ECOLOGgers,
A key paper on the subject needs reference in this discussion...Mario
Giampietro, Sergio Ulgiati and David Pimentel (1997 - BioScience v47)
look at the ancillary resource costs of biofuel production at the large
scale. Their scheme, which is inherently sensible, is to evaluate the
resource needs (water, labor, land) per net GJ of energy yield. As as
example, temperate (corn) and tropical (sugarcane) ethanol systems use
an estimated 150-200 tons of water per net GJ yielded. They extrapolate
these findings to estimate that meeting current energy needs in the US
with these biofuels will increase water extractions by 30-fold over
current withdrawals. Even with an order of magnitude error in their
estimates, this would create massive additional stress on the hydrologic
system, begging the question "What is sustainable?".
Regards,
Matt
