If the world follows the demographic habits of Europe — and that’s a big if — by the year 2200 it could be home to a population of less than half its current level, living in housing built for almost three times that number.

With the global population estimated to pass 7 billion on October 31, many of policymakers’ short-term worries revolve around providing resources for the additional 2-3 billion people expected to be born in the next half-century.

Numbers of this magnitude inevitably conjure up terrifying visions of shortage and chaos. But in fact improvements in food production and technology have allowed population growth to continue unimpeded and relatively smoothly, and the real potential nightmare is of a rapidly aging population, combined with collapsing birthrates in both rich and poor states.

Many demographers and long-term planners say the challenge for the next century will be less dealing with growing numbers of people and more managing the much larger population of aged and perhaps dependent people while finding new strategies to deliver prosperity, jobs and essential services.

The trend has already contributed to the current global financial crisis by driving up health and social care bills and perhaps also undermining productivity. But while politicians tie themselves in knots over short-term worries, experts say there is not enough discussion of longer-term demographic challenges.

“It’s not a world that’s going to look anything like any world or population that has existed before,” says Jack Goldstone, professor of public policy and a leading demographics expert at Washington’s George Mason University.

“We thought that overpopulation was going to force humanity to expand outward to the stars. That doesn’t look like the problem at all. And the policy framework isn’t set up at all to handle these longer-term issues.”

With many of the world’s poorer countries still seeing strong growth, the global fertility rate — the number of children born per couple — remains around 2.5, more than enough to replace every person currently alive.

But in richer countries, the rate has already nosedived. Russia, Singapore and several other developed countries have introduced policies to boost fertility but with mixed success.

Exact predictions vary, but most projections suggest the global population will peak at around 9 billion around 2070 and then start to fall, perhaps very fast.

For Now, A Crowded, Older World

In the Western world, that date will see both the children of the “baby boomers” — many of them childless or with fewer children, if current trends hold — reaching the end of their lives. In the developing world, the “youth bulge” — the large cohort of young people currently most striking in the Middle East — will also be dying off.

“The decline in fertility has gone the furthest certainly in the developed world but it is falling very rapidly in most middle-income countries and even some of the more successful lower-income countries,” said Daniel Cotlear, a population expert at the World Bank specializing in Latin America.

“With an aging population, that brings challenges.”

By 2030, more than a third of the population in a number of Western states as well as some Asian economies, such as Japan and Korea, will be aged over 65.

Many developing states, most notably China with its one-child policy but also a growing number of other nations, will follow suit — often without the financial resources to help pay for the cost of medical and nursing care.

“It’s the seminal issue of our time,” says Michael Hodin, executive director of the New York-based Global Coalition on Aging and a senior fellow at the Council on Foreign Relations.

“The numbers are stunning. The exact projections vary but it doesn’t really matter because they are all going in the same direction.”

In the developed world, most countries rely on a large number of working taxpayers to pay for the care and pensions of a relatively small group of elderly people. In poorer countries, extended families tend to look after the elderly.

Neither of those models, experts say, is designed to cope with the changed demographics of more old and fewer young.