Weeding out the hype

In the quest to shift to biofuels, one approach that has gained a following involves growing perennial grasses on abandoned or degraded crop and pasture land. In principle, the grasses grown there can be turned into fuel without jacking up food prices or degrading the environment.
Researchers at the Carnegie Institution of Washington and Stanford University are raising a yellow flag, however. With existing technologies, don’t count on this approach to supply more than about 8 percent of global energy needs and remain sustainable – even if 100 percent of these lands worldwide grew grasses to fuel the masses.

That contribution to the energy supply could be fairly high in places like Africa, where current demand is low. But for North America, Asia, and Europe, grass power is not likely to reach 10 percent of demand, the team estimates. And for North America, the amount of available land in the study is generous; it includes land set aside for conservation, which presumably would be unavailable for biofuel feedstock.

Abandoned and degraded land are not the only options for growing plants for biofuel, the team acknowledges. But if planners aim to ramp up production beyond what these unused lands can offer, they face some difficult trade-offs. The results appear in this week’s issue of Environmental Science and Technology.