Renewable? Yes. Climate-Friendly? No.

Photo: Christine Glade / istock

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Two studies paint a disappointing future if the world relies on today's renewable fuels to replace oil: Greenhouse gases may well increase. That runs counter to the widespread belief that burning the fuel from a crop would release only as much carbon dioxide as the next planting would absorb.

It could take 167 years, according to one study, before the net savings from a biofuel farm pays itself off in carbon emissions, assuming it was grown on existing corn fields. Even if the biofuel farm uses existing farmland, the scientists assume the demand for food will prompt the clearing of untouched forests and grasslands to grow food.

The equation is even worse in Brazil or Indonesia, where it might take more than 300 or 400 years for a sugarcane or palm oil plantation to account for the loss of rainforest. By that time, by some estimates, Greenland will have melted and sea levels will have swelled by dozens of feet.

Part of the equation, however, is the current slate of biofuel crops. It takes a lot of energy and emissions, in the form of fertilizer for one, to grow corn and make it into fuel. The world's other major biofuel crops, sugarcane and palm oil, have similar problems. Other crops, which can also be grown and re-grown on existing grasslands, require less energy to grow, and may be more favorable to the climate.

The study does, however, highlight the huge role that agriculture plays in global warming. While we focus on how we can reduce our electricity use to prevent emissions from power plants, and we focus on reducing our use of inefficient vehicles to burn less oil, the way we eat (and increasingly the fuel we grow) also has a big influence on the climate. Worldwide, agriculture accounts for 20% of human's contribution to global warming, according to United Nations estimates. (Want to lower your impact? The simplest way is to eat local, and eat less meat.)

The study also highlights how difficult the challenge of finding low-carbon solutions. In some sense, these studies point to the same problem: The lifestyle we're accustomed to is made possible by burning millions of years worth of the sun's energy, stored in decayed plants deep underground. There may not be land enough on Earth to both feed us and fuel our industry without altering the climate. If there is, these studies show, we haven't found it yet.

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