SpecialMomentArticle

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A special moment in history: the future of=20 population

(Cover Story) Bill McKibben.

The Atlantic Monthly, May 1998 v281 n5=20 p55(1998)

Abstract: The human population on Earth is growing = at an=20 alarming rate, despite the decision by most women to have fewer = children. The=20 planet can only support a certain number of people. Questions about what = will=20 happen if that number is exceeded are discussed.=20

Bill McKibben=20

Beware of people preaching that we live in = special times.=20 People have preached that message before, and those who listened sold = their=20 furniture and climbed up on rooftops to await ascension, or built boats = to float=20 out the coming flood, or laced up their Nikes and poisoned themselves in = some=20 California sub- division. These prophets are the ones with visions of = the=20 seven-headed beast, with a taste for the hair shirt and the scourge, = with=20 twirling eyes. No, bet- ter by far to listen to Ecclesiastes, the = original wise=20 preacher, jaded after a thousand messiahs and a thousand = revivals.=20

One generation passes away, and another = generation comes;=20 but the earth abides forever. . . . That which has been is what will be, = that=20 which is done is what will be done, and there is nothing new under the = sun. Is=20 there anything of which it may be said, "See, this is new"? It has = already been=20 in ancient times before us.=20

And yet, for all that, we may live in a special = time. We=20 may live in the strangest, most thoroughly different moment since human = beings=20 took up farm- ing, 10,000 years ago, and time more or less commenced. = Since then=20 time has flowed in one directiontoward more, which we have taken to be = progress.=20 At first the momentum was gradual, almost imperceptible, checked by wars = and the=20 Dark Ages and plagues and taboos; but in recent centuries it has = accelerated,=20 the curve of every graph steepening like the Himalayas rising from the = Asian=20 steppe. We have climbed quite high. Of course, fifty years ago one could = have=20 said the same thing, and fifty years before that, and fifty years before = that.=20 But in each case it would have been premature. We've increased the = population=20 fourfold in that 150 years; the amount of food we grow has gone up = faster still;=20 the size of our economy has quite simply exploded.=20

But nownow may be the special time. So special = that in=20 the Western world we might each of us consider, among many other things, = having=20 only one child--that is, reproducing at a rate as low as that at which = human=20 beings have ever voluntarily reproduced. Is this really necessary?Are we = finally=20 run- ning up against some limits?=20

To try to answer this question, we need to ask = another:=20 How many of us will there be in the near future? Here is a piece of news = that=20 may alter the way we see the planet--an indication that we live at a = special=20 moment. At least at first blush the news is hopeful. New demographic = evidence=20 shows that it is at least possible that a child born today will live = long enough=20 to see the peak of human population. =

Around the world people are choosing to have = fewer and=20 fewer childrennot just in China, where the government forces it on them, = but in=20 almost every nation outside the poorest parts of Africa. Population = growth rates=20 are lower than they have been at any time since the Second World War. In = the=20 past three decades the average woman in the developing world, excluding = China,=20 has gone from bearing six children to bearing four. Even in Bangladesh = the=20 average has fallen from six to fewer than four; even in the mullahs' = Iran it has=20 dropped by four children. If this keeps up, the population of the world = will not=20 quite double again; United Nations analysts offer as their mid-range = projection=20 that it will top out at 10 to 11 billion, up from just under six billion = at the=20 moment. The world is still growing, at nearly a record pacewe add a New = York=20 City every month, almost a Mexico every year, almost an India every = decade. But=20 the rate of growth is slowing; it is no longer "exponential," = "unstoppable,"=20 "inexorable," "unchecked," "cancerous." If current trends hold, the = world's=20 population will all but stop growing before the twenty- first century is = out.=20

And that will be none too soon. There is no way = we could=20 keep going as we have been. The increase in human population in the = 1990s has=20 exceeded the total population in 1600. The population has grown more = since 1950=20 than it did dur- ing the previous four million years. The reasons for = our recent=20 rapid growth are pretty clear. Although the Industrial Revolution = speeded=20 historical growth rates considerably, it was really the public-health=20 revolution, and its spread to the Third World at the end of the Second = World=20 War, that set us galloping. Vaccines and antibiotics came all at once, = and right=20 behind came population. In Sri Lanka in the late 1940s life expectancy = was=20 rising at least a year every twelve months. How much difference did this = make?=20 Consider the United States: if people died throughout this century at = the same=20 rate as they did at its beginning, America's population would be 140 = million,=20 not 270 million.=20

If it is relatively easy to explain why = populations grew=20 so fast after the Second World War, it is much harder to explain why the = growth=20 is now slowing. Experts confidently supply answers, some of them = contradictory:=20 "Development is the best contraceptive"-- or education, or the = empowerment of=20 women, or hard times that force families to postpone having children. = For each=20 example there is a counterexample. Ninety-seven percent of women in the = Arab=20 sheikhdom of Oman know about contraception, and yet they average more = than six=20 children apiece. Turks have used contraception at about the same rate as = the=20 Japanese, but their birth rate is twice as high. And so on. It is not = AIDS that=20 will slow population growth, except in a few African countries. It is = not=20 horrors like the civil war in Rwanda, which claimed half a million = lives--a loss=20 the planet can make up for in two days. All that matters is how often = individual=20 men and women decide that they want to reproduce.=20

Will the drop continue? It had better. UN = mid-range=20 projections assume that women in the developing world will soon average = two=20 children apiece--the rate at which population growth stabilizes. If = fertility=20 remained at current levels, the population would reach the absurd figure = of 296=20 billion in just 150 years. Even if it dropped to 2.5 children per woman = and then=20 stopped fall- ing, the population would still reach 28 = billion.=20

But let's trust that this time the demographers = have got=20 it right. Let's trust that we have rounded the turn and we're in the = home=20 stretch. Let's trust that the planet's population really will double = only one=20 more time. Even so, this is a case of good news, bad news. The good news = is that=20 we won't grow forever. The bad news is that there are six billion of us = already,=20 a number the world strains to support. One more near-doublingfour or = five=20 billion more peoplewill nearly double that strain. Will these be the = five=20 billion straws that break the camel's back?=20

Big Questions we've answered the question How = many of us=20 will there be? But to figure out how near we are to any limits, we need = to ask=20 something else: How big are we? This is not so simple. Not only do we = vary=20 greatly in how much food and energy and water and minerals we consume, = but each=20 of us varies over time. William Catton, who was a sociologist at = Washington=20 State University before his retirement, once tried to calculate the = amount of=20 energy human beings use each day. In hunter-gatherer times it was about = 2,500=20 calories, all of it food. That is the daily energy intake of a common = dolphin. A=20 modern human being uses 31,000 calories a day, most of it in the form of = fossil=20 fuel. That is the intake of a pilot whale. And the average American uses = six=20 times thatas much as a sperm whale. We have become, in other words, = different=20 from the people we used to be. Not kinder or unkinder, not deeper or = stupiderour=20 natures seem to have changed little since Homer. We've just gotten = bigger. We=20 appear to be the same species, with stomachs of the same size, but we = aren't.=20 It's as if each of us were trailing a big Macy's-parade balloon around, = feed-=20 ing it constantly.=20

So it doesn't do much good to stare idly out = the window=20 of your 737 as you fly from New York to Los Angeles and see that there's = plenty=20 of empty space down there. Sure enough, you could crowd lots more people = into=20 the nation or onto the planet. The entire world population could fit = into Texas,=20 and each person could have an area equal to the floor space of a typical = U.S.=20 home. If people were willing to stand, everyone on earth could fit = comfortably=20 into half of Rhode Island. Holland is crowded and is doing just=20 fine.=20

