President Barack Obama sought to clamp down Monday on power plant emissions with a federal plan that - if successful - would attempt to slow global warming by dramatically shifting the way Americans get and use electricity.

Touting the plan at a White House ceremony, Obama described his unprecedented carbon dioxide limits as the biggest step ever taken by the US on climate change.

On that point, at least, his opponents agreed. They denounced his proposal as egregious federal overreach that would send power prices surging, and vowed lawsuits and legislation to try to stop it.

"We're the first generation to feel the impact of climate change, and we're the last generation that can do something about it," Obama said. He added, "We only get one planet. There's no Plan B."

Obama's announcement sets off a years-long process for states to figure out how to comply.

Sixteen states - including energy-producing states like Kentucky, Wyoming and North Dakota - will face stricter emissions limits than they did under Obama's previous proposal. Montana's requirement more than doubled, from a 21 percent cut in the earlier plan to a 47 percent cut in the final version.

But other states like New Hampshire and Texas face more lenient cuts in the final plan. Three states got a pass from the Environmental Protection Agency and won't have to reduce emissions: Vermont, Alaska and Hawaii.

By the time the plan takes effect, Obama will be long out of office. Still, Obama was hoping that the plan would bolster his status as the first president to seriously tackle climate change, and galvanize other countries to take aggressive action to achieve a global climate treaty this year.

Under the plan, first proposed last year, the US must cut overall power plant emissions 32 percent by 2030, compared to 2005 levels. The Obama administration said it would cost $8.4 billion annually by 2030, but argued that power bills would decrease because people would use less electricity and rely more heavily on low-cost sources like wind and solar. The energy industry has dismissed those estimates as overly rosy.

Threats of legal action started arrived within minutes of Obama unveiling his plan. In Texas, Kentucky, Kansas, Indiana and Wisconsin, top officials said they would vigorously fight the rule, as did energy producers like Murray Energy Corp, a coal mining company.