Climaviation, an Innovative Project to Reduce the Impact of Aviation on the Climate

In what context was the Climaviation project created?

Nicolas Bellouin: Faced with global warming and the need to reduce carbon dioxide (CO₂) emissions, the aviation industry has embarked on a worldwide decarbonization strategy. The task is particularly difficult for this economic sector, where CO₂ emissions are still very high and where every innovation envisaged for aircraft must be tested and approved before being implemented.

In this context, the French Civil Aviation Authority (DGAC) has financed a five-year Climaviation project to explore different solutions to reduce the climate impact of aviation.

What is the project's objective?

N. B.: Everyone knows that aviation emits CO₂ and that these emissions must be reduced. But CO₂ is not the only culprit. Aircraft engines emit other compounds: nitrogen oxides, water vapor and particles. Under the certain conditions, water vapor and particulates form condensation trails behind the aircraft. Some of these trails persist and continue to expand, forming large fields of ice clouds that disrupt the Earth's radiation balance. This is one of the so-called "non-CO₂" effects of aviation.

According to recent climate modeling, the impact of these effects could be greater than that of CO₂. But it remains uncertain because of the complexity of the mechanisms to be modeled and the scales to be taken into account in the simulations. Many questions arise concerning the size and properties of the cloud cover induced by the trails, their lifetime in the atmosphere, the formation and composition of ice crystals, and the impact of a fuel change on the chemistry of the atmosphere.

The objective of the Climaviation project is therefore to understand and quantify these effects in order to better take them into account in climate impact reduction strategies.

What solutions are you exploring to reduce the impact of aviation on the climate?

N. B.: The aviation industry is stepping up its efforts to improve the efficiency of existing engines or to use alternative fuels with a low carbon footprint, or even new decarbonized energy carriers such as hydrogen.

We are also looking at alternative strategies that rely heavily on the existing fleet: changing flight altitudes, using updrafts, adjusting flight times, for example. While these strategies do not necessarily require technological change, it is necessary to verify that they are effective and to measure their short- and long-term impacts.

The DGAC therefore needs our scientific advice to determine which of these solutions not only reduce CO₂ emissions, but also limit the non-CO₂ effects.

This is a multi-disciplinary research project involving forces from Sorbonne University and ONERA. How is this collaboration structured?

N. B.: This project brings together about thirty scientists. Among them: atmospheric physicists, cloud physicists, chemists, observers and specialists in automatic pattern detection.

ONERA scientists know how to model the impact on the atmosphere of changing an engine or fuel on a space-time scale of a few seconds and a few meters behind the aircraft. At IPSL, we model what happens on much larger scales: at the level of the planet and over several hours, years or even centuries. Through our collaboration, we are trying to bridge the gap between these two orders of magnitude.

Our ambition is to connect ONERA's models to the climate models developed by IPSL in order to build perennial scientific tools that can be used to estimate the climate impact of any new solution proposed in aviation.