John Sheehan of the University of Minnesota, US, titled his talk, "Biofuels as a contact sport," borrowing from Stephen Schneider's recent book, Science as a Contact Sport, on the politics of climate change. Sheehan said that the politics of biofuels mirrors, and may even exceed, that surrounding climate change. What both issues have in common, he said, is that at their core lies the question of sustainable development.

For Sheehan, sustainable development has to do with the quality of life and is fundamentally a "profoundly ethical issue". The debate over biofuels has been a dysfunctional dialogue, he said, involving both technical scientific issues and questions of societal preferences. He stressed the need to be clear about the difference between controversial value choices and genuine scientific uncertainty.

One key area of debate and uncertainty is the impact of indirect land-use change, (ILUC), referring to land put into production of biofuel crops that was previously used for other purposes. Uwe Fritsche of the Institute for Applied Ecology in Darmstadt, Germany, pointed out that whether land-use change is indirect or direct actually depends upon one's point of view.

The European Union and its 27 member countries are grappling with the issue, said Fritsche, seeking to develop models of ILUC effects under various scenarios. Any governmental mandate, or even recommendation, to increase the use of biofuels represents a change from business as usual and poses several questions. First, how will markets react, and what changes in land use will result, and where will they occur? Then, one must ask what the net change in carbon flux will be as a result; it may be positive or negative.

Finally, one must allocate future resources as a result of these calculations, and there is no straightforward truth to apply, it is a matter of preferences, Fritsche said. Some existing models are robust but are on a scale that is too large for practical use by policymakers seeking specific answers for decisions on a local or regional level.

Richard Plevin of the University of California, Berkeley, US, returned to the theme of substantial ILUC uncertainties, especially concerning greenhouse-gas emissions from land converted to agriculture as a result of increased demand for biofuels. These emissions may be much higher than estimated by current models, but scientists cannot at present provide a "most likely" value, which he said is particularly significant in view of new fuel regulations developed by the US Environmental Protection Agency and by the state of California. Regulators simply do not at present have adequate data and models for their needs, he said.