Biofuels (fuels produced from organic biological materials, rather than fossil fuels) are already being used in small proportions as part of the fuel mix used to power planes. It is likely that the use of aviation biofuels will be both technically feasible and economically viable, particularly in a world of increasing carbon prices.
However, there is considerable uncertainty over the sustainability of their global production at large scale. The key factors contributing to this uncertainty include:

• Competition from other sectors to use biofuels in the future - the International Energy Agency (IEA) predicts that by 2050, biofuels will be required for use in shipping, road transport, for cooking and heating using biomass in developing countries, in Combined Heat and Power generation and for generating clean coal using Carbon Capture and Storage technology, as well as in aviation; If there was 100% biofuels penetration in aviation together with use of biomass in other sectors as envisaged in the IEA scenarios, 9.3 million km² of the world’s land would need to be set aside for the growth of feedstocks used to produce biofuels.

Source: E4tech (2009), IEA (2008), IEA (2009)

• The need to feed an increasing world population - the global population is projected to rise from 6.7 billion to 9.1 billion by 2050, with demand for food possibly increasing by up to 100% as people become richer.  There may be insufficient land available for growth of biofuels feedstock given the need to use available land and water for growth of food crops
• Limited confidence in methods to grow biofuels that do not require the use of agricultural land - Technological progress may make it possible to grow biofuels from waste, forest residues, algae, or using desert land and water from low-carbon desalination processes. But there are significant uncertainties around the viability and the pace of development of these routes.
• Lifecycle emissions reductions from biofuels - The emissions reductions actually achieved by using biofuels will depend on the emissions generated in their production and their direct and indirect impacts on land use. Biofuel feedstock production could for instance cause food production to shift to currently forested land, land with carbon rich soils, or less productive land where more intensive use of fertiliser is required.

Given these uncertainties we cannot be confident that there will be adequate land available for growth of biofuels feedstocks. It is therefore prudent to assume that a maximum penetration of 10% biofuels use in aviation is likely to be sustainable up to 2050.