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Ethanol

Ethanol Greenhouse Gas Emissions

Using ethanol as a vehicle fuel provides local and global benefits—reducing emissions of harmful pollutants and greenhouse gases.

Carbon dioxide (CO2) is the primary greenhouse gas implicated in global warming (others include methane and nitrous oxide). CO2 is produced when carbon that had been stored on or within the Earth is released into the atmosphere—such as when fossil fuels are burned. CO2 can also be removed from the atmosphere, primarily by the action of plants, which consume it during photosynthesis.

The CO2 released when ethanol is burned as a vehicle fuel is offset by the CO2 captured when crops used to make the ethanol are grown. As a result, ethanol-powered vehicles produce less net CO2 than gasoline-powered vehicles per mile traveled.

To get a picture of the true greenhouse gas reduction, life-cycle analyses are used to calculate CO2 emissions and uptake at each step of the ethanol and gasoline production and use processes. For ethanol, these steps include growing of the feedstock crops, transporting the feedstock to the production plant, producing the ethanol, distributing it, and burning it in vehicles. For gasoline, crude oil must be extracted from the ground, transported to an oil refinery, refined, distributed, and burned in vehicles.

Studies have shown that, when these entire fuel cycles are considered, using corn-based ethanol instead of gasoline reduces greenhouse gas emissions by 19% to 52%, depending on the source of energy used during ethanol production (see graph below). Using cellulosic ethanol provides an even greater benefit—reducing greenhouse gas emissions by up to 86%. Recent studies have shown the importance of incorporating assumptions about future crop production rates and land use into life-cycle analyses; these factors can affect net greenhouse gas emission calculations substantially.

Bar graph showing greenhouse gas emissions of transportation fuels by type of energy used processing. Gasoline is processed using petroleum. As corn ethanol is currently produced, it yields a 19% reduction in greenhouse gas emissions. Corn ethanol produced using natural gas yields a 28% reduction and produced using biomass yields a 52% reduction. Sugarcane ethanol produced using biomass yields a 78% reduction. Cellulosic ethanol produced using biomass yields an 86% reduction.

Source: Life-Cycle Energy and Greenhouse Gas Emission Impacts of Different Corn Ethanol Plant Types (PDF 606 KB); DOE Biomass Program Download Adobe Reader.

For more information, see Energy Balance of Ethanol and the U.S. Department of Energy Biomass Program's Environmental Benefits page. Use the Flexible Fuel Vehicle Cost Calculator to estimate greenhouse gas emissions savings from various FFV models. Learn more about Ethanol Emissions.