Under what conditions can we continue to fly in a world constrained by the scarcity of fossil resources and climate change? We, engineers, pilots, air traffic controllers, members of the Aéro Décarbo association, have been working on this issue for several years. Driven by the spirit of pioneers, heroes of the air and great humanists, we know that the equations of fluid mechanics make it possible to make machines fly as well as to model climatic phenomena. We therefore wish to address the issue of the decarbonization of air transport with the scientific rigor it deserves, without sacrificing our deep attachment to aviation.
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The aviation sector has committed to an objective of net zero CO2 emissions by 2050. While we welcome this historic commitment, we recall that it is not consistent with the physics of the climate. Our climate future in 2050 does not depend on the quantity of greenhouse gases that we will then emit, but on the sum of said emissions between now and 2050: this is the famous “carbon budget” calculated by the Group of intergovernmental experts on climate change. In our view, therefore, the problem is poorly posed: betting on reaching a target in 2050 means forgetting that we must now reduce our emissions by 5% per year to comply with the Paris Agreement.
The decarbonization of energy is the main lever for reducing emissions in the sector. It covers both sustainable aviation fuels (sustainable aviation fuels, SAF) than hydrogen. If these avenues are credible in terms of their technological feasibility, the fundamental question remains that of the available quantities of low-carbon fuel and the choice of inter-sector allocations in the event of too low production. Emmanuel Macron has set the objective of supplying 75,000 tons of sustainable kerosene to companies by 2030. On a global scale, the International Air Transport Association expects 24 million tons of SAF in 2030. As for the hydrogen, which requires the design of a new aircraft, the most optimistic hypothesis of the Airbus ZEROe program is a device capable of carrying 200 passengers over 3,700 kilometers in 2035. These elements are encouraging, but they remain significantly below the assumptions of the optimistic scenario published in 2021 in the report “Be able to fly in 2050”.
The methodological originality of this report is to calculate traffic growth as output data from a model taking as input a carbon budget set for the sector. Its most optimistic scenario, which is based on very ambitious industrial assumptions, allows us to hope for world traffic growth of +2.5% per year. But all it takes is a five-year delay in industry deadlines or half the expected development of SAFs for potential traffic growth to turn negative. However, recent SAF production announcements place us between these two scenarios at best.
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