If you’re using a carbon footprint calculator to assess your flight’s environmental impact, prepare for some surprises. The true effect of air travel can be significantly higher than what most CO₂ calculators indicate.

“These figures are quite alarming,” states Juma Sadukhan from the University of Surrey, UK. She and her team assessed four popular calculators against the one they developed.

For instance, consider a first-class flight on a B777 from Singapore to Zurich. At the time of this research, calculators from the International Civil Aviation Organization (ICAO) and the International Air Transport Association (IATA) estimated the emissions to be around 3000 kilograms of CO₂. In contrast, the Google Travel Impact Model (TIM) places the estimate around 5,000 kg, while MyClimate suggests about 8,000 kg. However, the in-flight emissions calculator developed by Sadukhan and her team estimates the actual emissions exceed 14,000 kg.

“The implications are substantial,” adds team member Eduardo Goan, in collaboration with the Austria-based Therme Group.

The new tool, called the Airline Passenger Dynamic Emissions Calculator (ATP-DEC), diverges from existing calculators in two main ways. Firstly, instead of assuming flights take a perfect route, it utilizes historical data to ascertain the most probable route, actual flight duration, and the time spent taxiing before takeoff and after landing, including the typical occupancy of the aircraft.

Unlike other calculators, this one is dynamic, as past flight data is continuously updated according to Goan. For example, many flights are now taking longer paths due to the conflict between Russia and Ukraine, a change that other calculators fail to recognize.

The second key difference is that ATP-DEC accounts for all the known factors influencing flight’s climate impact, such as contrail formation, nitrogen dioxide emissions, and water vapor. Notably, contrails can exert a greater warming influence than CO₂ emissions alone.

Other flight calculators often omit these factors or use generalized data. “They don’t adjust according to the type of aircraft, fuel efficiency, or environmental conditions,” says Sadukhan. “Our tool is far more comprehensive.”

Goan mentions that the team plans to make this calculator publicly accessible and is working on an app slated for release early next year. “If an airline wishes to incorporate ATP-DEC, they could start immediately,” he says, though establishing the necessary data connections might take weeks or even months.

Current flight emissions calculators may allow travelers to voluntarily contribute a modest fee to “offset” their carbon footprint. Nonetheless, several studies indicate that many offset programs fail to fulfill their claims.

An ICAO representative stated that the methodology for ICAO’s carbon emissions calculations can be accessed at: its website. “This calculator does not consider the climate change impacts of aircraft emissions using radiative forcing indices.” They noted that “Such multipliers need to be factored in, given the lack of a scientific consensus.”

“TIM is a free, precise, and transparent resource that assists consumers in selecting flights with lower emissions,” affirmed Dan Rutherford from the International Clean Transportation Council, a nonprofit organization that guides Google on enhancing its CO₂ calculator. “We will keep refining the model, including the integration of short-lived climate pollutants like contrails, to enhance its utility for the flying public.”

“We find this study to be a valuable contribution to the ongoing dialogue,” stated Kai Landwehr from MyClimate. Landwehr emphasized that no single method is foolproof due to the uncertainties surrounding the impacts of global warming, such as those resulting from contrails. However, utilizing improved and current data can boost accuracy. “We intend to update the calculator in the upcoming months to integrate best practices and insights from this research.”

IATA has also been approached for comments.