Environmental groups dominated a series of public meetings last week on the Environmental Protection Agency's plan to impose carbon-cutting rules on states if they refuse to enact them voluntarily.

The meetings were seen as key milestones in the rollout of some of the more controversial aspects of President Obama's climate change agenda, the centerpiece of which is greenhouse gas emission rules for power plants called the Clean Power Plan.

The meetings also helped the president set the stage for when he travels to Paris later this month to push for a global deal on emissions reductions. The emissions rules are considered key to the U.S. meeting its obligations under any deal. The Clean Power Plan requires states to reduce emissions a third by 2030. Most climate scientists blame greenhouse gases emitted from the burning of fossil fuels for driving manmade climate change.

While the public was invited to address the EPA at the meetings, the agency ended up hearing much more from supporters of the far-reaching climate rules than from detractors.

Prominent environmental groups dominated most of the sessions. At Thursday's session in Washington, activists clamored for the EPA to come down hard on states if the do not comply, while downplaying the switch from coal- to gas-fired power plants as a solution.

Groups such as Environment America and the Natural Resources Defense Council want the EPA to push ahead on wind and solar energy and not waste time waiting for the coal industry to catch up with cleaner technology or by switching to natural gas.

"We have neither the time nor the need to transition slowly from coal to gas," said Margie Alt, the head of Environment America at Thursday's public session in Washington. "We need to use this opportunity to leapfrog straight to efficiency and renewables."

The public meetings began in Pittsburgh, before the EPA arrived for two days of back-to-back sessions in Denver, Washington and, on Friday, Atlanta.

Friday's session had a more balanced list of presenters, where the United Mineworkers of America showed up in force among well-funded environmental groups such as the Sierra Club that are pushing for the end of coal-fired power plants.

The United Mine Workers union has been skeptical about the benefits of implementing the strict emission rules of the Clean Power Plan for the workers it represents. The union has said the rule would harm their livelihoods and pensions by eliminating demand for coal.

"We cannot solve global climate change on their backs," said the union's CEO, Cecil Roberts, when the rule was finalized earlier this year. The union is suing the agency over the rule. But Roberts is also looking past litigation and told a conference in West Virginia last month that a plan should be put in place to retrofit coal-fired power plants to use a mix of coal and natural gas. He argues that co-firing both fuels would bring down emissions, while keeping demand for coal in the mix under any emissions rules that may survive the courts.

The National Mining Association isn't as hopeful about the EPA rules under Obama. They say the administration's goal is not to make fossil fuels cleaner, but to phase them out altogether through a process known as "decarbonization." The association is suing the EPA over the regulations, along with 27 states.

Senate Republicans passed resolutions last week that would repeal the emission rules, even though they will be vetoed by the president.

Environmentalists want the EPA to stick to the decarbonizing agenda and not to buy into the idea of a protracted coal-to-gas switch.

"Not just limiting emissions, but also decarbonizing our electricity system needs to be the top priority of the Clean Power Plan implementation," Alt said. "We know exactly how we got here ... and we know exactly what we need to do."

To make sure states move in that direction, the groups want the EPA to have the strongest plan in place to deter states from refusing to comply.

The plan is called a Federal Implementation Plan, or FIP, which states say is the only reason they are looking to comply with the carbon rules, even while suing the Obama administration and arguing that the Clean Power Plan is unconstitutional.

"I hope there is no need for a Federal Implementation Plan," Alt said. "That said, should any state fail to meet any of the interim planning milestones or any of the emissions reductions I certainly hope [EPA] will impose and enforce a federal plan within a year of acknowledging a state lapse."