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 likely to shock many experts as it is far higher than many current estimates. A previous UN estimate had expected the world to have more than 10 billion people by 2100; currently, there are nearly 7 billion.

The new figure is contained in a landmark study by the United Nations Population Fund (Unfpa) that will be released this week. The report –The State of World Population 2011 – is being compiled to mark the expected moment this month when somewhere on Earth a person will be born who will take the current world population over the 7 billion mark, and 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 7 billion people."

The Earth has now doubled in population since the 1960s, boosted by high birthrates 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 birthrate 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 that 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, adding that he thought a level of 10-12 billion would be more likely by 2100.

Many policy experts believe that 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.

However, 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 make a point of trying 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.

• the following correction was published on 30 October 2011:

People and numbers: "Global growth fears put to the test" (News) said Africa "had fewer than 500,000 urban dwellers in 1950", but the United Nations Economic Commission for Africa puts the figure at 14.9% of total population – 33 million. Our story "Population of world could grow to 15bn by 2100" (News) named Prof Jack Goldstone as author of The Population Bomb. His book is The New Population Bomb (2010); the original Population Bomb (1968) was written by Paul and Anne Ehrlich.