Measuring and controlling non-CO2 effects in aviation

How can non-CO₂ effects be measured, monitored, regulated and controlled? Around 55 representatives from politics, administration, aviation, industry, research and associations discussed the future of aviation with us at our specialist event “Measuring and controlling non-CO₂ effects in aviation” at the Hessian State Representation in Berlin on April 18, 2024

The climate impact of air traffic is only partly caused by CO₂. Far less noticed - but no less relevant - are the so-called “non-CO₂ effects”. They are responsible for up to two thirds of the climate impact and are caused by nitrogen oxides, contrails or cirrus clouds and aerosol emissions.

The reason for their major climate impact is that emissions have a different effect at high altitudes than on the ground and the intensity of their climate impact depends on factors such as flight altitude, region, local position of the sun and weather conditions. Operational mitigation options therefore include the optimization of flight routes, which requires close cooperation between the weather service, air traffic control and airlines. On the technological side, for example, engines and fuel design can be adapted.

However, in order to measure mitigation effects, a practicable system for monitoring, reporting and verification (MRV) of non-CO2 emissions is required. Together with the audience, the experts intensively discussed what this could look like and which policy instruments are suitable for reducing non-CO2 effects in aviation.

An overview of the results

A view from research: The climate risk of non-CO2 effects

Prof. Dr. Christiane Voigt from the German Aerospace Center (DLR) illustrated the urgent relevance of non-CO2 effects: Not only do they contribute a comparatively large amount to climate impact, but the impact of these effects will almost triple compared to 2006 to 2050 due to the predicted growth in aviation. This makes a drastic reduction of the effects essential. However, research has reached the point where the effects can be quantified and measures can be derived.

The challenge of measuring and monitoring systems

A system that reliably records these effects is needed to measure and monitor non-CO2 effects. However, measuring the necessary flight data for monitoring is a challenge for science. Particularly with regard to the aviation industry, the system must meet the highest standards of precision and practicability, said Wolf-Dietrich Kindt from the German Aviation Association (BDL).

A key strategy: optimizing routing

Non-CO2 effects can be reduced by adapting the routing of airplanes. However, climate-optimized routing is associated with major adjustments in planning, bottlenecks and capacity restrictions, according to Dr. Ralph Leemüller from Deutsche Flugsicherung (DFS). Non-CO2 effects are caused, for example, by contrail cirrus, which are dependent on location and time of day. As only 5% of flights are responsible for the majority of cirrus clouds, measures in certain areas could minimize climate-impacting cirrus clouds.

Fuel design and the promising future of Sustainable Aviation Fuels (SAF)

Dr. Sandra Richter from DLR presented the fuel design option. By reducing the aromatics and sulphur contents, fossil kerosene could be made more climate-friendly until it is replaced by SAF. The use of pure e-kerosene could not only reduce the CO2 footprint, but also minimize the non-CO2 effects, as e-kerosene burns very cleanly.

The importance of emissions trading as a reduction measure

Dr. Olaf Hölzer-Schopohl from the German Environmental authority (UBA) emphasized the role of emissions trading as a political instrument for the possibility of reduction. The integration of non-CO2 effects into the EU Emissions Trading System (EU ETS) could be an effective solution for controlling non-CO2 effects. However, the precondition is that it is designed correctly in order to avoid creating false incentives so that CO2 and non-CO2 reductions are not played off against each other.

Many perspectives, but one consensus

In the panel, representatives from different perspectives discussed options for action and recommendations for policy instruments to mitigate non-CO2 effects in aviation. The regulatory perspective was represented by Dr. Nicole Grunewald from the Federal Ministry for Economic Affairs and Climate Action and Dr. Olaf Hölzer-Schopohl (UBA). Together with Jacob Rohm from the environmental organization Germanwatch, Wolf-Dietrich Kint (BDL) and Gregor Thamm (DFS), presentations were given on instruments such as MRV, EU-ETS and route optimization.

All stakeholders agreed that non-CO2 effects have a major impact on the climate and there is a need to reduce them. This requires a coordinated approach to tackle the climate impact of aviation.

For Download: The presentation slides in German