From David Pimentel, Cornell University, Tad Patzek, University of California, Florian Siegert, RSS GmbH, Mario Giampietro, Autonomous University of Barcelona and Helmut Haberl, Klagenfurt University
You propose that the Intergovernmental Panel on Climate Change should now rule on whether biofuels are good or bad for the planet (15 December 2007, p 3 and p 6).
However commendable the IPCC’s work has been in many other areas, we do not feel that its present structure ensures a sufficient breadth of relevant expertise and perspectives among those sharing writing authority so as to pronounce fairly and roundedly on this many-sided issue. We consider that notes in both the Third and Fourth Assessment Reports on biofuel crops for transport were markedly biased in their favour.
The Fourth Assessment Report (AR4) made tentative predictions of major emissions savings from biofuel expansion by 2030, but failed to warn that such “savings” could be negated by emissions from converting more land to monocultures. Additional environmental effects of such biofuel expansion plans, such as negative impacts on the resilience of an ecosystem, biodiversity or vital ecosystem services, were also not properly taken into account.
We suggest that a rigorous and fair scientific evaluation of the socioeconomic and ecological effects of biofuels should be undertaken before further biofuel incentives and large-scale investments are implemented without a proper scientific or indeed democratic basis. While we believe that IPCC procedures could, in principle, be appropriate to ensure a fair evaluation, the expertise that was available in drafting the AR4 mitigation report and the Summary for Policymakers was obviously not sufficient for that.
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From Jeremy Tomkinson, National Non-Food Crops Centre
We welcome vigorous debate on the sustainability of biofuels globally, but to argue that they are “good” is overly simplistic and “bad” is equally unhelpful.
Biofuels should not be thought of as one technology. With the right feedstock and processing they do reduce greenhouse gas emissions and provide income for growers and processors. As well as improving vehicle fuel efficiency, they are the only available near to medium-term options for reducing vehicle exhaust emissions: these are technologies which provide greenhouse gas savings within the existing infrastructure right now.
Crucially, current technologies are reported to typically produce between 30 and 60 per cent less greenhouse gas emissions compared with diesel and petrol. Emerging technologies that use waste or lignocellulosic feedstocks significantly reduce the dependence on nitrogen-hungry food crops. These advanced biofuels can produce over 90 per cent less greenhouse gas emissions than diesel or petrol.
Like the conversion of coal or any other solid fuel to a liquid, making liquid fuel from biomass is energy-intensive. The quantities of liquid fuels produced and the carbon dioxide released per tonne of biomass depend on the energy source used in the biomass processing plant.
The US could produce about 1.3 billion tonnes of renewable biomass per year. Burning this would release about as much energy as burning 10 million barrels of diesel fuel per day. If converted to ethanol, the energy value is equal to about 5 million barrels of diesel fuel per day. The remainder of the energy is used in the liquid-conversion process.
If a nuclear reactor or other energy source provided that energy, the equivalent of over 12 million barrels of diesel fuel per day could be produced. The potential for biomass liquids depends upon coupling biomass to nuclear or other greenhouse-free energy sources.
Oak Ridge, Tennessee, US
It would seem that a sensible line of research would be to try to extract useful fuel from seaweed.
Ithaca, New York, US , Berkeley
