World Population Reaches 6 Billion

Call this Y6B: The year of 6 billion, a milestone the world’s population is expected to reach this weekend.

The birth of the planet’s 6 billionth inhabitant, projected by the U.S. Census Bureau, also will mark another historic first: The world’s population has doubled in less than 40 years.

Despite a gradual slowing of the overall rate of growth, the world population is still increasing by about 78 million people a year. That’s the equivalent of adding a city nearly the size of San Francisco every three days, or the combined populations of France, Greece and Sweden every year, according to a coalition of environmental and population groups.

“It took all of human history for the world’s population to reach 1 billion in 1804 but little more than 150 years to reach 3 billion in 1960. Now, not quite 40 years later, we are twice that number,” said Amy Coen, president of Population Action International.

Even with a decelerating growth rate, the number of humans on the planet could nearly double by 2050, according to the coalition of population groups’ highest projections.

The impact will be sweeping, the coalition predicts. “Every 20 minutes the world adds another 3,500 human lives but loses one or more entire species of animal or plant life--at least 27,000 species per year,” it warns.

In addition, at least 300 million people already live in regions with severe water shortages. By 2025, the number is expected to be 3 billion if current growth rates continue.

The population is expanding despite a “reproductive revolution” that has prompted half of the world’s married women to use family planning techniques, compared with an estimated 10% only 30 years ago, according to the International Planned Parenthood Federation in London. In 61 of the world’s more than 190 countries, women’s fertility rates have dropped below the replacement level of 2.1 children per woman.

In the United States, the world’s third-most populous nation after China and India, 71% of women use some form of family planning. The U.S. fertility rate, or average number of births per woman, has dropped to 1.96.

Yet the United States has the highest fertility rate among wealthy industrialized countries. And because of the “momentum” of population growth--it takes about 70 years for the population to stabilize after a nation reaches a replacement-level fertility rate of 2.1 births per woman--the United States is expected to double its population of 270 million in 60 years if the current growth rate continues, according to Peter Kostmayer, national spokesman for Zero Population Growth.

While the United States marks Y6B this weekend, the United Nations has designated Oct. 12 as the day for international commemoration of the population milestone.

The biggest problems are encountered in poor countries that can’t cope with their current numbers. As much as 95% of future population growth beyond replacement level will be in the developing world.

Two other trends will have a considerable impact on growth.

First, an unprecedented 1 billion teenagers are entering their reproductive years, a “youthquake” that is considered the major reason for continued population growth.

“Their sheer numbers guarantee an enormous ‘momentum’ of population growth through 2050 and an urgent global need for reproductive health information and services, even with a continued declined in fertility rates,” the coalition stated.

The problem is exacerbated by the fact that 95% of those young people are in the developing world, which is already unable to provide education, housing, employment and health care for swelling populations.

At the other end of the spectrum is longevity--the unprecedented increase in the average human life span.

In 1950, the average life expectancy in poor nations was less than 40 years. It has since risen to 61 years. In rich nations, the average life span increased from 66 to 75 years, according to the Population Reference Bureau in Washington.

Reflecting the trend, this year the United Nations began publishing population categories for people aged 80 to 90 (almost 59 million) and 90 to 100 (7.3 million).

By 2025, there will be more than 1 billion people 60 and older, according to the reference bureau. And for the first time, the number of people 65 or older will begin to approach the number of children.

In rich countries, the wave of retirees “will fuel a massive outflow of savings from pension funds and a global shortage in capital for investment,” the bureau projects. Poor countries that haven’t developed social security programs because of shorter life spans will be unable to meet the financial, health care and housing needs of the first big wave of aging inhabitants.