But this ignores the balloons above our heads, = our hungry=20 shadow selves, our sperm- whale appetites. As soon as we started = farming, we=20 started setting aside extra land to support ourselves. Now each of us = needs not=20 only a little plot of cropland and a little pasture for the meat we eat = but also=20 a little forest for timber and paper, a little mine, a little oil well. = Giants=20 have big feet. Some scientists in Vancouver tried to calculate one such=20 "footprint" and found that although 1.7 million people lived on a = million acres=20 surrounding their city, those people required 21.5 million acres of land = to=20 support them-- wheat fields in Alberta, oil fields in Saudi Arabia, = tomato=20 fields in California. People in Manhattan are as dependent on faraway = resources=20 as people on the Mir space station.=20

Those balloons above our heads can shrink or = grow,=20 depending on how we choose to live. All over the earth people who were = once tiny=20 are suddenly growing like Alice when she ate the cake. In China per = capita=20 income has doubled since the early 1980s. People there, though still = Lilliputian=20 in comparison with us, are twice their former size. They eat much higher = on the=20 food chain, under- standably, than they used to:China slaughters more = pigs than=20 any other nation, and it takes four pounds of grain to produce one pound = of=20 pork. When, a decade ago, the United Nations examined sustainable = development,=20 it issued a report saying that the economies of the developing countries = needed=20 to be five to ten times as large to move poor people to an acceptable = standard=20 of living--with all that this would mean in terms of demands on oil = wells and=20 forests.=20

That sounds almost impossible. For the moment, = though,=20 let's not pass judg- ment. We're still just doing math. There are going = to be=20 lots of us. We're going to be big. But lots of us in relation to what? = Big in=20 relation to what? It could be that compared with the world we inhabit, = we're=20 still scarce and small. Or not. So now we need to consider a third = question: How=20 big is the earth?=20

Any state wildlife biologist can tell you how = many deer a=20 given area can sup- porthow much browse there is for the deer to eat = before they=20 begin to suppress the reproduction of trees, before they is for the deer = to eat=20 before they begin to suppress the reproduction of trees, before they = begin to=20 starve in the winter. He can calculate how many wolves a given area can = support=20 too, in part by counting the number of deer. And so on, up and down the = food=20 chain. It's not an exact science, but it comes pretty close--at least = compared=20 with figuring out the carrying capacity of the earth for human beings, = which is=20 an art so dark that anyone with any sense stays away from it.lmost any = level=20 they choose. Hunter-gatherers used 2,500 calories of energy a day, = whereas=20 modern Americans use seventy-five times that. Human beings, unlike deer, = can=20 import what they need from thousands of miles away. And human beings, = unlike=20 deer, can figure out new ways to do old things. If, like deer, we needed = to=20 browse on conifers to survive, we could crossbreed lush new strains, = chop down=20 compe- ting trees, irrigate forests, spray a thousand chemicals, freeze = or dry=20 the tender buds at the peak of harvest, genetically engineer new = strainsand=20 advertise the merits of maple buds until everyone was ready to switch. = The=20 variables are so great that professional demographers rarely even bother = trying=20 to figure out carrying capacity. The demographer Joel Cohen, in his = potent book=20 How Many People Can the Earth Support? (1995),reports that at two recent = meetings of the Population Association of America exactly none of the = more than=20 200 symposia dealt with carrying capacity.=20

But the difficulty hasn't stopped other = thinkers. This=20 is, after all, as big a question as the world offers. Plato, Euripides, = and=20 Polybius all worried that we would run out of food if the population = kept=20 growing; for centuries a steady stream of economists, environmentalists, = and=20 zealots and cranks of all sorts have made it their business to issue = estimates=20 either dire or benign. The most famous, of course, came from the = Reverend Thomas=20 Malthus. Writing in 1798, he proposed that the growth of population, = being=20 "geometric," would soon outstrip the supply of food. Though he changed = his mind=20 and rewrote his famous essay, it's the original version that people have = remembered--and lam- bastedever since. Few other writers have found = critics in=20 as many corners. Not only have conservatives made Malthus's name a = byword for=20 ludicrous alarmism, but Karl Marx called his essay "a libel on the human = race,"=20 Friedrich Engels believed that "we are forever secure from the fear of=20 overpopulation," and even Mao Zedong attacked Malthus by name, adding, = "Of all=20 things in the world people are the most precious."=20

Each new generation of Malthusians has made new = predictions that the end was near, and has been proved wrong. The late = 1960s saw=20 an upsurge of Malthusian panic. In 1967 William and Paul Paddock = published a=20 book called Famine1975!, which contained a triage list: "Egypt: = Can't-be-saved.=20 . . . Tunisia: Should Receive Food. . . . India: Can't-be-saved." Almost = simultaneously Paul Ehrlich wrote, in his best-selling The Population = Bomb=20 (1968), "The battle to feed all of humanity is over. In the 1970s, the = world=20 will undergo famines--hundreds of millions of people will starve to = death." It=20 all seemed so certain, so firmly in keeping with a world soon to be = darkened by=20 the first oil crisis.=20

But that's not how it worked out. India fed = herself. The=20 United States still ships surplus grain around the world. As the astute = Harvard=20 social scientist Amartya Sen points out, "Not only is food generally = much=20 cheaper to buy today, in constant dollars, than it was in Malthus's = time, but it=20 also has become cheaper during recent decades." So far, in other words, = the=20 world has more or less supported us. Too many people starve (60 percent = of=20 children in South Asia are stunted by malnutrition), but both the total = number=20 and the percent- age have dropped in recent decades, thanks mainly to = the=20 successes of the Green Revolution. Food production has tripled since the = Second=20 World War, out- pacing even population growth. We may be giants, but we = are=20 clever giants.=20

So Malthus was wrong. Over and over again he = was wrong.=20 No other prophet has ever been proved wrong so many times. At the = moment, his=20 stock is especially low. One group of technological optimists now = believes that=20 people will con- tinue to improve their standard of living precisely = because=20 they increase their numbers. This group's intellectual fountainhead is a = brilliant Danish economist named Ester Boserup--a sort of anti-Malthus, = who in=20 1965 argued that the gloomy cleric had it backward. The more people, = Boserup=20 said, the more progress. Take agriculture as an example: the first = farmers, she=20 pointed out, were slash-and-burn cultivators, who might farm a plot for = a year=20 or two and then move on, not returning for maybe two decades. As the = population=20 grew, however, they had to return more frequently to the same plot. That = meant=20 prob- lems: compacted, depleted, weedy soils. But those new problems = meant new=20 solu- tions: hoes, manure, compost, crop rotation, irrigation. Even in = this=20 century, Boserup said, necessity-induced invention has meant that = "intensive=20 systems of agriculture replaced extensive systems," accelerating the = rate of=20 food produc- tion.=20

Boserup's closely argued examples have inspired = a less=20 cautious group of popu- larizers, who point out that standards of living = have=20 risen all over the world even as population has grown. The most = important=20 benefit, in fact, that popu- lation growth bestows on an economy is to = increase=20 the stock of useful knowl- edge, insisted Julian Simon, the best known = of the=20 so-called cornucopians, who died earlier this year. We might run out of = copper,=20 but who cares? The mere fact of shortage will lead someone to invent a=20 substitute. "The main fuel to speed our progress is our stock of = knowledge, and=20 the brake is our lack of imagination," Simon wrote. "The ultimate = resource is=20 peopleskilled, spirited, and hopeful people who will exert their wills = and=20 imaginations for their own benefit, and so, inevitably, for the benefit = of us=20 all."=20

Simon and his ilk owe their success to this: = they have=20 been right so far. The world has behaved as they predicted. India hasn't = starved. Food is cheap. But Malthus never goes away. The idea that we = might grow=20 too big can be disproved only for the moment--never for good. We might = always be=20 on the threshold of a special time, when the mechanisms described by = Boserup and=20 Simon stop working. It is true that Malthus was wrong when the = population=20 doubled from 750 million to 1.5 billion. It is true that Malthus was = wrong when=20 the population doubled from 1.5 billion to three billion. It is true = that=20 Malthus was wrong when the population doubled from three billion to six = billion.=20 Will Malthus still be wrong fifty years from now?=20

