A recent post on a biofuel listserv asked, “For us great unwashed masses – what is the definition of “unsustainable biomass”, exactly?” It’s a perfectly reasonable question: I’ll take a swing, but it’s not simple.
First we have to define “sustainable,” a famously slippery term. Wikipedia currently offers this, “For humans, sustainability is the potential for long-term maintenance of well being, which has environmental, economic, and social dimensions.” The dimensions are all kind of stretchy, as we will see.
Now, what is biomass? Biomass is generally plant material, formed at some point in the relatively recent past. Basically solid (or liquid) solar energy that can be used to make biofuels. Fossil fuels are ancient solar energy too, but with the disadvantage that the carbon dioxide that’s released when fossil fuels are burned hasn’t been in the atmosphere for millions of years — causing an increase in the carbon dioxide levels in our modern atmosphere. Biofuels have the potential to be nearly carbon neutral: clearly biofuels can be better than fossil fuels, from a global climate change perspective.
So it might be natural to think that, since it is basically solar energy, biomass energy has no downside.
What could ever be wrong with biomass use for fuel? Lots of things, it turns out. Don’t get me wrong: I’m a biofuel guy. I’ve been making and selling biofuels, and thinking and writing about biofuels for years. But there’s a lot of irrational exuberance around biofuels these days. A quick answer to the question of what constitutes unsustainable biomass: it depends on how much you like driving and flying, but generally it would be unsustainable to use most biomass (forests, food crops, the trees that line your street) for fuel.