From the previous sections, it has become clear that in much expanding transport biofuel production, there may often be hard choices to make. Growing crops such as oil palm and corn for transport biofuels may contribute to energy security and mitigate price rises of fossil fuels but may generate for decades more greenhouse gases than fossil transport fuels and have an upward effect on food prices. Growing feedstocks on currently fallow land in the USA and Europe may mitigate the ef­fect of biofuel production on food prices and limit greenhouse gas emissions linked to the transport biofuel life cycle but is probably bad for biodiversity. Intensifying cropping for biofuel feedstocks may be conducive to limiting price increases for food and fuel but may also be unsustainable and have a negative impact on biodiver­sity (Sukhdev 2008). As large-scale production of transport biofuels may come at significant costs, one may well wonder whether preference should be given to other ways of providing for transport services.

So, we return to the alternative option of better energy efficiency in transport and better solar energy conversion in transport energy supply, raised in Sect. 6.3. Improved energy efficiency is not necessarily an easy alternative. Indeed, in many countries, as to cars, fossil fuel input per person-kilometre has remained virtually constant since the 1973 ‘oil crisis’. Potential gains in energy efficiency due to techni­cal progress were ‘eaten away’ by developments such as preferences for improved comfort and safety, lower occupancy of cars and increased congestion (Schipper et al. 1992). However, it is also known that increased fuel prices are conducive to increased energy efficiency in producing transport fuels and increased energy effi­ciency of transport (Schipper et al. 1992; Graham and Glaister 2005), and future prices may well be high (GAO 2007), so that may help in making improvements in energy efficiency more successful than was feasible in the past. To the extent that priority is to be given to renewables, the obvious alternative from the point of view of conversion efficiency (as pointed out in Chap. 2) is the use of physical con­

version technologies producing electricity, which can either be used for storage in batteries or be converted into H2 for use in fuel cells (Armor 2005; Evans 2008; Ros et al. 2009). Again, this is not an easy alternative. The costs thereof are as yet high, though they are expected to be much reduced over the coming decades (Martinot 2006; Braun 2008).