A Special Moment in History

BEWARE of people preaching that we live in special times. People have preached that message before, and those who listened sold their furniture and climbed up on rooftops to await ascension, or built boats to float out the coming flood, or laced up their Nikes and poisoned themselves in some California subdivision. These prophets are the ones with visions of the seven-headed beast, with a taste for the hair shirt and the scourge, with twirling eyes. No, better by far to listen to Ecclesiastes, the original wise preacher, jaded after a thousand messiahs and a thousand revivals.

Looking at Limits

THE case that the next doubling, the one we’re now experiencing, might be the difficult one can begin as readily with the Stanford biologist Peter Vitousek as with anyone else. In 1986 Vitousek decided to calculate how much of the earth’s “primary productivity” went to support human beings. He added together the grain we ate, the corn we fed our cows, and the forests we cut for timber and paper; he added the losses in food as we overgrazed grassland and turned it into desert. And when he was finished adding, the number he came up with was 38.8 percent. We use 38.8 percent of everything the world’s plants don’t need to keep themselves alive; directly or indirectly, we consume 38.8 percent of what it is possible to eat. “That’s a relatively large number,” Vitousek says. “It should give pause to people who think we are far from any limits.” Though he never drops the measured tone of an academic, Vitousek speaks with considerable emphasis: “There’s a sense among some economists that we’re so far from any biophysical limits. I think that’s not supported by the evidence.”

For another antidote to the good cheer of someone like Julian Simon, sit down with the Cornell biologist David Pimentel. He believes that we’re in big trouble. Odd facts stud his conversation—for example, a nice head of iceberg lettuce is 95 percent water and contains just fifty calories of energy, but it takes 400 calories of energy to grow that head of lettuce in California's Central Valley, and another 1,800 to ship it east. (“There’s practically no nutrition in the damn stuff anyway,” Pimentel says. “Cabbage is a lot better, and we can grow it in upstate New York.”) Pimentel has devoted the past three decades to tracking the planet's capacity, and he believes that we're already too crowded—that the earth can support only two billion people over the long run at a middle-class standard of living, and that trying to support more is doing great damage. He has spent considerable time studying soil erosion, for instance. Every raindrop that hits exposed ground is like a small explosion, launching soil particles into the air. On a slope, more than half of the soil contained in those splashes is carried downhill. If crop residue—cornstalks, say—is left in the field after harvest, it helps to shield the soil: the raindrop doesn’t hit as hard. But in the developing world, where firewood is scarce, peasants burn those cornstalks for cooking fuel. About 60 percent of crop residues in China and 90 percent in Bangladesh are removed and burned, Pimentel says. When planting season comes, dry soils simply blow away. “Our measuring stations pick up Chinese soil in the Hawaiian air when ploughing time comes,” he says. “Every year in Florida we pick up African soils in the wind when they start to plough.”

The very things that made the Green Revolution so stunning—that made the last doubling possible—now cause trouble. Irrigation ditches, for instance, water 17 percent of all arable land and help to produce a third of all crops. But when flooded soils are baked by the sun, the water evaporates and the minerals in the irrigation water are deposited on the land. A hectare (2.47 acres) can accumulate two to five tons of salt annually, and eventually plants won’t grow there. Maybe 10 percent of all irrigated land is affected.

Or think about fresh water for human use. Plenty of rain falls on the earth’s surface, but most of it evaporates or roars down to the ocean in spring floods. According to Sandra Postel, the director of the Global Water Policy Project, we’re left with about 12,500 cubic kilometers of accessible runoff, which would be enough for current demand except that it’s not very well distributed around the globe. And we’re not exactly conservationists—we use nearly seven times as much water as we used in 1900. Already 20 percent of the world’s population lacks access to potable water, and fights over water divide many regions. Already the Colorado River usually dries out in the desert before it reaches the Sea of Cortez, making what the mid-century conservationist Aldo Leopold called a “milk and honey wilderness” into some of the nastiest country in North America. Already the Yellow River can run dry for as much as a third of the year. Already only two percent of the Nile’s freshwater flow makes it to the ocean. And we need more water all the time. Producing a ton of grain consumes a thousand tons of water —that’s how much the wheat plant breathes out as it grows. “We estimated that biotechnology might cut the amount of water a plant uses by ten percent,” Pimentel says. “But plant physiologists tell us that’s optimistic—they remind us that water’s a pretty important part of photosynthesis. Maybe we can get five percent.”

