enormous effect. It’s like misreading a recipe and baking bread for two hours instead of one: it matters.

But the 1.5 parts per million annual increase is not a given; it seems nearly certain to go higher. The essential facts here are demographic and economic, not chemical. The world’s population has more than tripled in this century and, according to UN statistics released in May of 1989, is expected to double and perhaps nearly triple again before reaching a plateau in the next century. (At the moment, after a decade or two of improving, the trends may be getting worse—China’s fertility rate increased from 2.1 to 2.4 children per woman in 1986 and has remained there since.) And the tripled population has not contented itself with using only three times the resources. In the last century industrial production has grown fiftyfold. Four-fifths of that growth has come since 1950, and almost all of it, of course, has been based on fossil fuels. And in the next half century, the United Nations predicts, this $13 trillion economy will grow another five to ten times larger.

These physical facts are almost as stubborn as the chemistry of infrared absorption. They mean that the world will use more energy—between 2 and 3 percent more each year by most estimates. And the largest increases may come in the use of coal. That is bad news, since coal spews more carbon dioxide into the atmosphere than any other sort of energy (twice as much as natural gas, for instance). China, which has the world’s largest coal reserves and recently surpassed the Soviet Union as the world’s largest coal producer, has plans to almost double her coal consumption by the year 2000.

In other words, this is not something that has been happening for a long time. It is not a marathon or the twenty-four hours of Le Mans. It’s a hundred-yard dash, a drag race, getting faster all the time. If energy use and other contributions to carbon dioxide levels continue to grow exponentially, a model devised by the World Resources Institute predicts that carbon dioxide levels prior to the Industrial Revolution will have doubled by about 2040; if they grow somewhat more slowly, as most estimates predict, the level would double sometime around 2070. The leaders of the seven major industrial democracies agreed at their summit in mid-July 1989 to “strongly advocate common efforts” to limit carbon dioxide, but nothing more, in part because the solutions are neither obvious nor easy. For example, installing some sort of scrubber on a power-plant smokestack to get rid of the carbon dioxide would seem an obvious fix. But a system that removed 90 percent of the carbon dioxide would also reduce the effective capacity of the plant 80 percent. One oft-heard suggestion is to use more nuclear power. But because so much of our energy use is for things like automobile fuel, even if we mustered the political will and economic resources to quickly replace every single electric generating station with a nuclear power plant, our total carbon dioxide output would fall little more than a quarter. Ditto, at least initially, for cold fusion or hot fusion or any other clean method of producing energy. So the sacrifices demanded may be on a scale we can’t imagine and won’t like.

BURNING FOSSIL FUELS is not the only method human beings have devised to increase the level of atmospheric carbon dioxide. Burning down a forest also sends clouds of carbon into the air. Trees and shrubby forests still cover 40 percent of the land on earth, but this area has shrunk by about a third since preagricultural times, and that shrinkage, it almost goes without saying, is accelerating. In the Brazilian state of Pará, for instance, 180,000 square kilometers was deforested between 1975 and 1986; in the hundred years preceding that decade, settlers had hacked away about 18,000 square kilometers. “At night, roaring and red, the forest looks to be at war,” one correspondent wrote. The Brazilian government has tried to slow down the burning, but it employs only nine hundred forest wardens for an area larger than Europe.

This is not news—it’s well known that the rain forests are disappearing, and are taking with them most of the world’s plant and animal species. But forget for a moment that we are losing a unique resource, a cradle of life, irreplaceable grandeur, and so forth. The dense, layered rain forest contains three to five times more carbon per acre than an open, dry forest: an acre of Brazil up in flames equals three to five acres of Yellowstone. Deforestation currently adds between 1 billion and 2.5 billion tons of carbon to the atmosphere annually, 20 percent or more of the amount produced by fossil fuel burning. And that acre of rain forest, which has poor soil and can support crops for only a few years, soon turns to desert, or, at least, to pastureland.

And where there’s pasture there are cows, and what cows support in their intestines are huge numbers of anaerobic bacteria, which break down the cellulose that cows chew. That is why cows, unlike people, can eat grass. Why does this matter? Because those bugs that digest the cellulose excrete methane. Methane, or natural gas, gives off carbon dioxide when burned, though only half as much as oil. When it escapes into the atmosphere without being burned, though, it is twenty times more efficient than carbon dioxide at trapping solar radiation and warming the planet. So even though it makes up less than two parts per million of the atmosphere, it can have a significant effect. Even though much of the methane in the atmosphere comes from seemingly “natural” sources—the methanogenic bacteria—their present huge numbers are clearly man made. Mankind owns 1.2 billion head of cattle, not to mention a large number of camels, horses, pigs, sheep, and goats, and together they belch about 73 million metric tons of methane into the air each year, a 435 percent increase in the last century. The buffalo and wildebeest they displaced belched as well, but their numbers were not as great.

We have raised the number of termites, too, and still more dramatically. Termites have the same bacteria in their intestines as cows; that is why they can digest wood. We tend to think of termites as house wreckers, but in most of the world they are house builders, erecting elaborate, rock-hard mounds twenty or thirty feet high. Inside these fortresses an elaborate hierarchy of termites guards the queens—some of the termites sport sharp pincers longer than their bodies; others have heads shaped like drain plugs, so they can block up the interior passages against intruders; still others explode when attacked, or squirt poison. If a bulldozer razes a mound, worker termites can rebuild it in hours. They are like most animals in that their numbers are limited only by the supply of food. And when we hack down a rain forest, all of a sudden there’s dead wood everywhere—food galore. Termites have a “high digestion efficiency,” much higher than earthworms, says Patrick Zimmerman of the National Center for Atmospheric Research. They can break down 65 to 95 percent of the carbon in the wood they ingest. (Wood is 50 percent carbon.) And they can excrete phenomenal amounts of methane—a single mound might give off five liters a minute. As the deforestation has proceeded, termite numbers have boomed. There is now, some scientists estimate, a half ton of termites for every man, woman, and child on earth—that is, six or seven people’s worth of termites for every actual person.

Researchers differ on the importance of termites as a methane source, but everyone agrees about the rice paddies. The oxygenless mud of marsh bottoms has always sheltered methane-producing bacteria. (Methane is sometimes known as swamp gas.) But rice paddies may be even more efficient—the rice plants act almost like straws, venting as much as 115 million tons of the gas a year. Rice paddies, of course, increase in number and size every year, so that those 2.4 children per Chinese woman will have enough to eat.

