Key predictions

Population rise from 6.1bn to 9.3bn Poorest 48 countries' population grows from 658m to 1.8bn Rich countries remain stable at 1.2bn India accounts for 21% of world growth China accounts for 12%

The UN population trends report predicts that many richer countries, meanwhile, will see a decline in the size of their populations.

It predicts that even African countries hit badly by HIV and Aids will see population growth over the next half century.

And the percentage of old people will increase significantly, as life expectancy rises and birth rates fall.

50% increase

The population of the world is now just over 6bn.

The latest UN figures predict that by 2050 it will be 9.3bn - up from their previous prediction of just under 9bn.

The annual world population growth rate is 1.3% - about 77m people a year. Six countries - India, China, Pakistan, Nigeria, Bangladesh and Indonesia - account for half that total.

India's billionth person was born in May 2000

India has introduced a new population policy aimed at stabilising its numbers by 2045 - by which time it is expected to be the most populous country on earth.

Many richer countries, on the other hand - such as Japan, Germany, Italy and Hungary - are expected to see marked declines in their populations over the next 50 years.

Russia, Ukraine and Georgia will also experience sharp drops in population.

And with low birth rates in rich countries, only immigration will keep their populations from falling, the report says.

By contrast the number of people living in the 48 least developed countries in the world is expected to triple by the year 2050.

Aids effect

The report starkly illustrates the impact of Aids, noting that amongst the most affected countries, the epidemic will be responsible for more than 15million extra deaths in the 34 worst-hit countries over the next five years.

But despite that, the population of particularly badly affected African countries such as Botswana and Zimbabwe is still expected to rise significantly because of their high underlying fertility rates.

The report assumes that the chances of being infected with HIV will decline signficantly by 2015.

The UN population division also predicts that, on average, people will live longer in the year 2050.

This will lead to a tripling in the number of people over the age of 60 and a five-fold increase in the number of those over 80.

The population division has pointed out on several occasions that this increase in the percentage of elderly people in the population, which is especially marked in Europe, could have serious implications for future government policies in relation to immigration, pensions and other welfare issues.