Why is the climate impact of contrails so difficult to mitigate?

In the Earth's atmosphere there is a phenomenon that is as fascinating as it is controversial: condensation trails or "contrails". These diffuse formations, often mistaken for ordinary clouds, play an important role in the balance of our climate system. However, recent findings suggest that their impact on atmospheric warming may be greater than previously thought.

Condensation trails are formed when aircraft engines propel warm air laden with moisture and soot particles into cold parts of the upper atmosphere. When these emissions interact with cold air, they rapidly cool and condense, forming the characteristic contrails that follow aircraft. What appear to be harmless vapour trails actually harbour a powerful climatic influence.

In 2022, the UN Intergovernmental Panel on Climate Change (IPCC), one of the world's leading authorities on the environment, published a report that shed light on the important role of contrails in the Earth's energy balance. Surprisingly, the report suggested that contrails may contribute more to global warming than the combustion of jet fuel itself. However, this comes with a caveat: the large uncertainties presented by the impact of contrails, which in turn illustrates the lack of scientific understanding and the need for further research.

How do contrails contribute to global warming?

Unlike traditional clouds, which mainly reflect sunlight back into space, cirrus clouds and contrails play a dual role in the Earth's energy balance. During the day, they reflect incoming solar radiation, exerting a cooling effect on the Earth's surface. At night, however, they prevent the Earth's heat from escaping, resulting in a net warming effect.

Addressing the climate impact of contrails presents a large challenge. Unlike emissions from ground-based sources, which can be mitigated through technological advancements and regulatory measures, the formation of contrails depends on complex atmospheric conditions beyond human control. In addition, it is necessary to study whether modifying flight routes to avoid regions prone to condensation trails could result in longer routes, higher fuel consumption and higher operating costs for airlines.

Understanding contrail dynamics is crucial for mitigating aviation's environmental footprint and ensuring a sustainable future. For that the E-CONTRAIL project is integrating cutting-edge AI techniques and climate science into aviation research to bridge gaps in understanding aviation-induced climate impact.