It was early summer in 1988, and the Northeast was sweltering under an oppressive heat wave. In the Midwest, farmers were battling a serious drought. And at a congressional hearing, the atmospheric scientist James Hansen, director of NASA's Goddard Institute of Space Studies, made headlines by asserting that a worldwide siege of heat and drought was upon us, brought on by man's industrial activities. The dreaded "greenhouse effect" had arrived—perhaps as physical reality, certainly as a political issue. The New York Times, the nation's leading herald of environmental crisis, put the story on page one.
While few of Hansen's colleagues share the immediacy of his alarm, most scientists researching the question do agree that a major climate warming is in the offing. Yet in the subsequent months, the response of environmentalists has been rather muted—at least as far as specific policies are concerned.
The reason lies in the way the problem is usually formulated: How do we reverse the greenhouse effect and forestall the warming? To accomplish this sweeping goal, nothing less would do than the complete restructuring of our industrial civilization. A few environmentalists have issued prescriptions along those lines. Richard Houghton and George Woodwell of Woods Hole Research Center, writing in Scientific American, called for a "50 percent reduction in the global consumption of fossil fuels, a halting of deforestation, a massive program of reforestation. There is little choice."
Such cutbacks would indeed be required to end the buildup of carbon dioxide, but the cost would be intolerable—a worldwide economic collapse that would make the Great Depression look like a statistical blip. For the most part, therefore, few responsible observers are advocating such drastic actions. Even the Environmental Protection Agency's highly activist recommendations—calling for governments to intervene to hike the prices of fuels and to end deforestation, while promoting tree-planting, energy conservation, and alternative energy sources—would merely slow down the warming, not avoid it.
We cannot base sound policy on frenzied efforts to retain the climate of the 20th century. Rather, we must seek accommodation to the forthcoming warming. It does little good, as some environmentalists do, to propose that governmental actions can retain the climate to which we are accustomed. That is like saying that government ukases could have kept us in the age of coal, preventing us from ever tapping the world's wealth of petroleum and natural gas. Instead, we must understand the real threats posed by the greenhouse effect and learn to cope.
The problem arises from the worldwide use of coal, oil, and natural gas. When these fuels burn, they release carbon dioxide. This gas builds up in the atmosphere and acts to trap heat in its lower portions, raising global temperatures. (The same process occurs with the atmosphere's naturally present carbon dioxide and water vapor; if they did not trap heat, the sun would warm the earth to a global average temperature of around zero degrees Fahrenheit and the world would be shrouded in ice.)
Industrial activities account for only a small fraction of the world's total flow of carbon dioxide. Every year, some 759 billion metric tons of the gas enter the atmosphere, mainly from decay of vegetation, gases from volcanoes, and exchanges between atmosphere and sea, according to Houghton and Woodwell. As a minor additional source, some 18 billion tons come from fossil fuels. Yet this source is enough to tip the balance toward a global buildup, for only about 748 billion tons of carbon dioxide leave the atmosphere each year, chiefly through plant growth and dissolution in seawater. The net increase, 11 billion tons, can be regarded as entirely manmade.
As early as the turn of the century, and sporadically for several decades thereafter, various scientists suggested that man's activities might be affecting the climate. The first reasonably good study of this issue came only in 1975. That year, Syukuro Manabe and Richard Wetherald of Princeton University published results based on a detailed computer model. Specifically, they looked at the effects of doubling the atmospheric concentration of carbon dioxide, from 300 to 600 parts per million. They concluded that this doubling would raise the earth's mean surface temperature by three to eight degrees. More recent estimates, using improved models, predict a warming of five to nine degrees with this doubled concentration.
Computer models of such complex systems have come under attack for unjustifiably apocalyptic tendencies—the Club of Rome's predictions and the warnings of nuclear winter come to mind. But the greenhouse models appear more reliable. One can test them by demanding that with today's level of carbon dioxide they should accurately reproduce today's observed climate. The slight change of adding extra carbon dioxide to a model then produces a slight change in the climate—a global temperature rise of a few degrees—and this change then is quite believable.
Such temperature increases, occurring over the entire globe, could have dramatic consequences. A project called CLIMAP has compared the climate of the modern era to that at the height of the Ice Age, 18,000 years ago, when Chicago lay buried under glaciers a mile thick. The CLIMAP group used computer models similar to those of Manabe and Wetherald. They concluded that, on average, global temperatures in July of 16,000 B.C. were only nine degrees cooler than in July of recent years.
