Satellite-data derived study finds meeting renewable fuel targets is theoretically feasible, but would significantly impact agriculture mix
Roughly 80% of the current recovered harvest in the US would need to be re-allocated for the production of bioenergy crops to meet current renewable fuel targets with existing technology, according to a new study using satellite data led by researchers from the University of Montana. An alternative, according to the study to be published in the ACS journal Environmental Science & Technology, would be to convert more than 80% of managed rangeland, or nearly 60% of total rangeland, to biofuel crops.
The 2007 Energy Independence and Security Act (EISA) set a goal of increasing US biofuel production more than three-fold from 40 to 136 billion liters of ethanol per year by 2022. This implies an even larger increase in biomass demand (primary energy), from roughly 2.9 to 7.4 EJ yr-1, the authors note.
However, our understanding of many of the factors used to establish such energy targets is far from complete, introducing significant uncertainty into the feasibility of current estimates of bioenergy potential. Here, we utilized satellite-derived net primary productivity (NPP) data—measured for every 1 km2 of the 7.2 million km2 of vegetated land in the conterminous US—to estimate primary bioenergy potential (PBP).
Our results indicate that PBP of the conterminous US ranges from roughly 5.9 to 22.1 EJ yr-1, depending on land use. The low end of this range represents the potential when harvesting residues only, while the high end would require an annual biomass harvest over an area more than three times current US agricultural extent.—Smith et al.
The analysis found that while the EISA energy targets are theoretically feasible, meeting these targets utilizing current technology would require significant displacement of current crop harvest or conversion of rangeland. The authors reported that both options would significantly reduce the amount of food US farmers produce. They also noted that research shows that increased farming could lead to more polluted freshwater and accelerate global climate change.
Accordingly, energy planning should include iteratively and realistically constrained bioenergy estimates for effective incorporation of bioenergy potential into the national energy portfolio.—Smith et al.
The authors acknowledge funding from the Energy Biosciences Institute and the National Aeronautics and Space Administration.
William Kolby Smith, Cory C. Cleveland, Sasha C. Reed, Norman L. Miller, and Steven W. Running (2012) Bioenergy potential of the United States constrained by satellite observations of existing productivity. Environmental Science & Technology doi: 10.1021/es203935d