Carbon Offsets Will Only Carry You So Far

On the list of activities that form our carbon footprint, from air-conditioning to eating meat, air travel is near the top. Short of refusing to fly—as Greta Thunberg, the Swedish teen activist, did when she traveled from England to New York in a carbon-neutral sailboat—you can pay a third party to plant trees, destroy methane or build wind turbines in a bid to counterbalance the damage your flight has done to the environment.

Carbon-offset sellers will calculate your carbon footprint, whether you travel by bus, car, plane or train, and translate the tons of carbon dioxide emissions triggered by your trip into a dollar figure that can help fund carbon-reducing or carbon-prevention projects around the world.

Buying carbon offsets is not expensive, especially for short hops. But figuring out how effective your purchase is isn’t easy.

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Different shades of green. Carbon-offset sellers host calculators that estimate your flight’s carbon footprint, but the numbers are all over the map. For example, for a round-trip flight from Seattle to Miami, you could pay as little as $9.25 through Carbonfund.org; the cost, however, jumps to $24.98 if you include “radiative forcing,” which factors in the ability of greenhouse gases to alter temperature. Cool Effect suggests $6.11 for about 12 hours total in the air, and TerraPass’s calculator estimates $17.56 for the Seattle–Miami route.

Variables and assumptions, such as the type of plane or number of stops, affect the estimates, says Jennifer Andrews, project director at the Sustainability Institute at the University of New Hampshire. Rather than choosing your offset seller by price, consider which projects you want to support.

Check the company’s website to see how it chooses projects and evaluates their impact. The projects promising emission reductions should be real and additional (that is, the projects are only happening because of carbon-offset purchases). The projects should be verified by an independent third party, such as Gold Standard. The effect of the offset should be designed to be permanent. And the company should have accounted for leakage (such as the risk that deforestation might shift to another area unprotected by the project’s scope). Co-benefits, such as creating jobs or preserving natural habitats, are a plus.

Depending on the carbon-offset provider, you may or may not be able to specify the type of projects you want to fund. Tani Colbert-Sangree, a program officer at the Greenhouse Gas Management Institute, an educational nonprofit, says projects that capture a greenhouse gas and destroy it or make use of it, such as methane capture at landfills, are generally safer bets (even though their “additionality” may need to be evaluated). Forestry projects, while valuable, are riskier and face problems with permanence and leakage.

If you want more control over how your money contributes to environmental protection, consider donating to a green charity or nonprofit. For example, you could look for an or­ganization pushing for strong climate and energy policies or one working on local environmental issues, says Barbara Haya, a research fellow at the Center for Environmental Public Policy at the University of California, Berkeley. But the best way to reduce your carbon footprint, experts point out, is to cut back on activities that generate the carbon dioxide in the first place.