Irish saw that countries around the globe needed to build a boggling amount of clean-power projects to replace their fossil fuel infrastructure, while also providing enough energy for rising demand from China, India, and other rapidly growing countries. He realized that it would be very hard for renewables, which depend on the wind blowing and the sun shining, to do everything. And he knew that nuclear power, the only existing form of clean energy that could fill the gaps, was too expensive to compete with oil and gas.

But then, at a conference in 2011, he met an engineer with an innovative design for a nuclear reactor cooled by molten salt. If it worked, Irish figured, it could not only solve the problems with aging nuclear power, but also provide a realistic path to dropping fossil fuels.

"The question was, 'Can we do better than the conventional reactors that were commercialized 60 years ago?" Irish recalled. "And the answer was, 'Absolutely.'"

Irish was so convinced that this new reactor was a great investment that he bet his career on it. Nearly a decade later, Irish is the CEO of New York City-based Terrestrial Energy, a company that expects to have a molten-salt reactor online before 2030.