If nine degrees make the difference between Ice Age and a comfortable climate, and doubling the carbon dioxide concentration can make a difference of nine degrees, it becomes very important to estimate how long it might take for the atmospheric carbon dioxide to double. Since 1958, Charles D. Keeling of Scripps Institution of Oceanography has monitored month-by-month the atmospheric concentration of carbon dioxide. These measurements have shown a strong, marked rise: from 314 parts per million in 1958 to 348 ppm by 1988. Recent decades have shown a rate of increase of around 1.5 ppm per year, which would double the carbon dioxide concentration by the year 2150.
A further important clue to prospective change comes from the geological record. The glaciologist Willi Dansgaard has drilled long cores of ice from the Greenland and Antarctic polar caps. These contain records of ancient climates, and of the ancient atmosphere, across hundreds of thousands of years. Air trapped within the ice contains naturally present carbon dioxide, which is readily measured. In addition, the water of the ice contains two "fossil thermometers": isotopes of hydrogen and oxygen, which change their concentrations depending on the temperature.
An ice core drilled at Vostok, Antarctica, by French and Soviet scientists, has given some of the best available evidence on past changes. This core shows a very clear correlation of carbon dioxide with temperature: The isotope ratios in the fossil thermometers, as well as the carbon dioxide concentration, rise and fall virtually in lockstep across the past 160,000 years.
Interestingly, carbon dioxide levels in recent centuries—prior to the industrial era—were already higher than at any time since around 130,000 years ago. They have gone higher since. So the greenhouse effect may involve not only industrial civilization but also natural fluctuations. And we should be prepared for major climatic changes. The time of high carbon dioxide 130,000 years ago is known in geology as the Eemian interglacial, an era of unparalleled heat, when the warmth-loving hippopotamus lived in, of all places, Great Britain.
The oceans would have to warm perceptibly before the greenhouse effect would truly make itself felt over the continents. This has not happened and may not occur for several decades. Despite the press hysteria, the 1988 heat wave and drought appear to have been caused primarily by a warming in the eastern Pacific known as El Niño, which is due to natural causes. The restoration of normal warmth and rainfall in 1989, in turn, followed a Pacific cooling called La Niña. Neither of these was related to the greenhouse effect. The observed warmings to date are within the range of natural variations, and it may take another decade or two before theory and observation produce general agreement that the greenhouse indeed is at hand.
Nevertheless, there is good evidence for a worldwide increase in mean temperature of about one degree over the past century, with much of this rise having taken place since 1970. Worldwide temperature measurements, recorded over the years, tell of this. In addition, a number of glaciers have retreated. The maximal extent of sea ice, around Antarctica and in the Arctic seas, has declined. In the Alaskan and Canadian Arctic, the depth to permafrost has increased.
The forecasts are admittedly uncertain. Only in recent months have data been published that can permit an adequate understanding of the role of clouds in the earth's climate. Clouds aid in trapping heat from below, but they have the even larger effect of reflecting sunlight back into space, producing a net cooling. Uncertainties concerning the action of clouds are the reason that analysts give a range of possible values for the warming, such as "5 to 9 degrees with a carbon dioxide doubling," rather than a single, more definite value.
Unfortunately, this uncertainty offers little comfort. Michael MacCracken of Lawrence Livermore National Laboratory has compared a variety of computer models with one another and with real-world climate data. He concludes that the warming will amount in any case to several degrees, rather than being one degree or less. That is just what the computations have been showing all along.
Despite the uncertainties, we have abundant reason to expect that the next century or so will bring the sort of climatic change that we associate with a passage between geologic epochs. And since it is an ill wind that blows nobody good, it is natural to ask who will be helped and hurt and what the major anticipatable changes may be.
One such feared change—the threat of suffocation due to the using-up of oxygen—is wholly imaginary. Two other changes will be largely beneficial: warming the northern lands and staving off the next Ice Age. Three others will be unpleasant: hot weather, regional droughts, and major changes to ecosystems. Still, they are in line with longstanding trends and past experiences. But one result of the greenhouse warming does indeed pose a major threat. This is the melting of the Antarctic ice sheets, which could raise sea levels worldwide by close to 20 feet.
Taking these effects in turn, one begins with the allegation of a threat to the world's oxygen. This tale comes from environmentalists who are concerned over the widespread burning and deforestation of the Amazon. Some people assert that the Amazon is the world's "lungs," its prime source of new oxygen produced by photosynthesis. To bum the Amazon, then, would condemn us all to perish for want of oxygen to breathe.
