Overpopulation. It is the problem no one wants to talk about, much less tackle, The Dominion Post says.

It is also the problem that lies behind many of the issues that do grab the headlines - global warming, rising pollution levels and food shortages.

The United States census bureau estimated that, as the clock ticked over to 2008, there were 6,641,114,623 people in the world. By 2050 it estimates the world population will be 9.4 billion. The growth rate has been slowing in recent years, but only slightly.

There are ominous signs that the world might be reaching capacity, and even that it has gone beyond what is sustainable.

Last month the United Nations Food and Agriculture Organisation called for immediate help for poor countries hit by spiralling food prices.

Those countries were spending 25 per cent more on food imports in 2007 than they had in 2006, it noted, with "unprecedented price hikes for basic food, driven by historically low food stocks, droughts and floods linked to climate change, high oil prices and growing demand for bio-fuels".

Others have been pointing out that the Green Revolution, which through the introduction of new techniques and new hybrids enabled countries such as India to feed their growing populations, might have reached its end.

They fear increases in production in the next 50 years will not match those in the past four decades.

The FAO report came hard on the heels of one from the UN's global environmental outlook. That painted a grim picture of over-consumption.

Among other things, it pointed to a collapse of the world's fish stocks by 2050, through overfishing, with 212-times more fish being caught than the oceans could produce in a sustainable manner, and the increasing number of dead zones in the ocean where pollution, including fertiliser run-offs, has depleted oxygen.

The report also pointed out that, since 1987, the world's population has grown 34 per cent. Then the land available to each person was 2.6 hectares. Now, it is just a whisker above 2ha. By 2050, that will be down to 1.63ha.

Achim Steiner, the executive director of the UN programme that produced the report, told the New York Times, "life would be easier if we didn't have the kind of population growth rates that we have at the moment".

Like most others, he shied from the next step, saying instead that forcing people to stop having children would be a simplistic answer.

The issue of population control is fraught with difficulty.

There is something unpalatable about the rich nations of the world, which do not have rapidly increasing populations but which do gobble up an indefensibly large share of resources, suggesting that the teeming nations of the developing world should curtail their population growth. It is also surrounded by cultural and religious issues.

There is unease, too, in China over the one-child policy, some suggesting it has created a selfish generation that is causing social disruption and others arguing that it will hinder future development by limiting the size of China's labour force.

However, the pressure from an ever-expanding population on a world that is finite cannot be ignored forever.