By Brad Plumer
KATOWICE, Poland — Diplomats from nearly 200 countries reached a deal on Saturday to keep the Paris climate agreement alive by adopting a detailed set of rules to implement the pact.
The deal, struck after an all-night bargaining session, will ultimately require every country in the world to follow a uniform set of standards for measuring their planet-warming emissions and tracking their climate policies. And it calls on countries to step up their plans to cut emissions ahead of another round of talks in 2020.
It also calls on richer countries to be clearer about the aid they intend to offer to help poorer nations install more clean energy or build resilience against natural disasters. And it builds a process in which countries that are struggling to meet their emissions goals can get help in getting back on track.
The United States agreed to the deal despite President Trump’s vow to abandon the Paris Agreement. Diplomats and climate change activists said they hoped that fact would make it easier for the administration to change its mind and stay in the Paris Agreement, or for a future president to embrace the accord once again. The United States cannot formally withdraw from the agreement until late 2020.
Observers said United States negotiators worked constructively behind the scenes with China on transparency rules. The two countries had long been at odds because China had insisted on different reporting rules for developing countries, while the United States favored consistent emissions-accounting rules and wanted all countries to be subject to the same outside scrutiny.
“The U.S. got a clear methodology to make sure that China and India are meeting their targets,” said Jake Schmidt, international policy director at the Natural Resources Defense Council. “That creates the level playing field they have been asking for.”
Many of the attendees at this year’s United Nations climate talks — known as COP24, shorthand for their formal name — expressed disappointment at what they saw as half measures to deal with a mounting climate crisis. Greenhouse gas emissions are still rising around the world, and millions of people are facing increased risks from severe droughts, floods and wildfires.
But supporters of the deal reached Saturday said that they hoped the new rules would help build a virtuous cycle of trust and cooperation among countries, at a time when global politics seems increasingly fractured.
“Particularly given the broader geopolitical context, this is a pretty solid outcome,” said Elliot Diringer, executive vice president of the Center for Climate and Energy Solutions. “It delivers what we need to get the Paris Agreement off the ground.’’
“The fundamentals are in place,” Mr. Diringer added.
Not every country got what it wanted at the meeting, which had been scheduled to end on Friday. Developing nations were hoping for more robust promises on climate aid, but that issue has been postponed for future talks.
The negotiations over the Paris rule book, often dense and technical, were frequently bogged down by sharp political disputes inside the saucer-shaped convention center here in Katowice, at the heart of Poland’s coal country.
Midway through the conference, a huge fight over climate science, with the Trump administration at the center, threatened to derail the negotiations altogether.
Most delegates at the talks had wanted to formally endorse a major report issued in October by the United Nations scientific panel on climate change, which said that fossil-fuel emissions would have to fall roughly in half within 12 years to avoid severe climate disruptions.
But the United States and three other big oil producers — Saudi Arabia, Kuwait and Russia — tried to weaken the statement’s language, enraging delegates from some of the most at-risk nations. By Friday, negotiators had crafted compromise language that expressed “appreciation and gratitude” for the report.
Then, on Friday, Brazil’s delegation held up the talks all through the night because it was fiercely opposed to proposed changes in rules around carbon trading markets. Negotiators eventually agreed to table the issue until next year.
With a diplomatic framework still alive and rules of the road in place, analysts said it was now up to individual countries to come back before the 2020 talks with concrete pledges to cut emissions more deeply. A few countries, including Chile, Vietnam and Norway, have already said they would start that review process.
When world leaders signed the Paris agreement in 2015, they said they would try to limit the rise in global temperatures to roughly 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, above preindustrial levels to avoid climate-related disasters like widespread food shortages and mass coral die-offs.
But with global fossil-fuel emissions still rising each year, the planet is now quite likely to cross that temperature threshold within 35 years.
“The real test is what happens when countries go home,” said Alden Meyer, director of policy and strategy at the Union of Concerned Scientists. “All the decision text in the world doesn’t cut a molecule of carbon. You need action on the ground.”
In some countries, political obstacles to climate action are mounting.
For instance, at the Poland talks, several European Union officials pledged that the bloc would pursue stronger measures to cut emissions before 2020. But inside the union, discussions over a more ambitious climate target have dragged on, in part because Britain is distracted by Brexit; France is struggling with “Yellow Vests” protests; and Germany is grappling with its own difficulties in phasing out coal.
“We can’t ignore that there are a lot of headwinds,” said Laurence Tubiana, France’s former climate change envoy and a key architect of the Paris agreement.
Some experts at the talks argued that the march of cheaper, cleaner energy technologies would do far more to break the deadlock around climate policy than any complicated treaties could.
“Look at countries like China and India that are going ahead with renewables for their own reasons,” said Saleemul Huq, director of Bangladesh’s International Center for Climate Change and Development. “That’s what we need: for countries to move in that direction because it makes sense to them, not because they signed up for an agreement and they’re supposed to.”
Even some of the exhausted politicians in the thick of this week’s climate negotiations were ready to acknowledge the limits of diplomacy.
“Of course it’s important to have these rules, but a lot of the real action is happening by entrepreneurs; it’s happening by business people; it’s happening by the finance sector; by the money flowing; it’s happening at the city and state level,” said Catherine McKenna, Canada’s environment minister.
“Climate change is a complicated problem,” she said, “and it’s not going to be solved by national governments alone.”
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Brad Plumer is a reporter covering climate change, energy policy and other environmental issues for The Times’s climate team. @bradplumer