Aviation must reduce its CO2 emissions..
The aviation industry anticipates three categories of technological solutions to reduce its carbon dioxide emissions.
- Improving the energy efficiency of aircraft
- By improving their aerodynamics (long wing span, active wing) to improve lift and reduce drag.
- By reducing their weight (composite and functional structure).
- More efficient propulsion systems (e.g. RISE programme).
- Reduction of emissions associated with operations
- In flight, by optimising trajectories in relation to winds, flying in formation or on the ground, electrifying certain uses (taxiing, APU).
- It is also proposed to offset emissions (CORSIA programme) but the effectiveness of this offset is difficult to assess.
- Use of new fuels
- Sustainable Aviation Fuels (SAF) (electrofuels or biofuels) have a chemical composition close to that of kerosene and can be used without drastic modification of the infrastructure. But they will have to be produced in the necessary quantities (thanks to decarbonised electricity, in the case of electrofuels) and certified.
- Another approach, which involves a more profound change in supply logistics and aircraft design, is hydrogen (for example, the Airbus ZEROe programme).
.. without forgetting non-CO2 effects
There are three main non-CO2 effects:
- Condensation trails (contrails): These contrails are the most visible mechanism. They can form after the passage of an aircraft (depending on the properties of the engine plume and the atmosphere). Some contrails may also evolve into induced cirrus clouds and persist for several hours. These induced cirrus clouds would have a greater impact on the climate than CO2 emissions alone. Thus, avoiding their formation would reduce the impact of aviation on the climate.
- Nitrogen oxide (NOx) emissions : Aircraft engines, in addition to emitting CO2 and water, also emit nitrogen oxides (NOx). At high altitudes, NOx leads to a decrease in the concentration of atmospheric methane but to the formation of ozone. Both gases (ozone and methane) are powerful greenhouse gases. To date, it is estimated that the impact of NOx tends to warm the climate.
- The interaction of emitted particles with natural clouds: Among the products of kerosene combustion are solid or liquid particles that result from incomplete combustion in the engine. These particles, called aerosols, can influence the clouds naturally present in the atmosphere. These effects of aerosols on natural clouds have been little studied and their impact on climate has not been quantified.
Technical solutions to reduce the climate impact of aviation
Move the mouse over the table to get more information.
| Technological and operational solutions | CO2 | Contrails/ Induced cirrus |
NOx | Deployment complexity | Timeframe for large-scale deployment |
| Carbon offsetting | 
Reduces CO2 effects but effectiveness and quality of compensation variable and difficult to verify
|
 |
|
Existing | |
| Avoiding areas where contrails are formed |
Slight increase due to change of course
|
Diminution
|
Slight increase but possible decrease with lower altitude
|
Medium Introduction of metrics to identify trade-offs between CO2 and non-CO2 effects to ensure a beneficial effect on the climate |
10-15 years |
| Formation flights | 
Slight decrease due to fuel savings
|
Little or no effect?
|
Slight decrease due to fuel savings
|
Medium More constraints on flight planning and air traffic management |
|
| De-aromatized fuel |
Small decrease during flight but potential increase during production
|
Reduced radiative effects in the absence of aromatics?
|
|
Medium Introduction of a new fuel category |
|
| Biofuels |
CO2 reduction compared to kerosene (life cycle)
|
Reduced radiative effects in the absence of aromatics?
|
|
Medium Availability of sustainable biomass for production, investment and scale-up of the industry, cost. |
15-25 years |
| Electrofuel |
Potentially neutral if made from atmospheric CO2 and decarbonised electricity
|
Reduced radiative effects in the absence of aromatics?
|
|
High Technological maturity, energy efficiency and the need for decarbonised electricity, cost. |
|
| Hydrogen |
Potentially CO2 neutral if made from low-carbon energy sources
|
More frequent? But potentially lower optical thickness and shorter life?
|
|
Very high Complete redesign of aircraft and refuelling infrastructure. Associated investment. Production development. Cost. |
>30 years |