Bioenergy potential of the United States constrained by satellite observations of existing productivity

Background/Question/Methods

Currently, the United States (U.S.) supplies roughly half the world’s biofuel (secondary bioenergy), with the Energy Independence and Security Act of 2007 (EISA) stipulating an additional three-fold increase in annual production by 2022. Implicit in such energy targets is an associated increase in annual biomass demand (primary bioenergy) from roughly 2.9 to 7.4 exajoules (EJ; 10¹⁸ Joules). Yet, many of the factors used to estimate future bioenergy potential are relatively unresolved, bringing into question the practicality of the EISA’s ambitious bioenergy targets. Here, our objective was to constrain estimates of primary bioenergy potential (PBP) for the conterminous U.S. using satellite-derived net primary productivity (NPP) data (measured for every 1 km² of the 7.2 million km² of vegetated land in the conterminous U.S) as the most geographically explicit measure of terrestrial growth capacity.

Results/Conclusions

We show that the annual primary bioenergy potential (PBP) of the conterminous U.S. realistically ranges from approximately 5.9 (± 1.4) to 22.2 (± 4.4) EJ, depending on land use. The low end of this range represents current harvest residuals, an attractive potential energy source since no additional harvest land is required. In contrast, the high end represents an annual harvest over an additional 5.4 million km² or 75% of vegetated land in the conterminous U.S. While we identify EISA energy targets as achievable, our results indicate that meeting such targets using current technology would require either an 80% displacement of current croplands or the conversion of 60% of total rangelands. Our results differ from previous evaluations in that we use high resolution, satellite-derived NPP as an upper-envelope constraint on bioenergy potential, which removes the need for extrapolation of plot-level observed yields over large spatial areas. Establishing realistically constrained estimates of bioenergy potential seems a critical next step for effectively incorporating bioenergy into future U.S. energy portfolios.