Air travel, the most carbon-intensive mode of transport
Among all modes of transport, air travel is by far the one that emits the most greenhouse gases per kilometer traveled per passenger. A round-trip Paris-New York flight generates an average of 1.7 tonnes of CO₂ equivalent per passenger in economy class — nearly 20% of the average annual carbon footprint of a French person. And if you travel in business class, multiply that figure by 2.5 to 4, because you occupy much more space on the plane.
The impact of air transport is not limited to CO₂ alone. Contrails, nitrogen oxide emissions at high altitude, and cirrus cloud formation amplify the warming effect by an estimated factor of 2 to 4. In other words, the real climate impact of aviation is two to four times higher than CO₂ alone would suggest.
How much CO₂ does your flight emit?
Emissions vary considerably depending on the route, the aircraft, the airline, and the class. Here are some representative examples for a round trip in economy class, calculated using the ADEME methodology:
- Paris — Marseille: 185 kg of CO₂e (compared to 3 kg by TGV high-speed train)
- Paris — Barcelona: 220 kg of CO₂e
- Paris — London: 200 kg of CO₂e
- Paris — New York: 1,700 kg of CO₂e
- Paris — Bangkok: 3,200 kg of CO₂e
- Paris — Sydney: 4,800 kg of CO₂e
These figures include the radiative forcing index (RFI), which accounts for the amplifying effects of flying at high altitude. Without this factor, the figures would be roughly half — but would underestimate the real impact.
How to calculate the emissions of your flight?
Available tools
Several online tools allow you to calculate the emissions of your flights:
- Mon Impact Transport (ADEME): the French reference tool, transparent about its calculation methodologies
- myclimate.org: a recognized Swiss calculator, used by many airlines
- ICAO Carbon Emissions Calculator: the official tool of the International Civil Aviation Organization
- Atmosfair: a German organization offering a detailed calculation with RFI factor
Parameters that influence the calculation
- Travel class: business class = 2 to 3 times more emissions per passenger than economy
- Aircraft type: an Airbus A350 or Boeing 787 emits 25% less per seat than a 747
- Load factor: a half-empty flight doubles the footprint per passenger
- Stopovers: takeoff and landing phases are proportionally the most carbon-intensive
Should you offset your flights?
Carbon offsetting for flights is a divisive topic. On one hand, it helps fund useful climate projects and raises awareness of the impact of travel. On the other, it risks providing a clear conscience without actually reducing aviation emissions.
"Carbon offsetting cannot be an excuse to keep flying as if nothing were wrong. It must accompany a deep reflection on our travel habits." — Manifeste Pour un Réveil Écologique
The most consistent position is as follows: avoid avoidable flights, reduce the number of flights, and offset residual emissions with quality projects.
Certified offset programs for flights
Airline offerings
Most major airlines now offer offset options at the time of ticket purchase. Air France offers its "Air France KLM CO₂ Neutral" program, and Easyjet once offset all of its flights. However, the quality of these offsets is highly variable and often lacking in transparency.
Golden rule: do not blindly trust offsets offered by airlines. Always verify which standard certifies the funded projects.
Recommended independent organizations
- Atmosfair: a German non-profit organization, recognized by ADEME. Gold Standard certified projects, with a focus on energy efficiency in developing countries.
- myclimate: a Swiss foundation, Gold Standard and VCS projects, with a wide range of projects and detailed reports.
- South Pole: a major market player, with VCS, Gold Standard, and Label Bas-Carbone certified projects.
- Pure Leapfrog: specializing in energy efficiency projects in emerging countries.
The cost of offsetting a flight
As an indication, here are the offset costs by route, using Gold Standard projects at approximately 25 euros per tonne:
- Paris — Barcelona round trip: approximately 6 euros
- Paris — New York round trip: approximately 43 euros
- Paris — Bangkok round trip: approximately 80 euros
- Paris — Sydney round trip: approximately 120 euros
Alternatives to flying: the real solution
The best offset is the flight that never happens. Before offsetting, ask yourself: is this trip essential and, if so, can it be done by another means?
The train: the obvious alternative for medium-haul trips
In Europe, the high-speed rail network connects most major capitals in under 5 hours. Paris — London (2h20 by Eurostar), Paris — Amsterdam (3h30 by Thalys), Paris — Barcelona (6h30 by TGV), Paris — Milan (7h30). For distances under 1,000 km, the train is often competitive in door-to-door travel time and infinitely less impactful on the climate.
Long-distance coach
For tight budgets and flexible travelers, long-distance coaches (Flixbus, BlaBlaCar Bus) emit approximately 30 gCO₂/km per passenger — three to four times less than flying on comparable routes.
Slow travel and fewer but longer trips
Rather than taking three short weekend flights a year, consider a single longer trip by land. This approach reduces your footprint while deepening the travel experience.
For a comprehensive overview of alternatives to flying, see our article: Low-carbon travel: all the alternatives to flying.
The future: does sustainable aviation exist?
The aviation industry is banking on several technologies to decarbonize the sector:
- Sustainable Aviation Fuels (SAF): produced from biological waste or by synthesis, they can reduce emissions by 50 to 80%. But their production remains marginal (less than 1% of fuel used today) and their cost is prohibitive.
- Hydrogen aircraft: Airbus is targeting 2035 for its first models. Technologically promising but limited to short-haul flights in the medium term.
- Electric aircraft: limited to very short distances and small aircraft for several more decades.
The reality is that we will have to wait until at least 2035-2040 to see significantly less carbon-intensive commercial aircraft. Until then, reducing air traffic remains the only effective short-term lever.
To understand all the mechanisms of carbon offsetting and choose quality projects, read our complete guide: Carbon offsetting: the complete guide to understanding and taking action.
Conclusion: fly less, travel better
Carbon offsetting for flights is a legitimate and useful approach, provided it is done rigorously and does not serve as an alibi for multiplying air travel. The climate equation is simple: every avoidable flight that does not take place is infinitely more effective than an offset flight. Combine reduction and offsetting, choose quality certified projects, and make travel a more conscious experience.