In US President Bush’s State of the Union Address this week, he identified the US’s dependency on oil—especially the kind imported from badly-governed parts of the world—as a problem.

I couldn’t disagree with him there. And his plan to replace petroleum as an automotive fuel with plant-derived ethanol seems sound, at least initially.

I used to think it was a good idea, too, until I read a particular article about using elephant grass as a biomass fuel in Europe. One sentence in particular caught my eye:

If we grew Miscanthus on 10% of suitable land in [the 15-member] Europe, then we could generate 9% of the gross electricity production.

A little mathematics, however, leads to the alarming realisation that if we grew Miscanthus on 100% of suitable land, it would only cover 90% of electricity production. That still leaves out the significant fuel requirements of non-electric vehicular transport. Plus, there’s a small problem of where to grow food when all the land has been devoted to fuel crops! (To be fair, it’s not clear whether ‘suitable’ land includes or excludes land currently used for food production.)

In fact, it gets worse. Jeffrey Dukes calculated1 that the human race uses more than 400 years’ worth of organic matter each year. (This is of course due to the fact that oil contains a lot of dead organisms.) Fairly obviously, we aren’t going to be able to get that much out of the biosphere. It’s also naïve to imagine that mass farming of fuel crops will be without its own ecological consequences.

In fact, however, I still think that plant-derived ethanol is good idea to a certain extent. Some use of biofuel will certainly help to reduce oil dependence—not to mention free up oil for some of its other, arguably better, non-fuel uses. Increasing efficiency will also help; sadly, mention of that is completely absent from the State of the Union Address itself. Perhaps asking Americans to buy smaller cars is a political step too far.

I’m sure that other people have realised the same thing. Even if we ignore the pollution aspect, diminishing oil reserves will draw ever-higher monetary and political prices. Until we invent zero-point energy or desktop cold fusion, nuclear power really does seem to be the only feasible alternative. Nuclear power has its own noxious output, but it is at least more easily sequestered than the prehistoric carbon vented into the atmosphere by burning fossil fuels.

There is one more solution, of course: drastically reduce the number of human beings on the planet. That’s something of an ethical conundrum, though.

1 Statistic cited in George Monbiot’s essay on biodiesel.