Population: What to Do When There Are Too Many of Us

Editor's Note: The following is an excerpt from More: Population, Nature, and What Women Want by Robert Engelman. Copyright 2008 by the author. Reproduced by permission of Island Press, Washington, D.C.

All historical eras are shaped by the material and environmental realities of their time. Our own reflects the adjustments society and nature have made to accommodate the unprecedented 6.7 billion human beings now alive. And those changes are dramatic. The planet is warming dangerously as a result of the heat-trapping byproducts of our daily lives. Half of the primeval forests that existed at the end of the last ice age are gone. A mist of mercury and other toxic metals from coal combustion falls continuously on land and ocean, and to eat fish is to absorb these metals yourself. Half of us are now urban, rarely if ever meeting up with creatures wilder than crows, cockroaches, and, in some cities, packs of feral dogs.

And this is just where we are today, while the beat of growth goes on. Little if any of this would have transpired had human numbers peaked long ago. Such a peak might have occurred by now, even with the gains in life expectancy of the past century, if the status and reproductive intentions of women had found consistent support rather than silence and censure.

Beginning little more than a century ago, social acceptance of contraception began to grow and to spread around the world. That led to dramatic declines in birthrates that gathered force as human population throttled past a few billion. Who knows how much closer we would be to a meltdown of Greenland's ice or the collapse of critical ocean fisheries had this collective wisdom -- a public good derived from individuals acting in their private interest -- not dampened the rise of population? Given the increasingly plausible threat of one or more interacting environmental catastrophes, the slowing of population growth is a triumph of human wisdom and good fortune. This realization is only slowly dawning, however, on the community of journalists and other opinion leaders.

The dominant concerns in many countries about population aging and decline are hardly baseless. These developments may well challenge societies. Populations may have more old people than young for a while, because yesterday's baby boomers are heading toward old age even as young women are having fewer children. Over time, however, extreme age disparities should subside as these large generations pass on, the more so when average fertility returns to close to two children per woman. Assuming it will.

Some demographers, eyeing the stubborn low fertility of women in most of Europe and parts of east Asia, are beginning to wonder if such a return to replacement fertility is possible. Some allude in cautionary tones to the possibility of a "low-fertility trap," a vast pool of demographic quicksand that prevents women from ever returning to replacement fertility once their childbearing average drops below about 1.5 births. There's no real basis for such speculation, however. The world is too dynamic and our experience with intentionally low fertility far too new.

What might eventually unfold is something far more appealing: birth cohorts of consistently equal size across generations. The most demographically stable age structure for a population would be for each year's "class" of babies to be the same size as the one the year before, and ten, twenty-five, or fifty years before. No single age group, young or old, would naturally claim any more of society's attention than any other, at least based on their numbers. That's a population structure worth striving for.

For now, population aging is the inevitable outcome of two of the most positive developments of modern times: longer life spans and the realized intentions of women to have fewer children, later in their lives. Modern views on human rights and equality hardly would have allowed most women to continue giving birth to many more children than they wanted. And populations hardly could have continued growing in the twenty-first century at the same torrid pace as in the middle decades of the twentieth. Some populations had to be the first to experience the leveling off of growth and then decline, and in most cases this has occurred with no significant increases in death rates. That's rare, maybe even unprecedented, in human history.

Today, humanity still grows by 78 million people annually-the rough equivalent of a new Texas, California, and New York each year. Unless death rates rise catastrophically or birthrates plummet far more than anyone expects, the end of world population growth is still decades away. It's reasonable to expect that humanity will grow to 7 billion, 8 billion, or even higher before the number levels off for good reasons or bad.

What dominates our experience in the first decade of the third millennium are the technologies and institutions we have invented, disseminated, tinkered with, and improved over thousands of years to make human life on such scales possible. We've done well. Not only are more people alive than ever, but most of us live longer than our ancestors did. Quite a few of us spend our entire lives in comfort and with tools and toys that those ancestors never could have imagined.

I stress the adjustments we've made to adapt to our growing population because I grant Julian Simon, the late twentieth-century champion of perpetual population growth, this point: we human beings are, if not the "ultimate resource," at least awfully smart. When the going gets tough, the tough get patents. Had hunters and gatherers never run low on food and turned by necessity to cultivating it, we wouldn't have cities or symphonies or cell phones. I certainly wouldn't be typing on this laptop, anticipating a book that might appear in a bookstore window thousands of miles from my home. Innovation indeed is much of what makes human beings successful, but it also keeps the angels on the edge of their celestial seats, wondering, Can they do it again?

