THE growth of biofuel crops was embraced as a weapon against global warming, largely because they would absorb greenhouse gases as they grew, but there is a growing number of voices warning that their overall effect may be far less benign.

One analysis found that clearing forests and grassland to grow the crops releases vast amounts of carbon into the air - far more than the carbon spared from the atmosphere by burning biofuels instead of petrol.

Another study found that even using existing farmland increases greenhouse gas emissions because food production is shifted to other parts of the world, resulting in the destruction of more forests and grasslands to make way for farmland.

And quite apart from the possible environmental damage, many experts are also blaming much of the blame for recent soaring food prices on agricultural land being turned over to biofuel crops.