At the earliest, states won't submit plans until mid-2016; some states could have until 2018. So the true impact won't be known for years.
But that's not stopping the White House, environmental groups and the energy industry from serving up speculation in heaping doses.
What we know and don't know about the effects of the pollution rules:
The Obama administration says: The proposal will shrink electricity bills about 8 percent.
Supporters of energy deregulation say: "Americans can expect to pay $200 more each year for their electricity." — Institute for Energy Research, a group backed by the Koch brothers.
The reality: It depends how you crunch the numbers. The administration acknowledges that the price per kilowatt hour will go up a few percentage points. But the administration says your total power bill will be lower because the plan incentivizes efficiency and will drive down demand. In other words, you'll pay more for the electricity you buy, but you'll buy less of it.
Environmentalists say: "This is the biggest step we've ever taken for the biggest challenge we've ever faced." — League of Conservation Voters
The coal industry says: "The proposal will have practically no effect on global climate change." — American Coalition for Clean Coal Electricity
The reality: The plan would prevent about 430 million tons of carbon from reaching the atmosphere. It's a 30 percent cut over the next 15 years, but that's compared with 2005 levels. Since 2005, power plans have cut those emissions nearly 13 percent, so they're already about halfway toward the goal.
But U.S. fossil-fueled plants account for only 6 percent of global carbon emissions, and Obama's plan doesn't touch the rest of the world's emissions. It won't cut as big a chunk as Obama's previous fuel economy rules for cars and trucks.