Volume 7 | Number 2 | Spring 2008
Biofuels can significantly reduce global warming pollution from vehicles, but not all biofuels are created equal. We must expand our use of this resource carefully in order to avoid environmental damage.
By Patricia Monahan
The U.S. transportation sector is a major contributor to global warming: our cars and trucks emit more heat-trapping pollution (primarily carbon dioxide) than the entire economies of most countries. To dramatically reduce these emissions, we must improve vehicle fuel efficiency, reduce vehicle miles traveled, and shift to lower-carbon fuels such as hydrogen, electricity, and biofuels—fuels produced from plants or other biological material. All of these options can emit less global warming pollution than petroleum-based gasoline and diesel per unit of energy delivered.
Biofuels are quickly gaining support because they can be integrated more easily than electricity or hydrogen into our existing fuel distribution infrastructure, and offer potentially abundant domestic supplies. However, there is no guarantee that expanding biofuel production will significantly reduce global warming pollution, because not all biofuels are created equal. The emissions of each biofuel over its life cycle (i.e., from the time it is grown to its ultimate release from the exhaust pipe) can vary widely.
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Coal: Bad No Matter How You Burn It
The coal industry wants to convert coal into gasoline and diesel fuel, but “liquid coal” is a losing proposition for our health and environment. Over its life cycle, liquid coal releases nearly twice as much global warming pollution per gallon as regular gasoline. Even if most of the CO2 from the refinement process could be captured, liquid coal would still be responsible for 4 to 8 percent more global warming pollution over its life cycle than conventional gasoline. Increasing use of liquid coal would therefore make it virtually impossible to meet the emissions reduction targets needed to avoid the most dangerous consequences of climate change. What’s worse, coal mining—especially destructive strip mining and mountaintop removal—does permanent harm to ecosystems and landscapes. Toxic waste, water pollution, and habitat destruction should not be the legacy of our nation’s fuel system. |
New UCS analysis has separated the hope from the hype and determined that biofuels have the potential to cut global warming pollution, enhance our energy security, and strengthen local economies—but only if they are held to strict performance criteria that limit emissions while safeguarding the environment. To be truly successful, any policies designed to increase the use of these fuels must “count carbon” and “make carbon count.”
Counting Carbon
Petroleum is essentially the fossilized remains of carbon-based plants and animals. When we burn it in our cars and trucks, the carbon in the fuel bonds with oxygen in the air to form carbon dioxide (CO2). The burning of plant matter (or “biomass”) also releases CO2, but—because the carbon in biomass was recently absorbed from the air (unlike fossil fuels)—results in no net increase in atmospheric carbon.
Most global warming pollution analyses for cars and trucks only account for pollution released from the tailpipe. For example, a car emits about 20 pounds of CO2-equivalent emissions (CO2eq) for every gallon of gasoline it burns. But “upstream” emissions (pollution from mining and refining fuel) are also generated before the gasoline ever reaches your car’s fuel tank: fuel production contributes another five pounds of global warming pollution for each gallon of gasoline, bringing the total life cycle emissions to 25 pounds. In the case of biofuels, upstream emissions can be generated during the growing, harvesting, and processing of biomass. For example:
- Some crops require a lot of fertilizer to grow, and many commercial fertilizers release nitrous oxide (a potent global warming gas) as they degrade in the soil.
- Clearing forests and grasslands to grow crops can result in significant emissions of global warming pollution, as the carbon trapped in mature forests and plant roots is released into the atmosphere.
- Converting plants into liquid fuel involves various production processes (such as cooking and distilling grain) that require heat and electricity, which indirectly contribute to global warming pollution.
As the figure below shows, life cycle emissions may vary greatly depending on the feedstocks and refining processes used. On the upper end of the spectrum is “liquid coal,” which could increase heat-trapping emissions more than 80 percent compared with gasoline (see the sidebar); on the lower end is cellulosic ethanol, made from woody or fibrous plants, which may be able to reduce emissions more than 85 percent.
