President Obama and Chinese President Xi Jinping on Saturday formally joined a sweeping global agreement to cut greenhouse gases, moving the world toward a dramatic reduction in climate-warming emissions on a quicker time frame than previously imagined.
The ratification of the accord by the world's two biggest polluters, announced shortly after Obama's arrival here, jump-starts enactment of the landmark deal reached last year in Paris that commits virtually every country to lowering greenhouse gas emissions and slowing irreversible harm to the planet.
"Just as I believe the Paris agreement will ultimately prove to be a turning point for our planet, I believe that history will judge today's effort as pivotal," Obama said in a ceremony with Xi to make the ratification formal. "Today we are moving the world significantly closer to the goal that we have set."
Xi said he hopes other countries will step up their timeline for committing to the Paris accord, following China's example.
"When the old path no longer takes us far, we should make use of new methods," Xi said. "China is a responsible developing country and acts as a participant in global climate change efforts."
The leaders made their acts official by handing their documents of ratification — Obama's in a black folder, Xi's in red — to United Nations Secretary-General Ban Ki-moon.
The grand moment of diplomacy came on the heels of an awkward one. Upon his arrival at the airport, Obama was greeted by a short set of stairs at a side door to Air Force One, not the usual tall set of stairs that enable him to stand at the grand front door and enter a foreign country with the White House press corps recording the moment.
As soon as the pool of White House reporters came off the plane and onto the tarmac, a member of the Chinese delegation began yelling at White House staffers and demanding that the media leave the area right away.
A White House official protested, pointing out that this was the American president and airplane. The man replied, "This is our country," and moved to block senior White House officials from walking closer to the arrival scene, according to a pool reporter who was present.
The scene was a rocky precursor to the diplomatic highlight — not just of the week, but of Obama's entire record of achievement in China.
The joint proclamation by Obama and Xi cements their nations' commitments much more quickly than either side thought possible when the pair agreed in 2014 to a plan to cut carbon, which was designed to serve as a model for the larger accord. After their announcement two years ago in Beijing, most analysts believed it would take three to five years for a broad global deal to take effect.
The Paris agreement, named for the site of the U.N. summit where it was agreed upon in December, reflects each nation's individual promise to reduce greenhouse gas emissions with the ultimate goal of limiting global temperature rise. Though the final pledge fell short of its target of 2 degrees Celsius, it calls for signatories to regularly report on and revise targets to build in ambition for further progress, as Obama has said.
Backed by almost 200 nations, the pact would go into force when 55 countries representing 55% of the world's emissions give their formal assent. Only 23 other nations that account for about 1% of global emissions had done so before the U.S. and China joined in ratification. Together, the two nations emit nearly 40% of the world's carbon dioxide, and thus their pledges represent the most significant stride yet toward the pact taking effect.
The swift action is likely to spur other nations to move with more dispatch, both to formalize the deal and to cut emissions, said Jake Schmidt, director of international programs for the Natural Resources Defense Council.
"It creates a momentum," Schmidt said. "If you want to be a good global citizen, you need to act on climate change, and you need to do it now."
Brian Deese, Obama's top climate advisor, noted that Japan, South Korea, Brazil and Argentina are nearing completion of their ratification processes. The four represent an additional other 9% of global emissions.
Ratification entails varying degrees of difficulty in each nation.
Obama anticipated before the Paris deal was struck that ratification by the Senate was highly unlikely. Some Republican lawmakers question the role of humans in causing global warming, while others oppose Obama's climate change agenda for what they see as placing heavy burdens on business and threatening longstanding energy interests like coal.
As a result, the president's negotiators helped shape the Paris accord so it would not be defined as a treaty, which would require support from two-thirds of the Senate and legislative approval in some other countries as well.
The president is acting on what is instead called an executive agreement, which administration officials note has become increasingly common on environmental policy. But the decision infuriates critics, who say Obama sidestepped Congress to commit the U.S. to major carbon cuts.
Without enforceable provisions, the deal is symbolic, said Sen. James Inhofe of Oklahoma, chairman of the Senate Environment and Public Works Committee and a prominent climate change skeptic.
"This is another attempt by the president to go around Congress in order to achieve his unpopular and widely rejected climate agenda for his legacy," the Republican lawmaker said this week ahead of the ratification.
Senate Majority Leader Mitch McConnell (R-Ky.), another top Obama critic who represents a state that still closely identifies itself with its once-thriving coal industry, has long warned that Obama was making promises he was not in position to see through.
The U.S., under its commitments as part of the accord, will seek to reduce its greenhouse gas emissions more than a quarter by 2025, or to 28% below their 2005 level.
Ratification does not ensure the U.S. will be able to follow through on its promise, however. The primary mechanism to achieve that, the Clean Power Plan, is under legal challenge. In February, the Supreme Court issued a temporary stay of the plan.
Deese defended the strategy, saying the administration has carefully scrutinized the U.S. commitments and noting that Presidents George H.W. Bush and Ronald Reagan joined international environmental pacts using the same process.
For China, ratifying the Paris agreement was in some ways a natural decision, experts say — the initiative dovetails with the country's domestic effort to clean up its extreme air pollution, and lends its leaders international prestige.
China hit an environmental turning point in 2011, when a wave of horrific air pollution in Beijing sparked a popular backlash. Chinese media began reporting on the chronic smog, and its deleterious effects on public health; the government began gradually rolling out measures to monitor and disclose air pollution levels across the country.
Since then, China has become a world leader in renewable energy investments, introduced a detailed plan to control pollution and accelerated adoption of a nationwide carbon trade market, due to open next year.
Public support has been high, said Ma Jun, director of the Beijing-based nonprofit Institute of Public and Environmental Affairs.
"In the West, where you have blue skies every day and … you can drink from the tap, it's much harder to get the public behind you," she said. "But in China, the air, the water, all these concerns about safety from pollution, have created a public opinion in favor of environmental protection."
Experts say that China is likely to follow through on its promises. The country's coal consumption dropped in 2014 for the first time in more than a decade, according to China's National Bureau of Statistics. It fell even further in 2015. As part of Saturday's announcement, China is committing for the first time to release a long-term strategy for low-greenhouse gas development.
For environmental activists, the Obama-Xi meeting in Beijing was shaping up as a way to prod other nations along, as the two leaders did in April when they vowed to sign the Paris accord as soon as it opened for signatures and to formally join it this year.
"Four years ago, we started saying that China's coal consumption should peak in 2030, and most people said, 'You're crazy,' " Schmidt said. "Now the debate is, 'How soon before 2030?' It's quite clear that coal has already peaked."
Parsons reported from Hangzhou and Memoli from Washington. Times staff writer Jonathan Kaiman in Beijing contributed to this report.
4:10 a.m.: This article was updated with quotes from President Obama.