President Obama and Chinese President Xi Jinping struck a historic climate change agreement in Beijing last night, vowing that the world's two largest emitters of greenhouse gases will each undertake steep cuts in the coming decade and will work together toward a new global deal.

The United States will cut emissions 26 to 28 percent below 2005 levels by 2025, a target the White House declared can be met "under existing law"—that is, without the need for Congress to pass legislation. China will peak its fast-rising emissions by 2030 at the latest, while also increasing its share of non-fossil energy to 20 percent in that same period.

The U.S. target, already coming under fire from Republicans, will go into effect in 2020 and will become America's official offering for a new global agreement expected to be signed in Paris next year. According to the White House, the United States will double the pace of emissions cuts from a current average 1.2 percent annually to 2.3 to 2.8 percent per year in the early part of the next decade. The goal: an 80 percent cut in America's emissions by midcentury.

China, meanwhile, will deploy as much as 1,000 new gigawatts of nuclear, wind, solar and other zero-emissions generation to meet its goal.

"This is a major milestone in the U.S.-China relationship," Obama said at a joint news conference with Xi. "It shows what's possible when we work together on an urgent global challenge."

Noting that China has never before agreed to top out its emissions, Obama said he hopes the world's two largest economies can steer other countries toward a new global deal at the Paris conference.

"We have a special responsibility to lead the world effort to combat global climate change," Obama said. "We hope to encourage all major economies to be ambitious."

The agreement, months in the making, came together after a dinner at Xi's official residence, following lengthy bilateral talks on contentious issues ranging from trade to maritime disputes. Administration officials said the five-hour meeting lasted two hours longer than scheduled.

'Breakthrough' hailed by Democrats and others
Activists called the announcement nothing short of monumental. Coming just a week after Republicans seized control of the U.S. Senate in midterm elections, it sent an early signal that Obama has no intention of backing away from executive actions to rein in carbon pollution. Meanwhile, with key U.N. negotiations aimed at hammering out the 2015 global deal scheduled for Lima, Peru, next month, supporters said the news could not have come at a better time.

"This joint announcement provides both practical and political momentum towards a new, universal climate agreement in Paris in late 2015 that is meaningful, forward-looking and recognizes that combating climate change is not a five- or 10-year plan—but is a long-term commitment to keep a global temperature rise under 2 degrees [Celsius] throughout this century," said U.N. climate chief Christiana Figueres.

Former Sen. Tim Wirth (D-Colo.), who was undersecretary of state for global affairs under President Clinton and is the vice chairman of the U.N. Foundation, called the announcement "the political breakthrough we've been waiting for." Rep. Henry Waxman (D-Calif.) called it a "historic breakthrough" that could one day be seen as the "turning point" on climate.

Harvard University economist Robert Stavins, a longtime observer of the U.N. climate negotiations, called the Beijing deal "the most important development, in my mind, in the last decade—maybe the last 20 years."

For the first time in the history of the fraught diplomatic talks, he said, China has taken a concrete step away from the current Kyoto Protocol rules that demand only a handful of industrialized countries act unilaterally while hundreds of developing countries act on a voluntary basis. He described it as a sign that the Chinese leadership is thinking differently—not just about climate change, but about its role in the world.

"The reality is that if the 20th century was the American century, the Chinese realize the 21st century can be the Chinese century. And if it's your century, you lead," Stavins said.

Peter Ogden, a senior fellow at the Center for American Progress and former chief of staff to U.S. State Department Special Envoy for Climate Change Todd Stern, called the deal a sign of how far the the two countries have come since openly sparring at the 2009 climate summit in Copenhagen, Denmark.

"It would have been unimaginable to have this happen a year before Copenhagen," he said.

Still, Ogden noted, a number of key issues central to the 2015 agreement remain unresolved—like what legal form the deal will take, how countries will prove they are making progress on mitigation targets and how much money wealthy nations will pony up to help poorer ones cut carbon and prepare for the impacts of climate change.

"This is a hugely critical piece of the puzzle, but there are other pieces here," he said.

Overseas leaders applauded the announcement. But those pushing for countries to keep global temperatures from rising above 2 degrees Celsius by midcentury—the point at which scientists say the impacts will be catastrophic and irreversible—also pushed for more.

"This is a first step, but not the final step," said Marshall Islands Foreign Minister Tony de Brum, whose island nation risks being swamped by rising sea levels. De Brum called the Beijing deal "a watershed moment in the fight against climate change," but said top polluters must do more to bend the curve toward limiting emissions to the U.N.-recommended 40 gigatons by 2025.

"The proposed targets are significant, but we are not yet on track," he said.

China's coal consumption slowing as economy grows
Li Shuo, a climate and energy campaigner for Greenpeace China in Beijing, agreed.

"We welcome the announcement, but this should be the floor, not the ceiling. We think China could peak its carbon emissions much earlier than 2030," Li said.

Li argued that the best way for China's emissions to peak is for the government to cap coal consumption in the next five-year plan. Already, in the first nine months of this year, consumption slowed and even began to fall. During discussions earlier in the week at the Asia-Pacific Economic Cooperation (APEC) meeting, China's National Energy Administration said the country will try to keep its total coal use up to 4.2 billion tons by 2020.

"I don't worry that China and the U.S. will not be able to deliver their promise. They wouldn't announce it if they can't achieve the goal," Li said. "What I'm worried is that they will stay with the target and will not push further."

Republicans in the United States, meanwhile, vowed to stop the deal cold. In a statement to ClimateWire, Senate Republican leader Mitch McConnell called the joint plan "unrealistic" and insisted that carbon cuts will sink the American economy.

"Our economy can't take the President's ideological War on Coal that will increase the squeeze on middle-class families and struggling miners," McConnell said. "This unrealistic plan, that the President would dump on his successor, would ensure higher utility rates and far fewer jobs. The President said his policies were on the ballot, and the American people spoke up against them. It's time for more listening, and less job-destroying red tape. Easing the burden already created by EPA regulations will continue to be a priority for me in the new Congress."

Reporters Evan Lehmann and Coco Liu contributed.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500