Each new pressure point creates the need for new innovation, and each new innovation produces effects of its own, many of them unintended and quite a few problematic. Why do things bite back, to borrow from the title of a recent book? One reason (not actually mentioned in that book) is that it's getting crowded in here. In societies with low population densities relative to available natural resources, innovation's side effects often waft away, unimportant and unnoticed. In high-density societies, there's less tolerance for error, systems tend to be more sensitively balanced, and the scale of everything that people are doing is larger relative to the natural world. "When we try to pick out anything by itself," Scottish American conservationist John Muir wrote, "we find it is hitched to everything else in the Universe." So what happens when 7 billion people pick out 7 billion things?

Losing Nature

We're finding out. Much of the human behavior we find unsustainable today is not so in its essence, but in its scale. Julian Simon used to say that more people leads paradoxically to more nature, but the history I've presented in this book makes clear that over the long sweep of time the trend is otherwise. The planet is in the early stages of a species extinction episode not seen since the dinosaurs disappeared. If you could somehow ask Mother Nature what she attributes this to, I think she'd likely say not just "people," but "this many people."

Yes, some populous human societies plant trees to anchor vulnerable soils or set aside tracts of land for recreation or to preserve important ecosystems. How long the trees will grow remains a question, however. And the set-asides rarely protect all the land's wild inhabitants-not to mention the water or the steady climate that supports ecosystems over the long haul.

Protection is not necessarily forever. When the needs of growing populations press hard enough, in wealthy and poor countries alike, "set aside forever" often becomes a hollow promise. The biological reserve near where I swam years ago in southern Mexico is now pockmarked by the cleared land of impoverished squatters, whose needs can't ethically be denied or easily redirected to biologically less important land. Closer to my own home, the scarcity of affordable housing is undermining an agricultural reserve meant to save the last few farms of Montgomery County, Maryland. Wealthy societies tend to do a better job than poor ones of cleaning up environmental messes, but they rarely if ever improve upon what was there before the mess was made. Having more people might contribute in some cases to strengthening environmental protection, but not enough to matter over the long term.

In 1984 Simon and futurist Herman Kahn suggested that population growth can bring about more solitude, because more people own cars and elude the madding crowds on improved roads. It would be interesting to poll drivers around the world about this assertion today. Earlier, Kahn had predicted dramatically new energy sources and undersea cities by the year 2000. It's not just doomsayers on population and the environment whose forecasts sometimes don't pan out. So far, the twenty-first century is not proving at all kind to cornucopian predictions. While I was writing this book, the last backwaters of doubt that humans are propelling the planet toward uncontrolled warming dried up. Those who have claimed in the past that the environment just keeps getting better and better, thanks to wealth and technology, today seem strangely quiet.

"Ecosystems are at a tipping point, "wrote the Washington Post, not usually known for tree-hugging advocacy, "verging on a collapse from which they won't recover." A front-page news story on "oil's new era" in the Wall Street Journal gave the last word on the subject to energy consultant Henry Groppe, who glumly suggested, "We have entered the era of scarcity and price rationing" ...

Faces of Want

In the industrialized world we feel the impacts of population growth and density in traffic congestion, in the inability to afford a home, or in paychecks we might have stretched further in a less crowded world. In many developing countries the toll is far higher and climbing faster. To explore this is to wade into the endless debate on the relative weight of the many causes of modern hunger, poverty, and violent conflict present in so many developing countries. Some points, however, are clear and well documented. Well over 800 million people-the number has been rising in recent years-are chronically undernourished, and during the 1990s the countries with the highest population growth rates made the least progress in reducing hunger.

Scarcities of water, closely tied to the tension between nature's fixed supply and the needs of growing human populations, are increasingly commonplace. Urban areas bid up water's price. Farmers lose access to water for irrigation precisely when rising food demand forces new production to rely on irrigation rather than rain. After generations of subdivision, farm plots are now so small in densely populated African countries that few young adults can hope to marry and launch families without moving to the city. "If I had known I would have so little land to pass down to my sons," a Zambian tribal chief once commented to his niece, my friend Wanga Grace Mumba, "I wouldn't have had so many sons."

Land shortage helps explain the genocidal conflict in Rwanda, which has one of the lowest ratios of cropland to people and the second lowest ratio of renewable freshwater to people in mainland Africa. Such scarcities might also be behind the explosion of child abandonment seen most often among populations in which fertility is high and the use of contraceptives rare. Today some parents exile children they no longer want or no longer can support to urban streets. Or they sell them into early marriage, prostitution, or slavery.

Certainly the progressive degradation of cropland is among the reasons that the UN Population Division projects that in 2008, human beings will cross the threshold to being a mostly urban species. Cities have long stimulated the rich diversity of human culture, but in the world's most rapidly growing ones not many people are celebrating. Almost all urban expansions today are not planned neighborhoods, well supplied with infrastructure and services, but slums. Health indicators are often worse in cities than in the countryside that urban migrants left behind. "I think we know cities in Kenya can hardly sustain the population they have," observed Doug Keating of Oxfam International on the prospects for rural exodus to cities as the organization helped pastoralist communities in northeast Kenya cope with a withering drought.