And then there are landfills: 30 percent of a typical landfill is “putrescible,” Zimmerman says—it rots, creating methane. At the main New York City landfill on Staten Island, gas is pumped from under the trash straight to thousands of homes, but in most places it just seeps out.

What’s more, scientists have recently begun to think that these sources alone can’t account for all the methane. “If you look more carefully,” the Harvard physicist Michael McElroy says, “you do not come away with an awfully comfortable feeling.” For one thing, scientists have begun to be able to measure isotopic concentrations: there is a “light” methane from cattle and termites and rice paddies, but also a “heavy” methane from someplace else. And here—forget the poison-squirting termites—is where the story begins to get a little scary. An enormous amount of methane is locked up as hydrates in the tundra and in the mud of the continental shelves. These are, in essence, methane ices; the ocean muds alone may hold 10 trillion tons of methane. If the greenhouse effect is beginning to warm the oceans, if it is starting to thaw the permafrost, then some scientists say that eventually those ices could start to melt. Some estimates of the potential methane release run as high as .6 billion tons a year, an amount that could more than double the present atmospheric concentration. This would be a nasty example of a feedback loop, with the altered atmosphere causing further alterations: Warm the atmosphere and release methane; release methane and warm the atmosphere; and so on.

When all sources are combined, we’ve done an even more dramatic job of increasing methane than of increasing carbon dioxide. Samples of ice from Antarctic glaciers show that the concentration of methane in the atmosphere has fluctuated between 0.3 and 0.7 parts per million for the last 160,000 years, reaching its highest levels during earth’s warmest period. In 1987 methane composed 1.7 parts per million of the atmosphere. That is, there is now two and a half times as much methane in the atmosphere as there was at any time through three glacial and interglacial periods. And concentrations are rising at a regular 1 percent a year.

Man is also pumping smaller quantities of many other greenhouse gases into the atmosphere. Nitrous oxide, chlorine compounds, and some others all trap warmth even more efficiently than carbon dioxide. Scientists now believe that methane and the rest of these gases, though their concentrations are small, will together account for 50 percent of the projected greenhouse warming—that is, taken together they are as much of a problem as carbon dioxide. And as all these compounds warm the atmosphere, it will be able to hold more water vapor, itself a potent greenhouse gas. The British Meteorological Office calculates that this extra water vapor will warm the earth two-thirds as much as the carbon dioxide alone.

SO—WE HAVE INCREASED the amount of carbon dioxide in the air by about 25 percent in the last century, and will almost certainly double it in the next; we have more than doubled the level of methane; we have added a soup of other gases. We have substantially altered the earth’s atmosphere.

This is not like local pollution, not like smog over Los Angeles. This is the earth’s entire atmosphere. If you’d climbed some remote mountain in 1960 and sealed up a bottle of air at its peak, and did the same thing this year, the two samples would be substantially different. Their basic chemistry would have changed. Most discussions of the greenhouse gases rush immediately to their future consequences—is the sea going to rise?—without pausing to let the simple fact of what has already happened sink in. The air around us, even where it is clean, and smells like spring, and is filled with birds, is different, significantly changed.

That said, the question of what this new atmosphere means must arise. If it means nothing, we’d soon forget about it, since the air would be as colorless and odorless as before and as easy to breathe. And, indeed, the direct effects are unnoticeable. Anyone who lives indoors breathes carbon dioxide at a level several times the atmospheric concentration without ill effects; the federal government limits industrial workers to a chronic exposure of five thousand parts per million, or almost fifteen times the current atmospheric levels; a hundred years from now a child at recess will still breathe far less carbon dioxide than a child in a classroom.

This, however, is only mildly good news. The effects on us will be slightly less direct, but nevertheless drastic: changes in the atmosphere will change the weather, and that will change recess. The temperature, the rainfall, the speed of the wind will change. The chemistry of the upper atmosphere may seem an abstraction, a text written in a foreign language. But its translation into the weather of New York and Cincinnati and San Francisco will alter the lives of all of us.

The theories about the effects all begin with an estimate of expected warming. Arrhenius, you recall, said that doubling the preindustrial concentration of carbon dioxide would raise temperatures 9 degrees. The new wave of concern that began with Revelle and Suess’s article and Keeling’s Mauna Loa data has led to the development of vastly complex computer models of the entire globe. In those models the globe is divided into thousands of boxes, and each box is divided vertically into a large number of layers, usually ten or more, representing the various layers of the atmosphere and then of the land or ocean. The computer program, a sort of meteorological spreadsheet, first solves for each box the fundamental conservation laws of physics, and then goes on to calculate the transfer of mass, energy, and momentum from one box to the next—it “runs” the weather far into the future. You can change a variable—the amount of carbon dioxide in the air, for instance—and watch the result.

And the result, when increased carbon dioxide and other trace gases are taken as givens, does not differ all that much from what Arrhenius forecast. The models that have been constructed agree that when, as has been predicted, the level of carbon dioxide or its equivalent in other greenhouse gases doubles from pre–Industrial Revolution concentrations, the global average temperature will increase, and that the increase will be 1.5 to 4.5 degrees Celsius, or 3 to 8 degrees Fahrenheit. The results of all the global climatic models are consistent within a factor of two.

Perhaps the most famous of the computer programs is in the hands of James Hansen and his colleagues at NASA’s Goddard Institute for Space Studies, in, of all places, Manhattan. NASA used an early version of the model around 1970 to study the accuracy of predictions from satellite weather observations; when the Goddard weather group moved to Washington, Hansen, who was staying on in New York, decided he’d try the model on longer-term problems—on climate as opposed to weather. Over the years, he and his colleagues have fine-tuned the program, and even though it remains a rough simulation of the mightily complex real world, they have improved it to the point where they are willing to forecast not just the effects of a doubling of carbon dioxide but the incremental effects along the way—that is, the forecast not just for 2050 but for 2000.

In Dallas, for instance, a doubled level of carbon dioxide, or the equivalent combination of carbon dioxide and other gases like methane, would increase the number of days a year with temperatures above 100 degrees from 19 to 78 each year, according to Hansen’s calculations. On 68 days, as opposed to the current 4, the temperature wouldn’t fall below 80 degrees at night. One hundred and sixty-two days a year—half the year, essentially—the temperature would top 90 degrees. New York City would have 48 days a year above the 90-degree mark, up from 15 at present. And so on. Such increases would quite clearly change the world as we know it. One of Hansen’s colleagues observed to reporters, “It reaches one hundred twenty degrees in Phoenix now. Will people still live there if it’s one hundred thirty degrees? One hundred forty?” (Heat waves like that are possible, even if the average global increase, figured over a year, is only a couple of degrees, for any average conceals huge swings.) But we need not wait decades for that doubling to occur. These changes, Hansen and his colleagues wrote in a paper published in the fall of 1988 in the International Journal of Geophysics, should begin to be obvious to the man in the street by the early 1990s at the latest—that is, the odds of a very hot summer will, thanks to the greenhouse effect, be better than even beginning now.

