Julien Etchanchu, Senior Director, Sustainability Consulting
Maxime Meijers, Co-Founder and CEO, Estuaire
While carbon emissions have long been the benchmark for measuring aviation’s climate impact, they only tell part of the story. Today, non–CO₂ effects are gaining attention as science, regulation, and data capabilities evolve.
This reveals that just focusing on travel-related carbon emissions doesn’t give you a complete view of your environmental impact. To better understand what’s been missing, we sat down with Maxime Meijers, Co-Founder and CEO at Estuaire, a climate tech company specializing in non–CO₂ aviation intelligence, to explore how deeper, flight-level insight can help travel teams make more informed decisions.
Julien: When discussing aviation emissions, carbon usually dominates the conversation, especially in business travel. What are the key non‑CO₂ effects of flying and why do they matter?
Maxime: CO₂ gets most of the attention because it’s the easiest to measure, and remains a dominant driver of aviation’s long term climate affects as it accounts for around two thirds of aviation’s total climate impact. However, the rest comes from effects that happen directly at cruise altitude including: nitrogen oxides (NOₓ), water vapor, soot particles, and persistent warming contrails that form when hot exhaust meets cold, humid air, creating ice crystal clouds that trap outgoing heat for hours. This means in practice, two identical flights can have very different climate impacts depending on the atmospheric conditions at the time they fly. Based on our analysis of 38 million flights in 2025, we estimate around 975 MtCO₂ in direct aviation emissions, with an additional 156 MtCO₂e of warming impact from contrails alone.
These effects matter because, unlike CO₂ which persists for centuries, they are short-lived. This means avoiding them delivers an immediate climate benefit, which matters while we wait decades for full fleet decarbonization.
Julien: You mention a few different emissions sources outside of carbon. Which of these have the biggest climate impact and why?
Maxime: Contrails. These are the thin white cloud-like trails you sometimes see behind airplanes high in the sky. Most models estimate their warming impact is similar aviation-driven carbon emissions, though the figure can vary significantly depending on routing, altitude, timing, and atmospheric conditions.
Julien: With this in mind, what are the risks of ignoring non-CO₂ effects when companies are setting or reporting on travel‑related climate goals?
Maxime: The most immediate risk is that your climate targets become disconnected from your actual impact. Without accounting for your full impact, you could successfully hit your carbon reduction goals and still be contributing to warming at roughly the same rate. Beyond that, the regulatory direction is clear. The EU and ICAO are both moving toward frameworks and initiatives that account for non-CO₂ effects. So, companies that build the measurement capability now will be ready when those requirements become mandatory.
Julien: I agree, a proactive approach is key and we’re excited to partner with Estuaire to bring a new level of transparency on the full climate impact of flying for travel teams. Why do you think most corporate travel programs and data providers today struggle to see or measure non‑CO₂ impacts?
Maxime: It comes down to three key challenges: data availability, methodological complexity, and tooling.
Most travel management systems are built around itinerary data: routes, cabin class, distance, which is enough to provide a clear look in CO₂ impact. But this data alone isn’t enough to get a full picture of the non-CO₂ effects. Accounting for non-CO₂ effects requires flight-level data on altitude, timing, atmospheric, and weather conditions at the route level that most booking tools don’t capture. Also, the science itself is less settled than CO₂ accounting. There’s no single agreed multiplier, which means different methodologies produce different results. So applying an average factor across all flights introduces significant error, given that only 3% of flights generate about 80% of the contrail warming impact. A flight-by-flight approach using weather data is needed to accurately account for these non-CO₂ effects.
Julien: Beyond accuracy like you mentioned, how does our partnership help make non‑CO₂ impacts more visible and actionable for travel teams?
Maxime: The partnership is essentially about closing that data-to-decision gap. Estuaire brings flight-level non-CO₂ modelling grounded in route-specific atmospheric data. Advito brings the travel program integration, the data feeds and the reporting infrastructure. Together, companies can now access non-CO₂ metrics without building that capability themselves, and get a clear view of which routes and travel patterns carry a disproportionate climate impact beyond carbon.
Once you can see which routes and conditions drive the most warming, the decisions follow naturally. It can be as simple as flagging a high-impact departure time or routing and offering an alternative. For instance, avoiding late evening flights when atmospheric conditions are more likely to form persistent contrails, or selecting slightly different flight levels where feasible. Some of the most effective interventions don’t require grounding flights, just better information at the right moment. That’s what this partnership unlocks. At the reporting level, it shifts the conversation from estimates to actual impact, which makes the numbers more accurate.
Julien: Looking ahead, how do you see non‑CO₂ considerations shaping the future of sustainable business travel? Do you see non–CO₂ effects becoming a standard part of travel emissions reporting?
Maxime: I think it’s a question of when, not if. The regulatory signals are already there, the science is crystallizing, and the tooling now exists. What kept non-CO₂ out of standard reporting was that no one required it and it was hard to do well, both of which are changing. What I’d expect to see over the next three to five years is voluntary disclosure to lead, with mandatory requirements following.
Julien: We’ve seen this kind of evolution before in fuel emissions reporting. As regulations and standards advanced, programs moved beyond measuring fuel burned during a flight to also account for upstream fuel emissions. Non‑CO₂ effects represent a similar step forward.
In the past, you’ve worked with airlines and airports directly rather than business travel clients. In your opinion, what’s the main opportunity here?
Maxime: The most effective approach is simultaneous action across the ecosystem, and some airlines have already begun moving in that direction. At Estuaire, we actively work with airlines and airports to help integrate non-CO₂ considerations, such as contrails, into operational and decision-making processes, by evaluating operational constraints like air traffic, routing flexibility, and the potential impact of mitigation strategies on fuel consumption. Most travel managers and sustainability leaders are already familiar with CO₂ emissions, but booking platforms rarely have a practical way to account for non-CO₂ effects, such as contrails, in the options presented. Bridging that gap, by providing reliable data that helps with decision making and engaging airlines, is where the most immediate impact can occur.
As expectations around aviation emissions continue to evolve, understanding climate impact beyond carbon is quickly becoming essential. By bringing non‑CO₂ effects into focus, evaluating how impact varies by route, conditions, and travel patterns, you can start making more informed choices across your programs. Contact our team today to learn more.