In 2015, global passenger and freight commercial aircraft accounted for 866 million tonnes or 2.7% of energy use-related CO2 emissions, which is more than twice the amount released by the entire UK economy. If air passenger and freight revenue tonne-km (RTK) continue to grow at around 4.5% per year and aircraft fleet fuel use per RTK continues to decline by 2% per year, the projected stronger growth in RTK would lead to an increase in CO2 emissions by 2.5% per year, a doubling by 2050. This growth trend in CO2 emissions is in strong contrast to global efforts to reduce economy-wide CO2 emissions as mandated by the Paris Agreement.

Whereas simple arithmetic implies that a net zero-carbon aviation system can only be achieved through disruptive aircraft technologies and fuels, its most cost-effective composition remains unclear. Such knowledge is critical as vast investments will be required by aircraft manufacturers, fuel suppliers, airlines and airports to accomplish the transition. In addition, transitioning towards a net zero-carbon aviation system requires understanding the underlying technology roadmap, complemented by enabling policy measures and identification of early adopters. At the same time, the multiple time lags in the aviation system, from developing an early concept to fleet adoption of the final product, in addition to the long lifetime of commercial aircraft in the order of 25 years, demand swift action to generate a significant impact by mid-century. This, in turn, requires that all CO2 mitigation options are considered, including travel demand management, which necessitates an improved understanding of travel behaviour.

The TOZCA project will develop a comprehensive tool suite to simulate the most cost-effective transition toward a net zero-carbon aviation system by 2050 and a later 2070 date. Using this tool suite, the TOZCA project will identify the technological, economic and environmental synergies and trade-offs that result from drastic CO2 emissions reductions through changes in technology, fuels, operations, use of competing modes and change in consumer behaviour.