There are an infinite number of possible effects of such a temperature change. For example, the seas may well rise seven feet or more as polar ice melts and warmer water expands, while the interiors of the continents may dry up because of increased evaporation. Detailed studies have begun to emerge of what it will be like to live in this greenhouse world, and researchers have speculated on possible changes ranging from an increased spread of disease when insects spread north to the emergence of a warmer Canada as the globe’s great power. Some of the figuring is quite insane—Fortune recently pointed out that if parts of the polar ice cap began to thaw, American and Soviet nuclear submarines would be deprived of cover. Not only that: “The effect would be more damaging to the USSR. Because American submarines are faster and can travel farther than their Soviet counterparts, they are less dependent on hiding places under the ice cap.” But a discussion of the effects is premature. First, we should figure out if this is indeed going to happen, if the theory is valid. In recent years there have been, of course, any number of doom-laden prophecies that haven’t come true—oil is selling, as I write these words, at $18 per barrel, half its price just a few years ago.

The obvious check is to measure the temperature to see if it’s going up. But this is easier said than done, for, in the first place, the warming doesn’t show up immediately. Although, as Revelle and Suess found, the oceans don’t absorb much excess carbon dioxide, they can hold a lot of heat; the effects so far may be stored up in the seas, ready to re-radiate out to the atmosphere, the way a rock holds the sun’s heat through the night. Such a “thermal lag” could be as little as ten years, as much as a hundred.

And when you go to check the thermometers it won’t do to measure only a few places for only a few years because climate is “noisy”—full of random fluctuations and variability. To find what climatologists call the “warming signal” through this static of naturally cold and hot years requires a huge effort. Two such studies have been done, one at the University of East Anglia, the other by Hansen and his NASA colleagues. Each reached back almost a century, when scientists first began systematic weather observations. And, to find truly global averages, they included readings from thousands of land-based and shipboard monitoring stations. The two studies reached about the same conclusion: that the earth’s temperature had increased about 1 degree Fahrenheit in the past hundred years, a number consistent with, though somewhat smaller than, the predictions of the greenhouse models. And both sets of readings show that the four warmest years on record occurred in the 1980s—that the rise is accelerating at the same time that more gases enter the air, just as the models forecast. Indeed, the British model now lists the six warmest years on record as, in order, 1988, 1987, 1983, 1981, 1980, and 1986.

THE YEARS 1981 and 1983 were very hot, and some parts of the United States suffered severe drought. But no one except the affected farmers worried very much. It was weather. Even the scientists most committed to the greenhouse theories made no claims; “it must be said,” wrote Revelle in 1982, “that so far the warming trend has not risen above the ‘noise level.’ … Confidence in the carbon dioxide hypothesis will be much firmer if a warming trend exceeding the noise level becomes evident.” In 1988, though, the American drought caught everyone’s attention. It hit the heart of the grain belt, where most of the nation’s and much of the world’s food is grown. It followed a dry fall and winter, so its effects were quickly evident; the Mississippi River, for instance, sank to its lowest level since the navy began taking measurements in 1872. And just about the time that the pictures on the television began to grab everyone’s attention it got very, very hot in the urban East, where those in the government and the media establishment, among others, have their homes. It so happened that in late June, right as the anxiety was rising in a great crescendo—newscasters telling us that the next two weeks were crucial for corn fertilization, meteorologists issuing forlorn sixty-day forecasts—the Senate Committee on Energy and Natural Resources held a hearing on the greenhouse effect. It was actually the second part of the hearing. Part one had been held the previous November, when, in the words of Louisiana senator J. Bennett Johnston, the senators listened with “concern” as scientists said that one expected result of the greenhouse effect would be a drying of the Midwest. But now, said Senator Johnston, “as we experience 101-degree temperatures in Washington, D.C., and the [lack of] soil moisture across the midwest is ruining the soybean crops, the corn crops, the cotton crops,” “concern” is giving way to “alarm.” As at most congressional hearings, some of the senators on the panel made opening remarks before the witnesses spoke. Several senators said they had already read the report of Dr. Hansen, the day’s chief witness, and they predicted that it would startle listeners. Hansen’s report, Dale Bumpers of Arkansas said, should be “cause for headlines in every newspaper in America tomorrow morning.”

As it turned out, Senator Bumpers was not exaggerating. Hansen said he was ready to state, after exhaustive review of the records, that the warming signal was now apparent above the noise of normal weather. That there was only a 1 percent chance that the temperature increases seen in the last few years were accidental. That the theories and predictions had come true—that we now lived in the greenhouse world.

It was a claim no other established scientist had ever made—certainly not one on a government payroll. And though Hansen delivered his findings in the flat, dry tones of a good researcher, the reaction was much as the senators had expected: the next day’s New York Times, for instance, ran a story at the top of the front page under the headline “Global Warming Has Begun, Expert Tells Senate.” The message was finally getting across, nearly a century after Arrhenius and three decades past Revelle and Suess. But the heat of the day may have been a mixed blessing—though it focused everyone’s attention on the issue, it led most people to think that what Hansen had said was that the heat and drought of 1988 were greenhouse related. Strictly speaking, that is not what he had testified to. “It is not possible to blame a specific drought on the greenhouse effect,” he said. (Indeed many experts think that most of the drought and heat of 1988 was the result of tropical ocean currents and related natural phenomena.) However, said Hansen, there is evidence that the greenhouse effect “increases the likelihood of such events.” In other words, what we can blame the carbon dioxide and the methane for is a longer-range pattern. Even if the summer of 1988 had been cool and damp, even if there had been mushrooms growing in the wheat fields of Kansas, Hansen would have said the same thing. What had convinced him was not the anguished farmers of the Midwest or the ecstatic air-conditioner salesmen of the eastern cities, but the numbers his computer kept spitting at him. And if the next Fourth of July should see blizzards burying the Plains or even just the normal heat of an average summer, it might calm down those who still believe that the world is too big and too old to change, but it wouldn’t shake Hansen’s confidence in the implications of his hundred years’ worth of thermometer readings.

