This is a really big deal. (The original articles are here, behind the AAAS paywall.)There is now more than good reason to expect that no biofuel from seeds, possibly none (even cellulosic) grown on land that could grow food, will reduce global warming if substituted for petroleum products. The insight of the papers discussed in the article, and work by some others who have been worrying at this bone for years without anyone paying enough attention, is a remarkable synthesis of economics and plant/earth science.
The first piece of the puzzle is the recognition that if a piece of forest is cut down, or natural grassland plowed up, to grow biofuel, decay and/or burning of what was there before releases an enormous puff of carbon into the atmosphere that needs to be counted along with the carbon releases of the biofuel crop. Even spreading the initial release over decades of biofuel growing, it is large enough to push almost any biofuel’s global warming intensity way above that of gasoline, especially because it all occurs right at the beginning of the future rather than a few years or decades down the line.
The second piece is the recognition that it doesn’t matter where the biofuel is actually grown. Consider ethanol from corn grown in the US: the corn used is no longer in the food and feed corn market, so corn prices increase just as though a catastrophe suddenly destroyed a big part of the corn harvest. This price increase stimulates a variety of responses, including (in varying amounts that we will need to do some fancy economic modeling to estimate precisely):
-humans will eat less corn
-humans will eat less meat (this saves a lot of corn)
-farmers will grow more corn.
The last of these can happen, in turn, in three ways. First, corn growing will intensify with additional fertilization, and this generates N2O releases; N2O is a potent greenhouse gas. Second, some currently uncultivated land will be tilled and planted with corn (see the first piece above).
Third, land used for other crops will be committed to corn, for example by growing corn every year instead of a corn-corn-soybean rotation. Soybean prices now go up (remember, soybeans and corn both are traded internationally) and farmers (for example, in Brazil) convert some pasture to soybeans with the release of stored carbon noted earlier. This raises beef prices, so it becomes worth it to a marginal rancher to cut down another piece of forest for cows: another big puff of carbon. The global warming effects of these carbon releases are worldwide, of course; it doesn’t matter whether a pound of CO2 comes out of a coal power plant in China or a natural gas plant in the US or a piece of forest burned in Indonesia.
The bottom line of these complicated chains of events is that using crops for biofuels anywhere induces land use changes somewhere, and while the effect isn’t a simple acre-for-acre replacement, and we don’t know exactly how big the land-clearing carbon hit should be for a generic gallon of biodiesel or bioethanol, betting now is that it is most unlikely to be small enough to view crop-based biofuels as green substitutes for petroleum.
Small amounts of diesel and ethanol will probably be available from trash and agricultural waste like the tree branches and bark scraps the logging industry leaves around to decay, or cornstalks, or McDonald’s used frying oil, and these are environmentally OK because they don’t induce land use conversion. One of this week’s papers proposes that mixed perennials growing on abused or waste land may be beneficial from a global warming perspective, but this path is waiting for cellulose-to-starch conversion that is still in the very expensive developmental stage. And many smart folks in this business expect that algae growing in tanks in the desert (for example) can eventually be taught to make a lot of diesel cheap, with no land use implications. But for now, and for a while, biofuels generally are going over a very rough patch of road, a patch that may go on for years before new technologies smooth it out again.
A lot of money is being bet on, and a lot of policy has assumed, extensive substitution of biofuels (mostly ethanol for now) for petroleum as a global warming program. These publications are the sudden expansion of a cloud on the horizon no bigger than a hand into a very scary, dark overcast.