Andrew Perlman, 34

One of the biggest challenges in fighting global warming is reducing carbon dioxide emissions from the burning of coal, a cheap and abundant but dirty fuel. In 2004, serial entrepreneur Andrew Perlma­n founded GreatPoint Energy to commercialize a process for converting coal into methane (the main component of natural gas), which emits half as much carbon dioxide when burned to generate a given amount of electricity. The carbon dioxide that's produced in the conversion process is easy to capture for storage underground. GreatPoint, where Perlman is president and CEO, has built a demonstration plant in Somerse­t, MA, and plans to build its first commercial plant as soon as next year. Meanwhile, Perlman has cofounded additional ventures that are developing, among other things, cheaper desalination plants, antiobesity medicines, drugs that fight diseases of old age, and processes for converting garbage into bio­fuels and generating electricity by extracting heat from rocks located miles underground. -Kevin Bullis