Carbon pollution from private jets has soared in the past five years, with most of those small planes spewing more heat-trapping carbon dioxide in about two hours of flying than the average person does in about a year, a new study finds.

About a quarter million of the super wealthy — worth a total of $31 trillion — last year emitted 17.2 million tons (15.6 million metric tons) of carbon dioxide flying in private jets, according to Thursday’s study in the Nature journal Communications Earth & Environment. That’s about the same amount as the 67 million people who live in Tanzania