Global aviation emissions could be halved through maximising efficiency gains, new study shows
University of Oxford
A new study co-led by the University of Oxford has found that global aviation emissions could be reduced by 50-75% through combining three strategies to boost efficiency: flying only the most fuel-efficient aircraft, switching to all-economy layouts, and increasing passenger loads. Crucially, the study shows that around a 11% reduction in global aviation emissions is achievable immediately, by using the most efficient aircraft that airlines already have more strategically on routes they already fly.
Published today (7 January) in Nature Communications Earth & Environment, the researchers analysed more than 27 million commercial flights in 2023, covering 26,000 city pairs and nearly 3.5 billion passengers. This revealed enormous variability in emissions efficiency, with some routes producing nearly 900 grams of CO₂ per kilometre for each paying passenger - almost 30 times higher than the most efficient, at around 30 grams of CO₂ per kilometre.
Co-author Dr Milan Klöwer (Department of Physics, University of Oxford) said: “Our results clearly show that efficiency-focused policy could swiftly reduce aviation emissions by more than half, without reducing flight numbers or waiting for future fuels. These are tools that we can use right now.”
Globally, average aviation emissions were 84.4 grams of CO₂ per kilometre for each paying passenger in 2023. But the study identifies three practical levers to reduce this figure: operating only the most fuel-efficient aircraft, removing premium-class seating to carry more passengers, and raising passenger loads to 95%.
Aircraft model alone was found to make a significant difference, with emissions ranging from 60–360 gram CO₂ per kilometre for each passenger. According to the analysis, replacing all aircraft with the most efficient models - the Boeing 787-9 (long-haul) and the Airbus A321neo (short and medium-haul) - would result in fuel savings of 25% to 28%.
Dr Klöwer added: “While economically and practically unfeasible to replace all older aircraft short term, this analysis shows the potential more efficient aircraft have in comparison to other efficiency gains. Realistically, this would be a long-term transition – one that could be promoted by policies that reward efficiency, so that the most efficient aircraft are favoured whenever replacement decisions are made.”
Seating configurations also matter, since business and first-class seats are up to 5 times more CO₂-intense than economy class seats. The researchers found that increasing passenger numbers to the maximum seating configuration for the most efficient aircraft would further reduce emissions by 22% to 57%.
In 2023, aircraft passenger occupancy ranged from 20% to 100%, with an average of 79%. According to the analysis, increasing average occupancy to 95% would further reduce emissions by 16%.
If these three measures were applied globally, the study estimates that emissions could be reduced by between 50% and 75% -though this full reduction would require systemic changes. Nevertheless, the analysis found that airlines could reduce emissions by around 11% right now by flying their most efficient aircraft on routes where they already operate.
Lead author Professor Stefan Gössling (Linnaeus University) said: “Efficiency-based policies have a great potential to curb aviation emissions, and can be in airlines’ own economic interest. But the reality is that many airlines continue to fly with old aircraft, low passenger occupancies, and growing proportions of premium-class seating.”
The researchers suggest that efficiency improvements could be promoted using policy tools and market-based measures, such as emissions ratings for airlines, adjusted landing fees based on aircraft performance, and carbon intensity caps - drawing parallels to standards used in sectors like household appliances and vehicles.
The study was based on data from Airline Data, the International Civil Aviation Organization, and the International Air Transport Association. This showed that the regions with the most inefficient flights were Africa, Oceania, the Middle East, Central Asia, and North America. The regions with the most efficient flights were Brazil, India, and Southeast Asia.
The study also involved researchers from atmosfair providing data and the Munich University of Applied Sciences.
Notes for editors:
For media enquiries and interview requests, contact Dr Milan Klöwer milan.kloewer@physics.ox.ac.uk
A graph showing the emissions reductions is available on request.
The study ‘Large carbon dioxide emissions avoidance potential in improved commercial air
transport efficiency’ will be published in Nature Communications Earth & Environment at 10 am GMT / 5 am ET Wednesday 7 January 2026 at https://www.nature.com/articles/s43247-025-03069-4. To view a copy of the study before this under embargo, contact Dr Milan Klöwer milan.kloewer@physics.ox.ac.uk
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Journal
Communications Earth & Environment
Article Title
Large carbon dioxide emissions avoidance potential in improved commercial air transport efficiency
Article Publication Date
7-Jan-2026
Fewer layovers, better-connected airports, more firm growth
Research shows direct flights and links to key airports help multinational firms expand globally and decide where to invest.
Waiting in an airport for a connecting flight is often tedious. A new study by MIT researchers shows it’s bad for business, too.