Looking at Limits the case that the next = doubling, the=20 one we're now experi- encing, might be the difficult one can begin as = readily=20 with the Stanford biologist Peter Vitousek as with anyone else. In 1986 = Vitousek=20 decided to cal- culate how much of the earth's "primary productivity" = went to=20 support human beings. He added together the grain we ate, the corn we = fed our=20 cows, and the forests we cut for timber and paper; he added the losses = in food=20 as we over- grazed grassland and turned it into desert. And when he was = finished=20 adding, the number he came up with was 38.8 percent. We use 38.8 percent = of=20 everything the world's plants don't need to keep themselves alive; = directly or=20 indirectly, we consume 38.8 percent of what it is possible to eat. = "That's a=20 relatively large number," Vitousek says. "It should give pause to people = who=20 think we are far from any limits." Though he never drops the measured = tone of an=20 academic, Vitousek speaks with considerable emphasis: "There's a sense = among=20 some economists that we're so far from any biophysical limits. I think = that's=20 not supported by the evidence."=20

For another antidote to the good cheer of = someone like=20 Julian Simon, sit down with the Cornell biologist David Pimentel. He = believes=20 that we're in big trouble. Odd facts stud his conversationfor example, a = nice=20 head of iceberg lettuce is 95 percent water and contains just fifty = calories of=20 energy, but it takes 400 calories of energy to grow that head of lettuce = in=20 California's Central Valley, and another 1,800 to ship it east. = ("There's=20 practically no nutrition in the damn stuff anyway," Pimentel says. = "Cabbage is a=20 lot better, and we can grow it in upstate New York.") Pimentel has = devoted the=20 past three decades to tracking the planet's capacity, and he believes = that we're=20 already too crowdedthat the earth can support only two billion people = over the=20 long run at a middle- class standard of living, and that trying to = support more=20 is doing great damage. He has spent considerable time studying soil = erosion, for=20 instance. Every raindrop that hits exposed ground is like a small = explosion,=20 launching soil particles into the air. On a slope, more than half of the = soil=20 contained in those splashes is carried downhill. If crop = residuecornstalks,=20 sayis left in the field after harvest, it helps to shield the soil: the = raindrop=20 doesn't hit as hard. But in the developing world, where firewood is = scarce,=20 peasants burn those cornstalks for cooking fuel. About 60 percent of = crop=20 residues in China and 90 percent in Bangladesh are removed and burned, = Pimentel=20 says. When planting season comes, dry soils simply blow away. "Our = measuring=20 stations pick up Chinese soil in the Hawaiian air when ploughing time = comes,"he=20 says. "Every year in Florida we pick up African soils in the wind when = they=20 start to plough."=20

The very things that made the Green Revolution = so=20 stunningthat made the last doubling possiblenow cause trouble. = Irrigation=20 ditches, for instance, water 17 percent of all arable land and help to = produce a=20 third of all crops. But when flooded soils are baked by the sun, the = water=20 evaporates and the minerals in the irrigation water are deposited on the = land. A=20 hectare (2.47 acres) can accumulate two to five tons of salt annually, = and=20 eventually plants won't grow there. Maybe 10 percent of all irrigated = land is=20 affected.=20

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

What these scientists are saying is simple: = human=20 ingenuity can turn sand into silicon chips, allowing the creation of = millions of=20 home pages on the utterly fascinating World Wide Web, but human = ingenuity cannot=20 forever turn dry sand into soil that will grow food. And there are signs = that=20 these skeptics are rightthat we are approaching certain physical=20 limits.=20

I said earlier that food production grew even = faster than=20 population after the Second World War. Year after year the yield of = wheat and=20 corn and rice rock- eted up about three percent annually. It's a = favorite=20 statistic of the eternal optimists. In Julian Simon's book The Ultimate = Resource=20 (1981) charts show just how fast the growth was, and how it continually = cut the=20 cost of food. Simon wrote, "The obvious implication of this historical = trend=20 toward cheaper fooda trend that probably extends back to the beginning = of=20 agricultureis that real prices for food will continue to drop. . . . It = is a=20 fact that portends more drops in price and even less scarcity in the=20 future."=20

A few years after Simon's book was published, = however,=20 the data curve began to change. That rocketing growth in grain = production=20 ceased; now the gains were coming in tiny increments, too small to keep = pace=20 with population growth. The world reaped its largest harvest of grain = per capita=20 in 1984; since then the amount of corn and wheat and rice per person has = fallen=20 by six percent. Grain stockpiles have shrunk to less than two months'=20 supply.=20

No one knows quite why. The collapse of the = Soviet Union=20 contributed to the trend-- cooperative farms suddenly found the = fertilizer=20 supply shut off and spare parts for the tractor hard to come by. But = there were=20 other causes, too, all around the worldthe salinization of irrigated = fields, the=20 erosion of top- soil, the conversion of prime farmland into residential = areas,=20 and all the other things that environmentalists had been warning about = for=20 years. It's possible that we'll still turn production around and start = it=20 rocketing again. Charles C. Mann, writing in Science, quotes experts who = believe=20 that in the future a "gigantic, multi-year, multi-billion-dollar = scientific=20 effort, a kind of agricultural 'person-on-the-moon project,'" might do = the=20 trick. The next great hope of the optimists is genetic engineering, and=20 scientists have indeed managed to induce resistance to pests and disease = in some=20 plants. To get more yield, though, a cornstalk must be made to put out = another=20 ear, and conven- tional breeding may have exhausted the possibilities. = There's a=20 sense that we're running into walls. =

We won't start producing less food. Wheat is = not like=20 oil, whose flow from the spigot will simply slow to a trickle one day. = But we=20 may be getting to the point where gains will be small and hard to come = by. The=20 spectacular increases may be behind us. One researcher told Mann, = "Producing=20 higher yields will no longer be like unveiling a new model of a car. We = won't be=20 pulling off the sheet and there it is, a two-fold yield increase." = Instead the=20 process will be "incremental, torturous, and slow." And there are five = billion=20 more of us to come.=20

So far we're still fed; gas is cheap at the = pump; the=20 supermarket grows ever larger. We've been warned again and again about=20 approaching limits, and we've never quite reached them. So maybe--how = tempting=20 to believe it! they don't really exist. For every Paul Ehrlich there's a = man=20 like Lawrence Summers, the former World Bank chief economist and current = deputy=20 secretary of the Treasury, who writes, "There are no . . . limits to = carrying=20 capacity of the Earth that are likely to bind at any time in the = foreseeable=20 future." And we are talking about the futurenothing can be = proved.=20

But we can calculate risks, figure the odds = that each=20 side may be right. Joel Cohen made the most thorough attempt to do so in = How=20 Many People Can the Earth Support? Cohen collected and examined every = estimate=20 of carrying capacity made in recent decades, from that of a Harvard=20 oceanographer who thought in 1976 that we might have food enough for 40 = billion=20 people to that of a Brown University researcher who calculated in 1991 = that we=20 might be able to sustain 5.9 billion (our present population), but only = if we=20 were principally vegetarians. One study proposed that if photosynthesis = was the=20 limiting fac- tor, the earth might support a trillion people; an = Australian=20 economist proved, in calculations a decade apart, that we could manage=20 populations of 28 billion and 157 billion. None of the studies is wise = enough to=20 examine every variable, to reach by itself the "right" number. When = Cohen=20 compared the dozens of studies, however, he uncovered something pretty=20 interesting: the median low value for the planet's carrying capacity was = 7.7=20 billion people, and the median high value was 12 billion. That, of = course, is=20 just the range that the UN predicts we will inhabit by the middle of the = next=20 century. Cohen wrote,=20

