Senator Mitch McConnell of Kentucky, the Republican majority leader, has started an unusual pre-emptive campaign against the rules, asking governors to refuse to comply. Attorneys general from more than a dozen states are preparing legal challenges against the plan. Experts estimate that as many as 25 states will join in a suit against the rules and that the disputes will end up before the Supreme Court. 
 
 Leading the legal charge are states like Wyoming and West Virginia with economies that depend heavily on coal mining or cheap coal-fired electricity. Emissions from coal-fired power plants are the nation’s single largest source of carbon pollution, and lawmakers who oppose the rules have denounced them as a “war on coal.” 
 
 “Once the E.P.A. finalizes this regulation, West Virginia will go to court, and we will challenge it,” Patrick Morrisey, the attorney general of West Virginia, said in an interview with a radio station in the state on Friday. “We think this regulation is terrible for the consumers of the state of West Virginia. It’s going to lead to reduced jobs, higher electricity rates, and really will put stress on the reliability of the power grid. The worst part of this proposal is that it’s flatly illegal under the Clean Air Act and the Constitution, and we intend to challenge it vigorously.” 
 
 Although Obama administration officials have repeatedly said states will have flexibility to design their own plans, the final rules are explicitly meant to encourage the use of interstate cap-and-trade systems, in which states place a cap on carbon pollution and then create a market for buying permits or credits to pollute. The idea is that forcing companies to pay to pollute will drive them to cleaner sources of energy. 
 
 Mr. Obama tried but failed to push through a cap-and-trade bill in his first term, and since then, the term has become politically toxic: Republicans have attacked the idea as “cap and tax.” 
 
 But if the climate change regulations withstand legal challenges, many states could still end up putting cap-and-trade systems into effect. Officials familiar with the final rules said that in many cases, the easiest and cheapest way for states to comply would be by adopting cap-and-trade systems. 
 
 The rules take into account the fact that some states may refuse to submit plans, and on Monday, the administration will also unveil a template for a plan to be imposed on such states. That plan will include the option of allowing a state to join an interstate cap-and-trade system. ||||| Media playback is unsupported on your device Media caption President Obama: "I believe there is such a thing as being too late" 
 
 US President Barack Obama has unveiled what he called "the biggest, most important step we have ever taken" in tackling climate change. 
 
 The aim of the revised Clean Power Plan is to cut greenhouse gas emissions from US power stations by nearly a third within 15 years. 
 
 The measures will place significant emphasis on wind and solar power and other renewable energy sources. 
 
 However, opponents in the energy industry have vowed to fight the plan. 
 
 "I'm convinced no challenge provides a greater threat to the future of the planet," Mr Obama said. "There is such a thing as being too late." 
 
 Those opponents say Mr Obama has declared "a war on coal". Power plants fired by coal provide more than a third of the US electricity supply. 
 
 The revised plan will aim to cut carbon emissions from the power sector by 32% by 2030, compared with 2005 levels. 
 
 "We are the first generation to feel the impacts of climate change, and the last generation to be able to do something about it," Mr Obama said. He likened the plan to taking 166 million cars off the road in terms of environmental impact. He called taking a stand against climate change a "moral obligation". 
 
 Mr Obama brushed off the notion that the plan is a "War on Coal" that will kill jobs and said he is reinvesting in areas of the US known as "coal country". 
 
 "Scaremonging" tactics will not work to stop the proposal, he said. 
 
 "If we don't do it nobody will. America leads the way forward... that's what this plan is about. This is our moment to get something right and get something right for our kids," he said. 
 
 Image copyright AP Image caption US power stations are the country's largest source of greenhouse gases 
 
 The deal at a glance 
 
 What does it do to combat climate change in the US? 
 
 The Clean Power Plan sets standards to reduce CO2 emissions by 32% from 2005 levels by 2030, which is 9% more than the proposed rules previously set forth by the Obama administration. 
 
 How? 
 
 It sets carbon pollution reduction goals for power plants and requires states to implement plans to meet goals. States have until September 2016 to submit plans, but must comply by 2022. 
 
