Carbon debt for some biofuels lasts centuries

biofuels release greenhouse gas emissions through land conversion like deforestation. But an innovative new study by the Center for International Forestry Research (CIFOR) published in Ecology and Society has computed how long it would take popular biofuel crops to payoff the “carbon debt” of land conversion. While there is no easy answer—it depends on the type of land converted and the productivity of the crop—the study did find that in general soy had the shortest carbon debt, though still decades-long, while palm oil grown on peatland had the longest on average.

Looking at three different types of biofuels in six countries, the study found that soy grown in parts of Brazil would require 30 years to make-up its carbon debt, which is as good as it gets. Palm oil would require 59-220 years, while jatropha would require 76-310 years, depending on the type of land that was converted. But even at its lowest estimate palm oil replacing peatlands would require just over two centuries (206-220 years) to break even. This means, hypothetically, that palm oil established over drained peatland during Napoleon’s invasion of Russia would still be paying off its carbon debt today.

“It really matters how you produce biofuels and what land you grow it on as to whether you are going to get climate change benefits,” said Louis Verchot, CIFOR scientist and co-author of the study. “Biofuels that result in the conversion of natural ecosystems are never going to be emission efficient. This study argues for appropriate spatial planning and being aware that anything that you do in the name of the atmosphere could have unanticipated consequences unless you look at the whole production system.”

The study found that these three biofuel crops could only be deemed sustainable if grown on permanent crop or pastureland that was not already in use for growing foods, i.e. was degraded or abandoned, in order to prevent leakage.

“In the current reality, these restrictions would leave only a small potential window for sustainable biofuel production aimed at reducing CO2 emissions given the limited availability and/or productivity of these land uses,” the authors write. In other words, on a planet of 7 billion, its becoming nearly impossible to find available land that fits sustainable criteria.

Mongabay