The human population of the Earth now travels = in the zone=20 where a substantial fraction of scholars have estimated upper limits on = human=20 population size. . . . The possibility must be considered seriously that = the=20 number of people on the Earth has reached, or will reach within half a = century,=20 the maximum number the Earth can support in modes of life that we and = our=20 children and their children will choose to want.=20

Earth2 Throughout the 10,000 years of recorded = human=20 history the planetthe physical planethas been a stable place. In every = single=20 year of those 10,000 there have been earthquakes, volcanoes, hurricanes, = cyclones, typhoons, flo- ods, forest fires, sandstorms, hailstorms, = plagues,=20 crop failures, heat waves, cold spells, blizzards, and droughts. But = these have=20 never shaken the basic predictability of the planet as a whole. Some of = the=20 earth's land areasthe Mediterranean rim, for instancehave been = deforested beyond=20 recovery, but so far these shifts have always been local.=20

Among other things, this stability has made = possible the=20 insurance industry--has underwritten the underwriters. Insurers can = analyze the=20 risk in any venture because they know the ground rules. If you want to = build a=20 house on the coast of Florida, they can calculate with reasonable = accuracy the=20 chance that it will be hit by a hurricane and the speed of the winds = circling=20 that hurricane's eye. If they couldn't, they would have no way to set = your=20 premium--they'd just be gambling. They're always gambling a little, of = course:=20 they don't know if that hurricane is coming next year or next century. = But the=20 earth's physical stability is the house edge in this casino. As Julian = Simon=20 pointed out, "A prediction based on past data can be sound if it is = sensible to=20 assume that the past and the future belong to the same statistical uni-=20 verse."=20

So what does it mean that alone among the = earth's great=20 pools of money and power, insurance companies are beginning to take the = idea of=20 global climate change quite seriously? What does it mean that the payout = for=20 weather-related damage climbed from $16 billion during the entire 1980s = to $48=20 billion in the years 1990-1994? What does it mean that top European = insurance=20 executives have begun consulting with Greenpeace about global warming? = What does=20 it mean that the insurance giant Swiss Re, which paid out $291.5 million = in the=20 wake of Hurricane Andrew, ran an ad in the Financial Times showing its = corporate=20 logo bent sideways by a storm?=20

These things mean, I think, that the = possibility that we=20 live on a new earth cannot be discounted entirely as a fever dream. = Above,=20 Ishowed attempts to calculate carrying capacity for the world as we have = always=20 known it, the world we were born into. But what if, all of a sudden, we = live on=20 some other planet? On Earth2?=20

In 1955 Princeton University held an = international=20 symposium on "Man's Role in Changing the Face of the Earth." By this = time=20 anthropogenic carbon, sulfur, and nitrogen were pouring into the = atmosphere,=20 deforestation was already widespread, and the population was nearing = three=20 billion. Still, by comparison with the present, we remained a puny race. = Cars=20 were as yet novelties in many places. Tropical forests were still = intact, as=20 were much of the ancient woods of the West Coast, Canada, and Siberia. = The=20 world's economy was a quarter its present size. By most calculations we = have=20 used more natural resources since 1955 than in all of human history to = that=20 time.=20

Another symposium was organized in 1987 by = Clark=20 University, in Massachusetts. This time even the title made clear what = was=20 happening--not "Man and Nature," not "Man's Role in Changing the Face of = the=20 Earth," but "The Earth as Trans- formed by Human Actions." Attendees = were no=20 longer talking about local changes or what would take place in the = future. "In=20 our judgment," they said, "the biosphere has accumulated, or is on its = way to=20 accumulating, such a magnitude and variety of changes that it may be = said to=20 have been transformed."=20

Many of these changes come from a direction = that Malthus=20 didn't consider. He and most of his successors were transfixed by = sourcesby=20 figuring out whether and how we could find enough trees or corn or oil. = We're=20 good at finding more stuff; as the price rises, we look harder. The = lights never=20 did go out, despite many predictions to the contrary on the first Earth = Day. We=20 found more oil, and we still have lots and lots of coal. Meanwhile, = we're=20 driving big cars again, and why not? As of this writing, the price of = gas has=20 dropped below a dollar a gallon across much of the nation. Who can = believe in=20 limits while driving a Suburban? But perhaps, like an audience watching = a=20 magician wave his wand, we've been distracted from the real = story.=20

That real story was told in the most recent = attempt to=20 calculate our size--a special section in Science published last summer. = The=20 authors spoke bluntly in the lead article. Forget man "transforming" = naturewe=20 live, they concluded, on "a human-dominated planet," where "no ecosystem = on=20 Earth's surface is free of pervasive human influence." It's not that = we're=20 running out of stuff. What we're running out of is what the scientists = call=20 "sinks"--places to put the by-products of our large appetites. Not = garbage dumps=20 (we could go on using Pampers till the end of time and still have empty = space=20 left to toss them away) but the atmospheric equivalent of garbage=20 dumps.=20

It wasn't hard to figure out that there were = limits on=20 how much coal smoke we could pour into the air of a single city. It took = a while=20 longer to figure out that building ever higher smokestacks merely lofted = the=20 haze farther afield, raining down acid on whatever mountain range lay to = the=20 east. Even that, how- ever, we are slowly fixing, with scrubbers and = different=20 mixtures of fuel. We can't so easily repair the new kinds of pollution. = These do=20 not come from something going wrong--some engine without a catalytic = converter,=20 some waste-water pipe without a filter, some smokestack without a = scrubber. New=20 kinds of pollution come instead from things going as they're supposed to = go--but=20 at such a high volume that they overwhelm the planet. They come from = normal=20 human lifebut there are so many of us living those normal lives that = something=20 abnormal is happening. And that something is so different from the old = forms of=20 pollution that it confuses the issue even to use the word.=20

Consider nitrogen, for instance. Almost 80 = percent of the=20 atmosphere is nitrogen gas. But before plants can absorb it, it must = become=20 "fixed"--bonded with carbon, hydrogen, or oxygen. Nature does this trick = with=20 certain kinds of algae and soil bacteria, and with lightning. Before = human=20 beings began to alter the nitrogen cycle, these mechanisms provided = 90-150=20 million metric tons of nitrogen a year. Now human activity adds 130-150 = million=20 more tons. Nitrogen isn't pollutionit's essential. And we are using more = of it=20 all the time. Half the industrial nitrogen fertilizer used in human = history has=20 been applied since 1984. As a result, coastal waters and estuaries bloom = with=20 toxic algae while oxygen concentrations dwindle, killing fish; as a = result,=20 nitrous oxide traps solar heat. And once the gas is in the air, it stays = there=20 for a century or more.=20

Or consider methane, which comes out of the = back of a cow=20 or the top of a termite mound or the bottom of a rice paddy. As a result = of our=20 determination to raise more cattle, cut down more tropical forest = (thereby=20 causing termite populations to explode), and grow more rice, methane=20 concentrations in the atmosphere are more than twice as high as they = have been=20 for most of the past 160,000 years. And methane traps heat--very=20 efficiently.=20

Or consider carbon dioxide. In fact, = concentrate on=20 carbon dioxide. If we had to pick one problem to obsess about over the = next=20 fifty years, we'd do well to make it CO2--which is not pollution either. = Carbon=20 monoxide is pollution: it kills you if you breathe enough of it. But = carbon=20 dioxide, carbon with two oxygen atoms, can't do a blessed thing to you. = If=20 you're reading this indoors, you're breathing more CO2 than you'll ever = get=20 outside. For generations, in fact, engineers said that an engine burned = clean if=20 it produced only water vapor and carbon dioxide.=20

