When Swedish teen climate activist Greta Thunberg skipped flying in favor of a two-week Atlantic crossing to reach the United Nations Climate Summit in New York in September 2019, the nascent flight-shaming movement really took off. Protest groups such as Greenpeace and Extinction Rebellion are fueling the campaign by highlighting aviation’s role in global warming. The phenomenon could lead to lower passenger numbers, higher taxes on flights, and changes in jet and fuel technology.