The Swedes call it “flygskam,” or “flying shame,” the movement that encourages people to stop taking flights to lower their carbon footprints.

But should most Americans really be ashamed of getting on a plane to see grandma this holiday season?

The short answer: Probably not. If your flights are purely a luxury, though, that’s another matter.

A small group of frequent flyers, 12% of Americans who make more than six round trips by air a year, are responsible for two-thirds of all air travel and, by extension, two-thirds of aviation emissions, according to a new analysis by the International Council on Clean Transportation, a nonprofit research group.

Each of these travelers, on average, emits more than 3 tons of carbon dioxide per year, a substantial amount, particularly by global standards. And the most frequent flyers, those who take more than 9 round trips per year, emit the highest share.

If all Americans flew more than six times a year, the use of aviation jet fuel would increase about sixfold, and planes would easily surpass passenger cars as the largest source of carbon dioxide emissions, the International Council on Clean Transportation estimates.

“Our climate just can’t tolerate widespread frequent flying,” said Dan Rutherford, who directs the council’s aviation program. “At some level we need to figure out, collectively, which flights are necessary, and which are luxuries.”

Flying isn’t a big part of the average American’s carbon footprint. In fact, about half of Americans typically don’t fly at all. Another third flew up to five times a year, and were responsible for about a third of all emissions.

That means that most Americans should be more concerned with emissions from driving or from heating or cooling their homes.

The data gives a clearer picture of who is responsible for air travel emissions in the United States, which make up a quarter of global aviation emissions, more than any other country.

One note: Because so many Americans don’t fly, the U.S. per capita emissions rank much lower, in 11th place, after other high-income countries like Singapore, Finland and Iceland. And some of the fastest growth has been in developing countries, like China and India, where incomes, and a middle class that is more likely to fly, are rising.

Airline emissions could also be lowered with more fuel-efficient planes, of course. Plane manufacturers like Boeing and Airbus have competed to drive down fuel use in their models.

The problem is that air travel is growing many times faster than fuel efficiency gains, which more than cancels out the improvements in fuel efficiency. Meanwhile, the adoption of lower-carbon fuels that can reduce emissions, like biofuels, has been slow.

Because of this, emissions from air travel are growing faster than predicted in previous projections. Global civil aviation accounted for 918 million tons of carbon dioxide in 2018, or about the total annual emissions from Germany and the Netherlands, combined.

So what’s to be done to curb frequent flying? One idea, floated by a group in Britain called A Free Ride, would tax flyers progressively: Everyone gets one tax-free return flight each year, and a tax kicks in at a low rate from the second flight. Taxes then ratchet up for each additional flight in that year.

“We’re not trying to prevent ordinary people from taking their hard-earned holiday,” said Leo Murray, the group’s founder. “The annual family holiday isn’t the source of the problem here. We can still tackle climate change, and everyone can still go on holiday,” he said. “We’re talking about a small wealthy elite group of air travelers.”

And just this month, a commission based in Britain recommended banning air miles and frequent flyer programs so that airlines do not “incentivize excessive flying.” The report cites data showing frequent flyers “strongly tend to be wealthier and less price-sensitive,” and recommends they should “incur increasingly powerful taxation to discourage additional flights.”

Industry groups oppose such measures. “U.S. airlines are committed to reducing carbon emissions even further,” said Carter Yang, a spokesman for the airline industry group, Airlines for America. “That effort would be harmed, not helped, by proposals that would siphon away into government coffers the very funds needed to continue investing in new, more fuel-efficient aircraft, sustainable alternative aviation fuels,” and other innovations, he said.

Of course, many people find they must fly frequently for work. Business travel makes up roughly 30% of air travel in the United States, according to data from Airlines for America, a trade group representing airlines. But some corporations are starting to question whether all of that travel is really necessary in an age of email, Slack and teleconferencing. In Europe, companies are starting to give extra time off to employees who opt to travel by train or other less-polluting transportation options on vacation.

The British commission’s report also recommends that airlines should be required to list emissions data for each flight, just like many restaurants provide calorie counts on their menus, so travelers can make more informed choices. The least efficient airlines burn anywhere between 26% and 60% more fuel than their most efficient peers on comparable flights, according to research from the International Council on Clean Transportation.

For now, even frequent travelers can try to minimize their aviation footprints by choosing routes that fly newer aircraft. They could opt for routes that fly the more efficient A320neo plane, the fuel-efficient plane that Airbus announced in 2010. They could also keep in mind that a first-class seat can generate many times the emissions of an economy one because of the more spacious cabins. Travelers can also choose to offset a flight’s carbon emissions.

And of course, they could also think again about whether they really need to fly for the ninth time this year.

© 2019 The New York Times Company