pretty soon, passengers will be flying in zero—emission aircraft. but how did we get here? archive: the new machine is called, optimistically, the flyer. _ we've come a long way since the wright brothers' first flight in 1903. that day, they lifted the world into a new dimension. then we achieved bigger, faster planes. great, but that's also how we ended up with all these emissions. jet engines burn kerosene, which releases carbon dioxide, one of the main greenhouse gases causing climate change. the industry faces an enormous challenge to clean up its act, and that means coming up with new fuels. let's take a look at some of the options. there are biofuels, which are made out of things like plants or vegetable oils, but they still produce some harmful emissions. then there's electric. but although batteries are getting far more efficient,