Even the most incurious observer will have noticed the growing calls for a move away from fossil fuel dependence for our energy needs. A host of interrelated issues make this one of the most pressing technological challenges of our time. Whether it be the impact of fuel use (climate change, pollution) or the geopolitical consequences of where that fuel comes from, alternatives that didn't involve fossil fuels would plainly be beneficial.

In practice however, there is unlikely to be a single silver bullet that cures what ails us. Oil has a high energy density and is readily transported. Most of the hard work has already been done by the conversion of sunlight to chemical energy and then the slow geological conversion of those sugars and other complex molecules into crude oil. Fossil fuels will likely require application-specific replacements. For transportation needs, biofuels are currently enjoying widespread support, although they have many critics. The need to develop cleaner transportation fuels is highlighted by an article in PNAS this week1, which shows that transport accounts for around 15 percent of anthropogenic CO 2 emissions worldwide.

Brazil has a thriving biofuel industry, using its climate to grow sugar cane, which can then be refined to ethanol. However, this strategy is unsuited to most other regions due to shorter growing seasons. In the US, the current political vogue is for ethanol to be made from corn, despite corn-based ethanol's many problems, Already, increased demand for corn for energy uses has seen a huge increase in the crop's pricing, with serious knock-on consequences for poorer countries and their food supplies.



Image credit: USDA-ARS.

This week's PNAS has a second article2 that highlights a the potential of a rival of corn-based ethanol, a perennial plant known as switchgrass (Panicum virgatum). Switchgrass can be grown on marginal land not suited to corn, and requires much less in the way of agricultural inputs. Although energy yields are not quite as high as corn, the lower impact farming necessary results in 540 percent more renewable energy output than energy used to grow and process.

Even right now, that looks like a viable alternative to corn-based biofuel production that won't cause food riots in Mexico, but use of modern agronomics and genetics ought to be able to raise those energy yields relatively easily. Whether switchgrass has what it takes to compete with the powerful political and commercial interests behind corn remains to be seen.

1: PNAS, 2008. DOI: 10.1073/pnas.0702958104

2: PNAS, 2008. DOI: 10.1073/pnas.0704767105