How to Maximize Climate Benefits with current SAF limitations

With the RefMap Project concluding on 30/1/2026, the following post was written by RefMap partner UC3M (Aircraft Operations Lab) to provide an overview of their work and results in the project.

The aviation industry doesn’t have to wait decades for cleaner skies: smarter routes and strategic fuel choices can deliver real climate benefits today. That is a key conclusion of work by researchers at Universidad Carlos III de Madrid (UC3M) conducted as part of the RefMap Project.

Aviation’s climate impact goes beyond carbon dioxide. High-altitude emissions contribute to warming contrails and ozone formation, which together make up nearly two-thirds of the sector’s total climate footprint.

That’s where UC3M’s research comes in. Using a custom-built Flight Planning tool called ROOST V1.0, the team has shown that rerouting flights around climate-sensitive areas, paired with targeted use of Sustainable Aviation Fuels (SAFs), can reduce warming effects without major cost increases or operational disruptions.

Why Targeted SAF Use Makes a Big Difference

SAFs can cut well-to-wake CO₂-equivalent emissions by up to 94%, but they’re in short supply. Rather than blending SAF evenly across all flights, UC3M tested a smarter approach: use SAF only on flights forming strongly warming contrails, leading to reducing their life and thus, climate impact.

This strategic management of contrails is necessary because contrail cirrus clouds have a dual impact on the Earth's energy balance. They trap outgoing infrared heat emitted by the Earth (a warming effect) while simultaneously reflecting incoming solar radiation back into space (a cooling effect). Whether a contrail warms or cools the planet depends heavily on the balance between these two forces at the specific time and location of the flight.

The use of SAF reduces soot emissions, thereby shortening contrail lifetime and decreasing their radiative impact. Thus allocating SAF to flights with the strongest warming potential proves to be a highly effective strategy.

In other words, putting SAF where it matters most is far more effective than spreading it thinly across the entire network.

Results

For the case study, UC3M conducted a year-long optimization under a constant traffic scenario comprising the 150 busiest European routes.

The results indicate that a modest increase in operational cost can lead to a substantial reduction in the climate impact of contrails, primarily by avoiding the formation of warming contrails and, where possible and intended, enabling the formation of cooling contrails. The seasonal analysis reveals that during winter, contrail formation is generally avoided due to its predominantly warming effect driven by reduced daylight hours. In contrast, during spring, the increased solar radiation enables the strategic formation of cooling contrails.

Since the use of SAF reduces soot emissions, thereby shortening contrail lifetime and decreasing their radiative impact, allocating SAF to flights with the strongest warming potential proves to be a highly effective strategy. This targeted use can enhance contrail-related climate mitigation by 30–40%, regardless of whether a cost-optimal or climate-optimal strategy is employed.

Importantly, this level of mitigation is achieved using only 2% SAF (the target for 2025), though through targeted allocation. Notably, increasing the total SAF usage does not necessarily yield proportionally greater mitigation of contrail-induced climate effects.

What’s Next: A New Framework on the Horizon

UC3M is now preparing a new journal paper titled Aircraft Trajectory Optimization and Sustainable Aviation Fuels. The paper introduces a decision-making framework that blends climate-optimized routing and SAF use in a targeted, operationally feasible way, ensuring that every drop of cleaner fuel and every altered flight path delivers the maximum environmental return.

“We’re not just looking at what helps the climate — we’re looking at what works now,” said researcher Abolfazl Simorgh.

See the RefMap Climate Change Tool