 Why are some US states opposed? 
 
 Coal mining states such as Wyoming, West Virginia and Kentucky fear their economies would suffer and people would be laid off. 
 
 Is President Obama trying to set an example? 
 
 The Administration believes the plan will boost a major climate summit in Paris in December and encourage other countries to submit their own plans. 
 
 For more, read Breaking down the clean power plan 
 
 Each US state will have an emission-cutting goal assigned to it and must submit a proposal to the Environmental Protection Agency on how it will meet the target. 
 
 The BBC's Tom Bateman in Washington says President Obama will hope that Monday's announcement secures his legacy on climate change. 
 
 The measures, our correspondent says, would give the president the moral authority he needs to argue for global reductions in greenhouse gases at a major conference in Paris later this year. 
 
 However, several state governors are already saying they will simply ignore the plans. 
 
 In face of the criticism, the White House said the release of the plan was "the starting gun for an all-out climate push" by the president and his cabinet. 
 
 Hillary Clinton vow 
 
 In a video released by the White House, Mr Obama said the new limits were backed up by decades of data showing that without action the world faced more extreme weather and escalating health problems. 
 
 "Climate change is not a problem for another generation. Not any more," Mr Obama said. 
 
 "My administration will release the final version of America's Clean Power Plan, the biggest, most important step we have ever taken to combat climate change." 
 
 Democratic presidential candidate Hillary Clinton said she would defend the plan if she was elected to replace Mr Obama. 
 
 "It will need defending. Because Republican doubters and defeatists - including every Republican candidate for president - won't offer any credible solution," she said. 
 
 "The truth is, they don't want one." 
 
 One Republican presidential candidate, Marco Rubio, said the plan would be "catastrophic," while another, former Florida governor Jeb Bush, said the plan was "irresponsible and over-reaching". 
 
 "The Supreme Court ruled, it's very clear that the EPA has the authority to regulate greenhouse gas emissions, so regulation is inevitable and I think it's very irresponsible for the Republican leadership to go out there and say we don't have any solutions, this is all wrong, we don't believe in the science, so let's throw up our hands and do nothing," Heather Zichal, a former climate and energy adviser to the president and a key architect of the plan told the BBC's Matt McGrath. 
 
 "This will be an issue in the 2016 election and because the Democrats have a far more responsible policy position, it will allow them to prevail." 
 
 Correspondents say the emphasis on renewable energy sources marks a significant shift from the earlier version of the plan that sought to speed up a transition from coal-fired power to natural gas plants, which emit less carbon dioxide. 
 
 It is believed the revised plan will aim to keep the share of natural gas in US power generation at current levels. 
 
 Power stations are the largest source of greenhouse gases in the US and account for about one third of all such US emissions. 
 
 Analysis - Matt McGrath, environment correspondent 
 
 The big question for the president is how to ensure that these carefully crafted rules don't end up in the recycling bin of history. 
 
 The White House believes that by vesting the power to implement these changes in the hands of individual states, they are pulling the rug from Republican claims that this is another Washington imposed, big government boondoggle. 
 
 The president is calculating that the courts will uphold the rights of the EPA to regulate carbon emissions under the Clean Air Act, as they have done on a number of occasions in recent years. 
 
 He is also gambling that because of the uncertainty of the courts and the long lead time until the regulations bite, many Republican governors will grasp the nettle and accept the changes. 
 
 The president sees this plan as the cornerstone of his attempt to secure a global treaty on climate change in Paris at the end of the year. But he needs that conference to succeed almost as much as the beleaguered UN process needs him. 
 
 Getting a deal in the French capital may help "save the world" from the worst ravages of climate change. It would also make it very difficult for his successor to unravel the Clean Power Plan. ||||| Four weeks before the official rollout, the news for President Obama’s signature regulation on climate change suddenly went from bad to abysmal. 
 
