People today are flying more than ever, and that trend is set to continue: Last year, the International Air Transport Association reported that airline passenger numbers could almost double worldwide by 2037, to 8.2 billion annually.

But while more flying is great news for people who love to travel, it’s bad news for the environment. Flights were responsible for 2.4% of global energy-related carbon dioxide emissions in 2018 — a figure expected to grow more than threefold by 2050.

In the face of aviation’s rising emissions problem, the United Nations created the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA). The initiative aims to help airlines cancel out the environmental impact of growth in international flights after 2020, by making airlines buy carbon emissions reduction offsets.

However, it’s not just on airlines to make a difference. If you want to be an eco-friendly traveler, carbon offsets may work for you, too. Here’s what you need to know.

What are carbon offsets, and how do they work?

Carbon offsets offer a way to balance out your pollution by investing in projects that reduce emissions of CO2 or other greenhouse gases in the atmosphere. If you’re taking a long-haul flight from Minneapolis to Paris, for example, you can purchase a carbon offset to account for that specific environmental impact.

Such offset projects vary.

“It ranges from things like planting trees to improved forest management, where a timber company will allow trees to grow longer and increase the amount of carbon sequestered in the forest,” says Peter Miller, a program director for the Natural Resources Defense Council, a nonprofit environmental advocacy group. “It can be capturing of greenhouse gas emissions coming out of a landfill. It could be paying a rice farmer to adopt different practices that reduce the amount of methane coming out of their rice paddies.”

Offsets are measured in tons of carbon dioxide-equivalent (CO2e). You can figure out how much CO2e you’re on the hook for by using online calculators, either from an independent source or a project’s website. Next, you’d find a carbon offset project to support to essentially cancel out your pollution.

Some projects directly help the environment and humans simultaneously, such as building stoves in rural communities abroad that only require half the amount of wood of a traditional stove. Less wood means less toxic smoke in the house, as well as reduced carbon emission and spared forests.

As far as accounting for your carbon pollution goes, it doesn’t matter what the carbon offset project is as long as it matches your carbon output.

“By developing projects and investing in these projects to reduce emissions or increase sequestration, there’s a benefit to the climate,” Miller says.

Why should I buy carbon offsets?

You don’t have to be traveling to be concerned about your carbon dioxide emissions — anyone can buy a carbon offset. But because travel is particularly toxic to the environment, travelers may feel more compelled to account for their participation in the pollution.

“People underestimate how much emissions are associated with air travel,” says Seth Wynes, a researcher and author of a forthcoming book on climate change.

“It’s easy on a global level to say, ‘OK, air travel is only a small portion of global emissions depending on how you look at it, and therefore it’s not a giant contributor.’ But if you do fly, then each flight that you take is likely to be a large chunk of your personal carbon footprint in a year.”

In terms of carbon emissions, Wynes says, flying is a really inefficient way to travel, and prolific flying should be seen as a precious resource — not a necessity. But canceling your honeymoon to Greece or missing that board meeting in Arkansas is not always an option. So, when flights are unavoidable, buying carbon offsets is an easy, low-cost way to negate your flight’s impact.

“Offsets can be an important and valuable part of an overall carbon emission reduction strategy,” Miller says. “We all have a collective responsibility to avoid the looming climate crisis. Some people have chosen to not fly anymore as a way to avoid contributing to emissions in the first place. That’s not the answer that many people will adopt.”

How can I determine which programs are legitimate?

While buying carbon offsets to make up for your travel pollution is a noble effort, it can be pointless if you’re supporting the wrong program. And there are bad ones out there. It’s smart to be skeptical of an industry that has very little regulation and a major lack of transparency.

“Anybody or their brother can say, ‘I’m doing an offset project in my backyard to reduce emissions’ and go out there and sell people credits for their reduced emissions,” Miller says. “You have a willing buyer and a willing seller. And there may be zero credibility there.”

Don’t get duped. Before you get your credit card out, make sure the project is transparent and clearly defines how the emission reduction works and how it’s accounted for.

“It’s hard to ensure that emissions that get reduced by these projects are verifiable and are forever,” Wynes says.

To combat that issue, a carbon offset project should have reserves to account for future reversals. (For example, if you’re paying to plant a tree and the tree dies, the program should have a plan to make up for the carbon deficit.) The program also needs an objective regulatory body.

“A credible, fair project will have third-party verification,” Miller says. “You have a project implementer who does the project according to the protocol and an independent third party who reviews the implementation, reviews the project and ensures it is compliant with the requirements.”

Emission reductions should be tagged so each ton gets a unique serial number — without one, the same emissions reductions could get sold over and over. You also need to look for projects that are truly additional, meaning it wasn’t some already-existing effort now being advertised as a carbon offset.

“An additional project means that the only way the project would exist is because of the funding from the carbon markets,” says Marisa de Belloy, the CEO of Cool Effect, a San Francisco Bay Area nonprofit organization. “If I’m legally required to capture methane in my landfill site, I can’t sell carbon projects, because I had to do it anyway, so it wouldn’t be an additional project.”

How do I buy carbon offsets?

Once you’ve decided that you’d like to buy a carbon offset, browse sites such as Green-e, Gold Standard and de Belloy’s Cool Effect to find a reputable project to support. There are lots of programs out there to choose from, so pick one that strikes you personally. Do you want to support a program in a place you like to visit? Or maybe one in your home state? Once you’ve narrowed down your options, refer to the above advice on what to look for to guarantee a quality purchase.

To assure more bang for your buck, consider a project that does more than just reduce greenhouse gas emissions. You may be paying for the environmental side of the project, but it can have humanitarian benefits at the same time.

“There’s a whole range of forest projects that can have tremendous benefits in terms of the local ecosystem, native species or water storage,” Miller says. “An urban forestry project can be really helpful in terms of quality of life or jobs for disadvantaged communities.”

Are carbon offsets tax-deductible?

Yes. If you’re supporting a project that’s registered as a 501(c) (3) nonprofit organization, you can make your purchase tax-deductible. That means you get to reduce your impact on the environment and maybe ease your tax burden at the same time.

Are carbon offsets the only way to be a greener traveler?

Not at all. There are many small steps that you can take to nibble at the edges of the problem, including choosing direct flights. You can also encourage your company to invest in videoconferencing options to replace expensive and environmentally taxing business flights.

In the end, though, “really the best thing that you can do is not fly and find good alternatives to that,” Wynes says. “Take a vacation or staycation around where you live, or a local vacation where you take a trip by train is great.”