Here's the catch: that engine produces a lot of = CO2. A=20 gallon of gas weighs about eight pounds. When it's burned in a car, = about five=20 and a half pounds of carbon, in the form of carbon dioxide, come spewing = out the=20 back. It doesn't matter if the car is a 1958 Chevy or a 1998 Saab. And = no filter=20 can reduce that flowit's an inevitable by-product of fossil- fuel = combustion,=20 which is why CO2 has been piling up in the atmosphere ever since the = Industrial=20 Revolu- tion. Before we started burning oil and coal and gas, the = atmosphere=20 contained about 280 parts CO2 per million. Now the figure is about 360. = Unless=20 we do everything we can think of to eliminate fossil fuels from our = diet, the=20 air will test out at more than 500 parts per million fifty or sixty = years from=20 now, whether it's sampled in the South Bronx or at the South = Pole.=20

This matters because,as we all know by now, the = molecular=20 structure of this clean, natural, common element that we are adding to = every=20 cubic foot of the atmosphere surrounding us traps heat that would = otherwise=20 radiate back out to space. Far more than even methane and nitrous oxide, = CO2=20 causes global warming--the greenhouse effect-- and climate change. Far = more than=20 any other single factor, it is turning the earth we were born on into a = new=20 planet.=20

Remember, this is not pollution as we have = known it. In=20 the spring of last year the Environmental Protection Agency issued its = "Ten-Year=20 Air Quality and Emissions Trends" report. Carbon monoxide was down by 37 = percent=20 since 1986, lead was down by 78 percent, and particulate matter had = dropped by=20 nearly a quarter. If you lived in the San Fernando Valley, you saw the = mountains=20 more often than you had a decade before. The air was cleaner, but it was = also=20 dif- ferent--richer with CO2. And its new composition may change almost=20 everything.=20

Ten years ago I wrote a book called The End of = Nature,=20 which was the first volume for a general audience about carbon dioxide = and=20 climate change, an early attempt to show that human beings now dominate = the=20 earth. Even then global warming was only a hypothesisstrong and gaining=20 credibility all the time, but a hypothesis nonetheless. By the late = 1990s it has=20 become a fact. For ten years, with heavy funding from governments around = the=20 world, scientists launched satellites, monitored weather balloons, = studied=20 clouds. Their work culminated in a long-awaited report from the UN's=20 Intergovernmental Panel on Climate Change, released in the fall of 1995. = The=20 panel's 2,000 scientists, from every corner of the globe, summed up = their=20 findings in this dry but historic bit of understatement: "The balance of = evidence suggests that there is a discernible human influence on global=20 climate." That is to say, we are heating up the planet--substantially. = If we=20 don't reduce emissions of car- bon dioxide and other gases, the panel = warned,=20 temperatures will probably rise 3.6 Fahrenheit by 2100, and perhaps as = much as=20 6.3 .=20

You may think you've already heard a lot about = global=20 warming. But most of our sense of the problem is behind the curve. = Here's the=20 current news: the changes are already well under way. When politicians = and=20 businessmen talk about "future risks," their rhetoric is outdated. This = is not a=20 problem for the dis- tant future, or even for the near future. The = planet has=20 already heated up by a degree or more. We are perhaps a quarter of the = way into=20 the greenhouse era, and the effects are already being felt. From a new = heaven,=20 filled with nitrogen, methane, and carbon, a new earth is being born. If = some=20 alien astronomer is watching us, she's doubtless puzzled. This is the = most=20 obvious effect of our numbers and our appetites, and the key to = understanding=20 why the size of our population suddenly poses such a risk.=20

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

Twenty percent more bad storms, 10 percent more = winter=20 precipitation--these are enormous numbers. It's like opening the = newspaper to=20 read that the average American is smarter by 30 IQ points. And the same = data=20 showed increases in drought, too. With more water in the atmosphere, = there's=20 less in the soil, according to Kevin Trenberth, of the National Center = for=20 Atmospheric Research. Those parts of the continent that are normally = dry--the=20 eastern sides of mountains, the plains and desertsare even drier, as the = higher=20 average temperatures evaporate more of what rain does fall. "You get = wilting=20 plants and eventually drought faster than you would otherwise," = Trenberth says.=20 And when the rain does come, it's often so intense that much of it runs = off=20 before it can soak into the soil.=20

Sowetter and drier. Different.=20

In 1958 Charles Keeling, of the Scripps = Institution of=20 Oceanography, set up the world's single most significant scientific = instrument=20 in a small hut on the slope of Hawaii's Mauna Loa volcano. Forty years = later it=20 continues without fail to track the amount of carbon dioxide in the = atmosphere.=20 The graphs that it produces show that this most important greenhouse gas = has=20 steadily increased for forty years. That's the main news.=20

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

Other scientists had a hard time crediting = Keeling's=20 studythe effect seemed so sweeping. But the following April a research = team led=20 by R. B. Myneni, of Boston University, and including Keeling, reached = much the=20 same conclusion by means of a completely different technique. These = researchers=20 used satellites to measure the color of sunlight reflected by the earth: = light=20 bouncing off green leaves is a different color from light bouncing off = bare=20 ground. Their data were even more alarming, because they showed that the = increase was hap- pening with almost lightning speed. By 1991 spring = above the=20 45th parallel--a line that runs roughly from Portland, Oregon, to Boston = to=20 Milan to Vladivostok--was coming eight days earlier than it had just a = decade=20 before. And that was despite increased snowfall from the wetter = atmosphere; the=20 snow was simply melting earlier. The earlier spring led to increased = plant=20 growth, which sounds like a benefit. The area above the 45th parallel = is, after=20 all, the North American and Russian wheat belt. But as Cynthia = Rosenzweig, of=20 NASA's Goddard Institute for Space Studies, told The New York Times, any = such=20 gains may be illusory. For one thing, the satellites were measuring = biomass, not=20 yields; tall and leafy plants often produce less grain. Other = scientists, the=20 Times reported, said that "more rapid plant growth can make for less = nutritious=20 crops if there are not enough nutrients available in the soil." And it's = not=20 clear that the grain belt will have the water it needs as the climate = warms. In=20 1988, a summer of record heat across the grain belt, harvests plum- = meted,=20 because the very heat that produces more storms also causes extra = evaporation.=20 What is clear is that fundamental shifts are under way in the operation = of the=20 planet. And we are very early yet in the greenhouse era.=20

The changes are basic. The freezing level in = the=20 atmospherethe height at which the air temperature reaches 32 Fhas been = gaining=20 altitude since 1970 at the rate of nearly fifteen feet a year. Not = surprisingly,=20 tropical and subtropical glaciers are melting at what a team of Ohio = State=20 researchers termed "strik- ing" rates. Speaking at a press conference = last=20 spring, Ellen Mosley-Thompson, a member of the Ohio State team, was = asked if she=20 was sure of her results. She replied, "I don't know quite what to say. = I've=20 presented the evidence. I gave you the example of the Quelccaya ice cap. = It just=20 comes back to the compila- tion of what's happening at high elevations: = the=20 Lewis glacier on Mount Kenya has lost forty percent of its mass; in the=20 Ruwenzori range all the glaciers are in massive retreat. Everything, = virtually,=20 in Patagonia, except for just a few glaciers, is retreating. . . . We've = seen .=20 . . that plants are moving up the mountains. . . . I frankly don't know = what=20 additional evidence you need."=20

As the glaciers retreat, a crucial source of = fresh water=20 in many tropical countries disappears. These areas are "already = water-stressed,"=20 Mos- ley-Thompson told the Association of American Geographers last = year. Now=20 they may be really desperate.=20

As with the tropics, so with the poles. = According to=20 every computer model, in fact, the polar effects are even more = pronounced,=20 because the Arctic and the Antarctic will warm much faster than the = Equator as=20 carbon dioxide builds up. Scientists manning a research station at = Toolik Lake,=20 Alaska, 170 miles north of the Arctic Circle, have watched average = summer=20 temperatures rise by about seven degrees in the past two decades. "Those = who=20 remember wearing down-lined summer parkas in the 1970s--before the term = 'global=20 warming' existedhave peeled down to T-shirts in recent summers," = according to=20 the reporter Wendy Hower, writing in the Fairbanks Daily News-Miner. It = rained=20 briefly at the American base in McMurdo Sound, in Antarctica, during the = southern summer of 1997as strange as if it had snowed in Saudi Arabia. = None of=20 this necessarily means that the ice caps will soon slide into the sea, = turning=20 Tennessee into beachfront. It simply demonstrates a radical instability = in=20 places that have been stable for many thousands of years. One researcher = watched=20 as emperor penguins tried to cope with the early breakup of ice:their = chicks had=20 to jump into the water two weeks ahead of schedule, probably = guaranteeing an=20 early death. They (like us) evolved on the old earth.=20

