The human population is growing, but not exploding as some predicted. people are living longer, but birth rates are declining, reaching levels that make growth sustainable.

In short, human beings stand less chance of severely upsetting the earth's balance than they did 100 years ago. And, thanks partly to improvements in agricultural productivity and other scientific advances, the earth's resources seem capable of sustaining mankind's development at its current rate. We may even stand on the threshold of an era of global prosperity, if we can find a way to make the benefits unfolding in the developed world available to poorer people as well.

"The things that will come from the continuing revolution in technology really do offer unprecedented opportunities," says John Gannon, head of research at the CIA and one of principal authors of Global Trends 2015, a recently declassified CIA study of social and demographic trends. "The moral challenge is going to be how we get those benefits to developing countries that will not have the resources to pay.'

Some powerful executives agree, including Bill Gates, one of the people who helped make the technological revolution happen." Malthus was wrong", Mr Gates says, referring to the 18th century British philosopher who predicted the human population would grow uncontrollably until it exhausted the earth's resources and brought calamity on itself. "His math didn't take into account the influence and power of the human mind."

To be sure, challenges remain. The CIA study, for one, says that while the earth seems perfectly capable of meeting our food and energy needs, water is increasingly coming into short supply.

"By 2015, half of the worlds population will be living in countries that are water stressed," Mr Gannon says. "In the Middle East, this is already a major issue." Mr Gannon says water shortages need not lead to war, but could be a point of tension for future policy makers. "Policy makers will need to come to grips with this," he says, "They'd be well advised to start doing that now."

Another potent challenge will be urbanisation. As the population grows, more and more rural residents tend to leave the countryside is search of better life in urban centres. This vast migration will put massive stress on the cities' abilities to provide the expected social services. Nick Stern, the chief economist of World Bank, predicts two billion more people will live in cities with populations of more than 11 million 20 years from now, a situation that he says could lead to severe social stress. More of the world's biggest cities could become overtaxed, poorly serviced disease incubators, with a sprawling underclass at the bottom of the social ladder.

The CIA predicts that in 15 years there will be 15 cities in the world with more than 11 million people each. Some, like Bombay, already are experiencing explosive growth. The CIA predicts Bombay will have 27.4 million residents in 2015, up from 17 million today. "You do have to worry about their ability to provide basic services," Mr Gannon says. "Population growth on that scale has the seeds of catastrophe in it."But the overall trend is encouraging, despite these worrisome scenarios.

According to World Bank projections, the world will have 7.1 billion residents in 2015, up from 6.1 billion today. That would be a slowing of the growth rate; after all, the population has doubled in the past 42 years. (It stood at three billion in 1959.) A World Bank demographer thinks the population will stabilise around 10.5 billion in 2200. "The assumption is that fertility will keep declining to roughly a replacement level" by 2200, says Edward Bos, senior population specialist at the World Bank's health, nutrition and population desk, "and it may even settle below that."

The slowdown in population growth is driven by slowing birthrate. "The decline in birthrates in the world is the major event of the last 20 years," The World Bank's Mr Stern says. The World Bank expects the birthrate to decline to 17.8% of the population in 2015 from 20.9% today.

Infant mortality rates are expected to continue improving as well. According to a World Bank study, the global infant mortality rate should fall to 34.6% in 2015 from 51.7% today. Life expectancy is on the rise, too. In 2015, people are expected to live on average to 70.2 years old, up from 67.2 today, according to the World Bank.

Among the social changes expected to spring up from these developments, people will travel more, and there will be more migrants in all countries, seeking both high- and low-wage jobs. There will also be a, according to Mr Stern, an explosion of small and midsize companies and a general renaissance of small-scale free enterprise. "Governments will need to do more to promote small and medium-size enterprises," he says, adding that large companies on their own won't be capable of employing the growing number of people on the planet.

Disease is a sore point, although even here Mr Stern says the overall trend is encouraging, with the exemption of AIDS. Diseases such as smallpox and polio have been largely eradicated, he notes, although he adds that malaria and tuberculosis are mutating into strains that doctors are finding hard to cure. "We seem to be losing the fight a bit" with those two diseases, he says. "They're going in the opposite direction."

A technological breakthrough could help stop the spread of AIDS, Mr Stern says. "In terms of a catastrophic event (that might harm the human population even more severely). one might occur," he says, "but you also have the possibility that a cure for AIDS might be found in the next 15 years."