Flying hurts the planet. You can help it get better

One round-trip flight between New York and California generates about 20 percent of the greenhouse gases that your car emits over an entire year.

If you fly, you’re adding a significant amount of planetwarming gases to the atmosphere — there’s no way around it. But there are some ways to make your travel a little greener.

First, fly less. The most effective way is to fly less often. If everyone took fewer flights, airline companies wouldn’t burn as much fuel.

According to the World Bank, the average American generated about 16.4 metric tons of carbon dioxide in 2013; according to some calculations, a round-trip flight from New York to San Francisco emits about 0.9 metric tons of carbon dioxide per person. For an American, that represents about one-eighteenth of your carbon emissions for the year.

(The global average was about 5 tons.)

Should you drive instead? The longer the distance, the

more efficient flying becomes, because cruising requires less fuel than other stages of flight. So it’s certainly better to fly cross-country than to drive solo. If you’re taking a short trip, it may be better to drive.

Flying nonstop can help, too: The more times you take off, the more fuel you use. According to a 2010 report from NASA, about 25 percent of airplane emissions come from landing and taking off. That includes taxiing, which is the largest source of emissions in the landing-takeoff cycle.

If you fly, offset it. When you buy carbon offsets, you pay to take planet-warming carbon dioxide out of the atmosphere in exchange for the greenhouse gases you put in. For example, you can put money toward replanting trees, which absorb carbon dioxide from the atmosphere.

You can buy offsets through some airlines, such as Delta, United and JetBlue. But they don’t necessarily make it easy during the booking process; some airlines offer offsets only on separate sustainability pages. You can also buy offsets through other organizations.

To offset the carbon footprint of a single passenger traveling on United from New York to San Francisco in July and back again, Sustainable Travel International, which runs United’s offset program, offers two choices: Donate $8.95 to a wind farm in Texas or donate $10.75 to a forest conservation program in Peru.

All of the offset programs used by the major airlines are verified by independent third parties to make sure they do what they say.

Fly coach. According to a study from the World Bank, the emissions associated with flying in business class are about three times as great as flying in coach.

In business class and first class, seats are bigger, so fewer people are being moved by the same amount of fuel. The study estimates that a first-class seat could have a carbon footprint as much as nine times as big as an economy one.

At last, coach passengers have something to be happy about: smaller carbon footprints.

Listen to the flight attendants. Apparently, some of the rules about lowering and raising your window shades could help cut emissions.

When you land at a warm destination, flight attendants might ask you to shut your window shades, said Christine Boucher, a director of global environmental sustainability for Delta Air Lines.

The reason? It reduces the amount of fuel used to cool the aircraft when it’s sitting at the gate, she said.

Know your fuels. Commercial airlines have been using biofuels in some passenger flights since 2011, mixed with conventional petroleum-based fuels in varying amounts. The biofuels, which can come from sources like natural oils, seaweed and agricultural waste, can help reduce planetwarming emissions from aviation.

You can check the fuel efficiency of the airlines you fly. According to a report from the International Council on Clean Transportation, Alaska Airlines and Spirit Airlines were the most efficient domestic carriers in 2010. American Airlines and Allegiant Air were at the bottom of the list of the 15 largest airlines.