Have a question?
How do national governments calculate their share of greenhouse gas emissions from international air travel?
They don't—emissions from international flights are counted separately from any one country's emissions. But there are several ideas to change this.
November 28, 2022
Every year, countries report their national greenhouse gas emissions to the United Nations Framework Convention on Climate Change (UNFCCC), which established an international agreement for combating climate change. Included in these reports, or “national inventories,” are emissions from domestic air travel—but not emissions from international flights.
Instead, these emissions are included in a category called “bunker fuels,” together with emissions from international shipping, which is reported separately to the UNFCCC.
Considering the contribution of air travel to global CO2 emissions—about 2.5% of all emissions from burning fossil fuels1—it may come as a surprise that international travel often goes unmentioned in climate change agreements, such as the 2015 Paris Agreement. But these agreements are based on each country taking responsibility for reducing the emissions that occur within its borders, explains Jörgen Larsson, a researcher of sustainable consumption at Chalmers University of Technology in Gothenburg, Sweden. “This means that it is not obvious who should take responsibility for emissions from international aviation,” Larsson says.
This doesn’t mean, however, that no one is thinking about how emissions from international air travel should be credited to individual countries. In 1996, the UNFCCC listed eight allocation options for international bunker fuels, including based on where the fuel was sold, the country where the aircraft is registered, and the country of departure or destination.2
Each approach has pros and cons. Allocation based on fuel sales would credit more emissions to countries with large air travel hubs, such as the U.K. and Germany, and fewer to countries with no such hubs—even those whose residents are big international travelers.
Using country of departure is straightforward, but may overstate emissions from tourism hot spots like Iceland and Portugal. Iceland, for instance, emitted 3.5 tons of CO2 per person from international aviation in 2018; but when adjusted for tourism, this number falls to around 1 ton of CO2 per person, according to analysis by Our World in Data.3
One strategy to get around these challenges is to credit emissions based on passengers’ country of residence. Using Sweden as a case-study for this method, Larsson and colleagues found that international air travel by Swedish residents emitted the equivalent4 of 11 million tons of CO2 in 2014.5 This is similar to the country’s annual emissions generated by cars and much higher than the emissions from Sweden’s domestic air travel (0.9 million tons of CO2 equivalent).
Why does this matter? Like many wealthy countries, Sweden has much higher rates of international air travel than the global average. Larsson says that even if Sweden adopted a number of more sustainable travel technologies, like hydrogen fuel and high-speed rail, these wouldn’t be enough to meet global climate goals.6 “This means that air travel volumes must decrease if the aviation sector shall contribute to meeting this target.”
According to the United Nations, yearly emissions need to drop to between 2 and 2.5 tons of CO2 per person by 2030 to meet our global climate goals.7 Use any calculator that shows the per-person emissions from air travel—and there are many, developed by airlines, researchers, carbon offseters and more—and you’ll see that even one international flight eats quickly into this total.
For instance, the International Civil Aviation Organization (ICAO)’s Carbon Emissions Calculator shows that one passenger flying economy from Los Angeles to London and back will generate 880 kg of CO2.8 That’s between 35 and 45% of the per-person emissions budget laid out by the United Nations. And that’s just for one round trip.
Whatever allocation strategy and calculator is adopted, having a shared, worldwide system to equitably credit emissions from international air travel would provide decision-makers with the data and incentives they need to do something about this large contributor to climate change.
Thank you to Fran Butera of Honolulu, Hawaii, for the question. You can submit your own question to Ask MIT Climate here.
1 The International Council on Clean Transportation: "CO2 emissions from commercial aviation, 2018." September 19, 2019.
2 United Nations Framework Convention on Climate Change: "Communications from Parties Included in Annex I to the Convention: Guidelines, Schedule and Process for Consideration." Section III: Allocation and Control of International Bunker Fuels. June 25, 1996.
3 Our World in Data: Where in the world do people have the highest CO2 emissions from flying? November 9, 2020.
4 Like many activities that contribute to climate change, flying emits a mix of CO2 and other greenhouse gases. These are converted to "CO2 equivalent emissions" for ease of comparison.
5 Larsson, Jörgen, et al. "Measuring greenhouse gas emissions from international air travel of a country's residents methodological development and application for Sweden." Environmental Impact Assessment Review, Vol. 72, Sep. 2018. doi:10.1016/j.eiar.2018.05.013
6 Åkerman, Jonas, et al. "Low-carbon scenarios for long-distance travel 2060." Transportation Research Part D: Transport and Environment, Vol. 99, Oct. 2021. doi:10.1016/j.trd.2021.103010
7 UN Environment Programme: "Emissions Gap Report 2020." Chapter 6, "Bridging the gap—the role of equitable low-carbon lifestyles." December 9, 2020.
8 International Civil Aviation Organization: ICAO Carbon Emissions Calculator. Utilized November 28, 2022.