So you're booking your flight, and just when you're about to check out, the airline asks if you'd like to pay a little something to offset your share of the flight's pollution. Or, maybe you're an environmentally minded person, and you've heard you can buy these things called carbon offsets.

Are they worth it? Let's explore.

Why planes are so pollutive

A roundtrip flight from New York to Los Angeles emits more than 1,300 pounds (about 614 kilograms) of planet-warming carbon dioxide per passenger, according to an emissions calculator from the International Civil Aviation Organization. That's about the amount of pollution you'd save if you swore off meat for 17 months.

Jet engines burn fossil fuels, releasing planet-warming gases into the atmosphere. They also release water vapor, which

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