Press release

Experts expand the coverage of greenhouse gases in Travel Impact Model for flight emissions

JAN 30, 2024 – Today, the International Council on Clean Transportation (ICCT) announced a series of updates to the Travel Impact Model (TIM) that will more fully reflect the environmental impact of aviation and help people make more sustainable choices when planning air travel. The TIM was published by Google in 2022 as a tool to calculate flight emissions at the individual passenger level, and is currently used to display emission estimates on Google Flights, as well as other platforms such as, Expedia, and Skyscanner, through Google’s collaboration with the Travalyst coalition.

The updates were approved during recent meetings of the TIM’s independent Advisory Committee (AC), for which the ICCT functions as Secretariat. The AC is composed of experts from airlines, academia, government, and civil society, and was established in July 2023 to refine the TIM to make it the global standard for accurate, transparent, and consistent emissions disclosure for all fliers.

The following changes were approved by the AC and will be reflected soon in the emissions estimates on platforms using the TIM:

  • Taking into account all 6 Kyoto greenhouse gasses. The AC agreed to expand the scope of the TIM to include all 6 Kyoto gases, especially CO2, CH4 and N2O. This update means that the model will be able to accommodate changes that include climate effects beyond just CO2 emissions, and going forward the model outputs will be labeled as “CO2 equivalent” (CO2e).
  • Including well-to-tank emissions by default. Following the decision to account for all 6 Kyoto gases, the AC decided that the TIM should be expanded to reflect the climate effects resulting from the production and transportation of aviation fuels, commonly referred to as well-to-tank (WTT) emissions. The TIM will follow recommendations from ISO and the International Civil Aviation Organization’s CORSIA program to calculate these WTT emissions. This update sets the stage for crediting airlines that introduce new technologies to reduce GHG emissions, notably sustainable aviation fuel.
  • Integrating belly cargo. The AC determined that the CO2e resulting from a given flight should be apportioned over both passengers and any belly cargo being transported, using an assumed mass of 100 kg per passenger (including baggage) and 50 kg per seat. This decision, which reflects the mass of passenger service equipment, is an interim solution until international standards can be aligned.

“These changes are an important step in making the TIM more comprehensive and futureproof,” said Dan Rutherford, the ICCT’s Aviation Director and head of the TIM Secretariat. “The Advisory Committee will continue work in 2024 to provide even more consistent and transparent emissions estimates to travelers.”

““The Travel Impact Model plays a crucial role in the efforts to decarbonize aviation by accurately and transparently reflecting the full climate impact of air travel,“ said Andrew Chen, Principal for Aviation at independent nonprofit, RMI. “The work done to date is an important step to calculate true flight emissions and will allow for more exact greenhouse gas accounting for fossil and sustainable aviation fuels.”

In addition to the upcoming TIM changes, AC members also agreed to prioritize research on short-lived climate pollutants (SLCPs), specifically contrails. On average, contrails may impact the climate as much as CO2, but there is no consensus way to express that impact to consumers. The AC agreed to prioritize research on  how to differentiate contrail impacts by time, region, and airline and how to comprehensively communicate the impacts of SLCPs to consumers.


For further information on AC membership visit: and ICCT’s earlier press release:

Michael Doerrer and Shraeya Mithal

About the International Council on Clean Transportation 
The International Council on Clean Transportation (ICCT) is an independent research organization providing first-rate, unbiased research and technical and scientific analysis to environmental regulators. Our mission is to improve the environmental performance and energy efficiency of road, marine, and air transportation, in order to benefit public health and mitigate climate change. Founded in 2001, we are a nonprofit organization working under grants and contracts from private foundations and public institutions.