GLASGOW, Scotland — The United States and China jolted the United Nations climate summit here with a surprise announcement Wednesday, pledging the two countries would work together to slow global warming during this decade and ensure that the Glasgow talks result in meaningful progress.

The world’s two biggest greenhouse gas emitters said they would take “enhanced climate actions” to meet the central goals of the 2015 Paris climate accord — limiting warming to “well below” 2 degrees Celsius (3.6 Fahrenheit) beyond preindustrial levels, and if possible, not to exceed 1.5 degrees Celsius. Still, the declaration was short on firm deadlines or specific commitments, and parts of it restated policies both nations had outlined in a statement in April.

To try to keep those temperature limits “within reach,” Chinese and American leaders agreed to jointly “raise ambition in the 2020s” and said they would boost clean energy, combat deforestation and curb emissions of methane, a potent greenhouse gas.

“The United States and China have no shortage of differences,” U.S. special climate envoy John F. Kerry said in announcing the agreement Wednesday evening. “But on climate, cooperation is the only way to get this job done.”

U.S. special climate envoy John F. Kerry said at COP26 in Glasgow, Scotland, on Nov. 10, that the joint agreement with China is “a step we can build on.” (Reuters)

The United States and China, plus other major emitters such as the European Union, have come under fire in recent days for not yet delivering on some of the lofty rhetoric their leaders showcased last week.

But many leaders have demonstrated a willingness during COP26 to go further than they have before, as shown by a new draft of the agreement conference president Alok Sharma released barely 12 hours before the U.S.-China declaration came out.

The draft, which Sharma said he hoped would be signed by the end of the week, proposed a breakthrough not seen in three decades of U.N. climate negotiations: an explicit acknowledgment that nations must phase out coal burning faster and stop subsidizing fossil fuels.

“It’s fossil fuels that cause climate change,” said Mohamed Adow, director of the Kenya-based think tank Power Shift Africa. “Explicitly mentioning it gets on the path to addressing it.”

Many nations have come under scrutiny at the summit, but few have faced closer examination than the United States and China.

Speaking before Kerry at an unannounced news conference, Chinese special climate envoy Xie Zhenhua said that as superpowers, the two countries have a special obligation to work together on keeping the world a peaceful and sustainable place.

“We need to think big and be responsible,” Xie said, adding, “We both see that the challenge of climate change is an existential and severe one.” He acknowledged that “both sides recognize there is a gap between the current efforts and the Paris agreement goals.”

Both envoys on Wednesday said the joint declaration was a product of nearly three dozen negotiating sessions over the course of the year. While many of those meetings were virtual, U.S. and Chinese diplomats also had face-to-face talks in China, London and during the Glasgow summit.

The declaration also marked a payoff for the men who announced it. Kerry has spent this year pursuing extensive personal diplomacy, and he has broken with other Biden aides to advocate robust engagement with China on climate issues. Meanwhile, Xie — a veteran Chinese climate negotiator who led his delegation at previous talks in Copenhagen and Paris — came out of retirement to manage China’s climate diplomacy in the run-up to the high-profile talks in Glasgow.

The news drew various reactions on Wednesday night, from outright praise to skepticism over whether the agreement would lead to new and concrete action.

“Tackling the climate crisis requires international cooperation and solidarity, and this is an important step in the right direction,” U.N. Secretary General António Guterres tweeted.

“This is a challenge which transcends politics,” tweeted the E.U.'s top climate envoy, Frans Timmermans. “Bilateral cooperation between the two biggest global emitters should boost negotiations at #COP26.”

Manish Bapna, president of the Natural Resources Defense Council, agreed that having the United States and China on the same page on climate change trumps having them at odds. But, he added in a statement, if the world is to meet the goals it set six years ago in Paris, “we urgently need to see commitments to cooperate translate into bolder climate targets and credible delivery.”

China and the United States, which together account for about 40 percent of the world’s emissions, are central to any international accord on climate change.

The two nations have joined forces before with outsize influence, most notably when President Barack Obama and Chinese President Xi Jinping forged a similar partnership a year before the Paris climate accord, helping to make that landmark pact a reality.

But the run-up to this conference has proven sharply different.

A year ago, Donald Trump was president and he had withdrawn the United States from the Paris accord. The coronavirus pandemic had put global climate talks on hold.