There are excellent reasons to seek to save at least a few major tracts of rain forest, for they contain vast numbers of plant and animal species that have yet to be studied. But to call the Amazon the world's lungs reveals a woeful ignorance of the most basic chemistry. The rain forests produce great quantities of oxygen, true. But they also consume equally great quantities of oxygen when their plants die and decay. If the Amazon were a large net source of oxygen, this gas would be chemically balanced by large stores of "fixed carbon": humus, peat, lignite, coal, oil. The Amazon contains little or none of the above. In fact, the oxygen we breathe comes mainly from a source that no human activity could ever touch: the evaporation of seawater. This evaporation produces water vapor that breaks apart in the upper atmosphere, yielding hydrogen atoms that escape into space and oxygen atoms that are heavier and stay behind.
Warming of the northern lands is much more solidly established as a prospect for the future. The global computer models, predicting a worldwide average warming of five or more degrees with a doubling of carbon dioxide, also show that this warming would be substantially greater near the poles. Above the 80th parallel of latitude, the warming could amount to 18 degrees or more.
Agriculture could benefit enormously, both in Canada and the Soviet Union. Over a century or so, these countries might experience economic growth that would vastly enhance their prosperity. The Arctic Ocean might become navigable, with incalculable advantage for the development of Siberia and the other northern lands. The Northwest Passage could become a much-traveled sea route, linking Europe to the Far East. The Scandinavian countries would also prosper, contributing to the growing power of a unifying Europe.
Staving off the next Ice Age is another valuable consequence of a climate warming. The time between successive ice ages is called an interglacial; we have been living amid such a time for some thousands of years. In 1972, however, a group of researchers gathered at Brown University for a conference with the interesting title, "The Present Interglacial, How and When Will It End?" Reporting on the conference proceedings in Science, climate specialists George Kukla and R.K. Matthews stated: "When comparing the present with past interglacials, several investigators showed that the present interglacial is in its final phase…and that if nature were allowed to run its course unaltered by man, events similar to those which ended the last interglacial should be expected to occur perhaps as soon as the next few centuries."
One would not wish to write an environmental impact statement for such events. It is sufficient to note that the North American industrial heartland lies within 100 or so miles of the Great Lakes and Long Island—and that these geographic features mark the extent of the glaciers. (The Great Lakes were pressed downward by the weight of the ice, while other glaciers bulldozed material ahead of them to form Long Island.)
We would be eminently justified in doing whatever is necessary to prevent or delay the glaciers' return. And how fortunate we are if to do this we require no surge of global effort, no massive endeavors marshaling the world's concerted energies—nothing more than to continue with the growth of industry, the rise in living standards, and the attendant use of fossil fuels.
Still, the climate warmings will bring definite problems to wide areas. Chicago may experience the summer heat of New Orleans, while Boston swelters as if it were Washington, D.C. The greenhouse effect, then, might bring the climate of the Sun Belt to the Frost Belt. But Americans have already experienced an increase in mean temperature that has nothing to do with climate change. Large numbers of people from the Frost Belt have for some time been moving to the Sun Belt, and many more would like to follow. Air conditioning made possible the spectacular postwar boom in the South and Southwest, and it is fair to say that air conditioning would similarly advance as a way of life if summer heat becomes more burdensome in the North.
Regional droughts could pose a more dramatic problem. The word regional must certainly be emphasized, for the most elementary physics shows that a warmer world will evaporate more water and hence will produce more rainfall. The Manabe-Wetherald solution, for one, shows a 7 percent increase in total world rainfall. Yet this is hardly a 7 percent solution. Regional rainfall patterns are strongly influenced by seasonal movements of the jet stream and of high- and low-pressure areas. A general climate warming could well bring changes entirely similar to the 1988 El Niño, with its attendant drought and heat.
Rain-fed agriculture is a mainstay in much of the Midwest, and a sudden onset of drought would be ruinous. If the changes took place over decades, however, they would amount merely to a continuation of trends that have reduced the agricultural workforce to only 3 percent of all persons holding jobs. A boom in Alaskan and Canadian farming would certainly provide opportunities for many people. And the prospect of water shortages might well provide New York and other cities the incentive to rebuild their leaky and obsolete municipal systems.