“There are two logical time scales to consider,” he explained some months after giving his testimony. “One is the thirty years for which we have some measurements of carbon dioxide and other gases. The natural variability in temperature for the years between 1950 and 1980 is about .13 degrees Celsius. And our readings show that the global mean temperature has risen about .4 degrees in that period. The other logical choice would be to look at the larger record, the observations back to the 1800s. Over that period there’s been about a .6 degree Celsius rise. Now, over a longer period there’s also more natural variability—sources like sunspots, deep ocean circulation, and so forth.” The standard deviation, the randomness of temperature, over the longer period is plus or minus .2 degrees Celsius. In both cases, Hansen’s observed rise was almost exactly three times the standard deviation. “There’s no magic point where you pick out the signal,” he said. “There’s no point at which it switches over. But when it gets to three sigma—when it gets to three standard deviations—you’re getting to a level where it’s unlikely to be an accidental warming.” As the hearings closed for the day—after several other authorities supported his findings, forecast a wide range of effects (none pleasant), and called for strong action to reduce fossil fuel emissions—reporters gathered around the table asking questions. In response to one query, Hansen said, “It’s time to stop waffling so much. It’s time to say the earth is getting warmer.”

WHETHER OR NOT the warming has officially begun is probably a more important point for the politicians than for the scientists. Only a few months before Hansen’s testimony, the columnist George Will had spanked the then presidential candidate Senator Albert Gore of Tennessee for his long-held interest in the greenhouse effect and other issues “that are, in the eyes of the electorate, not even peripheral.” Will and, presumably, his readership were still back in about 1975, when a National Academy of Sciences report, on Understanding Climatic Change, devoted only two paragraphs to carbon dioxide. For at least the last eight years, though, a consensus has been growing in the scientific community that while a warming trend might not yet have appeared, it was inevitable: the National Research Council, the Environmental Protection Agency, the World Meteorological Organization, the United Nations Environmental Programme, and many other scientific groups issued voluminous reports outlining the “projected,” “predicted,” “expected,” “forecast” rise. The warming might have started or it might start a few years hence—if the theory was sound, it didn’t make much difference. The language of a 1983 National Academy of Sciences report is typical of this hedging: “The available data on trends in globally or hemispherically averaged temperatures over the last century, together with estimates of carbon dioxide changes over the period, do not preclude the possibility that some climatic changes due to increasing atmospheric projections might already be underway.” But “do not preclude,” “possibility”—these are words that land a subject on Nova, not the CBS Evening News, and so 1988’s summer heat, even if it were a freak unrelated to the composition of the atmosphere, was probably a necessary preliminary to any serious public discussion. It’s the difference between knowing that your two packs a day could very well give you cancer and hearing the doctor clear his throat and say, “I’ve got something to tell you.” Many scientists, even among those committed to the greenhouse theory, believe that the warming signal is not yet evident. Hansen, though well respected, was out on a limb, if a fairly stout one, and some have criticized not only his use of statistics but his willingness to speak with few caveats. Stephen Schneider, of the National Center for Atmospheric Research in Boulder, Colorado, and a longtime proponent of the greenhouse warming theory, offers a gambler’s analogy: the warm years of the 1980s, he said, are not “proof” of a warming, any more than the dealer’s drawing four aces is “proof” that he’s dealing from the bottom of the deck. “Different tastes cause 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 it has persisted for a very long time,” Schneider told the Senate six weeks after Hansen’s testimony. “Quite simply, accepting any particular signal-to-noise ratio as ‘proof’ of global warming reflects the personal judgment of the investigator.” A scientific panel concluded in early May 1989 that natural variations in temperature made it impossible to say “with any degree of confidence” that a warming was officially under way.

Some recent studies tend to agree with Hansen’s conclusion that the warming has already begun. Rainfall may have increased above 30 degrees north latitude and decreased beneath it, for instance, and there has been a “remarkable” increase in the amount of water vapor in the air over the Indo-Pacific, both results anticipated in the greenhouse models. And some investigators have found a “variable but widespread” warming of the Alaskan permafrost, which changes temperature much more slowly than the air and thus may provide a better record. On the other hand, some scientists have looked for the warming signal and found few indications of it so far. Kenneth E. F. Watt, a professor of environmental studies at the University of California at Davis, dismisses most of the Hansen and East Anglia temperature studies, saying, among other things, that they failed to correct enough for the “urban heat island effect,” a phenomenon well known to meteorologists in which, as “cities grow up around thermometers,” concrete and exhaust skew readings. (This heat island effect even has its converse—in Palm Springs, California, researchers reported that they had discovered a “cold island effect.” Temperatures had dropped 2 to 3 degrees Fahrenheit below those of the surrounding desert, apparently because of a surge in golf-course construction.) Even shipboard measurements suffer from this pollution, and so the scientists try to correct for phenomena like the heating of water in engine intake tubes.

There’s also no guarantee that factors much larger than the growth of cities aren’t skewing the results—sunspots are a prime contender, as are the strong El Niño currents of recent years. Weather is a strong force. Most climatologists agree that the drought of 1988, for instance, was the result of regularly fluctuating tropical ocean temperatures, which steered the North American jet stream, with its cargo of rainstorms, north of the Great Plains. In fact, in January 1989 Tim Barnett, a climate researcher at the Scripps Institution of Oceanography in La Jolla, California, forecast much cooler temperatures for the first part of the year, the result of a one-year La Niña, a tropical “cold event” that is the opposite of the better-known El Niño. In some parts of the ocean off equatorial South America the water temperature plunged nearly 7 degrees Fahrenheit last summer; Hansen saw the dip in his computer data, and agrees that it may make this year’s readings go up more slowly, or perhaps even go down. “But such things are bumps,” he says. The greenhouse effect is superimposed on top of them, like makeup on a face.

At any rate, there are very few objections to the theory as a whole; everyone in the scientific community agrees that the atmospheric concentration of carbon dioxide is on the rise, and almost everyone believes that it cannot help having some effect. To declare, as some editorialists have done, that the warming has not yet appeared and therefore the theory is wrong is like arguing that a woman hasn’t yet given birth and therefore isn’t pregnant.

