Greta Thunberg, the 16-year-old Swedish climate activist, arrived in New York last week on a solar-powered and emissions-free yacht after a 15-day voyage across the Atlantic. Along with her urgent message on climate change, Thunberg brings something that not many Americans are thinking about right now: flight shame. Thunberg is a non-flyer. She quit flying because of the greenhouse gases that are emitted during flights. Airplanes burn fossil-fuel based jet fuel and air travel is responsible for some 2 percent to 5 percent of the world’s carbon emissions, depending on whose numbers you use.