USS Clueless - Sequestering Carbon

Stardate 20020423.1946

(On Screen): Archer Daniels Midland wins another one in the Senate. A combination of farm-belt senators crossed party lines and voted to require a quadrupling of consumption of ethanol for vehicular use in the next ten years. And guess who's going to be making and selling the majority of that 5 billion gallons of ethanol per year? Just guess.

Of course, the rhetoric is running hot on it. It's an outright bribe to ADM. It's a way of becoming independent of the Arabs. It's a way of cutting carbon dioxide generation because corn is good at taking CO2 out of the air.

The Renewable Fuels Association, the ethanol industry’s trade association, argues that increased use of ethanol will help American farmers, reduce U.S. dependence on imported oil and counteract global warming, which may be caused by greenhouse gas emissions.

Since corn plants are very efficient at soaking up the greenhouse gas carbon dioxide as they grow, they help offset the CO2 produced every time someone drives a car or truck.

Well, no, not really. It depends enormously on what you do with the corn stalks afterwards. It's true that like all plants corn takes CO2 out of the air while it's growing, but if you burn the stalks afterwards then all that carbon will be released back into the air. The only way you can use this to permanently remove CO2 from the air is by burying all the stalks and leaves of the corn each year.

Let's run some numbers, shall we? Let's optimistically assume that 10% by weight of the corn plant is harvestable grain. (It probably isn't that high.) Let's assume a 25% conversion of grain into alcohol, also by weight. (It's doubtful it's that efficient.)

5 billion gallons of ethanol is 18.925 billion liters. Ethanol has a density of .789, so that's 14.931 billion kilograms. Each kilogram of ethanol would come from 4 kilograms of grain, leaving 36 kilograms of greenery behind, so we're looking at 537.5 billion kilograms of compost: a bit over half a billion metric tonnes.

There is no possible way we can bury a half a billion tonnes of compost every year. There's nowhere to put it, and the long term effects (on things like groundwater, for example) would be horrendous. This is a waste disposal problem to dwarf the amount of garbage that all our cities create. (Note that it would have to be buried near where it was grown; if you have to transport it long distances, you'll more than use up all the fuel you thought you were gaining by producing ethanol in the first place.)

That's not what is actually done. It's used for a number of different things, but in practice nearly all the carbon in it eventually ends up back in the air, via direct or circuitous routes, within a year. Some of it is used for animal feed; most of it gets burned.

That's also the problem with trying to claim that growing forests takes CO2 out of the air. It depends on what happens to the trees afterwards, but in the long run most of that carbon is rereleased, too, via rotting or forest fires. Only if the wood somehow gets buried does it permanently disappear, and that's uncommon.

I'm against Kyoto, and I'm also against stupid rhetoric about CO2 sequestration. Let's be real about this, shall we?

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