Abstract
It's about the land!
Biofuels are all the rage. Investment, production and consumption are booming, thanks mainly to U.S. and European government subsidies and promotion. This is driven in part by fear of environmental enemy number one - global warming. The simple, conventional wisdom is that biofuels have smaller carbon footprints than competing petrofuels.
Yet the inconvenient truth is neither simple nor conventional. Not simple, because alternative land use is important - at times overwhelmingly so - to the choice between the two. Alternative land use can tip the scales between choosing a biofuel or a petrofuel. Unconventional, not only in that petrofuels sometimes wear the smaller shoes, but also, generally speaking, where a crop is grown plays a more important role in the biodiesel-petrodiesel footprint than what type of crop is grown.
So central is land use that - at least from a global warming viewpoint - northern European farmers, rather than planting rapeseed for biodiesel, should plant trees and burn petrodiesel instead. Greenhouse gas emissions are reduced more by fueling with gasoline and preserving the Brazilian rain forest, than by knocking it down to grow sugarcane for bioethanol. Yet at the same time, it is better to convert a Malaysian rain forest into a palm oil plantation for biodiesel than it is to fill tanks with petrodiesel. Note that this is from a carbon footprint viewpoint only. Other issues, e.g., biodiversity, must be taken into account and we do not necessarily advocate cutting down the rain forest.). As we said - unconventional, and not simple. Four of the findings in our report follow.
Finding 1: Accounting for alternative land use has a substantial impact that can work in either direction, with the final result highly dependent upon case-specific criteria. For diesels, rapeseed (rapeseed is also known as canola, especially in North America.) biodiesel is a worse choice than petrodiesel. Soy biodiesel and palm biodiesel are better choices than petrodiesel. Yellow grease (used cooking oil from restaurants) biodiesel is neither better nor worse than petrodiesel. For spark-ignition fuels (gasoline and ethanol), stover ethanol and sugarcane ethanol are better choices than gasoline, while corn/maize ethanol is neither better nor worse. If sugarcane were grown on former tropical forest, however, then gasoline is a better choice than bioethanol.
Finding 2: Generally speaking, where a crop is grown plays a more important role in the biofuel-petrofuel footprint than what type of crop is grown. If alternative land use is accounted for and soybeans are grown on Midwest US cropland, soy biodiesel creates a smaller footprint than petrodiesel. But if the soybeans are grown on former tropical forest, then petrodiesel is a far better choice. In other words, greenhouse gas emissions are reduced more by fueling with petrodiesel and preserving the topical forest, rather than knocking it down to grow soybeans for biodiesel.
Finding 3: Converting wastes to biofuels produces smaller footprints than does using petrofuels or non-waste-derived biofuels. Admittedly, this finding would be pretty obvious without this study. Still, it is important enough to warrant mention, and this study has at least verified and quantified it.
Finding 4: Two much-touted alternative fuels - FT diesel and hydrobiodiesel - do not deliver more competitive carbon footprints. Fischer-Tropsch (FT) diesel, produced from so-called stranded natural gas without access to gas pipelines, weighs in with the deepest base case footprint in this study. Hydrobiodiesel, produced by hydrotreating vegetable or animal oils, comes out equal to or worse than conventional transesterified methyl esters. On the plus side, it avoids the use of "fossil carbon" in its production, and its fuel economy is better. On the minus side, its product yield is a bit lower, and the process uses a lot of hydrogen. Generating hydrogen in a steam reformer creates, relatively speaking, a lot of CO2.
Land-use policy must become part of energy policy and global warming policy.
Research further to this study may well conclude that we should let the deserts bloom. With agriculture, that is, while letting forests thrive on fertile land that does not need irrigation. Whether or not this is concluded, the point is that land use is inextricable from future energy supply and global warming. This has broad implications for how government departments and regulatory agencies are structured. Fortunately, many governments have integrated land-use planning and environmental regulation for years, so there is a strong base here already. |