What these scientists are saying is simple: human ingenuity can turn sand into silicon chips, allowing the creation of millions of home pages on the utterly fascinating World Wide Web, but human ingenuity cannot forever turn dry sand into soil that will grow food. And there are signs that these skeptics are right—that we are approaching certain physical limits.

I said earlier that food production grew even faster than population after the Second World War. Year after year the yield of wheat and corn and rice rocketed up about three percent annually. It’s a favorite statistic of the eternal optimists. In Julian Simon’s book The Ultimate Resource (1981) charts show just how fast the growth was, and how it continually cut the cost of food. Simon wrote, “The obvious implication of this historical trend toward cheaper food—a trend that probably extends back to the beginning of agriculture—is that real prices for food will continue to drop …. It is a fact that portends more drops in price and even less scarcity in the future.”

A few years after Simon’s book was published, however, the data curve began to change. That rocketing growth in grain production ceased; now the gains were coming in tiny increments, too small to keep pace with population growth. The world reaped its largest harvest of grain per capita in 1984; since then the amount of corn and wheat and rice per person has fallen by six percent. Grain stockpiles have shrunk to less than two months’ supply.

No one knows quite why. The collapse of the Soviet Union contributed to the trend—cooperative farms suddenly found the fertilizer supply shut off and spare parts for the tractor hard to come by. But there were other causes, too, all around the world—the salinization of irrigated fields, the erosion of topsoil, the conversion of prime farmland into residential areas, and all the other things that environmentalists had been warning about for years. It’s possible that we’ll still turn production around and start it rocketing again. Charles C. Mann, writing in Science, quotes experts who believe that in the future a “gigantic, multi-year, multi-billion-dollar scientific effort, a kind of agricultural ‘person-on-the-moon project,’” might do the trick. The next great hope of the optimists is genetic engineering, and scientists have indeed managed to induce resistance to pests and disease in some plants. To get more yield, though, a cornstalk must be made to put out another ear, and conventional breeding may have exhausted the possibilities. There’s a sense that we’re running into walls.

We won’t start producing less food. Wheat is not like oil, whose flow from the spigot will simply slow to a trickle one day. But we may be getting to the point where gains will be small and hard to come by. The spectacular increases may be behind us. One researcher told Mann, “Producing higher yields will no longer be like unveiling a new model of a car. We won’t be pulling off the sheet and there it is, a two-fold yield increase.” Instead the process will be “incremental, torturous, and slow.” And there are five billion more of us to come.

So far we’re still fed; gas is cheap at the pump; the supermarket grows ever larger. We’ve been warned again and again about approaching limits, and we’ve never quite reached them. So maybe—how tempting to believe it!—they don’t really exist. For every Paul Ehrlich there’s a man like Lawrence Summers, the former World Bank chief economist and current deputy secretary of the Treasury, who writes, “There are no … limits to carrying capacity of the Earth that are likely to bind at any time in the foreseeable future.” And we are talking about the future—nothing can be proved.

But we can calculate risks, figure the odds that each side may be right. Joel Cohen made the most thorough attempt to do so in How Many People Can the Earth Support? Cohen collected and examined every estimate of carrying capacity made in recent decades, from that of a Harvard oceanographer who thought in 1976 that we might have food enough for 40 billion people to that of a Brown University researcher who calculated in 1991 that we might be able to sustain 5.9 billion (our present population), but only if we were principally vegetarians. One study proposed that if photosynthesis was the limiting factor, the earth might support a trillion people; an Australian economist proved, in calculations a decade apart, that we could manage populations of 28 billion and 157 billion. None of the studies is wise enough to examine every variable, to reach by itself the “right” number. When Cohen compared the dozens of studies, however, he uncovered something pretty interesting: the median low value for the planet’s carrying capacity was 7.7 billion people, and the median high value was 12 billion. That, of course, is just the range that the UN predicts we will inhabit by the middle of the next century. Cohen wrote,

Stormy and Warm

WHAT does this new world feel like? For one thing, it’s stormier than the old one. Data analyzed last year by Thomas Karl, of the National Oceanic and Atmospheric Administration, showed that total winter precipitation in the United States had increased by 10 percent since 1900 and that “extreme precipitation events”—rainstorms that dumped more than two inches of water in twenty-four hours and blizzards—had increased by 20 percent. That’s because warmer air holds more water vapor than the colder atmosphere of the old earth; more water evaporates from the ocean, meaning more clouds, more rain, more snow. Engineers designing storm sewers, bridges, and culverts used to plan for what they called the “hundred-year storm.” That is, they built to withstand the worst flooding or wind that history led them to expect in the course of a century. Since that history no longer applies, Karl says, “there isn’t really a hundred-year event anymore … we seem to be getting these storms of the century every couple of years.” When Grand Forks, North Dakota, disappeared beneath the Red River in the spring of last year, some meteorologists referred to it as “a 500-year flood”—meaning, essentially, that all bets are off. Meaning that these aren’t acts of God. “If you look out your window, part of what you see in terms of the weather is produced by ourselves,” Karl says. “If you look out the window fifty years from now, we’re going to be responsible for more of it.”

