"It’s complicated, but we did the best job that we could to recognize that coal is in the mix today, and it is going to be in the mix almost at the same levels in 2030," McCarthy said. "But what you’re going to see in 2030 is more efficient plants. And you are going to see a lot more fuel diversity, with renewables and energy efficiency investments being made. This on the whole is great for the economy and it’s great for jobs."

Renewables are expected to increase as a result of the rule, though only slightly. EPA said it estimates sources like wind and solar will add 12 gigawatts of power by 2020 and another 9 gigawatts of power by 2030. The agency's projections show renewables would make about 9 percent of the country's generating capacity.

But the biggest projected growth was in natural gas. The sector is expected to grow 18 to 19 percent by 2030, with much of the increase coming by 2020. New natural gas-fired facilities are projected to increase from 85 thousand gigawatt hours without the rule to as high as 248 thousand gigawatt hours in one scenario EPA considered, an increase of 192 percent.

Natural gas producers welcomed the projection, if not the rule itself.