Greta Thunberg arrived in New York City on August 28 after a two-week, carbon-free trip across the Atlantic. The trip took two weeks because she traveled by high-speed yacht. It was carbon-free because the yacht had solar panels and hydro generators specifically so she would not need to fly.

Thunberg, sixteen, famously refuses to fly since, as a single individual, jet travel is the quickest and cheapest way to warm the planet. Air emissions account for between 2 and 3 percent of total global emissions and are rising quickly. In the United States alone, these emissions have gone up 26 percent since 2013. At current rates, they will triple by mid-century, right when the UN’s IPCC Report stated we must achieve net-zero emissions in order to stave off the worst of climate catastrophe. Clearly, that growth is unsustainable.

Unlike train fuel, jet fuel is largely untaxed. Deep, structural change of the entire fuel sector is necessary but will be difficult. As Bloomberg News noted in a recent headline: “Airlines were supposed to fix their pollution problem. It’s just getting worse . . . and there’s no solution in sight.” The message is clear: the private sector won’t fix itself.