Climate change and an increasing population could trigger a global food crisis in the next half century as countries struggle for fertile land to grow crops and rear animals, scientists warned yesterday.

To keep up with the growth in human population, more food will have to be produced worldwide over the next 50 years than has been during the past 10,000 years combined, the experts said.

But in many countries a combination of poor farming practices and deforestation will be exacerbated by climate change to steadily degrade soil fertility, leaving vast areas unsuitable for crops or grazing.

Competition over sparse resources may lead to conflicts and environmental destruction, the scientists fear.

The warnings came as researchers from around the world convened at a UN-backed forum in Iceland on sustainable development to address the organisation's millennium development goals to halve hunger and extreme poverty by 2015.

The researchers will use the meeting to call on countries to impose strict farming guidelines to ensure that soils are not degraded so badly they cannot recover.