Simultaneously as biofuels are blamed for increasing world hunger and landlessness ([1] Biofuels and World Hunger, SiS 49), scientists have been lifting the lid on biofuels’ massive contribution to global warming. Fatal flaw in bioenergy accounting

A team of thirteen scientists led by Timothy Searchinger at Princeton University, New Jersey, in the United States, pointed to a “far-reaching” flaw in carbon emissions accounting for biofuels in the Kyoto Protocol and in climate legislation. It leaves out CO2 emission from tailpipes and smokestacks when bioenergy is used, and most seriously of all, it does not count emissions from land use change when biomass is grown and harvested [2]

They said that replacing fossil fuels with bioenergy does not by itself reduce carbon emissions, because the CO2 released by tail pipes and smokestacks is roughly the same per unit of energy regardless of the source, while emissions from producing and/or refining biofuels also typically exceed those for petroleum as other critics have highlighted [3] (see Biofuels: Biodevastation, Hunger & False Carbon Credits, SiS 33). The team maintained that bioenergy reduces greenhouse emission only if the growth and harvesting of the biomass for energy captures carbon above and beyond what would be sequestered anyway, and offsets the emissions from energy use. This additional carbon may result from land management changes that increase plant uptake or from the use of biomass that would otherwise decompose rapidly.

For example, if unproductive land supports fast-growing grasses for bioenergy, or if forestry improvements increase tree growth rates, the additional carbon absorbed offsets emissions when burned for energy. Energy use of manure or crop and timber residues may also capture additional carbon. But harvesting existing forests for electricity adds net carbon to the air. That remains true even if limited harvest rates leave the carbon stocks of regrowing forests unchanged, because those stocks would otherwise increase and contribute to the terrestrial carbon sink.