AVIATION AND CLIMATE A LITERATURE REVIEW

Can we make future aircraft and aviation sustainable?

Can we characterize the impact of aviation on the climate?
Can CO2 and non-CO2 effects be compared?
What technological solutions are being studied today to make future aircraft and aviation sustainable?
Can we link the speed of change in air traffic to the fraction of the carbon budget devoted to aviation?
Can we make an assessment of available energy resources?

These questions drove the drafting of a reference report by ISAE-SUPAERO. The objective of this work is not to take sides or answer the various questions raised, because the answers depend largely on societal choices and technical-economic developments that are impossible to predict with certainty.
On the other hand, the aim of this report is to provide everyone, based on our position as scientists, with the necessary elements to build informed opinions on these issues, as objectively as possible. We hope, through a ripple effect, to spark debates and thus participate in the emergence of a collective position on these crucial issues.

Key messages of the aviation and climate a literature review

The ISAE-SUPAERO Aviation and Climate a literature review aims to provide scientific elements useful for understanding aviation, future aircraft stakes and climate issues. This work was subjected to a specific review process, involving both ISAE-SUPAERO staff and external researchers from different institutes.

Below are the 5 key messages from this report:

 Climate impact of aviation: estimates that depend on the perimeter

Aviation contributes to accentuating global warming through its CO2 emissions and several non-CO2 effects such as contrails. An assessment of the air sector’s impact can be limited to CO2 emissions alone, or all the effects can be taken into account. In the first case, commercial aviation was responsible for 2.6% of the world’s anthropogenic CO2 emissions in 2018. If we consider all the effects (CO2 and non-CO2), commercial aviation accounted for 5.1% of the climate impact over the 2000-2018. Period.

 Non-CO2 effects: promising strategies

Specific strategies for the reduction of non-CO2 effects provide a major lever for limiting aviation’s climate impact. Due to the short lifetime of non-CO2 effects, these strategies can be effective quite quickly. Even though more research is needed to reduce uncertainties, these strategies could be deployed in the short term. Nonetheless, these measures cannot replace efforts for reducing CO2 emissions in the sector.

 CO2 effects: limited technological opportunities in the short term

By 2050, breakthrough solutions should enable us to envisage low-carbon aircraft. In the shorter term, the only mature levers for reducing CO2 emissions within the time frames imposed by the climate emergency are incremental improvements in aircraft efficiency and the use of biofuels. Nonetheless, incremental improvements are coming up against technological limits, while the constraints of energy availability, production capacities and competition among uses risk reducing biofuel’s availability.

 Necessary arbitration between the amount of traffic and the share of the worldwide carbon budget allocated to the aviation sector

Beyond the technological and operational levers, the amount of traffic and the share of the worldwide carbon budget allocated to aviation are the two parameters that determine the sustainability of a pathway for the aviation sector. Their value must be set through political decisions. Limits to the aviation sector’s ability to rapidly reduce its CO2 emissions mean that if traffic grows at the rate foreseen by the aviation industry, it will consume a greater share of the carbon budget than its current share of emissions, thus requiring other sectors to reduce their emissions more quickly than the average.

 Uncertainties as to energy availability

The decarbonization of aviation fuels could be limited by the availability of low-carbon energy resources. Their massive use could then lead to a shift in the environmental problem, notably connected to land use. More generally, we need to think of the transition in the air sector from a systemic point of view in the context of our planet’s limits.

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AVIATION AND CLIMATE A LITERATURE REVIEW