Ever since the 1973 oil embargo, U.S. energy policy has sought to replace petroleum-based transportation fuels with alternatives. One prominent option is using biofuels, such as ethanol in place of gasoline and biodiesel instead of ordinary diesel.
Transportation generates one-fourth of U.S. greenhouse gas emissions, so addressing this sector’s impact is crucial for climate protection.
Many scientists view biofuels as inherently carbon-neutral: they assume the carbon dioxide (CO2) plants absorb from the air as they grow completely offsets, or “neutralizes,” the CO2 emitted when fuels made from plants burn. Many years of computer modeling based on this assumption, including work supported by the U.S. Department of Energy, concluded that using biofuels to replace gasoline significantly reduced CO2 emissions from transportation.
Our new study takes a fresh look at this question. We examined crop data to evaluate whether enough CO2 was absorbed on farmland to balance out the CO2 emitted when biofuels are burned. It turns out that once all the emissions associated with growing feedstock crops and manufacturing biofuel are factored in, biofuels actually increase CO2 emissions rather than reducing them.