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.

Potential Impact:
The TOZCA systems model and the related systematic analysis of how to transition toward a net-zero carbon aviation sector will enable more informed technology investments and policy decisions for reducing aviation sector CO2 emissions on both a national and international level, thus directly benefitting government and industry and ultimately furthering society at large. This important impact is articulated by many stakeholders in their letter of support.

For example, the CEO of the ADS Group writes "... the proposed research will be critical in helping us understand the route towards a 'whole system' net-zero CO2 emissions aviation system and the outcomes from the proposed research will be invaluable in understanding the policy interventions and technology investments required. This research is critical to enable the UK aerospace industry and Government to develop a shared approach to tackling climate change and to play a lead role in driving international policy and investments."

The CTO of the Aerospace Technology Institute states that "this work will be vital in guiding the UK's technology road map to a lower carbon future for aviation in the UK and will have broader global impact".

The Chair of Sustainable Aviation writes "This research proposal is important because it will enable a deeper, independent analysis of the aviation decarbonisation opportunities. Sustainable Aviation believes this will be invaluable in terms of building on the work our CO2 Road-Map has set out to date ... The new tool should also enable independent analysis of the situation for all stakeholders."

The Deputy Director, Aviation and Maritime Analysis Division at the DfT writes "This project ... will feed into informing the Departments UK based aviation carbon policy in the Aviation 2050 White Paper (and associated Aviation Carbon Road Map) and the international sphere in helping inform the UK's position at the United Nations ICAO climate negotiations. Whilst other studies are starting to emerge in this area, the proposed depth and detail of this proposal suggests it would be a significant step forward ..."

The Group Head of Sustainability at IAG writes "Robust analysis of the various technological, operational, business model and competitive facets of this challenge will help with strategy development. BA would find such a capability a valuable addition to the suite of fore-sighting capabilities upon which it draws for its development planning and its strategy to reduce carbon intensity."

The Interim Director of the Heathrow Centre of Excellence for Sustainability writes "Your proposal exploring how to mitigate greenhouse gas emissions while meeting demand and maintaining the economic and strategic importance of the sector speaks to the heart of the collective challenge ahead. The whole sector - and wider economy - stands to benefit from detailed academic research and robust systematic analysis."

The Chief Scientific and Technical Advisor for Environment and Energy at the US Federal Aviation Administration writes "This longer-range and system-level perspective will provide a needed strategic view that I anticipate will significantly inform government and industry decision-makers in the U.S. and U.K. in the decades to come."

Multiple paths will be pursued to maximise stakeholder benefit. In addition to disseminating results through the already existing website, conference presentations and publications, existing networks will be exploited. We will assemble an advisory board with 15-20 key stakeholder representatives from government, industry, and NGOs at the beginning of the grant lifecycle to ensure that the direction of the research is consistent with their needs. We will also organise three stakeholder workshops, which serve as milestones and as a vehicle to disseminate results to and receive feedback from stakeholders to refine the analyses in addition to a final conference.