A year after Hansen’s original testimony, in May of 1989, he returned to Capitol Hill to declare that his studies showed definite danger of future drought. The White House tried to alter his testimony, arguing that, in the words of presidential press secretary Marlin Fitzwater, “There are many points of view on the global warming issue.” But he didn’t point to any studies undercutting Hansen’s work, and the next day another government scientist, Schneider of the National Center for Atmospheric Research, assured the assembled congressmen that “there is virtually no scientific controversy” that more carbon dioxide means higher temperatures. “This is not,” he said, “a speculative theory.” THE ACCEPTED SCIENTIFIC WISDOM, then, is that the increase in carbon dioxide and other trace gases will soon heat the world if it hasn’t already done so. The consensus begins to break down, though, on the question of what happens after that. A large-scale change in the climate would undoubtedly set off a series of other changes, and some of these, in turn, would make the problem worse, while others might lessen it. Skeptics incline toward the latter view—to think that there is a possibility that the warming will trigger some natural compensatory brake. S. Fred Singer, a professor emeritus of environmental sciences at the University of Virginia, who is now chief scientist for the federal Department of Transportation, has also assumed a part-time role as greenhouse curmudgeon, expressing his doubts on various op-ed pages. He grants that the earth’s temperature should increase “provided all other factors remain the same.” But, he says, they won’t. “For example, as oceans warm and more water vapor enters the atmosphere, the greenhouse effect will increase somewhat, but so should cloudiness—which can keep out incoming solar radiation and thereby reduce the warming.” There are other possibilities. If changing climatic conditions caused the oceans to circulate water from the bottom to the top more quickly than the present five-hundred-year cycle, “older” water that could absorb a certain amount more carbon dioxide might reach the surface. Or higher levels of carbon dioxide might stimulate plant growth, thus pulling more carbon dioxide from the air. “The feedbacks are enormously complicated,” Michael MacCracken, of California’s Lawrence Livermore National Laboratory, told reporters. “It’s like a Rube Goldberg machine in the sense of the number of things that interact in order to tip the world into fire and ice.” The computer models have tried to incorporate such factors. In some cases, Hansen admits, we simply don’t have enough knowledge to do more than make educated guesses—the behavior of the oceans is something of a wild card, and so are the clouds (the difficulty of estimating cloud feedbacks is a major reason that most warming predictions are expressed as a range of temperatures and not as a single, firm number). But almost every doubt is double edged. It’s true that some types of clouds—bright, low-level stratocumulus clouds, say—reflect a lot of solar radiation and might tend to cool the earth. Monsoon clouds, on the other hand, are long and thin, and let in the sun’s heat while preventing its escape. Hansen’s work shows that clouds will most likely increase the greenhouse warming overall.

A variety of other feedback effects have also been identified and tallied up. For instance, every surface has its “albedo,” the degree to which it reflects the sun’s rays. A polar ice cap (or a white shirt) has a high albedo—a large proportion of the sun’s rays are immediately reflected back out to space. If the ice is replaced by dark blue ocean, more heat will be absorbed. Tropical rain forests absorb a lot of heat now; if they turn into deserts they may reflect more. The feedbacks are distinct from other phenomena that have always affected and will always affect temperature—volcanoes, for instance, which throw up so much dust that it acts as a veil, or El Niños, or increased radiance from solar flares. The various feedbacks are, rather, products of the warming signal, and they can either amplify or mute it.

In any event, the warming estimates provided by the greenhouse models are not worst-case scenarios. They are the middle ground. It is “equally likely,” Schneider told the Senate, that the warming forecasts are too low as that they’re too high.

SOME OF THE POTENTIAL FEEDBACKS are so vast that they might someday make us almost forget what originally caused the greenhouse warming. We have already looked at one: the potential release of the methane trapped in the tundra and the mud of the sea that would add enormously to the warming blanket around the earth.

But methane is a little hard to imagine. It’s easier—and more troubling—for me to think about the forest that surrounds my house in New York State’s Adirondack Mountains.

Twenty thousand years ago, my land was covered by glaciers which had spread slowly down from Canada, and which eventually retreated in the same direction. As the ice disappeared, in the words of a local writer, “the fierce ruthlessness of nature gave way to a benevolent mood. Rains came over the years to chasten the harshness of the landscape. The startling gaping holes in the earth were filled with crystal-clear water. Soft green foliage came to clothe the naked rock-hewn slopes.” This was a slow (albeit poetic) process, even now incomplete—some plant and animal species are still migrating up here. The great forests rose on the glacial till and soon created more soil for greater forests, and so on, a process first interrupted a couple of hundred years ago, when men cut down most of the woods. But the interruption was only temporary—around the turn of the century, New York State, in an early outburst of environmental consciousness, began buying huge tracts of land and declaring them “forever wild”—off limits to loggers and condo developers alike. As a result, it is one of those happy exceptions: a reforested, replenished zone, a second-chance wilderness.

But the trees that live here don’t do so because of the laws—they do so because of the climate. They have slowly marched north as the climate slowly warmed since the end of the Ice Age, and if it continued slowly warming they would slowly keep marching; the convoy of pines might march right out of here, and the mass of hardwoods found in lower Appalachian latitudes might eventually march in to replace them. But before we get too used to this marching metaphor it is worth recalling that trees are rooted to the ground—they die looking out at the sights they were born to. And, as forests are composed of trees, they can move only through the slow growth of new trees along their edges. In fact, researchers estimate that a forest naturally moves at most a half mile in a year. Which is fine, if that’s how slowly the climate is changing.

The computer models, however, project an increase in global average temperature as high as a degree Fahrenheit per decade. An increase of 1 degree in average temperature moves the climatic zones thirty-five to fifty miles north—that’s why, when you drive from Atlanta to New York the vegetation that lines the highways changes. So, if the temperature was increasing a degree per decade, the forest surrounding my home here would be due at the Canadian border sometime around 2020, which is just about the time that we’d be expecting the trees from a hundred miles south to start arriving. They won’t—half a mile a year, remember, is as fast as forests move. The trees outside my window will still be there; it’s just that they’ll be dead or dying.

Eventually, perhaps within a few decades, forests—or, at least, scrub—better adapted to the new conditions would replace the forests that had expired. But in the meantime those dead forests could release truly staggering amounts of carbon into the atmosphere. Trees are largely carbon—the burning of the tropical rain forests releases up to 3 billion tons a year into the atmosphere, compared with about 5.6 billion tons from the burning of fossil fuels. Last year’s Yellowstone fire alone released an estimated 2.8 percent as much carbon as all U.S. emissions from fossil fuels in a year—that is, in a few weeks, on only about a million and a half acres, the fires released as much carbon as ten days’ worth of driving, home heating, factory production, motorboating, and so on. All told, the forests, plants, and soil (which gives up its carbon much more rapidly as trees die) contain something more than 2 trillion tons of carbon, probably more than a third of it in the middle and high latitudes. “We’re working with maybe a trillion tons that could be mobilized,” says George Woodwell, an ecologist and the director of the Woods Hole Research Center. By contrast, the atmosphere now contains only about 750 billion tons. So even a fairly small change in the forests could substantially increase the amount of carbon in the atmosphere, exacerbating the warming. There are signs—frightening signs—that some of these feedback loops are starting to kick in, that the warm years of the 1980s may be triggering an endless cycle. In May 1989 Woodwell told Congress that the annual 1.5 parts per million in atmospheric carbon dioxide seemed to have suddenly surged upward in the last eighteen months to 2.5 parts per million. “I’m suggesting that the warming of the earth is increasing the decay of organic matter,” he said, adding that such an event has not been worked into the computer climate models and hence their estimates of future warming may be too low.

