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The World at 7 Billion People: How Much More Growth Can the Planet Support?

With global population expected to surpass 7 billion people this year, the staggering impact on an overtaxed planet is becoming more and more evident.

July 20, 2011

Yale Environment 360 / By Robert Engelman

Global warming, food and water crises, even international conflict -- you can trace all these societal problems to overpopulation.

Demographers aren't known for their sense of humor, but the ones who work for the United Nations recently announced that the world's human population will hit 7 billion on Halloween this year. Since censuses and other surveys can scarcely justify such a precise calculation, it's tempting to imagine that the UN Population Division, the data shop that pinpointed the Day of 7 Billion, is hinting that we should all be afraid, be very afraid.

We have reason to be. The 21st century is not yet a dozen years old, and there are already 1 billion more people than in October 1999 — with the outlook for future energy and food supplies looking bleaker than it has for decades. It took humanity until the early 19th century to gain its first billion people; then another 1.5 billion followed over the next century and a half. In just the last 60 years the world's population has gained yet another 4.5 billion. Never before have so many animals of one species anything like our size inhabited the planet.

And this species interacts with its surroundings far more intensely than any other ever has. Planet Earth has become Planet Humanity, as we co-opt its carbon, water, and nitrogen cycles so completely that no other force can compare. For the first time in life's 3-billion-plus-year history, one form of life — ours — condemns to extinction significant proportions of the plants and animals that are our only known companions in the universe.

Did someone just remark that these impacts don't stem from our population, but from our consumption? Probably, as this assertion emerges often from journals, books, and the blogosphere. It's as though a geometry text were to propound the axiom that it is not length that determines the area of a rectangle, but width. Would we worry about our individual consumption of energy and natural resources if humanity still had the stable population of roughly 300 million people — less than today's U.S. number — that the species maintained throughout the first millennium of the current era?

It is precisely because our population is so large and growing so fast that we must care, ever more with each generation, how much we as individuals are out of sync with environmental sustainability. Our diets, our modes of moving, and our urge to keep interior temperatures close to 70 degrees Fahrenheit no matter what is happening outside — none of these make us awful people. It's just that collectively, these behaviors are moving basic planetary systems into danger zones.

Yet another argument often advanced to wave off population is the assertion that all of us could fit into Los Angeles with room to wiggle our shoulders. The image may comfort some. But space, of course, has never been the issue. The impacts of our needs, greeds, and wants are. We should bemoan — and aggressively address — the gross inequity that characterizes individual consumption around the world. But we should also acknowledge that over the decades-long span of most human lifetimes, most of us are likely to consume a fair amount, regardless of where and how we live; no human being, no matter how poor, can escape interacting with the environment, which is one reason population matters so much. And given the global economic system and the development optimistically anticipated in all regions of the world, we each have a tendency to consume more as that lifetime proceeds. A parent of seven poor children may be the grandparent of 10 to 15 much more affluent ones climbing up the ladder of middle-class consumption.

This, in fact, is the story of China, often seen not as an example of population's impact on the environment but that of rapid industrialization alone. Yet this one country, having grown demographically for millennia, is home to 1.34 billion people. One reason the growth even of low-consuming populations is hazardous is that bursts of per-capita consumption have typically followed decades of rapid demographic growth that occurred while per-capita consumption rates were low. Examples include the United States in the 19th and 20th centuries, China at the turn of the 21st, and India possibly in the coming decade. More immediately worrisome from an environmental perspective, of course, is that the United States and the industrialized world as a whole still have growing populations, despite recent slowdowns in the growth rate, while already living high up on the per-capita consumption ladder.

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