Mitigation Strategies
Navigating the Path to Mitigation: Current Strategies and Innovations
Addressing the significant climate impact of aviation contrails requires a multi-faceted approach, encompassing both operational adjustments to flight management and technological advancements in fuels and propulsion. This section evaluates the primary strategies under investigation and development, examining their potential efficacy and practical challenges, with a particular focus on UK- and EU-led initiatives. Broadly, two avenues are being pursued: intelligently re-routing flights to prevent contrail formation in the first place, and reducing contrails at their source by cutting soot emissions through cleaner fuels and engines.
Operational Measures: Promise and Practicalities of Contrail Avoidance
The most actively explored near-term operational strategy involves modifying aircraft flight paths to avoid atmospheric regions conducive to the formation of persistent, warming contrails. Small altitude or route adjustments – climbing or descending a few thousand feet, or minor lateral deviations – can sometimes keep an aircraft out of an ISSR where contrails would form. Such diversions can be planned pre-flight (during flight planning) or made tactically in-flight based on real-time information or short-term forecasts.
Flight Path Optimization and ISSR Avoidance
Numerous trials and research projects are underway in Europe and globally to test the feasibility and effectiveness of contrail avoidance. Notable examples include Eurocontrol’s Maastricht UAC (MUAC) trials – which in 2024 conducted a live operational trial with German airlines involving over 100 contrail-avoiding flights – providing insights into dispatching contrail-optimized flight plans and air traffic controller (ATC) preferences for planned vs. tactical avoidance maneuvers. The SESAR CICONIA project (2023–2026), involving Airbus, NATS, Eurocontrol, several airlines (Air France, Swiss, easyJet), and research institutions, is developing concepts of operations for contrail mitigation; early results suggest that with appropriate procedures, operational mitigation could be applied to many flights, effectively reducing contrail impact without significant air traffic disruption. In the UK, NATS (the air navigation service provider) has led North Atlantic trials and is contributing to CICONIA, focusing on contrail mitigation in the busy North Atlantic flight corridor. Airlines such as Air France (with Météo-France) have also run trials rerouting around predicted contrail-prone areas.
Challenges: Despite promising findings, operational mitigation faces significant challenges. Altering flight paths often results in longer routes or suboptimal altitudes, causing increased fuel burn and CO2 emissions – a trade-off between reducing short-term contrail warming at the expense of higher long-term CO2 output. The net climate benefit depends on the metric and time horizon considered (e.g. 20-year vs 100-year GWP); some studies (e.g. by NATS) suggest contrail avoidance can yield a net climate benefit, but only if carefully managed. Other challenges include forecasting accuracy (to predict ISSR locations reliably), potential airspace capacity and ATC workload impacts when many flights need level changes, and ensuring any altitude changes do not compromise safety or conflict with other traffic. These complexities mean operational contrail avoidance must be implemented cautiously and often opportunistically (“low-regret” moves when conditions allow).
Advances in Forecasting and Real-Time Avoidance
Key to operational measures is improving our ability to predict contrail-forming regions. Ongoing research is focused on higher-resolution and more accurate forecasts of ISSRs, as well as real-time detection of ambient conditions. Improved on-board humidity/temperature sensors and AI/ML-enhanced prediction models are under development to give pilots and dispatchers better tools for contrail avoidance decisions. For example, the UK’s Contrail Forecasting and Analysis (COFA) initiative (hypothetical example) aims to integrate satellite data and atmospheric models to alert flights of contrail risk in their planned route. While promising, these efforts are still evolving, and forecasting uncertainties remain a major constraint on wide-scale operational contrail mitigation.
Fuel-Based Solutions: Reducing Soot to Reduce Contrails
The more fundamental approach to mitigating contrails is to tackle them at the source: reduce the soot particles that serve as ice-nucleating sites for contrails. This can be achieved by using cleaner-burning fuels with fewer aromatic compounds (which produce soot) or new engine technologies. Studies have shown that using blends of Sustainable Aviation Fuel (SAF) in place of conventional kerosene can cut soot particle emissions by 50–70%, leading to contrails with significantly lower ice particle concentrations and reduced warming impact:contentReference. However, current SAF usage remains very low (only ~0.3% of aviation fuel in 2024:contentReference, and even optimistic projections see perhaps 2–5% of jet fuel being SAF by 2030. Thus, while SAF can play a role, scaling up production and adoption is a challenge.
Lower-Aromatic Fuels and LCAFs
In addition to biofuel-based SAF, another promising avenue is Low Carbon Aviation Fuels (LCAFs) engineered to have low aromatic content even if derived from fossil feedstock. An LCAF is typically defined (by ICAO’s CORSIA) as a fossil-based jet fuel that achieves at least a 10% reduction in lifecycle CO2 emissions compared to conventional Jet A-1:contentReference[oaicite:40]{index=40}. This CO2 reduction is usually achieved via cleaner production processes (renewable energy in refineries, carbon capture, etc.). Notably, if such processes also yield a fuel with lower aromatics or fewer impurities, there can be co-benefits for contrail mitigation:contentReference. Lower aromatics mean less soot formation during combustion, which directly translates to fewer ice nuclei for contrails.
Case Study: DM-XTech’s Low-Aromatic LCAF – A UK Innovation
DM-XTech UK Ltd., a UK-based company, has developed an innovative LCAF specifically designed for very low aromatic content. Independent tests by the University of Sheffield have compared its properties and emissions to standard Jet A-1 fuel. Key properties of DM-XTech's LCAF relevant to contrail mitigation include:
- Low Aromatic Content: ASTM D1319 analysis showed only 8.5% aromatics by volume, substantially below the typical Jet A-1 specification (up to 25%). This dramatic reduction in aromatics is critical, as lower aromatics are directly linked to lower soot formation during combustion.
- Reduced Soot (nvPM) Emissions: Tests using a Honeywell 131-9A Auxiliary Power Unit showed DM-XTech's fuel produced significantly lower non-volatile particulate matter (nvPM) number and mass concentrations than standard Jet A-1:contentReference. Since nvPM is essentially soot, this provides strong evidence that the LCAF generates fewer soot particles (the seeds for contrail ice crystals).
- Other Fuel Properties: The LCAF also has very low olefin content (0.6% vol) and high saturate content (90.9% vol), with a density of 791.4 kg/m³ at 15°C. Trace element analysis indicates generally low levels of contaminants (e.g. very low sulfur); such purity may further contribute to cleaner combustion.
In summary, operational mitigation can deliver near-term contrail avoidance, but is limited by forecast accuracy and trade-offs with CO2. Meanwhile, cleaner fuels and engines tackle the contrail issue at its root by reducing soot. Ultimately, both approaches – smarter flight routing and cleaner combustion – will likely be needed in tandem to achieve substantial contrail warming reductions:contentReference. The next section discusses how current policy frameworks in the UK and EU address (or fail to address) these contrail mitigation strategies.