The world's population is expected to reach 7 billion by the end of 2011. (REUTERS/Jitendra Prakash)

As it stands, the world's population is expected to breach seven billion this year. That's double the number of people that lived on earth in the 1960s. According to recent projections by the United Nations, by 2100, there will be 10 billion of us cramming for space on planet earth.

Needless to say, those numbers are dramatically larger than anything the earth has experienced before - and scientists are very concerned about the impact this surplus of humans will have on the world. Namely, they are unsure whether or not the planet can actually sustain that many people.

While the 2100 predictions are frightening to many, demographers believe that by the end of the century, the global population will gradually level off. Researchers can't predict with any certainty when that may happen or at what level, but the debate rages on as to how the current level of population growth will impact the environment, economy, and quality of life.

Almost all the population growth to take place between now and 2050 is expected to be in less developed regions. Nearly half will be in Africa, where, in some parts, population is doubling every 20 years, making it impossible for communities to keep up with the growing demand for housing, roads, schools, and health clinics.

Meanwhile, populations of more developed countries will remain flat. This sparks economic concerns in the developed world as fewer working-age adults are around to support retirees living on pensions.

"Although the issues immediately confronting developing countries are different from those facing the rich countries, in a globalized world demographic challenges anywhere are demographic challenges everywhere," argues David Bloom of the Harvard School of Public Health.

According to a series of papers published in this week's "Science," growth began to accelerate with industrialization around 1750. The world didn't reach one billion people until 1800, and it took another 125 years to reach two billion. The numbers grew dramatically in the last 50 years from three million to seven million and peaked in the mid-1960s at a growth rate of two percent per year.

Today, the annual growth rate hovers around one percent.

According to researchers, in 2011, nearly 135 million people will be born and 57 million will die. That's a net increase of 78 million people.

While longer life spans and lower death rates play a role in explaining population growth, the variable that will make the greatest difference in how many people will live on earth in 100 years is fertility rates.

For example: If every woman had two babies, the world's population would remain as it is.

Yet, the global average is 2.5 births per woman. That's down from five in 1950, but the number varies drastically by geographical location.

According to the study published in "Science," ninety-seven percent of the projected population increase over the next century is expected to happen in developing nations where women will average five or more births. Statistically, women who matter more to society and have access to education end up having fewer children.

To many experts, this is proof that a worldwide investment in family planning programs that provide women education and access to contraception is vital to the survival of humanity.

"Every billion people we add to the planet makes life more difficult for everyone and will do more damage to the environment," says John Bongaarts, a demographer at the Population Council, a research organization in New York City.

"Can we support 10 billion people? Probably. But we would all be better off with a smaller population."

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