But now, 3½ years on, Americans’ love of flying has fully returned. Last month, the Transportation Security Administration logged 75.5 million passengers passing through airports in the United States — more than the 72 million who traveled in October of 2019. The TSA expects 30 million passengers to travel over the Thanksgiving holiday period alone. Globally, the International Civil Aviation Organization expects 2023’s passenger demand to outpace 2019’s by about 3 percent.

Experts say the social norms around travel, the desire to maintain connections with distant family and friends, and the relative convenience of air travel keep Americans flying. And as aviation returns, any hope of a lasting decrease in emissions from flying is disappearing — at least until technology improves.

Some aspects of flying don’t seem to have returned entirely; analysts say business travel, for example, has not fully returned to pre-pandemic levels and is unlikely to do so until next year. But traveling for vacation and other leisure activities has increased to offset the number of meetings now occurring via Zoom and other platforms. That’s similar to airline shocks of the past — after the 9/11 terrorist attacks and 2008 financial crisis, leisure travel was the first to rebound, while business travel took much longer.

Flying is responsible for approximately 2.5 percent of global greenhouse gas emissions but about 3.5 percent of the human-caused warming every year — because of the way planes affect the chemical composition of the sky. That might seem like a small amount, but by 2050, aviation emissions could triple — as countries develop and more people are able to afford flights.

Last year at a gathering of the International Civil Aviation Organization, nearly 200 nations pledged to achieve net-zero emissions in the aircraft sector by 2050. But at the moment, there is no truly “green” method of flying: Carbon offsets aren’t reliable, and the ramp-up of sustainable aviation fuels has been slow. The agreement also doesn’t include interim goals for 2030 or 2040 — or say how much individual nations have to cut back their aviation emissions.

Some people passionate about climate change and the environment — including some climate scientists — have signed pledges to cut back on, or entirely give up, flying. (While aviation is a small part of global climate emissions, it can be the largest part of an individual’s carbon footprint.)

But in a country like the United States, there are few easy alternatives. A study by the International Council on Clean Transportation found that if the country invested in high-speed rail, 54 percent of domestic flights could be replaced by train travel. But the country’s fastest train at the moment — Amtrak’s Acela from Boston to D.C. — operates at only half the speed of high-speed rail in other countries. California’s planned high-speed rail from San Francisco to Los Angeles, approved by state voters in 2008, still doesn’t have a planned opening date.

Dan Rutherford, program director for aviation and marine programs at the International Council on Clean Transportation, says the return to air travel is proceeding essentially as expected — but that’s not great news for those hoping to see a decrease in emissions. “We’re unlikely to achieve net-zero aviation emissions by 2050 if people resume flying like they did before covid,” he wrote in an email. “Strong policy interventions will be needed.”

Kevin Crowe contributed to this report.