During her annual New Year’s speech, Denmark’s prime minister announced that all domestic flights in the country would be “fossil-fuel free” by 2030. Sustainable aviation fuel, made from things like algae or household waste, and hydrogen-powered planes are expected to help the aviation industry transition away from fossil fuels in the long term. But is Denmark’s goal — a mere eight years away — realistic? The World’s Carolyn Beeler looks at the state of alternative fuels and renewable-powered planes to answer that question.