Your flight emissions are way higher than carbon calculators suggest

If you've used carbon emissions calculators to estimate the impact of the flights you take, brace yourself. The true impact of your flight may be several times higher than what conventional CO₂ calculators suggest.

“The numbers are shocking,” says Juma Sadukhan at the University of Surrey in the UK. She and her colleagues compared the numbers from four existing calculators with the results from one they created.

For example, let's say you're flying first class from Singapore to Zurich on a B777. At the time of the study, flight calculators from the International Civil Aviation Organization (ICAO) and the International Air Transport Association (IATA) estimated that it would emit the equivalent of about 3,000 kilograms of carbon dioxide. Google's Travel Impact Model (TIM) put it at around 5,000kg, while MyClimate put it at around 8,000kg. But according to a flight emissions calculator created by Sadhukhan and her colleagues, the actual amount is more than 14,000 kg.

“The impact is much higher,” says a team member Edward Gaughan University of Surrey and Therme Group, a spa company based in Austria.

The new calculator, called the Airline Passenger Dynamic Emissions Calculator (ATP-DEC), differs from existing ones in two ways. First, rather than assuming a flight follows an ideal route, it uses data from past flights to estimate the most likely route, flight time and time spent taxiing before takeoff and after landing, and how full the plane is likely to be.

“Unlike other calculators, this one is dynamic in the sense that past flight data is constantly updated,” says Gaughan. For example, many flights are taking longer routes because of Russia's war with Ukraine—something other flight calculators still don't take into account, the researchers say.

The second key difference is that ATP-DEC takes into account all known ways that flights affect the climateincluding contrail formationnitrogen dioxides and water vapor. Traces, for example, may have a greater warming effect than CO₂ emissions from an airplane.

Other flight calculators either don't take these factors into account at all or use an average. “They do not change depending on the aircraft, fuel conditions or external conditions,” says Sadhukhan. “Ours is more comprehensive.”

Gaughan says the team will make its calculator available to others and will also develop an app that will be released early next year. “If an airline wants to integrate ATP-DEC, we can start tomorrow,” he says. But it can take weeks or months to set up the necessary data feeds.

Flight emissions calculators sometimes offer passengers the opportunity to voluntarily pay a small fee. “compensate” for your emissions. However, some studies have concluded that many compensation schemes don't keep their promises.

An ICAO representative said that the ICAO carbon emissions calculation methodology can be found on the website his website. “The calculator does not quantify the impact of aviation emissions on climate change using the radiative forcing index. [a measure that accounts for non-CO2 gases] or other similar multipliers as scientific consensus has not yet been reached,” they said in a statement.

“TIM is an accurate, transparent and free resource that helps consumers choose lower-emission flights,” says Dan Rutherford of the International Council on Clean Transportation, a nonprofit that is helping advise Google on improving its CO₂ calculator. “We continue to refine the model, including the inclusion of short-lived climate pollutants such as contrails, to maximize its usefulness for flying passengers.”

“We appreciate this study as a valuable addition to the ongoing debate,” says Kai Landwehr in MyClimate. Uncertainty about the warming from, say, contrails means that no method can claim to be absolutely accurate, but using better, more up-to-date data will improve accuracy, Landwehr says. “We plan to update our calculator in the next couple of months and intend to incorporate the best practices and current knowledge outlined in this study.”

IATA has also been contacted for comment.