Elsewhere in the world, one cannot overlook the possibility of intensified drought in already-dry parts of Africa, such as Ethiopia and the sub-Saharan lands. Here, however, the real problem is not climate. Indigenous governments committed to private property and economic growth—and prepared to build highways and railroads—could readily ward off the starvation that brings these lands to the TV screen. (See "All the Hungry People," REASON, June 1988.) And it must be emphasized that, on balance, the worldwide increase in mean rainfall should bring an overall reduction in the extent of such marginal lands.
Then there is the prospect of environmental change, summed up in the question: How fast can trees migrate? Trees in forests are typically adapted to restricted ranges of temperature and hence of latitude. As climates warm, their appropriate ranges would shift northward, and might well do so more rapidly than their seeds could spread by natural means.
We have seen such developments in the last century, and on a particularly vast scale. Today we call such trends "ecocatastrophe," but a century ago they were "taming the wilderness." We cut the standing timber, broke the prairie to farmland—and produced a continent where hundreds of millions would live well, where previously fewer than a million had lived meanly. Since we could produce such sweeping environmental change in the 19th century, we surely will be able to intervene during the 21st—planting seedlings, helping the trees to migrate, and mitigating manmade environmental change with manmade restocking of the forests.
Still, in so complex a matter as climatic warming, much more is at stake than pleasant northern mildness or effects that, however unpleasant, represent extensions of ongoing trends. The warmings, again, stand to be more severe than in the last major time of high temperatures—the Eemian interglacial of 130,000 years ago. And the geological record of that era shows a clear and present danger.
This danger lies in a major sea-level rise, for the Eemian sea stood at least 20 feet higher than the sea does today. The evidence comes from fossil coral-reef terraces in Hawaii and Barbados. And there is excellent reason to believe that just such a rise in the sea will accompany the carbon dioxide warming.
Such a sea-level rise would be by far the worst effect of a climate warming. The greatest hardships would hit such locales as the Netherlands and New Orleans. Both have large portions of land already below sea level and are protected only by extensive dikes and levees. The inhabitants would have no recourse but to build these works higher, and hope.
Along the Gulf Coast, nearly a third of Louisiana would be submerged. The same would be true for the flat lowlands of Texas, which include Galveston, Corpus Christi, and parts of the Houston area. All of southern Florida, from Key West to Lake Okeechobee, would drown. So would all its coastal cities; only interior towns such as Tallahassee, Gainesville, Orlando, and Lakeland would be spared.
We would lose Savannah, Georgia; Charleston, South Carolina; four of Virginia's eight largest cities, as well as the Sacramento River flood plain in California that includes the city of that name. In Washington, D.C., the Lincoln Memorial would be swamped. The Mall would be flooded, and it would be possible to launch a boat from the White House lawn and row to just below the Capitol building.
Altogether, the United States would lose some 50,000 square miles of coastal lowlands, with a value of several trillion dollars. Similar losses would afflict every other continent. One must especially think of the hundreds of millions of people who live around the heavily populated deltas and estuaries of the Nile, the Niger, the Ganges, the Yangtze. In China, Egypt, Nigeria, and most certainly in Bangladesh, which already is right at sea level, throughout vast areas—all will be swept away.
Yet even as we contemplate such a natural disaster we must keep in mind that unlike a flood, hurricane, or earthquake, it would not occur quickly. The sea level would rise over centuries, not over days, and would give ever-adaptable humanity time to adjust.
Two distinct causes could contribute to such a sea-level rise. The nearer-term one would come into play as heat from the global warming soaked into the oceans, warming their water and bringing a thermal expansion of the sea. The EPA estimates the resulting sea-level rise at two to seven feet by the year 2100. No such rise has yet been detected; the sea has risen in the past 100 years by only four to six inches.
The rest of the sea-level rise, to the total of 20 feet, could come more slowly and from an entirely different source: the melting of polar ice. Glaciologists today are well aware of a body of ice that could indeed collapse and send sea levels surging to such an increase. This ice mass appears unstable and may well be at serious risk of melting in a time of global warming. It is the West Antarctic Ice Sheet.
The ice sheet rests upon bedrock up to a mile and a half below sea level. Ordinarily, the sea would tend powerfully to buoy up the ice and cause it to float away, but the ice is protected by fringing shelves of ice more than 1,000 feet thick, which float upon the sea. These act as icy barriers or buttresses that protect the main ice sheet from surging or collapsing into the surrounding seas.