You don't have to go to exotic places to watch = the=20 process. Migrating red-winged blackbirds now arrive three weeks earlier = in=20 Michigan than they did in 1960. A symposium of scientists reported in = 1996 that=20 the Pacific Northwest was warming at four times the world rate. "That = the=20 Northwest is warming up fast is not a theory," Richard Gammon, a = University of=20 Washington oceanog- rapher, says. "It's a known fact, based on simple=20 temperature readings."=20

The effects of that warming can be found in the = largest=20 phenomena. The oceans that cover most of the planet's surface are = clearly=20 rising, both because of melting glaciers and because water expands as it = warms.=20 As a result, low-lying Pacific islands already report surges of water = washing=20 across the atolls. "It's nice weather and all of a sudden water is = pouring into=20 your living room," one Marshall Islands resident told a newspaper = reporter.=20 "It's very clear that something is happening in the Pacific, and these = islands=20 are feel- ing it." Global warming will be like a much more powerful = version of=20 El Ni[plus or minus]o that covers the entire globe and lasts forever, or = at=20 least until the next big asteroid strikes.=20

If you want to scare yourself with guesses = about what=20 might happen in the near future, there's no shortage of possibilities.=20 Scientists have already observed large-scale shifts in the duration of = the El=20 Ni[plus or minus]o ocean warming, for instance. The Arctic tundra has = warmed so=20 much that in some places it now gives off more carbon dioxide than it = absorbs--a=20 switch that could trigger a potent feedback loop, making warming ever = worse. And=20 researchers studying gla- cial cores from the Greenland Ice Sheet = recently=20 concluded that local climate shifts have occurred with incredible = rapidity in=20 the past18 in one three-year stretch. Other scientists worry that such a = shift=20 might be enough to flood the oceans with fresh water and reroute or shut = off=20 currents like the Gulf Stream and the North Atlantic, which keep Europe = far=20 warmer than it would otherwise be. (See "The Great Climate Flip- = flop,"by=20 William H. Calvin, January Atlantic.)In the words of Wallace Broecker, = of=20 Columbia University, a pioneer in the field, "Climate is an angry beast, = and we=20 are poking it with sticks."=20

But we don't need worst-case scenarios: = best-case=20 scenarios make the point. The population of the earth is going to nearly = double=20 one more time. That will bring it to a level that even the reliable old = earth we=20 were born on would be hard-pressed to support. Just at the moment when = we need=20 everything to be working as smoothly as possible, we find ourselves = inhabiting a=20 new planet, whose carrying capacity we cannot conceivably estimate. We = have no=20 idea how much wheat this planet can grow. We don't know what its = politics will=20 be like: not if there are going to be heat waves like the one that = killed more=20 than 700 Chicagoans in 1995; not if rising sea levels and other effects = of=20 climate cha- nge create tens of millions of environmental refugees; not = if a 1.5=20 jump in India's temperature could reduce the country's wheat crop by 10 = percent=20 or divert its monsoons.=20

The arguments put forth by cornucopians like = Julian=20 Simonthat human intelligence will get us out of any scrape, that human = beings=20 are "the ultimate resource," that Malthusian models "simply do not = comprehend=20 key ele- ments of people"all rest on the same premise: that human beings = change=20 the world mainly for the better.=20

If we live at a special time, the single most = special=20 thing about it may be that we are now apparently degrading the most = basic=20 functions of the planet. It's not that we've never altered our = surroundings=20 before. Like the beavers at work in my back yard, we have rearranged = things=20 wherever we've lived. We've leveled the spots where we built our homes, = cleared=20 forests for our fields, often fouled nearby waters with our waste. = That's just=20 life. But this is dif- ferent. In the past ten or twenty or thirty years = our=20 impact has grown so much that we're changing even those places we don't=20 inhabitchanging the way the weather works, changing the plants and = animals that=20 live at the poles or deep in the jungle. This is total. Of all the = remarkable=20 and unexpected things we've ever done as a species, this may be the = biggest. Our=20 new storms and new oceans and new glaciers and new springtimesthese are = the=20 eighth and ninth and tenth and eleventh wonders of the modern world, and = we have=20 lots more where those came from.=20

We have gotten very large and very powerful, = and for the=20 foreseeable future we're stuck with the results. The glaciers won't grow = back=20 again anytime soon; the oceans won't drop. We've already done deep and = systemic=20 damage. To use a human analogy, we've already said the angry and = unforgivable=20 words that will haunt our marriage till its end. And yet we can't simply = walk=20 out the door. There's no place to go. We have to salvage what we can of = our=20 relationship with the earth, to keep things from getting any worse than = they=20 have to be.=20

If we can bring our various emissions quickly = and sharply=20 under control, we can limit the damage, reduce dramatically the chance = of=20 horrible surprises, preserve more of the biology we were born into. But = do not=20 underestimate the task.The UN's Intergovernmental Panel on Climate = Change=20 projects that an immediate 60 percent reduction in fossil-fuel use is = necessary=20 just to stabi- lize climate at the current level of disruption. Nature = may still=20 meet us halfway, but halfway is a long way from where we are now. What's = more,=20 we can't delay. If we wait a few decades to get started, we may as well = not even=20 begin. It's not like poverty, a concern that's always there for = civilizations to=20 address. This is a timed test, like the SAT: two or three decades, and = we lay=20 our pencils down. It's the test for our generations, and population is a = part of=20 the answer.=20

Changing "Unchangeable" Needs=20

when we think about overpopulation, we usually = think=20 first of the developing world, because that's where 90 percent of new = human=20 beings will be added dur- ing this final doubling. In The Population = Bomb, Paul=20 Ehrlich wrote that he hadn't understood the issue emotionally until he = traveled=20 to New Delhi, where he climbed into an ancient taxi, which was hopping = with=20 fleas, for the trip to his hotel. "As we crawled through the city, we = entered a=20 crowded slum area. . . . the streets seemed alive with people. People = eating,=20 people washing, people sleeping. People visiting, arguing, and = screaming. . . .=20 People, people, people, people."=20

We fool ourselves when we think of Third World = population=20 growth as producing an imbalance, as Amartya Sen points out. The white = world=20 simply went through its population boom a century earlier (when Dickens = was=20 writing similar des- criptions of London). If UN calculations are = correct and=20 Asians and Africans will make up just under 80 percent of humanity by = 2050, they=20 will simply have returned, in Sen's words, "to being proportionately = almost=20 exactly as numerous as they were before the European industrial=20 revolution."=20

And of course Asians and Africans, and Latin = Americans,=20 are much "smaller" human beings: the balloons that float above their = heads are=20 tiny in comparison with ours. Everyone has heard the statistics time and = again,=20 usually as part of an attempt to induce guilt. But hear them one more = time, with=20 an open mind, and try to think strategically about how we will stave off = the=20 dangers to this planet. Pretend it's not a moral problem, just a = mathematical=20 one.=20

* An American uses seventy times as much energy = as a=20 Bangladeshi, fifty times as much as a Malagasi, twenty times as much as = a Costa=20 Rican.=20

* Since we live longer, the effect of each of = us is=20 further multiplied. In a year an American uses 300 times as much energy = as a=20 Malian; over a lifetime he will use 500 times as much.=20

