You are booking a flight from London to New York. Before you pay, you spot a carbon figure beneath the fare. One platform says 386 kg of CO₂. Another, same route, same day, says 982 kg. A third offers to offset 0.6 tonnes for the price of a coffee. None of them explain their working. You pick the cheapest flight and move on.
This is not a niche problem for environmentalists. It is a basic transparency failure. And it makes it genuinely hard for ordinary travellers to make informed choices about their flight emissions.
Why flight emission numbers vary so wildly
Aviation emissions are complicated. But airlines often use that complexity as an excuse. The real problem is simpler: nobody forces them to use the same method. Right now, no law requires airlines or booking platforms to calculate emissions in a standard way. Everyone picks their own approach. And the choices they make change the number dramatically.
The biggest factor? Most platforms ignore what scientists call non-CO₂ effects. Planes do not just emit carbon dioxide. At high altitude, they also produce water vapour, which forms heat-trapping clouds. They emit nitrogen oxides, which create ozone. These effects do not last as long as CO₂. But in the short term, they roughly double or triple a flight’s total warming impact. Many platforms leave them out entirely. A smaller number looks better for business.
3X
Typical variation in CO₂ estimates for the same flight across platforms
2 – 4X
How much more warming aviation causes beyond CO₂ alone
0
Legally binding international standards for per-flight emissions reporting
Seat class matters too. A business class seat takes up three to four times the floor space of an economy seat. A fair method charges emissions proportionally. Most platforms do not do this. They divide total emissions equally across all seats. So flying business from London to New York is not a 500 kg decision. An honest figure is closer to 2 tonnes.
The type of aircraft and how full it is also make a big difference. A half-empty plane burns more fuel per passenger than a packed one. You almost never see this reflected in the figure on your screen.
A business class seat takes up three to four times the space of economy. Most platforms do not tell you this when they show you a carbon number.
Who sets the rules – and why that is a problem
The main aviation industry body, IATA, publishes its own carbon calculator method. Many airlines use it. But IATA represents airlines – it is not an independent regulator. Critics say its method leaves out non-CO₂ effects and uses average fuel figures rather than real aircraft data. When an industry sets its own measuring stick, the stick tends to be generous.
Other organisations publish stricter methods. The European Environment Agency has one. The UK Government has another. The German nonprofit atmosfair uses one more – and gets much higher figures than the industry does. None of these methods are required by law for consumer-facing information.
WHAT A RIGOROUS ESTIMATE SHOULD INCLUDE
- Actual fuel burn for the specific aircraft type, not fleet averages
- A multiplier for non-CO₂ warming effects (typically 1.7 to 4, depending on method)
- Seat class weighting based on cabin floor space
- Load factor – how many seats were actually filled
- Upstream emissions from producing the fuel, not just burning it
The result is a race to the smallest number. Airlines and platforms compete to show you a figure that will not make you think twice. This is not transparency. It is the appearance of transparency – deployed to achieve the opposite.
How to accurately calculate your flight emissions
The system is not honest yet. But you can still make better decisions.
Start with the atmosfair flight emissions calculator. It is one of the most rigorous free tools available. It applies a full methodology, including non-CO₂ effects. myclimate also offers a free tool and transparently shares their calculation principles based on European standards. Treat any figure from an airline’s own calculator with scepticism. Check whether they even publish their method. If they do not, that tells you something.
Flying business or first class? Multiply the platform’s figure by three. It is a rough adjustment. But it gets you much closer to reality than the figure you were shown.
If you do offset your flight, scrutinise the scheme. Look for Gold Standard or Verified Carbon Standard certification. Avoid schemes based on forestry – trees can burn down, removing the carbon they supposedly stored. No offset can fully undo a flight’s warming. But some schemes are less fictional than others.
Why this is not just your problem – but still worth caring about
You should not have to do any of this. Deciphering competing methods, applying manual corrections, auditing offset schemes – none of this should fall on individual travellers. The right answer is regulated, standardised reporting. One method, independently checked, displayed consistently at the point of sale. With real consequences for non-compliance. The EU is moving in this direction. Others are slower.
But asking the question still matters – even imperfectly. Travellers who interrogate the numbers send a signal. Platforms that lose bookings because they cannot explain their method face pressure to improve. Choosing providers who publish audited figures over those who hide behind averages moves money in the right direction.
Your flight’s footprint is real. The number on the booking page probably is not. Start there.