Today, along the ice shelves' outer edges, immense flat-topped bergs continually are breaking off to float northward. This breaking-off is called calving, and a general climatic warming, amplified in the polar regions, could bring an increase in calving that would destroy the protective ice shelves.
In this scenario, once the polar temperature warmed sufficiently, the largest ice shelves would rapidly break up, falling to pieces that would float off as enormous bergs. The main West Antarctic Ice Sheet, lacking its protective barrier, then would surge into the sea. The consequence would be a reduction of West Antarctica to a scattering of islands—and a permanently raised global sea level.
How long might it take for the seas to rise? The question of time scales rests on issues that are particularly uncertain: the time for the seas to warm and the time for major ice sheets to collapse. Several glaciologists have proposed that the last major ice sheet to melt—the Laurentide, which overlay Hudson Bay 8,000 years ago—collapsed over 200 years. Though minuscule on geologic time scales, this period is already far beyond the reach of any conceivable policy or plan in human affairs. If the melting of Antarctica should take longer—500 or 1,000 years—then it would represent nothing more than a long-term trend in the background of the future development of cities and of human civilization. By building seawalls, and by encouraging future growth in the direction of higher ground, communities would cope with the fact that from one generation to the next, sea levels would rise by another foot.
Over time, energy sources will also develop, through the natural play of demand and supply, that will reduce the buildup of carbon dioxide. Nuclear power could already substitute for fossil fuels to provide electricity; its lack of carbon dioxide output may in time lead environmentalists to rue the day they opposed it so strenuously.
Over the longer term, solar energy may yet emerge as an economically viable source of electric power. With little fanfare, the prospects for solar cells have been advancing steadily. In the mid-1970s, the cost of their electricity was $15 per kilowatt-hour. Current systems reduce this cost to 30 cents, and some companies are building new facilities that promise a further reduction to 15 cents. That is within reach of the cost range, 6 to 12 cents per kilowatt-hour, that would make solar cells competitive with other future sources of electric power. Early in the next century, solar cells could emerge as the lowest-cost option for producing large blocks of electric power.
Eventually, too, hydrogen derived through electrolysis of water could substitute for the uses of fossil fuels that demand portability—powering automobiles, for instance—and might displace natural gas as a heating source. But, we must remember, in the United States it has taken some 60 years for each new energy source to rise from initial introduction to dominance within the economy. Within the world at large, the transition period has been closer to a century.
We should therefore anticipate that the concentration of carbon dioxide in the atmosphere will double, and perhaps more than double, before the rise of new energy sources within free-market economies brings the problem under control. So we should expect to experience, and to cope with, all the changes that the warming will bring—including the rise in sea levels. The geologic record strongly suggests that it is already too late to save the West Antarctic Ice Sheet, that it will inevitably melt as the world adjusts to a new equilibrium. All we may hope for, then, is that the seas will take several centuries to rise, rather than one or two, and that the resulting changes might be accommodated within the ongoing development of human civilization.
We know so little. To cite only the most severe of the effects of warming—the sea-level rise—three pertinent questions carry very large levels of ignorance: What level of climate warming will melt the Antarctic ice sheets? How long will it take? Might an economics-driven transition to new energy sources occur quickly enough to forestall this event?
Until we know the answers to these questions, we have no basis for policy. Nor should we take refuge in the idea that any action that reduces carbon dioxide is necessarily a good thing. After all, carbon dioxide is a byproduct of industrial growth and of a prosperous economy. Ill-considered actions against this gas could give us the worst of both worlds: an imperfect reduction in its emissions that barely delays the warming and robs us of the prosperity that might allow us to cope with its effects.
Good intentions are no substitute for knowledge, and fashionable activism cannot fill in gaps of ignorance. Lacking the needed answers, we cannot even accurately assess the future significance of the carbon dioxide that is already in the air. Still less can we propose a global plan designed to save the world. The most we can do is anticipate that we will cope, and muddle through.
Canadian cities will discover air conditioning. Midwestern farmers may move to Alaska. East Coast cities may make it a priority to rebuild their waterworks. Forestry companies and the Department of the Interior will plant warm-weather trees in the Appalachians. Builders will look toward higher ground. Vast engineering works—dikes, seawalls, aqueducts—may come forth against drought and rising seas. And through it all, worldwide prosperity will continue to give humanity the tools to deal with these changes, and to thrive in the face of the resulting difficulties.
Contributing Editor T.A. Heppenheimer is a widely published science writer.