* Even if all such effects as the clearing of = forests and=20 the burning of grasslands are factored in and attributed to poor people, = those=20 who live in the poor world are typically responsible for the annual = release of a=20 tenth of a ton of carbon each, whereas the average is 3.5 tons for = residents of=20 the "consumer" nations of Western Europe, North America, and Japan. The = richest=20 tenth of Americansthe people most likely to be reading this = magazineannually=20 emit eleven tons of carbon apiece.=20

* During the next decade India and China will = each add to=20 the planet about ten times as many people as the United States willbut = the=20 stress on the natural world caused by new Americans may exceed that from = new=20 Indians and Chinese combined. The 57.5 million Northerners added to our=20 population during this decade will add more greenhouse gases to the = atmosphere=20 than the roughly 900 million added Southerners.=20

These statistics are not eternal. Though = inequality=20 between North and South has steadily increased, the economies of the = poor=20 nations are now growing faster than those of the West. Sometime early in = the=20 next century China will pass the United States as the nation releasing = the most=20 carbon dioxide into the atmosphere, though of course it will be nowhere = near the=20 West on a per capita basis.=20

For the moment, then (and it is the moment that = counts),=20 we can call the United States the most populous nation on earth, and the = one=20 with the highest rate of growth. Though the U.S. population increases by = only=20 about three mil- lion people a year, through births and immigration = together,=20 each of those three million new Americans will consume on average forty = or fifty=20 times as much as a person born in the Third World. My daughter, four at = this=20 writing, has already used more stuff and added more waste to the = environment=20 than most of the world's residents do in a lifetime. In my thirty-seven = years I=20 have probably outdone small Indian villages.=20

Population growth in Rwanda, in Sudan, in El = Salvador, in=20 the slums of Lagos, in the highland hamlets of Chile, can devastate = those=20 places. Growing too fast may mean that they run short of cropland to = feed=20 themselves, of firewood to cook their food, of school desks and hospital = beds.=20 But population growth in those places doesn't devastate the planet. In = contrast,=20 we easily absorb the modest annual increases in our population. America = seems=20 only a little more crowded with each passing decade in terms of our = daily lives.=20 You can still find a parking spot. But the earth simply can't absorb = what we are=20 adding to its air and water.=20

so if it is we in the rich world, at least as = much as=20 they in the poor world, who need to bring this alteration of the earth = under=20 control, the question becomes how. Many people who are sure that = controlling=20 population is the ans- wer overseas are equally sure that the answer is=20 different here. If those people are politicians and engineers, they're = probably=20 in favor of our living more efficiently--of designing new cars that go = much=20 farther on a gallon of gas, or that don't use gas at all. If they're=20 vegetarians, they probably sup- port living more simply--riding bikes or = buses=20 instead of driving cars.=20

Both groups are utterly correct. I've spent = much of my=20 career writing about the need for cleverer technologies and humbler = aspirations.=20 Environmental damage can be expressed as the product of Population x = Affluence x=20 Technology. Surely the easiest solution would be to live more simply and = more=20 efficiently, and not worry too much about the number of = people.=20

But I've come to believe that those changes in = technology=20 and in lifestyle are not going to occur easily and speedily. They'll be = begun=20 but not finished in the few decades that really matter. Remember that = the=20 pollution we're talking about is not precisely pollution but rather the=20 inevitable result when things go the way we think they should: new = filters on=20 exhaust pipes won't do any- thing about that CO2. We're stuck with = making real=20 changes in how we live. We're stuck with dramatically reducing the = amount of=20 fossil fuel we use. And since modern Westerners are practically machines = for=20 burning fossil fuel, since virtually everything we do involves burning = coal and=20 gas and oil, since we're wedded to petroleum, it's going to be a messy=20 breakup.=20

So we need to show, before returning again to = population,=20 why simplicity and efficiency will not by themselves save the day. Maybe = the=20 best place to start is with President Bill Clinton--in particular his = reaction=20 to global warming. Clinton is an exquisite scientific instrument, a man = whose=20 career is built on his unparalleled ability to sense minute changes in = public=20 opinion. He under- stands our predicament. Speaking to the United = Nations early=20 last summer, he said plainly, "We humans are changing the global = climate. . . .=20 No nation can escape this danger. None can evade its responsibility to = confront=20 it, and we must all do our part."=20

But when it comes time to do our part, we = don't. After=20 all, Clinton warned of the dangers of climate change in 1993, on his = first Earth=20 Day in office. In fact, he solemnly promised to make sure that America = produced=20 no more green- house gases in 2000 than it had in 1990. But he didn't = keep his=20 word. The United States will spew an amazing 15 percent more carbon = dioxide in=20 2000 than it did in 1990. It's as if we had promised the Russians that = we would=20 freeze our nuclear program and instead built a few thousand more = warheads. We=20 broke our word on what history may see as the most important = international=20 commit- ment of the 1990s.=20

What's important to understand is why we broke = our word.=20 We did so because Clinton understood that if we were to keep it, we = would need=20 to raise the price of fossil fuel. If gasoline cost $2.50 a gallon, we'd = drive=20 smaller cars, we'd drive electric cars, we'd take busesand we'd elect a = new=20 President. We can hardly blame Clinton, or any other politician. His = real goal=20 has been to speed the pace of economic growth, which has been the key to = his=20 popu- larity. If all the world's leaders could be gathered in a single = room, the=20 one thing that every last socialist, Republican, Tory, monarchist, and = trade=20 unionist could agree on would be the truth of Clinton's original = campaign=20 admonition: "It's the economy, stupid."=20

The U.S. State Department had to send a report = to the=20 United Nations explain- ing why we would not be able to keep our Earth = Day=20 promise to reduce green- house-gas emissions; the first two reasons = cited were=20 "lower-than-expected fuel prices" and "strong economic growth." The = former=20 senator Tim Wirth, who until recently was the undersecretary of state = for global=20 affairs, put it nakedly: the United States was missing its emissions = targets=20 because of "more prolonged economic activity than expected."=20

America's unease with real reductions in = fossil-fuel use=20 was clear at last year's mammoth global-warming summit in Kyoto. With = utility=20 executives and Republican congressmen stalking the halls, the U.S. = delegation=20 headed off every attempt by other nations to strengthen the accord. And = even the=20 tepid treaty produced in Kyoto will meet vigorous resistance if it ever = gets=20 sent to the Senate.=20

Changing the ways in which we live has to be a=20 fundamental part of dealing with the new environmental crises, if only = because=20 it is impossible to imagine a world of 10 billion people consuming at = our level.=20 But as we calculate what must happen over the next few decades to stanch = the=20 flow of CO2, we shouldn't expect that a conversion to simpler ways of = life will=20 by itself do the trick. One would think offhand that compared with = changing the=20 number of children we bear, changing consumption patterns would be a = breeze.=20 Fertility, after all, seems biologicalhard-wired into us in deep = Darwinian ways.=20 But I would guess that it is easier to change fertility than=20 lifestyle.=20

perhaps our salvation lies in the other part of = the=20 equation--in the new tech- nologies and efficiencies that could make = even our=20 wasteful lives benign, and table the issue of our population. We are, = for=20 instance, converting our econ- omy from its old industrial base to a new = model=20 based on service and informa- tion. Surely that should save some energy, = should=20 reduce the clouds of carbon dioxide. Writing software seems no more = likely to=20 damage the atmosphere than writing poetry.=20

Forget for a moment the hardware requirements = of that new=20 economy--for instance, the production of a six-inch silicon wafer may = require=20 nearly 3,000 gallons of water. But do keep in mind that a hospital or an = insurance company or a basketball team requires a substantial physical = base.=20 Even the high- est-tech office is built with steel and cement, pipes and = wires.=20 People work- ing in services will buy all sorts of things--more = software, sure,=20 but also more sport utility vehicles. As the Department of Energy = economist=20 Arthur Rypinski says, "The information age has arrived, but even so = people still=20 get hot in the summer and cold in the winter. And even in the = information age it=20 tends to get dark at night."=20

