A decade ago, back when climate change began to emerge as a serious concern, scientists and environmentalists composed a menu of possible future alternatives to burning carbon. Both solar power and wind power seemed likely to be massively expensive. In contrast, biofuels—the conversion of plants into fuel—seemed like it might be a low-cost winner. Both the government of the United States and European governments have invested billions of dollars in developing biofuels. In Britain, for example, subsidies and mandates were used to stimulate a shift to burning wood pellets made from sawdust and tree waste.[1] In the United States, the government mandated and subsidized the mixing of ethanol—a biofuel made from corn—with gasoline. Anywhere from 30 to 40 percent of America’s corn crop now goes to ethanol.

In fact, costs for wind and solar power dropped sharply over the same period that biofuels were being developed. However, until we transform battery technology it will not be possible to use solar or wind power for transportation. Many people continue to count on biofuels as a substitute for carbon-burning.[2] A 2014 report from the Intergovernmental Panel on Climate Change (IPCC) urged replacing carbon with biofuels as an affordable means to hold back climate change. The International Energy Agency speculates that it may be possible to provide over a quarter of world transportation fuel needs by 2050. More immediately, the United States projects that 12 percent of its transportation fuel will come from biofuels within a decade. Similarly, the European Union projects a sharp increase in the role of biofuels to power transportation between today (2.5 percent) and 2020 (10 percent).

Now people are re-thinking this strategy.[3] For one thing, biofuel production has turned out to be massively inefficient: a huge amount of land is required to produce a meager amount of energy. (The 30-40 percent of the American corn crop devoted to ethanol reduces gas consumption by only about 6 percent.) The energy content of all current biomass (food crops, fodder for animals, lumber, biofuels) is about 220 exajoules. The IPCC estimates that the biofuels component alone will have to reach 250 to 300 exajoules by the end of the 21^st Century to hold back climate change. This implies a massive expansion of biofuel acreage.

Skeptics believe it unlikely that farm productivity can actually be increased much on the ground, as opposed to on a chalk-board. The world faces an increasing demand for food as both population and incomes in developing countries rise. These will more than eat up any increase in productivity, leading to continued expansion of lands devoted to crops. The American bet on ethanol has driven up world food prices. Harvesting trees for biofuel seems like even more of a losing proposition. It reduces the amount of carbon dioxide captured by trees while increasing the amount of carbon dioxide emitted.

Clearly, there are no simple solutions to the climate problem. It is going to take time to discover the best approaches, even though we seem to be short of time. Government hasn’t entirely succeeded at picking “winners” from among contending solutions. Decisions can have unanticipated consequences that turn out to be hard to un-do. Rather like the origins of the climate problem in the first place.

[1] The chief beneficiary of this effort may have been the members of the U.S. Industrial Pellet Association, which supplies much of the European demand.

[2] Eduardo Porter, “A Biofuel Debate: Will Cutting Trees Cut Carbon,” NYT, 11 February 2015.

[3] Justin Gillis, “New Report Urges Western Governments to Reconsider Reliance on Biofuels,” NYT, 29 January 2015. The story reports on a World Resources Institute study released on Friday.