WASHINGTON (AP) — President Barack Obama's wide-ranging plan to combat global warming would for the first time put limits on carbon pollution from new and existing power plants.

Obama on Tuesday announced plans to reduce domestic carbon dioxide emissions by 17 percent between 2005 and 2020 and "put an end to the limitless dumping of carbon pollution."

Other aspects of the plan would boost renewable energy production on federal lands, increase efficiency standards and prepare communities to deal with higher temperatures. The 12 hottest years on record all have occurred in the past 15 years.

Obama's plan would be put in place through executive order, bypassing Congress, which has stalemated over climate legislation in recent years.

Some questions and answers about the climate plan:

Q: What is Obama proposing?

A: The linchpin of his plan is a timetable to limit carbon dioxide emissions from new and existing power plants. Forty percent of U.S. carbon emissions, and one-third of greenhouse gases overall, come from electric power plants, according to the federal Energy Information Administration. The Obama administration already has proposed controls on new plants, but those controls have been delayed.

Under Obama's plan, the Environmental Protection Agency will issue a new proposal by late September to regulate greenhouse gases from new power plants. By next June, EPA will propose guidance for states to regulate greenhouse gas emissions from existing power plants. Greenhouse gases are blamed for global warming.

Both proposals are expected to be made final in 2015, with states required to submit plans to regulate greenhouse gases from existing power plants no later than June 2016.

Q: What else does he want?

A: Obama's plan also would expand development of renewable energy such as wind and solar power on public lands. The president hopes to generate enough electricity from renewable energy projects to power the equivalent of 6 million homes by 2020, effectively doubling the electric capacity federal lands now produce. He also set a goal to install 100 megawatts of energy-producing capacity at federal housing projects by the end of the decade.

Obama also announced $8 billion in federal loan guarantees to spur investment in technologies such as carbon "capture" systems that can keep carbon dioxide produced by power plants from being released into the atmosphere.

Q: What legal authority does Obama have to restrict greenhouse gas emissions by power plants?

A: A 2007 Supreme Court ruling declared that under the Clean Air Act the EPA has authority to regulate greenhouse gas emissions as air pollutants. After the Bush administration resisted such steps, the EPA in 2009 under Obama concluded that greenhouse gases endanger human health and welfare, triggering controls on automobiles and other large sources.

Until this year, the Obama administration always has said it preferred to address global warming through legislation rather than executive action. However, in his State of the Union address in February, Obama declared that if Congress would not act on global warming, he would.

Q: What is the states' role?

A: Ultimately it is up to states to develop standards for greenhouse gas emissions from power plants, but they do so under federal guidelines established under the Clean Air Act.

Q: Is legal action likely?

A: Yes, legal challenges are a near certainty. Some legal experts question whether the Clean Air Act allows the EPA to limit carbon pollution from existing plants before finalizing rules for future plants.

Roger Martella, an EPA general counsel under President George W. Bush, said Obama's proposals are "very much in uncharted legal waters. This is not a settled area of law."

Even if courts uphold the EPA's right to act, further legal challenges are likely. Scott Segal, director of the Electric Reliability Coordinating Council, a coalition of utilities and energy companies, said previous EPA regulations have had technical and methodological errors that had to be fixed, often under court order.

Q: What is the political reaction to the president's plan?

A: Obama cited global warming as top priority in his first presidential campaign and he suffered a major defeat in the Senate when a climate bill was withdrawn without a vote. The president largely ignored the issue during his campaign for re-election in 2012, but mentioned it on election night and recommitted to fight climate change at the start of his second term. Environmental activists have been irked that Obama's high-minded goals never materialized into a comprehensive plan.

Republicans quickly dismissed the plan announced Tuesday as a "war on coal" and jobs. "It's tantamount to kicking the ladder out from beneath the feet of many Americans struggling in today's economy," said Senate Republican leader Mitch McConnell of Kentucky, a major coal-producing state.

Environmental groups offered a mix of praise and wariness that Obama would follow through on his ambitious goals. "People are happy that the president is finally staking out ownership of this important issue. That enhances the idea that something will get done," said Frank O'Donnell, executive director of the advocacy group Clean Air Watch.

Bill Snape of the Center for Biological Diversity said Obama's proposal "isn't big enough, doesn't move fast enough to match the terrifying magnitude of the climate crisis."

Q: What's the industry's reaction?

A. Nick Akins, CEO of Ohio-based American Electric Power, one of the nation's largest utilities, said in an interview Tuesday that as long as utilities like his are given enough time to transition to a cleaner fleet of power plants, Obama's plan can be carried out "without a major impact to customers or the economy."

Tom Kuhn, president of the Edison Electric Institute, which represents electric power companies, said officials look forward to working with the administration as it develops the plan, along with members of Congress and the states, "which will play a critical role."

Q: What about the Keystone XL Pipeline?

A: In a surprise move, Obama offered a rare insight into his deliberations on Keystone XL, a proposed oil pipeline from Canada to Texas Gulf Coast refineries that has sparked an intense fight between environmental activists and energy producers. The White House has insisted that the State Department is making the decision independently, but Obama said Tuesday he's instructing the department to approve it only if the project won't increase overall net emissions of greenhouse gases. "Our national interest would be served only if this project does not significantly exacerbate the problem of carbon pollution," Obama said.

Obama's remarks appeared designed to reassure environmentalists, but they also could indicate an easing of the way for the pipeline, if the carbon standard is met, as pipeline supporters argue.

"The almost five-year review of the project has already repeatedly found that these criteria are satisfied," said Russ Girling, president and CEO of TransCanada, the Calgary-based company that has proposed the pipeline.

But Daniel J. Weiss, a senior fellow at the liberal leaning Center for American Progress, said that "for the first time, the president has set a do-no-climate harm standard before he approves the Keystone XL pipeline. That will be difficult standard to meet."