There are now 6.8 billion of us as of 2009—a doubling since the 1960s and four times as many as just a century ago. As a result, more and more places on the globe are fantastically, swarmingly crowded, especially cities along the coastlines, where people keep settling in ever greater densities. Yet a full city today can mean an empty village or town across the country, or on the other side of the world. Our growth has taken place in surprising ways.
The human population continues to expand by more than 200,000 people every day. With more than one billion teenagers in the world today just now reaching their most fertile years, we can expect the boom in births to continue for decades to come. The latest UN projections have the global population reaching 9.2 billion by the middle of this century. Even that colossal number may be too small, however, since it's based on the assumption that family sizes will drop throughout developing regions—an assumption no way guaranteed to hold true. After significant progress from the 1970s on, family planning efforts have faltered in many areas in recent years, leading to population spikes in dozens of countries in the Middle East, Africa, and elsewhere.
Some of the worst predictions of a generation ago—global famine, widespread resource exhaustion—have not come to pass on a global scale. Yet from the crowded streets of Lagos and Mumbai (Bombay), to the suburban sprawl of the United States, to disappearing tropical forests around the world, the harmful effects of more people than the planet can comfortably support are apparent almost anywhere we look.
Not all countries grow the same, of course. Virtually all of the expected population increase in the near future will come in developing countries, while the population of the more developed countries would be declining slightly, were it not for large-scale migration. In much of Europe, where explosive growth started with the industrial revolution two centuries ago, and in Korea, Japan, and elsewhere, national populations have stabilized or are starting to contract. This brings challenges of its own, as successively smaller generations struggle to care for and support their elders.
These problems pale in comparison to the stresses of rapid population growth in the developing world, where the great majority of the growth continues to occur. Already in parts of Africa, the Middle East, South Asia, and Latin America, rapid population growth is contributing to grinding poverty, environmental degradation, political instability, or war.
Humanity is also on the move as never before. More than 3 percent of the global population—more than 200 million people—live outside their country of birth, and uncounted millions more have moved, or been moved, within their home borders. A great deal of this movement is forced, either by economic pressures or, increasingly, by damage to the environment or human conflict—both of which are exacerbated by rapid population growth.
Our numbers, our mobility, and the immediacy of communication all conspire to make Earth seem smaller, even as our impact upon it grows larger by the day. From climate change to resource depletion to species extinction and a hundred other planetary ills, every environmental issue is intensified by global population, and by the growing consumption of the wealthy and the growing desperation of the poor. If we are to preserve the biological wealth of our planet and increase the well-being of its people, we must first understand our own population dynamics.