The question of whether the world needs biofuels is approached by examining the feasibility of doing without them. Even with aggressive reductions in travel growth, shifts to mass transport modes, strong effi ciency improvements, and deep market penetration by vehicles running on electricity and hydrogen, there remains a large demand for dense liquid fuels in 2050 (80% of transportation fuel) and even in 2075 (50%). This demand is due largely to aviation, ocean shipping, and long-haul trucking. Acknowledging the signifi cant uncertainties involved in such projections and the challenges faced by all candidate technologies and fuels, we conclude that it will likely be diffi cult to achieve a low-carbon transport sector without widespread use of biofuels, and that aggressive efforts to develop sustainable, low-carbon biofuels alongside other options are warranted.

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