Targeting the white trails left by aircraft could delay aviation’s contribution to global warming by around 10 years, according to new research commissioned by Transport & Environment (T&E).
Contrails, the white lines that form behind aircraft flying through cold, humid air, have a climate impact on a similar scale to aviation’s CO₂ emissions, despite being produced by only a small proportion of flights, according to a new review by Klima Consulting.
The report, commissioned by T&E and authored by former IPCC scientist Olivier Boucher, finds that avoiding contrails could significantly reduce aviation’s near-term warming impact. Without action, aviation’s contribution to global warming could reach 0.08°C by 2040. If contrail warming were halved from 2030 onwards, that threshold could instead be reached around 2050.
The researchers estimate that halving contrail warming could avoid around 0.025°C of warming by 2050 and 0.049°C by 2070.
In a 2°C climate pathway, contrail avoidance could effectively free up 3–5 percentage points of the global temperature budget available between 2025 and 2050, which would otherwise be consumed by aviation.
A small number of flights cause most contrail warming
The potential impact is particularly significant because contrail warming is highly concentrated among a relatively small number of flights.
Research cited by T&E found that just 3% of flights were responsible for around 80% of contrail warming in 2019. Many of the flights with the greatest impact take place at night and during winter, when atmospheric conditions are particularly favourable for persistent contrails.
That means airlines do not necessarily need to reroute or reschedule large numbers of flights to make a difference. Changing the altitude or route of selected flights – or operating them at a different time – can prevent the atmospheric conditions needed for persistent contrails to form.
At current traffic levels, halving global contrail warming could avoid an estimated 67 to 225 million tonnes of CO₂ equivalent per year, measured over a 100-year period. T&E says that is equivalent to 7% to 23% of global aviation CO₂ emissions in 2025.
The organisation compares the figure with the annual emissions of between 15 million and 50 million petrol-powered passenger cars.
“Contrails are the low-hanging fruit of aviation decarbonisation,” said Diane Vitry, T&E’s aviation director. She said rerouting or rescheduling a relatively small number of flights could delay aviation’s contribution to global warming by a decade.
Vitry argued that reducing contrails could provide the aviation sector with a “unique window of opportunity” while calling on the industry to act on a measure she said is already known to work and is relatively inexpensive.
Aviation still has no binding contrail rules
Despite the potential climate impact, there are currently no binding measures at either European or global level specifically aimed at reducing aviation’s non-CO₂ climate effects.
T&E says uncertainty over the science has been used as a reason for delaying action. Its new review argues that the scientific evidence is now sufficiently robust for governments to introduce contrail-avoidance measures under the precautionary principle.
The report acknowledges that important uncertainties remain, particularly around humidity forecasting and the real-time verification of contrails using satellites. However, it concludes that these uncertainties should not prevent Europe from beginning to deploy contrail avoidance measures.
The European Commission began monitoring aviation’s non-CO₂ emissions in 2025. As part of its proposed revision of the EU Emissions Trading System, it has also proposed giving airlines free ETS allowances when they successfully avoid contrails.
T&E is calling for the EU to expand its non-CO₂ monitoring scheme to cover all flights from 2027 and for the European Parliament and European Union member states to support the proposed ETS incentives.
First large-scale trial is coming
The technology is now moving from research towards operational testing.
This winter, a consortium involving the United Kingdom government and air traffic control organisations will conduct what is being billed as the world’s first oceanic airspace-scale trial of contrail avoidance. The North Atlantic trial will test AI-driven methods for identifying and avoiding flights likely to generate persistent contrails.
The approach could involve small changes to flight paths or altitudes rather than major changes to airline operations.
But contrail avoidance is not a replacement for cutting aviation’s CO₂ emissions.
The warming benefit lasts only for as long as the avoidance measures remain in place. The report therefore argues that contrail mitigation needs to be combined with sustained reductions in aviation’s CO₂ emissions.
T&E’s recommendations include expanding EU monitoring of non-CO₂ aviation emissions, creating incentives through the EU ETS for airlines that avoid contrails, and directing further research towards the uncertainties that matter most for operational deployment.
The new report, ‘A Way Forward for Contrail Mitigation‘, is based on a review of the current scientific and technological evidence on aviation contrails.
