The need for electrifying the aviation industry is clear. Not only is air travel responsible for 2 percent of the world’s carbon dioxide emissions, but it also has a particular warming effect as planes flying at high altitudes spew nitrogen oxides and other particulates that heat up the atmosphere. The question is: when will we see electric planes in the sky? It may still be a few decades before buzzing motors will replace the roar of jet engines in the skies, but some research shows that engineers are making slow and steady progress on this front. We’ve already seen electric aircraft pull off some impressive feats. In 2017, a solar-powered aircraft flew around the world without using a single drop of fuel. And smaller two-to-four passenger electric planes are already in production. Still, major advancements need to be made in order to create batteries that can muster up enough energy to fly a Boeing 737 over long distances. By some estimates, long-distance travel via electric planes should be available around 2050. Norway, however, is a bit more ambitious, stating last year that it wants all domestic flights to be electric by 2040. The race is on to build batteries big enough for planes to fly on clean electricity.