Twenty percent more bad storms, 10 percent more winter precipitation—these are enormous numbers. It’s like opening the newspaper to read that the average American is smarter by 30 IQ points. And the same data showed increases in drought, too. With more water in the atmosphere, there’s less in the soil, according to Kevin Trenberth, of the National Center for Atmospheric Research. Those parts of the continent that are normally dry— the eastern sides of mountains, the plains and deserts—are even drier, as the higher average temperatures evaporate more of what rain does fall. “You get wilting plants and eventually drought faster than you would otherwise,” Trenberth says. And when the rain does come, it’s often so intense that much of it runs off before it can soak into the soil.

So—wetter and drier. Different.

In 1958 Charles Keeling, of the Scripps Institution of Oceanography, set up the world’s single most significant scientific instrument in a small hut on the slope of Hawaii’s Mauna Loa volcano. Forty years later it continues without fail to track the amount of carbon dioxide in the atmosphere. The graphs that it produces show that this most important greenhouse gas has steadily increased for forty years. That’s the main news.

It has also shown something else of interest in recent years—a sign that this new atmosphere is changing the planet. Every year CO2 levels dip in the spring, when plants across the Northern Hemisphere begin to grow, soaking up carbon dioxide. And every year in the fall decaying plants and soils release CO2 back into the atmosphere. So along with the steady upward trend, there’s an annual seesaw, an oscillation that is suddenly growing more pronounced. The size of that yearly tooth on the graph is 20 percent greater than it was in the early 1960s, as Keeling reported in the journal Nature, in July of 1996. Or, in the words of Rhys Roth, writing in a newsletter of the Atmosphere Alliance, the earth is “breathing deeper.” More vegetation must be growing, stimulated by higher temperatures. And the earth is breathing earlier, too. Spring is starting about a week earlier in the 1990s than it was in the 1970s, Keeling said.

Other scientists had a hard time crediting Keeling’s study—the effect seemed so sweeping. But the following April a research team led by R. B. Myneni, of Boston University, and including Keeling, reached much the same conclusion by means of a completely different technique. These researchers used satellites to measure the color of sunlight reflected by the earth: light bouncing off green leaves is a different color from light bouncing off bare ground. Their data were even more alarming, because they showed that the increase was happening with almost lightning speed. By 1991 spring above the 45th parallel—a line that runs roughly from Portland, Oregon, to Boston to Milan to Vladivostok—was coming eight days earlier than it had just a decade before. And that was despite increased snowfall from the wetter atmosphere; the snow was simply melting earlier. The earlier spring led to increased plant growth, which sounds like a benefit. The area above the 45th parallel is, after all, the North American and Russian wheat belt. But as Cynthia Rosenzweig, of NASA’s Goddard Institute for Space Studies, told The New York Times, any such gains may be illusory. For one thing, the satellites were measuring biomass, not yields; tall and leafy plants often produce less grain. Other scientists, the Times reported, said that “more rapid plant growth can make for less nutritious crops if there are not enough nutrients available in the soil.” And it’s not clear that the grain belt will have the water it needs as the climate warms. In 1988, a summer of record heat across the grain belt, harvests plummeted, because the very heat that produces more storms also causes extra evaporation. What is clear is that fundamental shifts are under way in the operation of the planet. And we are very early yet in the greenhouse era.

The changes are basic. The freezing level in the atmosphere—the height at which the air temperature reaches 32 degrees F—has been gaining altitude since 1970 at the rate of nearly fifteen feet a year. Not surprisingly, tropical and subtropical glaciers are melting at what a team of Ohio State researchers termed “striking” rates. Speaking at a press conference last spring, Ellen Mosley-Thompson, a member of the Ohio State team, was asked if she was sure of her results. She replied, “I don’t know quite what to say. I’ve presented the evidence. I gave you the example of the Quelccaya ice cap. It just comes back to the compilation of what’s happening at high elevations: the Lewis glacier on Mount Kenya has lost forty percent of its mass; in the Ruwenzori range all the glaciers are in massive retreat. Everything, virtually, in Patagonia, except for just a few glaciers, is retreating …. We’ve seen … that plants are moving up the mountains …. I frankly don’t know what additional evidence you need.”

