We believe that insufficient attention is paid to the social and environmental costs incurred at regional scales by biofuel production in Brazil (A. K. Duailibe Nature 468, 1041; 2010).

Brazil's Alagoas state covers almost 28,000 square kilometres, roughly half of which used to be rainforest. Sugar-cane plantations have now taken over coastal regions, including flood plains.

A study commissioned by the Alagoas government reveals that just 13.1% of the state's original rainforest has survived 35 years of the sugar-cane ethanol programme. This amounts to an average loss of 3,736 hectares of rainforest per year in what was formerly one of the world's 34 biodiversity hotspots. This environmental catastrophe is already taking its toll. Heavy rainfall in the region last year led to severe floods that destroyed thousands of buildings.

Despite academic and political controversy, most people believe biofuels to be 'clean'. In fact, ethanol production leaves a dirty footprint in one of Brazil's poorest states.