The current war over biofuels, such as ethanol from corn and sugarcane, has the same flavor. Boosters call biofuels eco-saviors; detractors say they will eat up vast amounts of farmland and natural habitats, not to mention drive up food prices (as the burgeoning use of corn for ethanol has in the U.S.) and yield almost no reductions in greenhouse-gas emissions anyway. But as Jörn P. W. Scharlemann and William F. Laurance of the Smithsonian Tropical Research Institute in Panama note in the current issue of Science, whether biofuels are a net good or a net evil depends on what aspects of the environment you care about.
Compared to petroleum, they note, “nearly all biofuels diminish greenhouse-gas emissions.” But switchgrass is a much better feedstock than corn or soy, and the exact greenhouse balance sheet depends on local growing conditions (are you going to use a lot of petroleum-based fertilizer?). More central, they argue, the “focus on greenhouse gases and energy use is too narrow. The arguments that support one biofuel crop over another can easily change when one considers their full environmental effects.”
For instance, sugarcane such as that used in Brazil to make ethanol doesn’t look as green if, to grow it, you raze carbon-rich tropical forests to make the sugarcane fields, causing vast greenhouse-gas emissions. And if you care about not only greenhouse emissions but also about biodiversity and soil protection, then turning jungles into sugarcane fields looks even worse. And are you planning to use nitrogen fertilizers, as corn and rapeseed require? In that case, you’ll be emitting a lot of nitrous oxide, a greenhouse gas that also destroys stratospheric ozone.
A study done for the Swiss government and summarized by Scharlemann and Laurance compared gasoline, diesel, and natural gas with 26 biofuels, assessing the total environmental impact of each. Of the 26, 21 reduce greenhouse-gas emissions by more than 30 percent relative to gasoline. But 12 of 26—including corn ethanol, Brazilian sugarcane ethanol and soy diesel, and Malaysian palm-oil diesel—have worse environmental impacts than fossil fuels. The best biofuels are produced from organic material that isn’t specially grown for that purpose, such as biowaste or recycled cooking oil, or ethanol from grass or wood.
All in all, a welcome reminder that weighing enviro-costs and benefits of biofuels is no easier than the diaper decision.
