Biofuels may not be the greenest option for airlines after all, says MIT, and can sometimes result in higher greenhouse gas emissions than traditional fossil fuels.
In 2008, Virgin Atlantic became the first commercial airline to fly a plane on a blend of biofuel and petroleum, with several others carrying out test flights. But according to the MIT team, they may be making a mistake, as a biofuel’s origins can mean that it's not the greenest choice after all.
"What we found was that technologies that look very promising could also result in high emissions, if done improperly," says James Hileman, principal research engineer in the Department of Aeronautics and Astronautics. "You can’t simply say a biofuel is good or bad — it depends on how it’s produced and processed, and that’s part of the debate that hasn’t been brought forward."
Hileman and his team performed a life-cycle analysis of 14 fuel sources, including conventional petroleum-based jet fuel and 'drop-in' biofuels that can directly replace conventional fuels with little or no change to existing infrastructure or vehicles. They calculated the emissions throughout the life cycle of a biofuel, including harvesting it, transporting it and converting it to fuel, as well as its combustion.
"All those processes require energy, and that ends up in the release of carbon dioxide," he says.
In particular, the team found that emissions varied widely depending on the type of land used to grow biofuel components such as soy, palm and rapeseed.
For example, biofuels derived from palm oil emitted 55 times more carbon dioxide if the palm oil came from a plantation located in a converted rainforest rather than a previously cleared area. Depending on the type of land used, biofuels could ultimately emit 10 times more carbon dioxide than conventional fuel.
"Severe cases of land-use change could make coal-to-liquid fuels look green,” says Hileman.
The challenge, he says, is in finding large areas of land to cultivate enough biomass, in a sustainable fashion, to feed demand. One solution could be to explore crops like algae and salicornia that don’t require deforestation or fertile soil to grow.