As the glaciers retreat, a crucial source of fresh water in many tropical countries disappears. These areas are “already water-stressed,” Mosley-Thompson told the Association of American Geographers last year. Now they may be really desperate.

As with the tropics, so with the poles. According to every computer model, in fact, the polar effects are even more pronounced, because the Arctic and the Antarctic will warm much faster than the Equator as carbon dioxide builds up. Scientists manning a research station at Toolik Lake, Alaska, 170 miles north of the Arctic Circle, have watched average summer temperatures rise by about seven degrees in the past two decades. “Those who remember wearing down-lined summer parkas in the 1970s—before the term ‘global warming’ existed—have peeled down to T-shirts in recent summers,” according to the reporter Wendy Hower, writing in the Fairbanks Daily News-Miner. It rained briefly at the American base in McMurdo Sound, in Antarctica, during the southern summer of 1997—as strange as if it had snowed in Saudi Arabia. None of this necessarily means that the ice caps will soon slide into the sea, turning Tennessee into beachfront. It simply demonstrates a radical instability in places that have been stable for many thousands of years. One researcher watched as emperor penguins tried to cope with the early breakup of ice: their chicks had to jump into the water two weeks ahead of schedule, probably guaranteeing an early death. They (like us) evolved on the old earth.

You don’t have to go to exotic places to watch the process. Migrating red-winged blackbirds now arrive three weeks earlier in Michigan than they did in 1960. A symposium of scientists reported in 1996 that the Pacific Northwest was warming at four times the world rate. “That the Northwest is warming up fast is not a theory,” Richard Gammon, a University of Washington oceanographer, says. “It’s a known fact, based on simple temperature readings.”

The effects of that warming can be found in the largest phenomena. The oceans that cover most of the planet’s surface are clearly rising, both because of melting glaciers and because water expands as it warms. As a result, low-lying Pacific islands already report surges of water washing across the atolls. “It’s nice weather and all of a sudden water is pouring into your living room,” one Marshall Islands resident told a newspaper reporter. “It’s very clear that something is happening in the Pacific, and these islands are feeling it.” Global warming will be like a much more powerful version of El Niño that covers the entire globe and lasts forever, or at least until the next big asteroid strikes.

If you want to scare yourself with guesses about what might happen in the near future, there’s no shortage of possibilities. Scientists have already observed large-scale shifts in the duration of the El Niño ocean warming, for instance. The Arctic tundra has warmed so much that in some places it now gives off more carbon dioxide than it absorbs—a switch that could trigger a potent feedback loop, making warming ever worse. And researchers studying glacial cores from the Greenland Ice Sheet recently concluded that local climate shifts have occurred with incredible rapidity in the past—18 degrees in one three-year stretch. Other scientists worry that such a shift might be enough to flood the oceans with fresh water and reroute or shut off currents like the Gulf Stream and the North Atlantic, which keep Europe far warmer than it would otherwise be. (See “The Great Climate Flip-flop,” by William H. Calvin, January Atlantic.) In the words of Wallace Broecker, of Columbia University, a pioneer in the field, “Climate is an angry beast, and we are poking it with sticks.”

Changing “Unchangeable” Needs

WHEN we think about overpopulation, we usually think first of the developing world, because that’s where 90 percent of new human beings will be added during this final doubling. In The Population Bomb, Paul Ehrlich wrote that he hadn’t understood the issue emotionally until he traveled to New Delhi, where he climbed into an ancient taxi, which was hopping with fleas, for the trip to his hotel. “As we crawled through the city, we entered a crowded slum area …. the streets seemed alive with people. People eating, people washing, people sleeping. People visiting, arguing, and screaming …. People, people, people, people.”

We fool ourselves when we think of Third World population growth as producing an imbalance, as Amartya Sen points out. The white world simply went through its population boom a century earlier (when Dickens was writing similar descriptions of London). If UN calculations are correct and Asians and Africans will make up just under 80 percent of humanity by 2050, they will simply have returned, in Sen’s words, “to being proportionately almost exactly as numerous as they were before the European industrial revolution.”

And of course Asians and Africans, and Latin Americans, are much “smaller” human beings: the balloons that float above their heads are tiny in comparison with ours. Everyone has heard the statistics time and again, usually as part of an attempt to induce guilt. But hear them one more time, with an open mind, and try to think strategically about how we will stave off the dangers to this planet. Pretend it’s not a moral problem, just a mathematical one.