The United Nations will warn this week that the world's population could more than double to 15 billion by the end of this century, putting a catastrophic strain on the planet's resources unless urgent action is taken to curb growth rates, the Observer can reveal.
That figure is far higher than many estimates - the UN had expected the world to have more than 10 billion people by 2100. There are currently nearly seven billion.
The new figure is contained in a landmark study by the United Nations Population Fund (Unfpa) to be released this week.
The report, called The State of World Population 2011, will mark the expected moment this month when somewhere on Earth birth will take the current world population over the seven billion mark, and it will be released simultaneously in cities across the globe.
Some experts reacted with shock to the figure. Roger Martin, chairman of Population Matters, which campaigns on population control, said that the Earth was entering a dangerous new phase. "Our planet is approaching a perfect storm of population growth, climate change and peak oil," he said.
"The planet is not actually sustaining seven billion people."
The Earth has now doubled in population since the 1960s, boosted by high birth rates in Africa, Asia and Latin America as the spread of medicine and better healthcare has seen the mortality rate for young children decline.
This has easily offset the general decline in the birth rate of advanced countries. It has also been boosted by an increase in lifespans of people across the world.
Some experts reacted with scepticism that the population would really hit the upper end of the predicted spectrum of growth and reach 15 billion so quickly.
Professor Jack Goldstone of George Mason University, author of The Population Bomb, said he thought world leaders would act to ensure the Earth's population would start to plateau below that higher level. "The means and the desire to reduce the number of children people have is spreading around the world," he said. He thought 10-12 billion would be more likely by 2100.
Many policy experts believe the world governments and NGOs have the tools to limit and control the world's population. The key effort, many say, is simply making sure that effective family planning spreads throughout the developing world.
"What's really critical is the political commitment of governments. Family planning is not actually that expensive," said John Bongaarts, vice-president of the New York-based Population Council.
Campaigners on family planning issues often come across cultural and religious factors that make educating women and reducing the size of families difficult. Some governments try to increase their populations, while many religious groups preach against the use of contraceptives.
The Population Research Institute, a Virginia-based group linked to anti-abortion organisations in America, last week welcomed the news that the world's population was set to hit 7 billion this month. Humanity's long-term problem is not going to be too many children, but too few," said the institute's president, Steven Mosher.