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Airbus explains how aircraft contrails could worsen climate change

In a content published this Friday, March 7, 2025, aerospace manufacturer Airbus explains how aircraft contrails could worsen climate change.

Aviation emits more than just carbon dioxide, so Airbus and the industry as a whole are playing a proactive role in addressing these non-CO2 emissions.

What are they and how can they be mitigated?...Burning fuel creates both carbon dioxide (CO2) and non-CO2 emissions. The main non-CO2 emissions are water vapor and nitrogen oxides, collectively known as NOx. They also include sulfur oxides, carbon monoxide, soot, unburned hydrocarbons and aerosols.

Under certain conditions, water vapor and some non-CO2 emissions can cause contrails—also called condensation trails, or “contrails” for short—which are the white streaks you see behind aircraft at altitude.

They’re essentially cirrus clouds of ice. Although contrails reflect incoming solar radiation and trap outgoing heat, they have a net warming effect on the atmosphere. There’s still uncertainty about the magnitude of the effect, but all climate models agree that it exists.

Difficult to measure... Contrails form when water vapor in an aircraft’s exhaust turns into ice crystals, also encapsulating the non-CO2 emissions in the exhaust.

Their formation and size are influenced by a variety of factors, making their presence difficult to predict with certainty. For example, some ice crystals are larger than others. This is a good thing, because they’re heavier and dissipate more quickly, making the contrail shorter-lived.

Although contrails that cool the atmosphere do exist, most are considered to have a warming effect, including all contrails emitted at night, since there is no sunlight to reflect back into space (cooling effect), leaving only the effect of keeping Earth’s heat from escaping back into space (warming effect).

While only 10%-15% of aircraft contrails are persistent and most last only a few hours, they can exacerbate climate change by trapping heat radiating from the Earth’s surface. Their length can be significant: the average contrail is 150 kilometers long, equivalent to about ten minutes of flight time.

Balancing CO2 and non-CO2 impacts...The effect of non-CO2 emissions on the climate can be mitigated by accurately predicting the conditions under which contrails will form and persist. This allows flights to navigate around, below or above the most likely locations for contrail formation, if air traffic control allows. However, these alternative trajectories are occasionally longer, increasing both CO2 emissions and the cost of operating the flight. This is a delicate balance, but it only concerns a limited number of flights. It is estimated that just 10% of flights, mainly long-haul, create 80% of warming contrails. 

To reduce or mitigate the impact of these flights, the aviation industry is accelerating research into the most effective solution, with many collaborations combining research with testing of solutions. Indeed, in the context of the European Union-funded SESAR Joint Undertaking, Airbus is leading CICONIA, a project that aims to introduce more accurate weather forecasts to help determine optimal flight trajectories and planning. 

In addition, Airbus is involved in several projects that analyze different fuel types and compositions to determine the optimal blend to mitigate non-CO2 emissions. This includes studying all compositions of alternative aviation fuels for CO2 and non-CO2 emissions, and the size of the ice crystals formed from the water vapour they emit.

Airbus emphasises that it is actively working with the research ecosystem to understand the impact of real flights, with different fuel types and trajectories, on the formation of contrails. This will improve the modelling of the impact of contrails in the long term.

Airbus Information