The loss of forest cover, closely tied in developing countries to the ongoing need for more farmland, is among the biggest destroyers of species in a wave of extinctions comparable to those that occurred in the earth's remote and unpeopled past. It's an instructive irony that the places friendliest to the survival of biological diversity include the Demilitarized Zone between the two Koreas, various guerrilla-held areas of Colombia, and the "radioactive nature preserve" known as Chernobyl in the Ukraine.

Without tree roots to anchor it, deforested soil easily changes form during heavy rains into flowing mud that seeks its own level-sometimes on top of a village. This is a sadly common story in densely populated and rapidly deforesting countries from the Philippines to Guatemala. The Ugandan farmers who hurt themselves falling off their steeply sloping fields, whose story opened this book, run the risks they do because nearby level land was deforested long ago and is already taken or has been farmed to exhaustion.

Human incursions into forests sometimes spur new pathogens to discover what a vast and inviting pool of protoplasm human bodies present. We're a bug's banquet. Our domesticated animal companions and livestock spread their own pathogens around in the wild, threatening species that have far smaller populations than theirs. We know from history that most infectious diseases tend to be closely related to population density and mobility, but the pace of pathogen exchange is occurring far more rapidly today than ever before. Malarial mosquitoes thrive in the pond waters of deforested land, and scientists are now confident that HIV/AIDS made its way from chimpanzees to humans a few decades ago, probably when a bushmeat hunter penetrated the forest, butchered his quarry, and absorbed some of its blood.

In some places, even the traditional lifestyles of indigenous people who thrived in forests for centuries are no longer sustainable. Wildlife Conservation Society biologists Elizabeth Bennett and John Robinson calculated that tropical rainforests can support at most one subsistence hunter per square kilometer. "More than that and you're depleting the resource," Bennett told the New York Times. "There are few corners of the tropics at this moment that have so few people. You can probably still have it in remote sections of Amazonia. In Sarawak [in Malaysia], the indigenous people have the legal right to hunt. But there's been a population explosion, and there are three of them for every square kilometer of forest. That's three times the sustainable number. If they all employ their rights, they'll hunt out the forest."

Bennett was not blaming indigenous people, who themselves suffer the effects of the growth of non-indegenous populations around them, for hunting out the forest. You might just as well blame an individual driver for a traffic jam. But the unsustainability is real, no matter how much we respect the dignity of indigenous individuals. It stems not from subsistence hunting itself, which is ancient, but from hunters' high population density, which is recent.

Bags of Ice

Thousands of years ago, subsistence hunters running out of prey, like those in Sarawak, became farmers whose descendents launched the world's great city-based civilizations. Such past adaptations made humans what we are today, but humanity stands in a quite different place now. Sum up the total mass of human beings, add all our pets and livestock (40 million farm animals are born each year in the United States alone), and factor in our processing of energy and materials. We are a biological and geological force never previously witnessed. What once may have been win-win strategies of adaptation are now more often win-lose strategies-or desperation lose-lose plays. We are bulls in a china shop. Almost any turn we make sends the porcelain flying.

The use of fossil fuels and the Industrial Revolution itself began as science-based adaptations to energy scarcity and unsustainability. Coal, a dirty fuel long thought inferior to wood, was first used on a large scale around the sixteenth century as the forests of Europe were exhausted by large-scale land clearance for farming and the burning of wood for fuel and iron smelting.

Today, the world burns nearly 5 billion metric tons of coal each year. That's about three-quarters of a ton for each person on earth, with comparable combustion of oil and natural gas for each of us-all driving a human induced warming of the planet whose endpoint we can't yet imagine. Even though the thought of tempering growth is not yet mainstream, the implausibility of growth without end is becoming more obvious in a closed-atmosphere, carbon-constrained world.

Humanity's energy dilemma becomes more obvious when we think clearly about alternative fuel sources. Adaptations, again, become problems. The sheer scale of human energy use is so vast that even today's small steps toward replacing fossil fuels with biofuels boost food prices and put ecologically valuable land at risk. The calories needed to keep a Hummer humming could feed a hundred humans. And anyone wealthy enough to own a Hummer can outcompete a hundred hungry people for the energy stored in plants.

Enough solar energy to dent fossil-fuel use significantly would require panels and mirrors covering thousands of square miles of land, much of it valuable for other purposes. Enough windmills to do the same would draw howls of protest for visual pollution, their tendency to slice up heedless birds and bats, and the likelihood that large enough fields of turbines might even affect local weather.

