After years, or even decades, of denial and doubt, the aviation sector is beginning to take a serious look at the problem of contrails, whose heating power is said to be greater than that of CO2. Research and testing are in full swing, and some solutions are beginning to take shape. This is particularly the case with contrail avoidance, which involves slightly altering flight trajectories to avoid cold, humid areas where contrails tend to linger. However, there are still concerns with this solution – we’ll look at them below.

Reducing traffic is the fastest and most effective way to reduce the climate impact of aviation because there is no better way to reduce its overall impact, both in terms of CO2 and contrails. But reducing contrails is proving to be a particularly interesting way to reduce the climate impact of remaining flights because:

The effect is immediate.

It’s a cooling effect (as if CO2 were being removed from the atmosphere), whereas when CO2 emissions are reduced, they do continue but at a lower rate, and therefore increase global heating.

The effect is massive. If all contrails were eliminated, it would be like removing 57 Gt of CO2 from the atmosphere, or 1.7 times the amount emitted by aviation since 1940 (Lee et al. 2021, Table 2). More recently, other researchers (Bickel et al, 2025) have revised downwards the 2021 estimate that was used as a reference, but this does not call into question the need or the benefits of reducing contrails.

It’s fairly easy and inexpensive…

The most widely studied method of reducing contrails is relatively easy and inexpensive compared to the solutions adopted to reduce CO2. It involves slightly modifying the flight paths of the flights expected to pass through cold and humid areas which enable water vapour to condense and form cirrus clouds continuing for several hours.

This method allows for a targeted approach, as only 3% of flights generated 80% of the heating caused by contrails in 2019 (mainly night flights, in winter, in cold areas). It requires little investment and is a no-regrets solution.

Another approach is to reduce the emissions of particles on which water vapour condenses, either by treating fuels or by improving their combustion in aircraft engines. This approach has been less studied, but is no less interesting as it would also reduce air pollution in and around airports.

However, there are still some reservations about avoiding contrails because:

• The benefits only last as long as the procedure is implemented. If, for any reason, it were to be abandoned, all its benefits would be immediately cancelled out.
• Even though it requires little investment, experts believe that it will not be widely implemented for another 10 years, which is too late given the urgency of the climate crisis.
• The aviation sector could be tempted to moderate its efforts to reduce CO2 emissions and use its efficiency as an excuse to avoid traffic reduction measures, which are the only way to curb the deadly accumulation of this long-lived greenhouse gas.
• Airspace congestion will not always allow for the diversion of desired flights (but fortunately, many of the most heating flights take place at night and in winter, when traffic is at its lowest).
• Avoiding areas prone to contrails may slightly increase fuel consumption, and therefore CO2 emissions, but this CO2 penalty remains well below the expected gains.
• Its actual effectiveness is difficult to assess. Observation cannot be used because it is impossible to know what would have happened if the aircraft had not changed its trajectory. We are therefore limited to using mathematical models, the results of which may differ (Martinez et al, 2025).

Let’s avoid contrails – but that doesn’t mean we shouldn’t reduce traffic!

Climate change is serious enough that we cannot afford to ignore a very promising solution that we helped bring to light from the shadows the aviation sector wanted to keep it in. But we cannot put all our eggs in this “easy” basket, which does nothing to reduce CO2 emissions, the accumulation of which will destroy our planet’s climate for centuries. We will therefore continue to insist that, in the absence of a genuine solution for CO2, it is essential not only to halt the irresponsible growth of air traffic, but to drastically reduce it.