But even more recently, relations have been tense. The Biden administration has maintained Trump-era trade sanctions, including ones imposed on China’s exports of solar panels. China’s crackdown on pro-democracy demonstrators in Hong Kong and the mass imprisonment of ethnic minority Uyghurs living in western China have exacerbated those tensions.

In addition, the Chinese president declined to travel to Glasgow — a blow to early hopes that COP26 would forge a far-reaching agreement to catapult the world back onto a more sustainable trajectory. During his time in Glasgow, President Biden called Xi’s absence a “big mistake.”

Few details were immediately available about the implications of Wednesday’s declaration. For example, it did not identify an earlier date at which China’s carbon emissions will peak. The country has said it plans to start decreasing emissions by 2030, or earlier if it can, and that it will erase its carbon footprint by 2060.

Nor was it clear whether a promise to cooperate on renewable energy meant that the United States is considering lifting trade measures against Chinese-made solar panels and other green technology, a significant irritant in the relationship.

Xie did not say whether China would accept a clause in the draft agreement that says countries would agree to stop funding for coal. China has done that for foreign coal plants it was financing, but it has not agreed to halt the construction of coal plants domestically.

China this year is experimenting with a carbon emissions market in a bid to lower emissions from its power sector. Xie said if that is successful, China would apply it to other parts of the economy, starting with the industrial sector.

Kerry said there were many discussions about helping China accelerate this transition and begin to shrink its emissions, but ultimately that was a decision for its leaders. “We peaked on peaking,” he joked.

But, Kerry said, China did commit to rapidly develop a plan to reduce its methane emissions and dial down coal “as fast as is achievable.” That commitment does not mean China is joining a U.S.-European pledge — signed by more than 100 nations — to reduce methane emissions by nearly one-third by 2030. But it signaled an important recognition from Beijing that methane plays a key role in increasing the Earth’s warming.

Wednesday marked China’s biggest splash at a climate conference where it has not had a major presence over the past 10 days. Representatives of other high-emissions countries such as India and Brazil have had high-profile speaking engagements and frequently wander the national pavilions in the exhibition area. Chinese negotiators have been more active behind the scenes, policymakers say.

One European negotiator said the significance of the U.S.-China accord was no guarantee that the broader talks in Glasgow would succeed. “It doesn’t mean they found a deal on all problems already,” the negotiator said in a text message, speaking on the condition of anonymity because the official was not authorized to comment publicly.

As negotiators from nearly 200 countries haggle over every line and phrase of the international agreement in the coming days, the specifics of any final deal will probably evolve.

The draft proposal released Wednesday aims to make the most ambitious goal of the 2015 Paris climate agreement — limiting the average global temperature rise to no more than 1.5 degrees Celsius — achievable.

The text notes that current national pledges are insufficient to avert catastrophic warming and urges countries — especially those that have not adopted more ambitious targets since the Paris agreement was signed — to update their carbon-cutting plans before the end of next year.

If countries stick to their current pledges, a U.N. report has found, the world will probably warm 2.5 degrees Celsius (4.5 degrees Fahrenheit) by the end of the century, an amount that scientists have said would lead to ever more catastrophic effects.

Many activists and delegates from vulnerable nations were unimpressed with the overall shape of the emerging deal. They noted that even the reference to fossil fuels, which includes no fixed timeline, could get watered down. And they criticized the rest of the proposal, while still in flux, as too weak.

Late Wednesday afternoon, British Prime Minister Boris Johnson returned to Glasgow to make a final push as the negotiations reach a critical point. He acknowledged that whatever the talks produce is “not going to arrest climate change right here, right now. That is just impossible.”

But he said negotiators must find a way to shape an agreement that moves the world in the right direction.

“It is crucial now that we show high ambition. That’s what we’re trying to do. And the opportunity is there,” Johnson said, adding that the possibility of failure persists. “The risk of sliding back, I think, would be an absolute disaster for the planet.”

For his part, Kerry said that while many hurdles remain before anyone could declare the Glasgow summit a success, Wednesday’s formal partnership with the Chinese can only help the chances that world leaders will choose solidarity.

“We could leave here not working together, the world wondering where the future is going to be,” he said. “Or we can leave here with people working together in order to raise the ambition and move down a better road.”