The production of biofuels, which has tripled between 2002 and 2007, has significant economic, social and environmental costs. So says _The State of Food and Agriculture 2008_ report from the Food and Agriculture Organization of the United Nations (FAO).

Biofuels make up just over 1% of the world's transport fuel consumption, but "this figure is expected to double over the next decade", says Terri Raney, senior economist at the FAO and co-editor of the report.

The report recommends that small farmers are given help to increase the types of market at which they can sell their crops. It also backs the further development of second-generation biofuels, from woods and grasses, which are not yet commercially available but could result in fewer greenhouse-gas emissions.