Want to get people to fly less? Stop funding billion-dollar airport expansions.

During the 12-day travel period around this Thanksgiving holiday, a record-breaking 31.6 million passengers are expected to fly on U.S. airlines—a 3.7 percent increase over 2018.

Airports are bracing for even bigger crowds than last year’s record-high numbers, as airlines warn passengers about long lines and excruciating waits. This was, of course, by design: this year, U.S. airlines added an estimated 859 flights per day to the peak Thanksgiving travel days.

Now compare the U.S. Thanksgiving travel experience to what’s happening at European airports. The overall number of people flying in Europe is down over last year. Dutch airline KLM is encouraging potential passengers to fly less to help reduce emissions. The CEO of Air France said the industry isn't doing enough to combat climate change. Countries are discussing banning private jets and even inventing new phrases like “flight shaming,” causing passengers to reconsider how they travel.

The debate about how bad flying really is, from an emissions perspective, has consumed the conversation about personal carbon footprints over the past year. The aviation industry is responsible for 3 percent of all emissions globally, but emissions from jets carry more adverse effects because they’re released higher into the atmosphere. (Buying carbon offsets doesn’t guarantee those effects will be erased, and jet fuel alternatives are on a distant horizon.) Plus, airborne emissions are growing much faster than other sources—with the potential to explode as startups propose “air taxi” services.

But—as with many other contributors to climate change—simply urging people to change human behavior will not guarantee an impact until the infrastructure that enables that behavior is itself changed.

In this case, airports are the problem, and U.S. cities need to stop prioritizing, funding, and building them.

A new report by the United Nations Environmental Program argues that if every piece of fossil-fuel infrastructure that’s currently planned ends up being built, the planet would exceed the limit on global warming set by the Paris agreement within ten years.

It’s easy to target certain elements of fossil-fuel infrastructure in and around our cities: coal plants, oil refineries, highway interchanges, even car companies that won’t adopt cleaner emissions standards. Yet airports always seem to get a pass. We need to start seeing airports for what they are: a big problem that, without an intervention, will get much worse.

We talk a lot about the concept of induced demand for highways, where building wider roads just enables more driving, making traffic, pollution, and climate change worse. But what about induced demand for air travel? Isn’t pouring billions into airport infrastructure just like widening highways?

Take LaGuardia Airport’s new $8 billion concourse in New York City. It’s being built explicitly for flights to nearby domestic destinations, including Boston and Washington D.C. In other words—places with existing rail connections, including one with brand-new, nonstop high-speed service. Just a few miles away, JFK airport is also starting a $13 billion overhaul that will add two more concourses.

In all, New York’s Port Authority is allocating over $28 billion to expand airports that all serve the same region. Can you imagine the impact if that same figure had been poured into the regional rail system? Or a desperately needed rail tunnel under the Hudson River?

With their acres of parking lots and queues of vehicles, airports are also magnets for driving, which is the country’s largest source of emissions. Without reliable, high-capacity public transit connections—most American airports fail miserably at this—virtually all passengers and employees must use cars to get there. And increasing sprawl is pushing airports farther and farther away from city centers. As airports grow without substantially improving ground connections, the problem becomes worse and worse.

Look at what’s happened at Los Angeles International Airport. As part of a major expansion pegged to the Olympics, the airport is connecting the terminals to the city’s rail system (kind of), but it’s also spending $2 billion to build what’s being billed as the “largest car-rental facility in human history.” That’s like bragging about adding decades of traffic, smog, and emissions to LA streets.

Even places that have have made great strides when it comes to reducing transportation emissions don’t seem to see airports as part of the same solution. Washington officials are proposing a second major airport for the Seattle metropolitan area, in one of the few parts of the country where transit ridership is actually growing. The region has invested so significantly in car alternatives that it has seen people shift their behavior as a result. Now the state—including Governor Jay Inslee, who ran for president on a climate change platform—is going to ignore all that progress by plopping down another airport?

Domestic travel cannot change until we have viable alternatives. Those alternatives are within reach: Amtrak is on the verge of being profitable, and the agency is planning big changes that will transform train travel in the U.S. There’s a reason airline magnate Richard Branson is investing in rail here, too: Funneling additional money to regional rail systems could easily wipe out dozens of 100-mile short-hop airline routes. This would eliminate some of the country’s most carbon-intensive flights, since most fuel is burned during takeoff and landing. Plus it would take even more cars off highways for people who drive the same routes now.

Some countries are proposing additional taxes for airline passengers, which could help fund low-carbon alternatives. The U.S. already taxes airline tickets, but where does that money go? Over the last three decades, $15 billion has been funneled to hundreds of tiny airports that are kept operational with federal money, mostly so government officials can use them. Imagine if that money had been going to passenger rail improvements this whole time!

It’s not too late to change course. Peter Kalmus is a climate scientist who runs the online community No Fly Climate Sci, a resource to help Americans fly less. He hasn’t flown since 2012, when he realized flying made up over 75 percent of his carbon footprint. Kalmus frequently posts about how changing the country’s airline habits presents a unique opportunity to transform how we think about low-carbon travel.

“How about we do the climate stuff we know we’re going to have to do eventually, now?” he says. “Like divesting from fossil fuels and ramping down our flying? Both open social space for policy change.”

Flight shame might eventually sweep the nation. But “maybe consider not flying” isn’t good enough. Flying is usually the cheapest, fastest option for travel, and it is often the only option for people who don’t live near large cities. We need elected officials who will make the low-carbon alternatives a priority. We have hundreds of climate mayors representing most major U.S. cities who have pledged to dramatically reduce emissions. These mayors should be presenting a comprehensive zero-emission plan for getting everyone from one U.S. city to another.

Shaming people for flying might feel like a righteous path to decarbonizing air travel. But the real enemies here are the players of the airport-industrial complex pushing exorbitant expansions of fossil-fuel infrastructure that simply repeat the mistakes of the past. The shame should be reserved exclusively for them.