Even the best of green intentions can sometimes go awry. That's the message from a new study in today's issue of the journal Science. In recent years demand for ethanol and other biofuels—gasoline substitutes made from fermenting corn, sugar and other crops—has taken off. To satisfy this demand, farmers are cutting down native forests to make new farmlands or switching from food to energy crops, which drives up the cost of food. And the worst part is it may actually be hurting the environment by causing more carbon to be released into the atmosphere—from clearing land—than is saved from emissions. David Tilman, a co-author of the report and an ecology professor at the University of Minnesota, spoke with NEWSWEEK's Karen Pinchin. Excerpts:
What is the appeal of biofuels in reducing the world's dependency on fossil fuels?
Tilman: The appeal is that biofuels are renewable; you can grow the same crop, year after year, on the same plot of land. The next appeal is that they take carbon dioxide from the air, use it to make sugars, and then we take those plants to make biofuels. It seems like all we're doing is recycling the carbon from the plant, then into our car, and so forth. Those are the two main ideas that led to the interest in biofuels. Those ideas still have great potential. What we're learning is that although there are some ways to do it right, there are also some ways to do it wrong.
In your study you make a clear distinction between biofuels made from land cleared especially to grow biofuel crops and fuels made from waste products. What is the biggest difference between the two?
It's not that all biofuels are horrible. Here's the problem: the world has become more interested in biofuels—not just the United States but also Brazil, Malaysia and Indonesia, among others. In order to grow biofuels, farmers have gone to fertile land near them, rain forest or grassland, and they have started to grow biofuels. But when you do the calculations, there are immense amounts of soils and vegetation on the earth, and when you clear them, carbon is released. For every one of these cases, where you are clearing native ecosystems to grow biofuels, we found that the amount of carbon dioxide released from cutting the trees, burning some of them, and having their roots decay was much, much greater than the net benefit provided by the biofuels. We found that there was a period of time where you do break even, where the biofuel started providing an advantage. The longest was 400 years and the shortest was 17, but the average was half a century. It might give us a benefit 50 years later, but it's not a very wise environmental policy.
You also talk about food.
The world needs food; people need food. If I have fertile land, I can't eat electricity. Food demand is going up around the world, which is why the price of food is going up. If you use farmland in North America to grow biofuels, [you're forcing a farmer somewhere else to clear-cut forest to grow food crops]. You've effectively cut down a rain forest. That has a startlingly large effect.
There are many things we can do to use fossil energy more effectively, but it's not ethical to try to deny people in developing countries the right to clear their land to grow food and feed themselves.
What did you look at in your study?
We looked at all of the current biofuels that are being made around the world and asked if they were causing native ecosystems to be turned into land that would be used to grow the crop. Essentially, all of them are doing that. We then determined the kind of ecosystem that was being converted into cropland, how much carbon that ecosystem has, on average, in its vegetation and its soils. From that we calculated the carbon debt, the amount of carbon that would likely be released by growing this crop. Then for each biofuel we calculated its greenhouse gas benefit, then divided the total carbon debt by the annual carbon benefit from the biofuel, and the number you get from that is the number of years it takes before the biofuel gives you a greenhouse gas emission. Until you get to that number of years, you're worse off growing and using the biofuel than just using gasoline or diesel. We did this in seven different cases, with seven different ecosystems and places around the world. We also did two alternatives, where there were large greenhouse gas benefits growing the biofuels that don't require clearing native ecosystems around the world.
How much carbon do those rotting waste products from land clearing actually produce?
If you look at a tree, and get rid of the water in it, half of the dry weight of the tree is carbon. If you think about how large the atmosphere is and how much carbon dioxide it can hold, there is actually just as much [additional] carbon in the vegetation of the earth. There's twice as much [again] being held in the soils of the earth, which is released when land is cleared for farming.