Under the rule, states will be given a flexible timeline to create a plan for reducing carbon pollution, with plans due by June 2016. The program for reducing emissions will vary by state, depending on their unique situations. For example, states can make improvements at power plants by generating more electricity from clean energy, such as wind or solar, or by increasing energy efficiency.
"States can choose the right mix of generation using diverse fuels, energy efficiency and demand-side management to meet the goals and their own needs," the EPA said.
Each state will also have different targets. "States that burn a lot of coal would begin their reductions from a higher emissions level than those that burn natural gas, which emits less carbon dioxide," the Los Angeles Times explains.
In addition to cutting carbon emissions by 30%, the Clean Power Plan aims to reduce other pollutants, like nitrogen oxides and sulfur dioxide by 25%.
The EPA estimates that the plan will save up to $93 billion in energy and health costs by preventing more than 6,000 premature deaths, 150,000 asthma attacks, and 490,000 missed work or school days.
The agency also said the new rule will lower electricity bills roughly 8% by increasing energy efficiency.
The EPA will be listening to feedback on the proposal over the next year. The agency plans to finalize the regulations by next June.
The regulation is significant since power plants are the the largest source of carbon pollution in the United States, accounting for around one-third of the nation's greenhouse emissions.
Here's a handy chart from the EPA, laying out what greenhouse gas pollution includes.