With parts of their country huddled in the Arctic circle, it's little surprise that Swedes have long relied on air travel to warm their frozen toes in milder southern climes.

The mass exodus from northern Europe to, well anywhere south, usually begins towards the end of summer, peaking as winter casts entire days in darkness.

But today, more and more Swedes are taking the long way out of town — as in, by train car or boat. Anything but a plane. A big reason for that is the growing stigma around planes as a source of planet-warming gases. With some 20,000 planes in service around the world — and 50,000 expected in the air by 2040 — you might imagine the growing burden air travel heaps on our increasingly unhappy atmosphere.

Many Swedes certainly do. In fact, air travel has become a subject of such shame and scorn there's even a new word for it: flygskam, which translates literally to "flight shame."

And if you happen to like the train, you can take pride in the newly minted term "tågskry," which literally translates as "train brag."

It's all adding up to fewer passengers at airports, as Swedes clamor to train and bus stations instead. Local flights, in particular, are feeling the flygskam. The number of domestic passengers has dropped by 15 percent in April, compared with the same month last year.

What's more, one in four Swedes recently surveyed cite the environment as the biggest reason for keeping their feet on the ground. It also helps when celebrities like opera singer Malena Ernman publicly declare they won't fly again.

And who wouldn't be swayed by the passion of her daughter, 16-year-old Greta Thunberg? The famed climate activist hasn't set foot on a plane since 2015. In fact, when Thunberg toured Europe last month, it was by bus. Her round-trip journey to the World Economic Forum in Davos, Switzerland involved more than 60 hours on various trains — a jarring contrast with the record number of private jets ferrying wealthy attendees in and out of the forum.

Greta Thunberg holds a microphone during a Fridays for Future protest in Hamburg Greta Thunberg, seen here at a Fridays for Future protest in Hamburg, Germany, in March, started the student protest movement. (Photo: Adam Berry/Getty Images)

But can environmental shaming really threaten the industry?

Rickard Gustafson, chief executive of Scandinavian Airlines, seems to think so. In a recent interview with a Danish newspaper, he said he was convinced the flygskam movement was hurting air traffic.

Even more worrisome, at least for the industry, is the possibility that flygskam spreads its wings beyond northern Europe.

At an airline summit in Seoul this week, the Swedish movement proved to be a major talking point among industry leaders.

"Unchallenged, this sentiment will grow and spread," Alexandre de Juniac, head of the International Air Transport Association, reportedly warned attendees..

Could flygskam soar across the ocean to North America? We could certainly use the inspiration — especially considering the vast distances trains can take us on a continent thoroughly stitched together by railroad tracks.

And even though cars aren't innocent when it comes to greenhouse gases — according to scientists, cars and trucks account for nearly a fifth of all U.S. emissions — they're getting dramatically cleaner. Even today, cars are a better environmental bet than planes.

As The New York Times points out, Americans merely have to take one round-trip flight between New York and California to produce about 20 percent of the greenhouse gases that their car generates in a year.

Of course, there's one niggling detail about the movement that doesn't get so much attention. How much vacation time do northern Europeans get? Would you be comfortable asking your boss for a month's vacation so you can take a bus to Belize?

Just tell her it's not for you. It's for the planet.

Sweden has invented a word to shame people for flying
The Swedish 'flygskam' translates as 'flight shame' — and it seems to be working.