"Green collar jobs" could more than double in the next 10 years, making it the fastest growing employment sector, according to a new report by the US Conference of Mayors.

The report, US Metro Economies: Current and Potential Jobs in the US Economy, estimates that there are roughly 750,000 jobs related to the green sector in the US today. By 2018, it says that this could grow to 2,540,800. By 2038, the figure could reach 4.2 million jobs.