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Biofuels Energy from plant matter. There is a limited place for this in a sustainable energy system; managed woodland for burning fuel, conversion of waste products to liquid fuels, and perhaps a small amount of cropland for biofuel to allow aviation in the low carbon world. If land is used for biofuel crops instead of food crops, the nutritional sacrifice is huge for just a small contribution to the world's energy supply. An explosion in biofuels as a replacement for oil would present a real threat to global nutrition. (See Are biofuels bonkers?,

Low carbon flying is a hard nut to crack, but solutions look possible. The most obvious one is use biofuel. Unfortunately, we saw on page 78 that the trade-off between fuel and food is incredibly steep. If the biofuel used was made from wheat, the amount of it required would be enough to meet the calorific needs of all the passengers for a whopping four years and would require 1.5 square miles of prime California land for a year to produce it13

Whatever its low carbon credentials, biodiesel should not be thought of as a major part of our energy solution. Going down this route would put huge strain on the global food system and risk widespread malnutrition.

If the biodiesel came from wheat grown on our square metre, even assuming 100% efficiency of conversion, you could get enough to drive about one mile. To look at in another way, enough wheat to provide a person's calorific needs for a day will only provide enough biodiesel to power car for 2.7 miles. That is a steep trade off!