The manufacture, delivery, and consumption of fuel for transportation currently accounts for more than a third of the United States’ total global warming pollution. Reducing this sector’s sizable impact on climate change will not only require more fuel-efficient vehicles and fewer miles driven, but also fuels that generate significantly less heat-trapping carbon dioxide (CO2) than today’s gasoline and diesel.

California has set a positive example for the rest of the nation to follow with its Low Carbon Fuel Standard (LCFS), which will require the state’s fuel providers to reduce the global warming pollution from their various transportation fuels an average of 10 percent by 2020. This policy represents an improvement over the current federal Renewable Fuel Standard because it addresses the total heat-trapping emissions reduced over the full life cycle of a given fuel (i.e., from the time it is grown or extracted to its ultimate release from the exhaust pipe).

The LCFS gives providers the flexibility to choose which fuels they will use to meet their 10 percent goal. Until renewable hydrogen and electricity become viable options, “biofuels” produced from sugars, starches, oils, and other plant-based material (or biomass) will likely be providers’ main choice for reducing heat-trapping emissions in the short term because these fuels can be integrated relatively easily into the existing fuel distribution infrastructure.

Policy makers must bear in mind, however, that expanding the use of biofuels does not guarantee significant decreases in global warming pollution. This expansion could also have unintended consequences such as increased smog, strain on water supplies, or decreased soil quality. Not all biofuels are created equal.

A Better Biofuel?

Most of the biofuel used in the United States today takes the form of ethanol made from corn kernels. Burning ethanol generates no net carbon emissions because the carbon stored in plants was recently pulled from the atmosphere through photosynthesis. However, a lot of fossil fuels are burned in the growing and processing of corn, and industrial farming operations also generate substantial emissions of heat-trapping nitrous oxide.

At current production levels, corn ethanol offers only a small (10 to 25 per-cent) reduction in global warming emissions compared with gasoline. Even if this percentage were improved via more efficient production methods, corn’s long-term potential as a biofuel feedstock is limited; using all our corn to make ethanol (with nothing left for food or animal feed) would only displace perhaps 15 percent of our gasoline demand by 2025.

Greater emissions reductions may be possible through alternative feedstocks such as switchgrass and other perennial crops. These “cellulosic” forms of biomass (so named for the long chains of sugars that form a plant’s cell walls) require significantly less fossil fuel to produce, resulting in an estimated 70 to 90 percent reduction in heat-trapping emissions compared with gasoline. Cellulosic ethanol could also enhance U.S. energy security by diversifying our fuel resources, and alleviate the pressure on crops needed for food and animal feed.

A Diet that Works

Renewable fuels offer us a promising opportunity to make substantial cuts in our global warming pollution, provided we adopt policies that encourage the development of fuels that generate less emissions over their entire life cycle. California’s Low Carbon Fuel Standard provides lawmakers around the country with a model for such a policy. To learn more about biofuels, visit the UCS website at www.ucsusa.org/smartbioenergy.

Steven Bantz, formerly a senior analyst in the Clean Vehicles Program, is now pursuing a teaching career.
 

Also in This Issue of Catalyst
Dangerous Climate Change	The Space Age at 50	A Shift Toward Cleaner Cars?
Heat-trapping Gases	Vehicles' New Low-Carbon Diet