Life Cycle Global Warming Pollution Relative to Gasoline  (click image to enlarge) |
It is important to note that there is significant uncertainty in quantifying emissions, as some sources of global warming pollution are well understood while others, particularly land conversion and fertilizer use, are not. Most life cycle models, for example, do not account for land conversion, though recent studies indicate emissions from this process may be significant. Thus, while most life cycle models typically estimate that corn ethanol cuts global warming pollution about 20 percent on average compared with gasoline, some researchers estimate that it may actually increase global warming pollution significantly. Similarly, soy-based biodiesel is generally credited with a 50 percent reduction in global warming pollution, but there is also research indicating that it may more than double emissions compared with diesel.
The Importance of Our Choices
The stakes are extremely high when it comes to determining the mix of transportation fuels we will use to reduce our heat-trapping emissions. This becomes clear when comparing three scenarios designed to displace 37 billion gallons of gasoline (roughly equivalent to 10 percent of annual U.S. consumption). For each scenario, we evaluated each fuel’s CO2-equivalent life cycle emissions and made the following assumptions: compared with today’s gasoline, conventional biofuels (such as corn ethanol) emit 20 percent less global warming pollution, advanced low-carbon biofuels (such as cellulosic ethanol) emit 70 percent less, and high-carbon liquid coal emits 80 percent more. We also assumed that 25 percent of the total demand for alternative fuels will be met with conventional biofuels while the share provided by liquid coal and advanced biofuels varies. This produced the following results (see the figure below):
- Under a high-carbon scenario (in which liquid coal meets 75 percent of the total demand for alternative fuels), global warming pollution would increase by 233 million metric tons (mmt) CO2eq—which would have the same impact as adding approximately 34 million cars to the road (about two years’ worth of new vehicle sales at today’s rate).
- Under a carbon-neutral scenario (in which liquid coal and advanced biofuels each meet 37.5 percent of the total demand), emissions would be reduced by just 5 mmt CO2eq—the same as removing 0.8 million cars from the road.
- Under a low-carbon scenario (in which advanced biofuels meet 75 percent of the total demand), emissions would be reduced by more than 244 mmt CO2eq—the same as removing approximately 35 million cars from the road.
Global Warming Pollution from Three Alternative Fuel Scenarios  (click image to enlarge) |
Making Carbon Count
Without an accounting system that will measure the carbon emissions of our transportation fuels over their entire life cycle, we risk losing a precious opportunity to cut our global warming pollution substantially. Therefore, we need policies that will complement existing vehicle standards by ensuring the transportation fuel industry does its part—along with automakers and consumers—to reduce emissions.
Fortunately, policy progress is beginning to take shape at the state and federal levels that will bring us closer to a low-carbon fuel future. As described in the last issue of Catalyst, California established its Low Carbon Fuel Standard early last year, which requires the state’s fuel providers to reduce global warming pollution from their various transportation fuels at least 10 percent per gallon by 2020. Arizona, Minnesota, New Mexico, Oregon, and Washington are considering similar regulations as well.
At the national level, the newly passed energy bill includes an aggressive renewable fuel standard (RFS) that could boost biofuel production fivefold, from 7 billion gallons today to 36 billion gallons by 2022. While questions remain on whether this target is achievable, UCS helped ensure that the RFS included specific requirements for reducing global warming pollution.
Looking Beyond Carbon
A successful diet focuses on more than one area of improvement, and a low-carbon diet is no different. It cannot ensure a sustainable fuel production system by focusing on carbon emissions alone. For example, capturing CO2 from oil and coal production could technically make these fuels “low-carbon,” but their extraction, refinement, and transport would still create significant environmental problems including water and air pollution, land degradation, and loss of wildlife habitats. And, if done wrong, biomass production could cause similar damage, reduce access to food, and even jeopardize the long-term viability of the biomass resource itself.
The most comprehensive low-carbon fuel policies will have to provide adequate safeguards to ensure that fuels are produced in a sustainable manner. While there is no international consensus on a single accounting system that would certify biofuel production as “sustainable,” efforts are under way both in Europe and the United States to develop consistent metrics. Marrying a low-carbon fuel standard with environmental protections will give us a head start on the road to cleaner transportation fuels.
Patricia Monahan is deputy director of the Clean Vehicles Program.