Yes, when it gets dark, you could turn on a = compact=20 fluorescent bulb, saving three fourths of the energy of a regular = incandescent.=20 Indeed, the average American household, pushed and prodded by utilities = and=20 environmentalists, has installed one compact fluorescent bulb in recent = years;=20 unfortunately, over the same period it has also added seven regular = bulbs.=20 Millions of halogen torchere lamps have been sold in recent years, = mainly=20 because they cost $15.99 at Kmart. They also suck up electricity:those = halogen=20 lamps alone have wiped out all the gains achieved by compact fluorescent = bulbs.=20 Since 1983 our energy use per capita has been increasing by almost one = percent=20 annually, despite all the technological advances of those = years.=20

As with our homes, so with our industries. = Mobil Oil=20 regularly buys ads in leading newspapers to tell "its side" of the = environmental=20 story. As the com- pany pointed out recently, from 1979 to 1993 "energy=20 consumption per unit of gross domestic product" dropped 19 percent = across the=20 Western nations. This sounds goodit's better than one percent a year. = But of=20 course the GDP grew more than two percent annually. So total energy use, = and=20 total clouds of CO2, continued to increase.=20

It's not just that we use more energy. There = are also=20 more of us all the time, even in the United States. If the population is = growing=20 by about one percent a year, then we have to keep increasing our = technological=20 efficiency by that much each yearand hold steady our standard of = livingjust to=20 run in place. The President's Council on Sustainable Development, in a=20 little-read report issued in the winter of 1996, concluded that = "efficiency in=20 the use of all resources would have to increase by more than fifty = percent over=20 the next four or five decades just to keep pace with population growth." = Three=20 million new Americans annually means many more cars, houses, = refrigerators. Even=20 if everyone con- sumes only what he consumed the year before, each = year's tally=20 of births and immigrants will swell American consumption by one=20 percent.=20

We demand that engineers and scientists swim = against that=20 tide. And the tide will turn into a wave if the rest of the world tries = to live=20 as we do. It's true that the average resident of Shanghai or Bombay will = not=20 consume as lavishly as the typical San Diegan or Bostonian anytime soon, = but he=20 will make big gains, pumping that much more carbon dioxide into the = atmosphere=20 and requiring that we cut our own production even more sharply if we are = to=20 stabi- lize the world's climate.=20

The United Nations issued its omnibus report on = sustainable development in 1987. An international panel chaired by Gro = Harlem=20 Brundtland, the Prime Minister of Norway, concluded that the economies = of the=20 developing countries needed to grow five to ten times as large as they = were, in=20 order to meet the needs of the poor world. And that growth won't be = mainly in=20 software. As Arthur Rypinski points out, "Where the economy is growing = really=20 rapidly, energy use is too." In Thailand, in Tijuana, in Taiwan, every = 10=20 percent increase in economic output requires 10 percent more fuel. "In = the Far=20 East," Rypinski says, "the transition is from walking and bullocks to = cars.=20 People start out with electric lights and move on to lots of other = stuff.=20 Refrigerators are one of those things that are really popular = everywhere.=20 Practically no one, with the possible exception of people in the high = Arctic,=20 doesn't want a refrigerator. As people get wealthier, they tend to like = space=20 heating and cooling, depending on the climate."=20

In other words, in doing the math about how = we're going=20 to get out of this fix, we'd better factor in some unstoppable momentum = from=20 people on the rest of the planet who want the very basics of what we = call a=20 decent life. Even if we airlift solar collectors into China and India, = as we=20 should, those nations will still burn more and more coal and oil. "What = you can=20 do with energy con- servation in those situations is sort of at the = margin,"=20 Rypinski says. "They're not interested in fifteen-thousand-dollar clean = cars=20 versus five- thousand-dollar dirty cars. It was hard enough to get = Americans to=20 invest in efficiency; there's no feasible amount of largesse we can = provide to=20 the rest of the world to bring it about."=20

The numbers are so daunting that they're almost = unimaginable. Say, just for argument's sake, that we decided to cut = world=20 fossil-fuel use by 60 per- cent--the amount that the UN panel says would = stabilize world climate. And then say that we shared the remaining = fossil fuel=20 equally. Each human being would get to produce 1.69 metric tons of = carbon=20 dioxide annually--which would allow you to drive an average American car = nine=20 miles a day. By the time the population increased to 8.5 billion, in = about 2025,=20 you'd be down to six miles a day. If you carpooled, you'd have about = three=20 pounds of CO2 left in your daily ration--enough to run a highly = efficient=20 refrigerator. Forget your com- puter, your TV, your stereo, your stove, = your=20 dishwasher, your water heater, your microwave, your water pump, your = clock.=20 Forget your light bulbs, compact fluorescent or not.=20

I'm not trying to say that conservation, = efficiency, and=20 new technology won't help. They willbut the help will be slow and = expensive. The=20 tremendous momentum of growth will work against it. Say that someone = invented a=20 new furnace tomorrow that used half as much oil as old furnaces. How = many years=20 would it be before a substantial number of American homes had the new = device?=20 And what if it cost more? And if oil stays cheaper per gallon than = bottled=20 water? Changing basic fuelsto hydrogen, say--would be even more = expensive. It's=20 not like running out of white wine and switching to red. Yes, we'll get = new=20 technologies. One day last fall The New York Times ran a special section = on=20 energy, featuring many up-and-coming improvements: solar shingles, = basement fuel=20 cells. But the same day, on the front page, William K. Stevens reported = that=20 international negotiators had all but given up on preventing a doubling = of the=20 atmospheric concentration of CO2. The momentum of growth was so great, = the=20 negotiators said, that making the changes required to slow global = warming=20 significantly would be like "trying to turn a supertanker in a sea of=20 syrup."=20

There are no silver bullets to take care of a = problem=20 like this. Electric cars won't by themselves save us, though they would = help. We=20 simply won't live efficiently enough soon enough to solve the problem.=20 Vegetarianism won't cure our ills, though it would help. We simply won't = live=20 simply enough soon enough to solve the problem.=20

Reducing the birth rate won't end all our = troubles=20 either. That, too, is no silver bullet. But it would help. There's no = more=20 practical decision than how many children to have. (And no more mystical = decision, either.)=20

The bottom-line argument goes like this: The = next fifty=20 years are a special time. They will decide how strong and healthy the = planet=20 will be for centuries to come. Between now and 2050 we'll see the = zenith, or=20 very nearly, of human population. With luck we'll never see any greater=20 production of carbon dioxide or toxic chemicals. We'll never see more = species=20 extinction or soil erosion. Greenpeace recently announced a campaign to = phase=20 out fossil fuels entirely by mid-century, which sounds utterly quixotic = but=20 couldif everything went just righthappen.=20

So it's the task of those of us alive right now = to deal=20 with this special phase, to squeeze us through these next fifty years. = That's=20 not fair--any more than it was fair that earlier generations had to deal = with=20 the Second World War or the Civil War or the Revolution or the = Depression or=20 slavery. It's just reality. We need in these fifty years to be working=20 simultaneously on all parts of the equationon our ways of life, on our=20 technologies, and on our pop- ulation.=20

As Gregg Easterbrook pointed out in his book A = Moment on=20 the Earth (1995), if the planet does manage to reduce its fertility, = "the period=20 in which human numbers threaten the biosphere on a general scale will = turn out=20 to have been much, much more brief" than periods of natural threats like = the Ice=20 Ages. True enough. But the period in question happens to be our time. = That's=20 what makes this moment special, and what makes this moment hard. = S=20

Bill McKibben ("A Special Moment in History") = is the=20 author of several books about the environment, including The End of = Nature=20 (1989) and Hope, Human and Wild (1995). His article in this issue will = appear in=20 somewhat different form in his book Maybe One: A Personal and = Environmental=20 Argument for Single-Child Families, to be published this month by Simon = &=20 Schuster.=20