 Already, the Senate’s top Republican was urging a nationwide boycott of the carbon-cutting proposal known as the Clean Power Plan. Fourteen states had joined in a lawsuit seeking to block the rule even before it became final. Then came a blow from the Supreme Court: a surprise June 29 decision blocking the White House’s previous attempt at curbing pollution from coal-burning power plants. 
 
 By July 7, the head of the Environmental Protection Agency was testily deflecting questions over whether the Clean Power Plan — a pillar of the White House’s climate-change strategy — could survive the gantlet of legal and political challenges it faced. 
 
 “We certainly know how to defend against lawsuits, for crying out loud,” EPA Administrator Gina McCarthy told reporters at a Washington news conference. 
 
 [White House set to adopt sweeping curbs on carbon pollution] 
 
 White House officials pressed ahead with the proposal, ultimately deciding on an altered version that will be formally adopted at a ceremony Monday. But while the revised rule expresses lofty aims, the details reflect real, practical concerns about the battles still to come: an expected onslaught of litigation and legislation designed to derail the rule. 
 
 The final shape of the Clean Power Plan was hashed out over months of often contentious meetings as administration officials debated how to balance two competing objectives. On one side were advocates who pushed for the deepest possible cuts in U.S. greenhouse-gas pollution to help build momentum for international climate talks this December in Paris. On the other were experienced regulators and lawyers who saw trouble ahead as the proposed rule picked up growing numbers of opponents in Congress and in the utilities industry. 
 
 As expected, some of the opponents went on the attack Sunday, hours after elements of the revised regulation were made public. Critics called the new version badly flawed and liable to be tossed out by judges. 
 
 “The EPA still has created an untested foundation for the rule,” said Scott Segal, director of the Electric Reliability Coordinating Council, an association of power companies that will be subject to the regulation. “It has tread upon established constitutional principles and undermined the sense of federalism that is essential to the Clean Air Act.” 
 
 But other observers said the administration appeared to have gotten exactly what it wanted. Supporters said the revisions to the regulation undercut the most salient legal and political objections raised by critics, including the claim that the plan will unfairly burden poor people or will lead to disruptions in the power supply. At the same time, the plan appears capable of achieving its goals of encouraging greater adoption of renewable energy as well as dramatic reductions in heat-trapping carbon pollution over the next 15 years, said S. William Becker, executive director of the National Association of Clean Air Agencies, an independent group that represents state regulators. 
 
 “EPA has struck the right balance,” Becker said. “The agency has strengthened its legal defense of the program without sacrificing environmental integrity.” 
 
 [Clinton promises to build on Obama climate plan as critics weigh in] 
 
 In this Jan. 20 photo, a plume of steam billows from the coal-fired Merrimack Station in Bow, N.H. (Jim Cole/AP) 
 
 First proposed a year ago, the Clean Power Plan is the administration’s boldest attempt to date to reduce emissions blamed for climate change. The rule takes aim at coal-fired power plants and requires every state to reduce pollution from electricity generation, the biggest single source of greenhouse-gas emissions. 
 
 The revised plan sets a goal of cutting carbon pollution from power plants by 32 percent by the year 2030, compared with 2005 levels — a 9 percent jump from the previous target of 30 percent — while rewarding states and utility companies that move quickly to expand their investment in solar and wind power. 
 
 The original proposal introduced in June 2014 drew skepticism from many states and furious opposition from congressional Republicans, particularly lawmakers from coal-producing states. In March, Senate Majority Leader Mitch McConnell (R-Ky.) wrote a letter to all 50 governors urging them to ignore the EPA rule, calling it “extremely burdensome and costly” and on “shaky legal grounds.” Six states vowed to boycott the rule, and Democratic governors joined Republicans in lawsuits to block its implementation. 
 
 Against a backdrop of rising criticism, EPA and White House officials convened a series of private meetings to determine whether and how to change the proposal. At the EPA, McCarthy, a former Massachusetts environmental official and veteran of numerous fights over pollution laws, presided over daily meetings in the agency’s wood-paneled Alm conference room to hash out possible revisions with the agency’s air-quality officials and lawyers. Later the sessions moved to the Old Executive Office Building, where White House and State Department officials grappled over the rule’s final form. 
 
