The biofuels bonanza will crash unless producers can guarantee their crops have been produced responsibly, the UN's environment agency chief has said.

Achim Steiner of the UN Environment Programme (Unep) said there was an urgent need for standards to make sure rainforests weren't being destroyed.

Biofuel engineers also had to show their products did not produce more CO2 than they negated, he told BBC News.

Critics say biofuels will lead to food shortages and destroy rainforests.
 

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