New MIT research shows that not all climate actions are equal for human health. Cutting air travel can produce far larger air quality benefits than switching to clean power, even when carbon reductions are the same.
When companies and universities pledge to shrink their carbon footprints, they often focus on two big levers: buying cleaner electricity and cutting back on air travel. New research from MIT suggests those choices can have dramatically different impacts on the air people breathe — even when they reduce the same amount of carbon dioxide.
Using detailed data from two universities and one company in the Boston area, MIT researchers found that air travel causes about three times more damage to air quality than comparable electricity use. That means an organization that trims emissions by canceling flights could deliver far greater near-term health benefits than one that achieves the same carbon cuts by purchasing renewable power.
The study, published in Environmental Research Letters, is an early attempt to answer a question many institutions face as they try to “go green”: which actions do the most good, not just for the climate, but for people’s health right now?
The team wanted to look beyond carbon totals and examine the other pollutants that come along for the ride when fossil fuels are burned.
From a climate perspective, carbon dioxide is a global problem. It mixes throughout the atmosphere, so a ton emitted in Boston has the same warming effect as a ton emitted in Beijing. But the health impacts of air pollution are far more local and regional.
“From a climate standpoint, CO2 has a global impact because it mixes through the atmosphere, no matter where it is emitted. But air quality impacts are driven by co-pollutants that act locally, so where those emissions occur really matters,” lead author Yuang (Albert) Chen, an MIT graduate student, said in a news release.
Those co-pollutants include nitrogen oxides and sulfur dioxide, which react in the air to form fine particulate matter and ground-level ozone, a key ingredient in smog. Exposure to these pollutants is linked to heart and lung disease and premature death, and the damage depends heavily on where and how they form, local weather, existing pollution levels and how many people live downwind.
The MIT team built a systems-level modeling pipeline to capture those complexities.
They started with real-world energy and flight data from the three organizations. They then linked that information to power plant emissions, aviation emissions on specific routes, and statistical relationships between air quality and mortality. All of that fed into an atmospheric chemistry and transport model that simulates how pollutants move and transform in the air.
“We had to do multiple sensitivity analyses to make sure the overall pipeline was working,” Chen added.
Finally, the researchers converted both climate and air quality impacts into monetary terms, using methods commonly applied in climate economics. Prior work has estimated the climate damages from a ton of CO2 at about $170 (in 2015 dollars). On top of that, the MIT team calculated that air pollution from electricity use adds about $88 in damages per ton of CO2 emitted, while air pollution from air travel adds about $265 per ton.
In other words, the same ton of CO2 can carry very different health price tags depending on whether it comes from a power plant or a plane.
Senior author Noelle Selin, a professor in the MIT Institute for Data, Systems, and Society (IDSS) and the Department of Earth, Atmospheric and Planetary Sciences (EAPS). said one of the most striking findings was how widely aviation pollution spreads.
“A real surprise was how much aviation impacted places that were really far from these organizations. Not only were flights more damaging, but the pattern of damage, in terms of who is harmed by air pollution from that activity, is very different than who is harmed by energy systems,” Selin, who is also the director of the MIT Center for Sustainability Science and Strategy, said in the news release.
Most aircraft emissions occur at high altitudes, where atmospheric chemistry and winds differ from conditions near the ground. That can amplify their air quality impacts and carry pollution across continents. The study notes that countries such as India and China can experience outsized effects from aviation emissions due to high existing pollution levels, which make it easier for fine particles and smog to form.
The researchers also zoomed in on short-haul flights. They found that regional trips have a relatively larger impact on local air quality than longer domestic flights, as more of the emissions occur closer to the ground and near population centers.
“If an organization is thinking about how to benefit the neighborhoods in their backyard, then reducing short-haul flights could be a strategy with real benefits,” Selin added.
Electricity use tells a different but equally location-dependent story. Two organizations might buy the same amount of power and emit the same amount of CO2, but if one draws from plants near dense cities and the other from plants in sparsely populated areas, the health impacts can diverge sharply.
In the study, one university’s electricity-related emissions fell over a densely populated region, while the corporation’s emissions were spread over less populated areas. Even though their climate impacts were identical, the university’s emissions were linked to 16% more estimated premature deaths.
That kind of contrast underscores a central message of the research: the path to net-zero emissions matters, not just the destination.
“If we are trying to get to net zero emissions, that trajectory could have very different implications for a lot of other things we care about, like air quality and health impacts. Here we’ve shown that, for the same net zero goal, you can have even more societal benefits if you figure out a smart way to structure your reductions,” added Selin.
The work also challenges a common assumption in corporate and campus climate planning.
“You can’t just assume that all CO2-reduction strategies will have equivalent near-term impacts on sustainability. You have to consider all the other emissions that go along with that CO2,” Selin added.
For decision-makers, the implications are practical. An institution looking to maximize public health benefits might prioritize cutting short-haul flights or targeting the dirtiest, most population-exposed sources of electricity first, even if those actions are more complicated than buying generic renewable energy credits.
“These results show that, if organizations want to achieve net zero emissions while promoting sustainability, which unit of CO2 gets removed first really matters a lot,” added Chen.
Next, the team plans to quantify the climate and air quality impacts of train travel, to see whether replacing short flights with rail could deliver meaningful benefits. They also want to explore how different types of U.S. energy infrastructure, including data centers, shape pollution patterns and health outcomes.
As more companies, universities and governments commit to net-zero timelines, the MIT study suggests that the most impactful climate strategies will be those that look beyond carbon counts and ask a broader question: which actions clean up the air for the most people, as quickly as possible?