Storing carbon in new forests will face the constraint that, as one analyst suggested glumly, "as the human population continues to grow ... the earth's surface will be too disturbed." Hydrogen as a fuel raises the question not only of what type of energy will be used to separate the element from water molecules, but of where that water will come from and what will be the impact of water vapor emitted by hundreds of millions of vehicles. Nuclear energy leaves us with the potential for proliferating weapons-grade plutonium and waste that takes hundreds of human lifetimes to become harmless. "No primary energy source, be it renewable or nonrenewable," write Jeffrey Chow, Raymond Kopp, and Paul Portney, analysts with the environmental think tank Resources for the Future, "is free of environmental or economic limitations."

But suppose we fail to make this essential shift away from carbon-based fuels. Then, we can try to cool the earth's fevered surface literally with smoke and mirrors-massive injections of sulfur dioxide mist into the stratosphere, perhaps, or trillions of small reflective panels sent into orbit around the planet. Feasible? Safe? Probably not, but such options are taken more seriously as the gap grows continually wider between actions taken and actions needed to avert future climate change.

One of my favorite Big Fixes is the oft-mentioned idea of towing polar icebergs to relieve freshwater scarcity. But how do you lasso an iceberg? How do you tow it, break it up, and distribute it? One group of scientists calculated recently that there's enough ice in the world's largest recorded iceberg -- a frozen island the size of Jamaica that broke off the Ross Ice Shelf in Antarctica in March 2000 -- to provide everyone on earth a ten-pound bag of ice cubes every day for the next seventy-five years. The scientists didn't account, of course, for population growth. But more to the point, what happens when the iceberg is used up? The world's people will be standing there, more numerous than ever and parched, waiting for bags of ice that will no longer arrive.

One way to reduce climate dangers, of course, is to disperse the risk of unintended consequences by diversifying the alternative sources of energy used. The more sources of energy, the less any one of them needs to be relied upon and scaled up to massive proportions. That makes dangerous side effects and tipping points less likely. Another strategy for avoiding climate risk is simply to use less energy of all kinds through improving efficiency. There's plenty of room for that now. But just as dieting gets harder with each pound lost, the more efficient energy consumption gets, the harder it is to find the next improvement in energy efficiency.

For long-term reductions in energy consumption, population decline counterbalances this problem nicely. The current momentum of population growth all but guarantees there won't be population declines for several decades. Those are precisely the decades during which humanity could make the easiest gains in energy efficiency. And just about when energy use is about as efficient as it can be in an imperfect world, human population could begin to shrink. That will remove much of the burden of squeezing additional water from the stone of a super-efficient global energy system. The need to reduce demand for fossil fuels will grow more urgent with each passing year as the global climate warms and the illusion of endless carbon-free energy gradually fades. And population decline reduces energy demand, all else equal, without any hardship for anyone.

This is a more sensible strategy than trying to turn icebergs into ice cubes, but that idea is at least innocuous. Other proposed Big Fixes-from genetic engineering to feed the hungry to nuclear energy to avoid toasting the planet-are dangerous. As a species, we're running out of resilience to stand the cures for what ails us. Increasing numbers of people in all walks of life and all corners of the world are starting to know this in their guts, if not necessarily to think it through in their heads. About the most appealing vision on the horizon is the likelihood that rapid human population growth soon will be something for the history books. Just when we can see the wall we're hurtling toward, we're braking our demographic growth through the realized intentions of hundreds of millions of women and their partners to have just one or two children, when and only when it suits them to do so.

Dreams of People Everywhere

... There are good reasons why the importance of population growth to the loss of nature is little studied and rarely remarked on. It's next to impossible to quantify or otherwise separate out the impact of demographic scale from the many other reasons the environment appears to be crumbling around us. But I suspect the larger problem is ignorance and the resulting hopelessness about population growth ("you can't stop people from having children") or, worse, the fear of blame.

Who wants to be seen as implying that parents who have three or more children and want decent lives for them are somehow more at fault for our environmental problems than governments or corporations or drivers of sport utility vehicles? It's not that there's any compelling research absolving population growth as a long-term force in environmental degradation. It's just that researchers don't like to risk their reputations by appearing to hold prolific parents answerable for the sorry state of nature. "No demographer," demographer Donald Bogue wrote recently in challenging his colleagues to explore the social and environmental impacts of migration, "wants to be seen as a neo-nativist"-or even someone worried about population growth.

This is not only understandable, in many ways it's commendable. The history of science makes clear that we're in a far better place than we were in the nineteenth century, when some biologists backed up racism with dubious science. Most of us would rather err on the side of believing that every human being is of equal worth and has an equal right to direct her or his own life. The challenge is to maintain these convictions and yet objectively face the root causes of problems, striving to imagine ways to resolve them that are consistent with our values. Population is one realm where this is not only possible, but powerfully appealing-the success of a values-based strategy is already evident. Leave to women, more than to anyone else, the decision about when and how often to bear children. The history I've explored in this book suggests that doing so has moderated population growth in the past, and contemporary evidence makes clear that it does exactly that today.

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