{"id":8914,"date":"2026-04-29T17:25:45","date_gmt":"2026-04-29T16:25:45","guid":{"rendered":"https:\/\/www.greenairnews.com\/?p=8914"},"modified":"2026-04-29T17:25:48","modified_gmt":"2026-04-29T16:25:48","slug":"european-aviation-non-co2-research-report-highlights-uncertainties-and-knowledge-gaps","status":"publish","type":"post","link":"https:\/\/www.greenairnews.com\/?p=8914","title":{"rendered":"European aviation non-CO2 research report highlights uncertainties and knowledge gaps"},"content":{"rendered":"\n

A non-CO2 expert task group set up by the European Union Aviation Safety Agency (EASA) has published a report that highlights key knowledge gaps and uncertainties surrounding the scientific understanding of aviation non-CO2 effects on the climate. The report by Task Group 4 of the Aviation Non-CO2 Expert Network (ANCEN) synthesises the current state of understanding and while acknowledging the non-CO2 effects are known to contribute a large fraction of the aviation sector\u2019s effective radiative forcing, it says the associated uncertainties remain substantially higher than for CO2. It identifies priority areas where further research is needed. The report coincides with published outcomes from contrail avoidance trials carried out by Thales and French aircraft operator Amelia and also Google, Flightkeys and American Airlines.<\/strong><\/p>\n\n\n\n

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With funding from the EU\u2019s Horizon Europe research and innovation programme, ANCEN<\/a> was established by EASA in 2024 in response to the growing interest in reducing the climate impact from aviation non-CO2 emissions and will run until Q3 2027. With a European network of experts, its objective is \u201cto provide technical support on the development, agreement and implementation of effective action within Europe and internationally to mitigate the overall climate impacts from aviation taking into account both CO2 and non-CO2 emissions.\u201d<\/p>\n\n\n\n

Stakeholder groups represented in the network include the scientific community, academia, aircraft manufacturers, aircraft operators, fuel producers, air navigation service providers, NGOs, regulators, analysts and policymakers. There are seven task groups in all, with Task Group 4 responsible for investigating the gaps and uncertainties on aviation non-CO2 climate effects. Its new report<\/a> was led by Dr Ulrike Burkhardt of DLR (the German Aerospace Center) and Professor David S. Lee of Manchester Metropolitan University.<\/p>\n\n\n\n

The report reviews the main sources of uncertainty across four major areas: contrails and contrail-cirrus clouds, indirect aerosol effects, NOx impacts on atmospheric composition and smaller direct forcing components such as sulphur, soot and water vapour.<\/p>\n\n\n\n

It explains how the uncertainties arise from incomplete knowledge of the background atmosphere, gaps in observational data, limitations in process understanding and the way key processes are represented in climate models.<\/p>\n\n\n\n

Mitigation challenges include the fact that options to reduce non-CO2 impacts do so at the expense of increasing another, typically CO2. There are also large differences in the lifetime of aviation\u2019s climate change components, ranging from hours to thousands of years, plus there is an unclear time horizon for which the climate impact is to be reduced and what the report describes as the associated ethical implications.<\/p>\n\n\n\n

\u201cThe identified uncertainties must be considered in order to support the evaluation of mitigation strategies,\u201d say the authors.<\/p>\n\n\n\n

The report develops and outlines the first stage of a way forward, consisting of a prioritisation of research needed to tackle the different areas of uncertainty.<\/p>\n\n\n\n

\u201cThe prioritisation cannot be simply based on a rough estimate of the size of the uncertainty but rather needs to balance high priority uncertainties with tractable potential ways forward, that is to say an assessment of areas in which progress is likely from new observations, process understanding and modelling approaches,\u201d it asserts.<\/p>\n\n\n\n

It adds that much of the modelling studies of contrail cirrus and the aerosol-cloud interactions has been based upon \u201ca fairly basic state of modelling\u201d, and that until recently, only a few models for contrail cirrus have been available, \u201cleading to large uncertainties\u201d.<\/p>\n\n\n\n

The authors recommend a follow-up report be undertaken to identify mitigation options and pathways, and \u201cto clearly separate the inherent science uncertainties identified in this report from additional uncertainties arising from the mitigation approaches \u2026\u201d.<\/p>\n\n\n\n

\u201cProgress in estimating the climate impact of aviation emissions and devising and evaluating mitigation options can only come from a cooperation of scientists working in many areas, ranging from measurements, process and climate modelling to ethics,\u201d they conclude.<\/p>\n\n\n\n

Meanwhile, trials continue to take place where flights are re-routed to avoid the formation of contrails.<\/p>\n\n\n\n

Aerospace technology giant Thales and French airline Amelia launched an initiative in 2024 in which some flights between Paris and Valladolid in Spain had their flight plans modified by changes to an aircraft\u2019s altitude. The initiative is part of the DECOR project, which is supported by the France 2030 investment plan.<\/p>\n\n\n\n

Out of 6,400 flights operated in 2025, the plans for 59 flights were chosen to be modified for their high-impact potential. After modelling analysis, the partners now estimate<\/a> 2,000 to 2,500 net tonnes of CO2e were avoided at the expense of 0.1% of additional fuel consumption. This is based on radiative forcing modelling that shows the contribution of contrails to global warming to be of the same magnitude as CO2, although the partners acknowledge the warming mechanisms associated with the two effects are very different.<\/p>\n\n\n\n

Amelia said it intends to continue deploying contrail avoidance into its flight planning tools during 2026.<\/p>\n\n\n\n

The contrail avoidance trial involving American Airlines, Flightkeys, Contrails.org and Google is covered in a study<\/a> published in March. The goal of the trial, conducted over a 17-week period in early 2025, was to reduce observable contrail formation on the airline\u2019s North Atlantic network using a satellite-based validation system rather than relying on modelling results.<\/p>\n\n\n\n

Researchers and technology providers worked with the airline to test contrail-aware flight planning on more than 2,400 transatlantic flights, with around half the flights randomly assigned to do the testing, while the rest served as a control group. As the trial was voluntary, dispatchers released contrail flight plans for around 15% of the eligible flights and only 112 flights actually flew the optimised plan. In interviews conducted after the trial, dispatchers cited several operational reasons for not using the plans more often, including workload, turbulence and weather considerations, preference to stay within the North Atlantic organised track system and limitations in the flight planning interface.<\/p>\n\n\n\n

However, for those flights that followed the plan, geostationary satellite observable contrail formation fell by around 62%, with an estimated 69% reduction in contrail warming.<\/p>\n\n\n\n

\u201cThe results provide strong evidence that navigational contrail avoidance is physically effective and operationally feasible,\u201d concludes the study.<\/p>\n\n\n\n

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Photo: DLR<\/strong><\/p>\n\n\n\n

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Christopher Surgenor<\/strong>
Editor<\/p>\n\n\n

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