Looking at air travel and multinational firm formation over a 30-year period, the researchers measured how much a strong network of airline connections matters for economic growth. They found that multinational firms are more likely to locate their subsidiaries in cities they can reach with direct flights, and that this trend is particularly pronounced in knowledge industries. The degree to which a city is embedded within a larger network of high-use flights matters notably for business expansion too.
The team examined 142 countries over the period from 1993 through 2023 and concluded that pairs of cities reachable only by flights with one stopover had 20 percent fewer multinational firm subsidiaries than cities with direct flights. If two changes of planes were needed to connect cities, they had 34 percent fewer subsidiaries. That equates to 1.8 percent and 3.0 percent fewer new firms per year, respectively.
“What we found is how much it matters for a city to be embedded within the global air transportation network,” says Ambra Amico, an MIT researcher and co-author of a new paper detailing the study’s results. “And we also highlight the importance of this for knowledge-intensive business sectors.”
Siqi Zheng, an MIT professor and co-author of the paper, adds: “We found a very strong empirical result about the relationship of parent and subsidiary firms, and how much connectivity matters. The important role that connectivity plays to facilitate face-to-face interactions, build trust, and reduce information asymmetry between such firms is crucial.”
The paper, “Air Connectivity Boosts Urban Attractiveness for Global Firms,” is published today in Nature Cities.
The co-authors are Amico, a postdoc at the MIT-Singapore Alliance for Research and Technology (SMART); Fabio Duarte, associate director of MIT’s Senseable City Lab; Wen-Chi Liao, a visiting associate professor at the MIT Center for Real Estate (CRE) and an associate professor at NUS Business School at the National University of Singapore; and Zheng, the STL Champion Professor of Urban and Real Estate Sustainability at CRE and MIT’s Department of Urban Studies and Planning.
The study analyzes 7.5 million firms in 800 cities with airports, comprising a total of over 400,000 international flight routes. The research focused only on multinational firms, and thus international flights, excluding domestic flights in large countries.
To conduct the analysis and build their new database, the researchers used flight data from the International Civil Aviation Organization as well as firm data from the Orbis database, run by Moody’s, which has company data for over 469 million firms globally. That includes ownership data, allowing the researchers to track relationships between companies. The study included firms located within 37 miles (60 kilometers) of an airport, and accounted for additional factors influencing new-firm location, including city size.
By analyzing industry types, the researchers observed that air connectivity matters relatively more in knowledge industries, such as finance, where face-to-face activity seems to matter more. Alternately, a knowledge-industry firm with auditors periodically showing up to conduct work can lower costs by being more reachable.
“We were fascinated by the heterogenity across industries,” Liao says. “The results are intuitive, but it surprised us that the pattern is so consistent. If the nature of the industy requires face-to-face interaction, air connectivity matters more.” By contrast, for manufacturing, he notes, road infrastructure and ocean shipping will matter relatively more.
To be sure, there are multiple ways to define how connected a city is within the global air transportation network, and the study examines how specific measures relate to firm growth. One measure is what the paper calls “degree centrality,” or how many other places a city is connected to by direct flights. Over a 10-year period, a 10 percent increase in a city’s degree centrality leads to a 4.3 percent increase in the number of subsidiaries located there.
However, another kind of connectedness is even more strongly associated with subsidiary growth. It’s not just how many cities one place is linked to, but in turn, how many direct connections those linked cities themselves have. This turns out to be the strongest predictor of subsidiary growth.
“What matters is not just how many neighbor [directly linked] cities you have,” Duarte says. “It’s important to choose strategically which ones you’re connected to, as well. If you tell me who you are connected to, I tell you how successful your city will be.”
Intriguingly, the relationship between direct flights and multinational firm growth patterns has held up throughout the 30-year study period, despite the rise of teleconferencing, the Covid-19 pandemic, shifts in global growth, and other factors.
“There is consistency across a 30-year period, which is not something to underestimate,” Amico says. “We needed face-to-face interaction 30 years ago, 20 years ago, and 10 years ago, and we need it now, despite all the big changes we have seen.”
Indeed, Zheng adds, “Ironically, I think even with trade and geopolitical frictions, it’s more and more important to have face-to-face interactions to build trust for global trade and business. You still need to reach an actual place and see your business partners, so air connectivity really influences how global business copes with global uncertainties.”
The research was supported by the National Research Foundation of Singapore within the Office of the Prime Minister of Singapore, under its Campus for Research Excellence and Technological Enterprise program, and the MIT Asia Real Estate Initiative.
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Written by Peter Dizikes, MIT News
Journal
Nature Cities
Article Title
"Air connectivity boosts urban attractiveness for global firms"
