Planet feels strains of people pressure

Earth: The only home we have, and it is not expanding

By Environment Correspondent Alex Kirby

If you think of the earth as a Noah's Ark, a life-friendly speck floating through the sterile immensities of space, you will appreciate that its passenger capacity is limited.

Some scientists have tried to set a numerical limit, suggesting that a population of around two billion people would be the "ideal" for human wellbeing.

Many religious leaders argue that no limit is necessary, because (they believe) providence will ensure that, however numerous we are, nobody will go short.

Experience suggests that both groups are wrong, and that we have to accept a trade-off between growing numbers and quality of life.

The Ark, in other words, will sail on. But it will sink lower in the water, and life for many on board will be increasingly wretched.

Just three of the most urgent pressures it faces show how precarious its voyage is becoming.

Food

The area available for producing grain for each person alive today has fallen by half since 1950, to 0.12 hectares.

So farmers are turning to increasingly marginal land on hillsides and in tropical forests.

The immediate result is deforestation which can make flooding more frequent and more severe. The longer-term consequence is the impoverishment of the soil itself.

And the soil, in many countries, is being eroded by wind and water, leaving even less productive land.

Grain supplies face growing pressure

The European Environment Agency describes soil loss on the continent through erosion and development as "worryingly high".

Feeding the grain that is available to animals for meat uses much more than consuming it directly.

So the desire for meat that goes with rising living standards puts more pressure on food supplies.

Water

By 2050, the amount of fresh water available per person will be about 25% of the 1950 figure.

There is less fresh water to go round

One of China's two main rivers, the Yellow river, has run dry for part of each year since 1985.

In 1997, it failed to reach the sea on 226 days.

On every continent, water tables are dropping - under the north China plain, which produces nearly 40% of the Chinese grain harvest, the fall averages 1.5 metres a year.

Underground water reserves in many countries are being used faster than they are replenished.

Cities

When 2000 dawns, 47% of the world's people will be living in cities.

They go there, often, not because they have much real hope of a better life, but to escape rural desperation.

City streets are seldom gold-paved

Population growth there means ever-smaller plots of land for succeeding generations, till there is too little left for survival.

But city life is polluted and unhealthy, and ultimately unsustainable, sucking in resources from far away and spewing out wastes for disposal somewhere.

Further threats

There are plenty of other problems for the Ark's passengers to worry about:

• fish catches from the world's oceans have reached - or passed - their sustainable limits
• human activities, notably farming and industry, are changing the climate
• we are driving other species to extinction at an unnatural rate
• the growth of demand for energy looks impossible to meet without new, sustainable technologies
• there is a growing problem in every country of waste disposal.

Science will come to the rescue in some cases, certainly. And a more sensible distribution of what is available would make life tolerable - and possible - for many on the edge.

The world could probably accommodate at least four or five times as many south Asians as north Americans or west Europeans.

But the Ark is not a one-class ship.