NTNU researchers used actual flight data, such as the kind shown in this screenshot from Flight Radar 24, combined with information about the plane and engine types to calculate the aviation-related greenhouse gas emissions from 197 countries in 2019. Screenshot: https://www.flightradar24.com/

Climate emissions from air travel 50 per cent higher than reported

A new study that looked at nearly 40 million flights in 2019 was able to calculate the greenhouse gas emissions from air travel for nearly every country on the planet. At 911 million tonnes, the total emissions from aviation are 50 per cent higher the 604 million tonnes reported to the United Nations for that year.

For the first time ever, researchers have harnessed the power of big data to calculate the per-country greenhouse gas emissions from air travel for 197 countries covered by an international treaty on climate change.

When countries signed the 1992 United Nations Framework Convention on Climate Change treaty (UNFCCC), high-income countries were required to report their aviation-related emissions. But 155 middle and lower income countries, including China and India, were not required to report these emissions, although they could do so voluntarily.

This matters because the United Nations Framework Convention on Climate Change relies on country reports of emissions during negotiations on country-specific emissions cuts.

“Our work fills the reporting gaps, so that this can inform policy and hopefully improve future negotiations,” says Jan Klenner, a PhD candidate at NTNU’s Industrial Ecology Programme and the first author of the new article, which was recently published in Environmental Research Letters.

air travel

Jan Klenner was the first author of a new paper that provides the first-ever inventory of aviation emissions on a country-by-country basis. Photo: NTNU

The new data show that countries such as China, for example, which did not report its 2019 aviation-related emissions, was second only to the United States when it came to total aviation-related emissions.

“Now we have a much clearer picture of aviation emissions per country, including previously unreported emissions, which tells you something about how we can go about reducing them,” said Helene Muri, a research professor at the Norwegian University of Science and Technology’s Industrial Ecology Programme. Muri was one of Klenner’s supervisors and a co-author of the paper.

Big surprises – or not

As might be expected, the United States is at the top of the list of emitters when it comes to the total sum of aviation emissions for both international and domestic flights.

Here’s an example of how the new model, AviTeam, can fill important knowledge gaps. The map on the top shows the international aviation emissions that were reported to the United Nations in 2019 under the UNFCCC treaty. The lower map shows international aviation emissions from 197 countries, including those who did not report in 2019, based on the AviTeam model.  The bar graph on the bottom shows the 30 top emitters from international travel.  Illustration: Klenner et al., 2024.

“When we looked at how emissions are distributed per capita, we could see that economic well-being leads to more aviation activity,” Klenner said.

That analysis also showed that wealthy Norway, with just 5.5 million people, was third place overall, just behind the US and Australia, when domestic emissions were calculated on a per-capita basis.

Helene Muri air travel emissions

Helene Muri, a research professor at NTNU’s Industrial Ecology Programme. Photo: Titt Melhuus

Klenner tested the model he developed for this analysis by using data from Norway.  He published a paper reporting those results in 2022.

You might think that Norway’s geography – a long, narrow country with lots of mountains and a sparsely populated northern area – would be the culprit behind the numbers.

But Klenner’s 2022 analysis showed that fully 50 per cent of Norway’s domestic flights were between the country’s major cities, Oslo, Trondheim, Stavanger, Bergen and Tromsø.

“The per person emissions in Norway were incredibly high,” Muri, who also co-authored that paper, said.  “With this data set we can confirm that from a Norwegian perspective we have a lot of work to do, because we are third in the world when it comes to emissions per person from domestic emissions.”

A role for big data

Anders Hammer Strømman, a professor at NTNU’s Industrial Ecology Programme and Klenner’s co-supervisor, said one important aspect of the study is that it shows how big data can be used to help in regulating climate emissions. Strømman was also a co-author of the new paper.

“I think it very nicely illustrates the potential in this type of work, where we have previously relied on statistical offices and reporting loops that can take a year or more to get this kind of information,” he said. “This model allows us to do instant emissions modeling – we can calculate the emissions from global aviation as it happens.”

The model, called AviTeam, is the first to provide information for the 45 lesser-developed countries that have never inventoried their greenhouse gas emissions from aviation. Strømman says the model provides these countries with information that might be otherwise difficult or impossible for them to collect.

Anders Hammer Strømman, a professor at the Industrial Ecology Programme. Photo: Geir Mogen/NTNU

The ability to calculate nearly real-time aviation emissions could also provide an important tool as the industry makes changes to de-carbonize.

“In the transition where we’re talking about the introduction of new fuels
and new technologies, this type of big data allows us to identify those types of corridors or operations where it makes sense to test those strategies first,” Strømman said.

This research has been financed by FME NTRANS – Norwegian Centre for Energy Transition Strategies – NTNU.

Reference: Klenner, Jan; Muri, Helene Østlie; Strømman, Anders Hammer. (2024) Domestic and international aviation emission inventories for the UNFCCC parties. Environmental Research Letters