The scale of the problem of providing a significant replacement for fossil fuels using first-generation biofuels is illustrated in Table 8.4. The agricultural land required to supply 15% of the US transport fuels for a number of crops has been calculated. For

the temperate crops such as soybean and rapeseed, this would require 67 and 42% of the agricultural land, respectively, and even with the highest yield crop, oil palm, 7.2% of the land would be needed. Unfortunately crops such as oil palm are unsuit­able for growth in temperate climates. The table does make a good case for biodiesel from alternative sources such as microalgae.