Weighing Water

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Science  26 Mar 2010:
Vol. 327, Issue 5973, pp. 1555
DOI: 10.1126/science.327.5973.1555-a

In comparing competing sources of energy, many recent analyses have focused on relative conversion efficiencies and associated greenhouse gas emissions. However, other potentially limiting factors also contribute to the value of a given approach. Based on the prediction that fresh water will become one of the most limited resources in the future, Mulder et al. estimated the energy return on fresh water input (for production and processing) across a range of energy technologies. One of the more striking outcomes of the analysis is that the most efficient petroleum-based energy source (diesel fuel) yields over two orders of magnitude more energy per volume of fresh water used than does biomass. Such a vast difference in return on water invested suggests that policies striving to replace fossil fuels with biomass resources—their many other appealing characteristics notwithstanding—may exacerbate the increased burden on a global fresh water supply already stressed from the higher agricultural demands of a more populated world (though feedstock shifts may relieve some of this pressure). Solar and wind technologies show potential advantages in this context.

AMBIO 10.1007/s13280-009-0003-x (2010).

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