But forget the carbon for a moment, forget the feedback loops. The trees will die. Consider nothing more than that—just that the trees will die. When I walk outdoors in the morning, instead of the slopes of trees, instead of the craggy white pines on the ridge toward Buck Hill, there may be yellowing and browning leaves and needles, thinning crowns, dead branches, and rotting stumps. Or maybe, after what the World Resources Institute calls a “transition period,” a “shrubby woodland that is adapted to a wider variety of environmental conditions” will appear. It may be personal prejudice, nothing more, but I prefer trees to shrubs. You can keep your sumac bush—give me yellow birch, tamarack, blue spruce, the swamp maple first to change its color in the fall, rock maple, hemlock. This vast decline, this forest “dieback,” is not some distant proposition. A report described to a congressional committee last summer found that “reproductive failure and forest dieback is estimated to begin between 2000 and 2050.” A University of Virginia study predicted what Michael Oppenheimer of the Environmental Defense Fund called “biomass crashes” in the pine forests of the Southeast over the next forty years if the warming continues. “Things like birch trees and many evergreens [in the Northeast] may have a hard time surviving, even in the next ten to twenty years,” Hansen told reporters.

WHEN TREES DIE, it is always hard, unfortunately, to say just why. “It’s never going to be obvious that the climate change is doing it,” Woodwell says. “Pine trees are often attacked by a boring insect, the ips. The insects come from miles around to a weakened tree. So when it dies, people say it was an ips infestation. Sugar maples are going out all over—acid rain, and the accumulation of heavy metals like aluminum in the soils, and then the pear thrip, which is another insect that goes after weak trees. In every case it looks like some special cause—a fungus or a pest.” Alf Johnnels, of the Swedish Museum of Natural History, compared the situation to a famine: “There are relatively few people who die directly from starvation; they die from dysentery or various infectious diseases.” In one sense it makes no difference. The tree is dead one way or another, and the carbon released. But in another way it is tragic, for it masks a vital piece of knowledge—the transition from “traditional” pollutants to these new horrors whose causes and effects are everywhere. When Eleanor of Aquitaine, wife of King Henry II, moved out of Tutbury Castle in Nottingham because of the smoke from wood stoves; when London, as early as the thirteenth century, barred coal combustion because of the smog; when Lake Erie nearly died—all these were traditional pollutants, local in their effect, obvious in their action, their sources relatively easy to identify and, often, to deal with. Love Canal; the lethal smog in Donora, Pennsylvania; the acid streams in the coal country of West Virginia—all traditional pollution.

But in the late 1960s and early 1970s, people in Scandinavia and the northeastern United States began to notice damage to forests in areas a long way from any obvious source of pollution. Eventually, they began to measure the pH of rainfall, and of the lakes where the rain collected. What they found was startling: the rainfall was turning acid. Its pH, normally around 5.6, often fell below 5.0. Measurements of clouds around mountaintops showed that in their acidity they resembled vinegar or lemon juice, not water vapor.

Acid rain was not a new concept or even a new phrase; Robert Angus Smith, the inspector general of the Alkali Inspectorate for the United Kingdom, coined the term in the late nineteenth century. His data on the chemistry of rainfall around Europe correlated nicely with his maps of heavy coal-burning regions and strong wind currents. He even speculated that the acid rainfall might damage trees. But, like the calculations of Arrhenius, the notion was forgotten immediately, and not remembered until quite recently. (Until 1986, Britain itself relied on ten thousand schoolchildren with lemonade bottles to collect its rainwater for analysis.) And even when many researchers in the 1970s and 1980s did begin to point to coal burning as the culprit, they had a hard time making headway with their arguments, for acid rain, besides being colorless, tasteless, and odorless, is not a traditional pollutant. It comes from a distance to do its damage. Or, really, it’s halfway between a traditional pollutant and the new sources of environmental destruction, like the global warming. In some ways it’s the same old coal smoke that has always darkened urban areas. But to get the nasty stuff out of sight (and, it was hoped, mind) the electric utilities, whose generating stations cause most of the problem, built ever-taller smokestacks—429 stacks taller than two hundred feet (many of them taller than seven hundred feet) were built in the midwestern and southeastern United States in the 1970s. Since the emissions spew out high above the ground, winds carry them great distances—hundreds, even thousands, of miles. Under the right conditions, sulfur dioxide and nitrogen oxides in the emissions are transmuted into nitric and sulfuric acid that eventually drift to the ground or fall in the rain. And there they weaken the trees and acidify the lakes to the point of sterility.

There is no question that the damage is increasing. Between 1964 and 1979 half the mid- to high-elevation red spruce trees in Vermont died; in Sweden all bodies of fresh water are now acidic, roughly fifteen thousand of them too sour to support aquatic life; rainfall in southern China has grown more acidic than the badly damaged parts of the Atlantic seaboard; even in the American West the pH of rainfall has plummeted to the point where two-thirds of the region’s lakes now have “limited acid-neutralizing capacity.” Central Europe, small and highly industrialized, has perhaps been hardest hit. When the Worldwatch Institute was working on its first State of the World Report in 1983, recalled director Lester Brown, and staff member Christopher Flavin, it “debated whether to report that a West German forest survey had found some eight percent of that nation’s forests showing signs of damage, possibly from air pollution and acid rain. That discovery, though disturbing, seemed little cause for international alarm.” But by 1988—that is, five years later—“over one-half of West Germany’s forests are damaged, and the link to air pollution is all but conclusive.” Still, for a decade or more, nothing was done save studies. And partly this was because, for the first time, the people doing the polluting were at some remove from the pollution. In such a situation the usual environmental ideas don’t work, because the problem is outside our normal way of thinking. For some years one of the chief (and admirable) slogans of environmentalists has been “Think globally, act locally.” It is true that one can work most effectively close to home instead of futilely addressing all the world’s problems. But as the reality changes, so must the perception. Our local problem here in the Adirondacks—acid rain—has its cause in Ohio and Kentucky. And now, as the climate warms, our local problem—the death of trees—starts to have its causes everywhere. Everywhere. A factory in Japan is as deadly as a burning rain forest in Brazil, a Communist coal mine in Romania, a capitalist utility in West Virginia. Or as the blue 1981 Honda parked in the driveway twenty feet from where I sit, or as the wood stove warming my back.