 “It is an understatement to say that the administrator and the agency were under tremendous pressure to get the rule done and, more importantly, to get it right,” said an administration official who attended many of the sessions. 
 
 While all the participants expressed support for a robust rule, McCarthy would face the additional burden of having to defend the proposal in front of skeptical congressional panels and, ultimately, in court, said the official, who spoke on the condition of anonymity to describe internal deliberations. 
 
 “She recognized the amount of scrutiny this rule will be under, both politically and legally,” the official said. “She has been leading the charge to ensure that it is airtight, that all the legal t’s are crossed and i’s dotted, and that it adheres strictly to the Clean Air Act.” 
 
 Among those pushing for the strongest possible rule was Secretary of State John F. Kerry, who will represent the United States in talks later this year on a proposed international climate treaty. Kerry “pushed very hard internally” for a tough regulation, according to a diplomatic official familiar with the private discussions, arguing that the United States needed to set a strong example if it expected other countries to join in a global pact to reduce greenhouse-gas pollution blamed for accelerating Earth’s warming. 
 
 “He wanted to make the rule as strong as possible to keep the United States on track for meeting its commitments,” said the official, who also spoke about the deliberations on the condition of anonymity. 
 
 The discussions were nearing the homestretch when the Supreme Court issued its June 29 ruling blocking the EPA’s 2011 regulation curbing emissions of mercury and other toxins from coal-fired power plants. The court’s 5-to-4 decision did not overturn the EPA’s regulation but said the agency erred in failing to properly consider the cost imposed on businesses and ratepayers. 
 
 The court’s decision cheered opponents of the Clean Power Plan while casting a pall over the now thrice-weekly gatherings of White House and EPA officials to draft the final version of the rule. 
 
 “While the court decision was hardly a resounding defeat, it made clear what was at stake,” said the administration official who participated in the internal discussions. 
 
 The court decision was an impetus for a number of changes that softened the rule’s impact on states. In the end, White House officials agreed to extended compliance timelines, giving states an additional two years and increased flexibility to help them meet pollution-cutting targets. 
 
 A “safety valve” feature was added so states could appeal for additional extensions if disruptions to the power supply appeared likely. Whole sections of the proposal were cut because of concerns that they made the rule vulnerable to court challenges. 
 
 But while the regulation was softened in some ways, it was strengthened in others. Pollution-cutting goals were toughened, and a new Clean Energy Incentive Program was added to reward states for acting quickly to invest in renewable energy. The end result was a rule that was both technically strong and legally solid, said Paul Bledsoe, who was a climate-change aide in the Bill Clinton White House. 
 
 “The final regulations clearly show the administration walking a fine line,” Bledsoe said. “For the moment they seem to have struck a remarkable balance, providing a secure position from which to negotiate forcefully with other nations in Paris later this year.”
– President Obama will officially unveil his plan to dramatically cut greenhouse-gas emissions later today—and there is an army of lawyers ready to pounce. The Clean Power plan imposes tough limits on power plant emissions and dozens of corporations are preparing to fight what they call a "war on coal," as well as up to 25 states, reports the New York Times. The measure will give each state an emission-cutting target to meet, with a goal of cutting power-plant emissions by around a third by 2030, but several governors have already said they plan to simply ignore the limit, setting up legal battles expected to end up before the Supreme Court, the BBC reports. The court blocked an emissions-limiting plan in June. The Environmental Protection Agency, however, sounds as if it is ready for the fight. 'We certainly know how to defend against lawsuits, for crying out loud," EPA Administrator Gina McCarthy said last month when she was asked about looming challenges to the plan. An administration insider tells the Washington Post that McCarthy was under a lot of pressure to create a legally solid rule—especially after the Supreme Court defeat. "She recognized the amount of scrutiny this rule will be under, both politically and legally,” the source says. “She has been leading the charge to ensure that it is airtight, that all the legal t’s are crossed and i’s dotted, and that it adheres strictly to the Clean Air Act."