A new container ship sailing from South Korea to Denmark this summer is the first to run on green methanol -- made from methane captured from food waste at landfills -- which can cut a ship's emissions by 65-70%. Maersk, one of the world's largest shipping companies, ordered the ship two years ago, has another 25 on order, and is retrofitting older ships to use the fuel. By the end of the decade, Maersk --which operates more than 700 ships, and owns 300 of them -- plans to transport a quarter of its ocean cargo using green fuels. Globally, shipping is responsible for around 1 billion tons of CO2 emissions per year, and while other technology to cut emissions is being developed, Maersk chose to move forward with green methanol because it was feasible. Three years ago, no ships of this type were on order. Now five other major carriers are also buying them, with 120 in the works. The next challenge is scaling up fuel production and reducing the cost.