Biofuels Turn Out to Be a Climate Mistake

Biofuels are usually regarded as inherently carbon-neutral, but once all emissions associated with growing feedstock crops and manufacturing biofuel are factored in, they actually increase CO2 emissions rather than reducing them, writes John DeCicco of the University of Michigan.  According to DeCicco, biofuels are actually more harmful to the climate than gasoline.

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.

Biofuel boom, climate blunder

Federal and state policies have subsidized corn ethanol since the 1970s, but biofuels gained support as a tool for promoting energy independence and reducing oil imports after the September 11, 2001 attacks.  In 2005 Congress enacted the Renewable Fuel Standard, which required fuel refiners to blend 7.5 billion gallons of ethanol into gasoline by 2012.  (For comparison, in that year Americans used 133 billion gallons of gasoline.)

In 2007 Congress dramatically expanded the RFS program with support from some major environmental groups.  The new standard more than tripled annual U.S. renewable fuel consumption, which rose from 4.1 billion gallons in 2005 to 15.4 billion gallons in 2015.

Our study examined data from 2005-2013 during this sharp increase in renewable fuel use. Rather than assuming that producing and using biofuels was carbon-neutral, we explicitly compared the amount of CO2 absorbed on cropland to the quantity emitted during biofuel production and consumption.

Existing crop growth already takes large amounts of CO2 out of the atmosphere.  The empirical question is whether biofuel production increases the rate of CO2 uptake enough to fully offset CO2 emissions produced when corn is fermented into ethanol and when biofuels are burned.

Most of the crops that went into biofuels during this period were already being cultivated; the main change was that farmers sold more of their harvest to biofuel makers and less for food and animal feed.  Some farmers expanded corn and soybean production or switched to these commodities from less profitable crops.

But as long as growing conditions remain constant, corn plants take CO2 out of the atmosphere at the same rate regardless of how the corn is used.  Therefore, to properly evaluate biofuels, one must evaluate CO2 uptake on all cropland.  After all, crop growth is the CO2 “sponge” that takes carbon out of the atmosphere.

When we performed such an evaluation, we found that from 2005 through 2013, cumulative carbon uptake on U.S. farmland increased by 49 teragrams (a teragram is one million metric tons).  Planted areas of most other field crops declined during this period, so this increased CO2 uptake can be largely attributed to crops grown for biofuels.

Over the same period, however, CO2 emissions from fermenting and burning biofuels increased by 132 teragrams.  Therefore, the greater carbon uptake associated with crop growth offset only 37 percent of biofuel-related CO2 emissions from 2005 through 2013.  In other words, biofuels are far from inherently carbon-neutral.

Read more at Biofuels Turn Out to Be a Climate Mistake