THE BEST EXAMPLE of the global nature of the new pollution is probably the depletion of the ozone layer. Ozone, or O3, is a molecule in which three oxygen atoms are bound together. It is formed in the stratosphere when intense ultraviolet solar radiation splits ordinary oxygen molecules, O2, into their two constituent atoms. When that happens, most of the oxygen atoms simply recombine as O2, but some join as triplets and others adhere to O2 molecules, in both cases forming ozone. Ozone in turn absorbs ultraviolet radiation. That radiation tears it apart, forming O2 and O, and the dance continues, with all the elements in balance in the atmosphere, and much of the incoming ultraviolet absorbed—fortunately, since too much ultraviolet can damage plant and animal cells, causing, among humans, skin cancer and eye damage, and killing many smaller and more sensitive organisms.

This dance had gone on uninterrupted since the Archean era, a span of time measured in billions of years. Then, in 1928, a group of chemists at General Motors invented a nontoxic gas, a combination of carbon, chlorine, and fluorine atoms, which they labeled a chlorofluorocarbon, or CFC. (The group was led by Thomas Midgley, who also advanced the human race by formulating tetraethyl lead as a gasoline additive, and who may now hold the record for most banned substances produced by a single man.) The chlorofluorocarbons, though perhaps the ultimate proof that what is good for General Motors is not good for America, seemed at first to have a number of desirable features: they could be used as coolants in refrigerators, and also as propellant gases in spray cans. Since they were inert, they didn’t affect the contents of what they propelled—when you pushed the button on the green can it sprayed green paint. The number of CFC compounds quickly grew into the dozens, of which CFC 11 and CFC 12 (the numbering system, devised by the DuPont Company, refers to the number of fluorine and chlorine atoms) were the most commercially important. The chlorofluorocarbons are now used for a wide variety of jobs. Besides refrigerating 75 percent of the food consumed in the United States, and propelling much of the world’s aerosol spray, they serve as foaming agents for plastics and as cleaning agents for computer circuit boards, they fumigate granaries and cargo holds, and they insulate pipelines and trucks. And they make egg cartons, and those foam coffee cups and fast-food packages.

Chlorofluorocarbons have been effectively marketed even to individual consumers—for instance, some automobile dealers send out annual notices urging that their customers come have their air conditioners flushed and the CFC coolant replaced, even though this is generally unnecessary. Between 1958 and 1983 the average production of CFC 11 and CFC 12 grew 13 percent a year, and could continue to grow more or less indefinitely, since large reserves of fluorspar, the source of the key ingredient, have been located.

However, besides being inert, nontoxic, and widely useful, chlorofluorocarbons have a pair of other unusual properties. One is that, unlike many chemicals in the atmosphere that decay in hours, days, weeks, or months, the CFCs are so chemically unreactive that they often can stay intact for a century or more. (CFC 11 lasts seventy-five years on the average, and CFC 12 a hundred and ten.) This gives them plenty of time to rise slowly through the atmosphere until they reach the stratospheric altitudes, a process that may take five years. And when they get there, they react chemically with the ozone molecules, destroying them. For instance, a single atom of chlorine in the CFCs may react with ozone—O3—to create a molecule of O2 and a molecule of chlorine monoxide. Then, in a second reaction, the chlorine monoxide reacts with a single oxygen molecule (O) to form O2 and the single atom of chlorine is freed again, to seek out and destroy more ozone. A single molecule of chlorine can destroy thousands of ozone molecules.

And just as methane joins carbon dioxide to warm the atmosphere, several other compounds, including methyl chloroform and carbon tetrachloride, assist the CFCs in ozone destruction. Methyl chloroform and carbon tetrachloride are solvents. Another family of man-made compounds, the halons, are popular as home fire extinguishers because they don’t cause water damage. But they contain bromines, which are a hundred times more efficient than the chlorine compounds at ozone destruction. Therefore, though there are many fewer home fire extinguishers than air conditioners, the halons may cause a quarter of the ozone loss.

SCIENTISTS FIRST BEGAN to think seriously about the chlorofluorocarbons (which, like carbon dioxide, also trap heat) in the early 1970s. James Lovelock, the independent British scientist best known for formulating the Gaia hypothesis, which holds that the earth is a single living organism, was the first to measure the chemicals in the air. He showed that they were both widespread and persistent in the earth’s atmosphere, but concluded, in what he later described as “one of my greatest blunders,” that “the presence of these compounds constitutes no conceivable hazard.” A year or two later, Sherwood F. Rowland of the University of California at Irvine, and Mario Molina, now at the Jet Propulsion Laboratory in Pasadena, first demonstrated the ozone-destroying capability of the chlorine atoms and suggested the magnitude of the problem. Rowland has recalled, “I just came home one night and told my wife, ‘The work is going very well, but it looks like the end of the world.’ ” Their findings—especially the vision of a nation underarm-deodorizing its way to total destruction, expiring not with a bang but with a floral hiss—led to an American decision to ban chlorofluorocarbons as an aerosol propellant. However, most of the rest of the world continued to spray, and the compounds continued to be used for other purposes; their use continued at an almost uninterrupted double-digit rate of annual growth.

