Beyond 7 billion

After remaining stable for most of human history, the world's population has exploded over the last two centuries. The boom is not over: The biggest generation in history is just entering its childbearing years. The coming wave will reshape the planet, and the impact will be greatest in the poorest, most unstable countries...

Even with birthrates falling, the huge number of people in their childbearing years means world population will continue to soar... The China effect - Even with its curbs on population growth, the nation is having an enormous ecological impact on the planet.... China's 'one-child' policy has slowed population growth and brought prosperity — but it couldn't avert massive damage to the environment....

The colossal industrial expansion of recent decades has depleted natural resources and polluted the skies and streams. China now consumes half the world's coal supply. It leads all nations in emissions of carbon dioxide, the main contributor to global warming. Pollutants from its smokestacks cause acid rain in Seoul and Tokyo.

China's experience shows how rising consumption and even modest rates of population growth magnify each other's impact on the planet.

The country's population of 1.3 billion is increasing, even with the controls on family size. What is driving the growth is that hundreds of millions of Chinese are still in their reproductive years. On such a huge base, even one or two children per couple adds large numbers — an effect known as population momentum.

Moreover, the Chinese are living better overall: consuming more food, energy and goods than ever. One-fourth of the population — the equivalent of everyone in the United States — has entered the middle class...

The compounding forces of economic and population growth are a source of increasing concern to scientists. An international team of 1,300 researchers organized by the United Nations concluded that evidence points to "abrupt and potentially irreversible changes" in ecosystems in the next few decades, including mass extinctions and rapid climate change...