In this study, maps of land availability were assessed using high-resolution satellite imagery. Samples from these maps were selected and crowdsourcing of Google Earth images was used to determine the type of land cover and the degree of human impact.
Based on this sample, a set of rules was formulated to downwardly adjust the original estimates for each of four scenarios that were previously used to generate the maps of land availability for bioenergy production.
In the earlier maps estimates of additional land available for bioenergy production range from 320 to 1411 million ha. These estimates were generated from four scenarios regarding the types of land suitable for bioenergy production using coarse-resolution inputs of soil productivity, slope, climate, and land cover.
The adjusted land availability estimates range from 56 to 1035 million ha depending upon the scenario and the rule set used when the sample is corrected for bias. Scientists say these numbers should not be considered as definitive estimates but should be used to highlight the uncertainty in attempting to quantify land availability for biofuel production when using coarse-resolution inputs  .
Figure 1. High-resolution satellite images, like this one from Google Earth, showed clear evidence of land use by humans in areas that the previous map had identified as available for biofuel production. © 2013 Google Earth; © 2013 Geo-Eye.
 Fritz S, See L, Valin H (2013). Current issues and uncertainties in estimating global land availability for biofuel production.Biofuels,4(4), 343-345.
 Fritz S, See L, van der Velde M, Nalepa RA, Perger C, Schill C, McCallum I, Schepaschenko D, Kraxner F, Cai X, Zhang X, Ortner S, Hazarika R, Cipriani A, Di Bella C, Rabia AH, Garcia A, Vakolyuk M, Singha K, Beget ME, Erasmi S, Albrecht F, Shaw B, Obersteiner M (2013). Downgrading recent estimates of land available for biofuel production. Environmental Science & Technology, 47(3), 1688-1694.
X. Cai and X. Zhang, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
Last edited: 22 May 2014
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