The problem, as with carbon dioxide and the warming, is that there was more theory than observation. Not that anyone had much quarrel with the theory, but political action had to wait for some major scare. The Vienna Convention of 1985, for instance, brought together all sorts of countries, which agreed on the “general obligation” to control CFCs but took no actual action. The United States, Canada, and several European countries wanted an aerosol ban (since they already had one); most of the Europeans, though, wanted a reduction in aerosol uses and some hazy cap on future production. Pending a decision on a specific protocol, the meeting was content to urge countries to control emissions “to the maximum extent practicable.” Then, two months after that vague manifesto, the British Antarctic Survey at Halley Bay, which had been monitoring the Antarctic stratosphere since 1957, reported that a huge hole had suddenly developed in the ozone high above the South Pole. Actually, it was not so sudden: American Nimbus monitoring satellites had been recording the hole for at least five years, but the computers had been instructed to ignore sharp changes like the one observed in the ozone. (Men and women in the street have no monopoly on complacency. Scientists who program computers are like the rest of us—they expect that if nature changes at all it will do so slowly and steadily. Anomalous results, they assume, mean broken instruments and not a broken world.) “All along,” Rowland said, “critics complained that ozone depletion was not based on real atmospheric measurements—until, that is, the ozone hole appeared. Now we’re not talking about ozone losses in 2050. We’re talking about losses last year.” Rowland and Molina’s models had not predicted the Antarctic ozone hole that the British found, and for a while some scientists believed that the window (perhaps too homey a phrase for something the size of the continental United States) was a natural phenomenon of the pole. Since it appeared at the same time each year—September and October—they postulated some climatic cause. But in 1987 an international team of researchers established once and for all that man-made chemicals were what caused the ozone loss. It appears that global winds tend to move air from the equator to the poles, carrying the CFCs with them. During the Antarctic winters, according to Harvard’s McElroy, the difference in temperatures between the middle latitudes and the poles forms a strong pressure gradient that starts the air moving. This spinning air forms large-scale vortices of cyclonelike winds, with temperatures inside dropping as low as minus 130 degrees Fahrenheit. Clouds of microscopic ice crystals form in these vortices, and chemicals are produced on their surfaces that are responsible for the very rapid destruction of ozone. Inside the vortices as much as 50 percent of the ozone may disappear. And then, as the vortex breaks up after a month and a half, its low-ozone air mixes with the surrounding atmosphere, lowering the earth’s overall ozone level. It’s like watering down beer. According to McElroy, the world has lost between 1 and 3 percent of its ozone. In 1987 scientists noticed the first signs that a similar hole develops in the height of the Arctic winter—that is especially because the areas adjacent to the North Pole are much more densely populated than those around the South. Already, monitoring stations in spots as far apart as North Dakota and Switzerland have recorded wintertime drops in the ozone layer of up to 9 percent. And a study conducted by a NASA Ozone Trends panel early in 1988 concluded that stratospheric ozone levels in the Northern Hemisphere had declined as much as 3 percent in the last twenty years—much more than the models predicted. By 1987, global ozone depletion was at the level forecast for the 2020s.

The ozone hole was enough of a shock that many politicians urged action. (Not all—the Reagan administration’s interior secretary Donald Hodel urged that Americans who were worried about skin cancer and retina damage simply don baseball caps and sunglasses.) In a follow-up to the Vienna Convention, diplomats agreed in a document known as the Montreal protocol to a 50 percent reduction in chlorofluorocarbon production to be phased in by century’s end. That was pretty radical action. The accord, noted the Worldwatch Institute in its generally gloomy State of the World 1988 survey, represents “an important psychological victory.… It indicates that the international community is capable of cooperating when faced with a common threat.” Unfortunately, that unprecedented level of cooperation would still allow the level of ozone-destroying chlorine in the atmosphere to increase dramatically.

A report released in 1988 by the Environmental Policy Institute concluded that only a rapid and total phaseout of all ozone-destroying chemicals could begin to stabilize ozone levels in the next few decades. Chemical companies, needless to say, have not been overjoyed at such a prospect. “The rapid, complete shutdown of CFCs that some people are calling for would have horrendous consequences,” said a spokesman for the Alliance for a Responsible CFC Policy, an industry arm, adding, in an odd choice of metaphor, “The cure would kill the patient.” Still, the leading CFC producers finally announced they’re searching for substitutes so they can leave the business. And the EPA seems convinced. Even before the Montreal accord took effect, the agency concluded that its provisions would allow chlorine levels to triple, and in September 1988 EPA administrator Lee Thomas called for a quick phaseout of CFC production and a freeze on the other ozone-destroying chemicals. British prime minister Margaret Thatcher, though she took many years to see the danger, has said that the halfway cuts are not enough; at a major ozone conference in London in the spring of 1989 she led the way in urging a total ban.

Anything less will clearly be insufficient. Under the Montreal accord, “we’re on an upward ramp that will level off at about ten percent depletion,” said Michael Oppenheimer of the Environmental Defense Fund. “We’re headed rapidly into the realm of dangerous UV radiation.” No exact map of that realm exists. Not even the scariest models predicted anything like the Antarctic hole. The Environmental Policy Institute lists as a worst-case scenario the possibility that as much as 25 percent of the atmosphere’s ozone could be depleted by the middle of the next century unless emissions are cut dramatically. (A nuclear war, by contrast, would destroy 30 to 70 percent of the ozone layer.) If ozone levels declined 20 percent, two hours in the sun would blister exposed skin.

FOR THE MOMENT, however, forget about effects. The physical consequences of increasing the level of carbon dioxide and lowering the amount of ozone in the atmosphere will in some cases be staggering, but they are no more staggering than the simple fact of what we have done. Look at them one way and the changes are small enough. Carbon dioxide will increase, if it doubles in concentration, from .035 percent of the atmosphere to .06 or .07 percent of the atmosphere. If all the ozone currently above a particular spot on the globe were compressed to atmospheric pressure, it would be a tenth of an inch thick; in the nastiest of futures it might shrink to perhaps a twelfth of an inch. But the level has already shrunk, if only by a percent or two. It is different, markedly different, different everywhere on earth.

And the changes—many of them, at least—are irrevocable. They are not possibilities. They cannot be wished away and they cannot be legislated away. To prevent them, we would have had to clean up our collective act many decades ago. Though scientists disagree about whether or not the warming has begun, they do not argue that carbon dioxide hasn’t increased, or that the increase won’t have an effect. The “thermal equilibrium”—the heat storage—of the oceans may be saving us at the moment. But if so it is only a sort of chemical budget deficit. Sooner or later our loans will be called in. The latest estimates predict that man’s release to date of carbon dioxide and other gases will warm the atmosphere as little as 1 degree Fahrenheit or as much as 2.8. And we continue, of course, to burn oil and cut trees and grow rice.

We have done this ourselves, by driving our cars, building our factories, cutting down our forests, turning on our air conditioners. The exact physical effects of our alterations—even whether or not they will be for the worse—are for the moment beside the point. They will be dealt with in the second half of this book, which is about the future. For now, simply recognize the magnitude of what we have done. In the years since the Civil War, and mostly in the years since World War II, we have changed the atmosphere—changed it enough so that the climate will change dramatically. Most of the major events of human history have gradually lost their meaning: wars that seemed at the time all important are now a series of dates that schoolchildren don’t even try to remember; great feats of engineering now crumble in the desert. Man’s efforts, even at their mightiest, were tiny compared with the size of the planet—the Roman Empire meant nothing to the Arctic or the Amazon. But now, the way of life of one part of the world in one half century is altering every inch and every hour of the globe.