Taking aim at global warming, President Barack Obama introduced a politically charged plan Monday to order big and lasting cuts in the pollution discharged by America’s power plants. But the plan, though ambitious in scope, wouldn’t be fully realized until long after Obama’s successor took office and would generate only modest progress worldwide.

Obama’s proposal to force a 30 percent cut in carbon dioxide emissions, by the year 2030 from 2005 levels, drew immediate scorn from Republicans, industry groups and even a few Democrats who are facing fraught re-election campaigns in energy-dependent states. Environmental activists were split, with some hailing the plan and others calling it insufficiently strict to prevent the worst effects of global warming.

In all likelihood, the plan marks one of the most significant steps Obama will take to shape the country he governs during his final years in office. Stymied by Congress on nearly every front, Obama has turned to actions he can take on his own, but has found limited means to effect the type of sweeping change he has envisioned in his two campaigns.

The effort would cost up to $8.8 billion annually in 2030, the EPA projected. But the actual price is impossible to predict until states decide how to reach their targets — a process that will take years.

Obama, in a conference call with public health leaders, sought to head off critics who have argued the plan will kill jobs, drive up power bills and crush the economy in regions of the U.S.

“What we’ve seen every time is that these claims are debunked when you actually give workers and businesses the tools and the incentives they need to innovate,” Obama said.

Never before has the U.S. sought to restrict carbon dioxide from existing power plants, although Obama’s administration is also pursuing the first limits on newly built plants. While the plan would push the nation closer to achieving Obama’s pledge to reduce total U.S. emissions by 17 percent by 2020, it still would fall short of the global reductions scientists say are needed to stabilize the planet’s temperature.

Connie Hedegard, the European Union’s commissioner for climate change, called the rule “the strongest action ever taken by the U.S. government to fight climate change.” But she also said, “All countries, including the United States, must do even more than what this reduction trajectory indicates.”

Fossil-fueled U.S. power plants account for 6 percent of global carbon dioxide emissions, so even a steep domestic cut affects just a portion worldwide. And even with the new limits, coal plants that churn out carbon dioxide will still provide about 30 percent of U.S. energy, according to predictions by the Environmental Protection Agency, down from about 40 percent today.

Power plants are America’s largest source of greenhouse gases, accounting for 38 percent of annual emissions. Plants have already reduced carbon emissions nearly 13 percent since 2005, meaning they are about halfway to meeting the administration’s goal.

The 645-page proposal forms the linchpin of Obama’s campaign to deal with climate change, and aims to give the U.S. leverage to prod other countries to act when climate negotiations resume in Paris next year.

At home, however, the power plant limits won’t cut as big a chunk out of greenhouse gas emissions as Obama’s move to tackle pollution from cars and trucks. That separate effort is to double fuel economy for vehicles made in model years 2012-25.

And the drawn-out timeline for the power plant plan, coupled with threats by opponents to block it, infused Monday’s announcement with uncertainty.

“I know people are wondering: Can we cut pollution while keeping our energy affordable and reliable? We can, and we will,” said EPA Administrator Gina McCarthy.

Turning to the four-decades-old Clean Air Act, the EPA is giving customized targets to each state, then leaving it up to those states to develop plans to meet their targets. Some states will be allowed to emit more and others less, leading to an overall, nationwide reduction of 30 percent.

West Virginia, for example, must reduce the pollution it puts out per unit of power by 19 percent compared to 2012. Ohio’s target is a 28 percent reduction, while Kentucky will have to find a way to make an 18 percent cut.

On the other extreme, New York has a targeted reduction of 44 percent. But New York already has joined with other Northeast states to curb carbon dioxide from power plants, meaning it’s further along than many other states. The EPA said states like New York wouldn’t be punished for being proactive.

Although Obama initially wanted each state to submit its plan by June 2016, the draft proposal shows states could get extensions until 2017. If they join with other states, as New York has done, they could have until 2018, kicking full implementation of the rules well into the next president’s administration.

That raises the possibility that shifting political dynamics in Washington could alter the rule’s course. Although Obama could veto action by Congress to block the rule, he can’t ensure that his successor will do the same.

A few Democrats joined a chorus of Republicans in vowing to obstruct the rules legislatively. Rep. Nick Rahall, a vulnerable West Virginia Democrat, said he would not only back legislation but also join lawsuits. Republican House Speaker John Boehner simply called Obama’s plan “nuts.”

Another potential hitch: governors who refuse to cooperate. If a state declines to develop a plan, the EPA can create one itself. But how EPA could force a state to comply with that plan remains murky.

The administration said the nearly $9 billion price tag will be offset numerous times over by health savings from reductions in other pollutants like soot and smog that will accompany a shift away from dirtier fuels.

To meet their targets, states could make power plants more efficient, reduce the frequency at which coal-fired power plants supply power to the grid, and invest in more renewable, low-carbon energy sources.