Surging crude oil prices have strengthened the argument for green energy created by cultivating food crops such as sugar cane to make ethanol fuel and vegetable oils to make biodiesel.

The politics of water will become critical as demand for water from rising populations and the needs of industry increase, said Pearce, editor of Britain's New Scientist magazine.

About one billion people lack access to clean drinking water, Pearce said in a keynote speech to the two-day Sugaronline conference in Geneva.

Vast quantities of water were needed to cultivate crops, with two-thirds of the world's water used in agriculture, Pearce said.

"Sugar is one of the thirstiest crops in the world," he said, estimating that 600-800 tonnes of water were required to grow one tonne of cane.

Brazil, the world's biggest sugar producer, has a thriving biofuels industry, converting about half its cane into fuel ethanol to power vehicles.

Pearce said the booming sugar business aimed at powering cars for the affluent had become a key component in water politics because of concerns over water scarcity.

In the past 30 years world food production had doubled to meet food demand from a growing population, but the amount of water used had tripled.

Part of the answer was to boost the efficiency of irrigation infrastructure.

"You can't irrigate the world's ethanol needs without huge gains in irrigation efficiency," Pearce said.