With the United States absent from the UN annual international climate summit for the first time in three decades, China is stepping into the limelight as a leader in the fight against global warming.

Its country pavilion dominates the entrance hall of the sprawling COP30 conference grounds in Brazil's Amazon city of Belem, executives from its biggest clean energy companies are presenting their visions for a green future to large audiences in English, and its diplomats are working behind the scenes to ensure constructive talks.

Those were Washington's roles, but they now reside with Beijing.

"Water flows to where there is space, and diplomacy often does the same," Francesco La Camera, director general at the International Renewable Energy Agency, told Reuters.

He said China's dominance in renewable energy and electric vehicles was bolstering its position in climate diplomacy.

China’s transformation from a quiet presence at the UN’s Conference of the Parties summits to a more central player seeking the world’s attention reflects a shift in the fight against global warming since US President Donald Trump’s return to office.

Long a skeptic of climate change, Trump has again pulled the United States - the world's largest historic emitter - from the landmark international Paris Agreement to limit global warming. This year, for the first time ever, he declined to send an official high-level delegation to represent US interests at the summit.

"President Trump will not jeopardize our country’s economic and national security to pursue vague climate goals that are killing other countries," White House spokeswoman Taylor Rogers told Reuters.

But critics warn the US withdrawal from the process cedes valuable ground in the climate negotiations, particularly as China, currently the world's top greenhouse gas emitter, rapidly expands its renewable and EV industries.

"China gets it," said California Governor Gavin Newsom during a visit to the conference earlier this week. "America is toast competitively, if we don't wake up to what the hell they're doing in this space, on supply chains, how they're dominating manufacturing, how they’re flooding the zone."

BEAUTIFUL WORLD

Unlike previous years, when China had a modest pavilion with just a handful of seats available for mostly technical and academic panels, its COP30 pavilion occupies prime space near the entrance next to host country Brazil.

Cups of sustainable Chinese single-origin coffee, panda toys and branded swag lure in passers-by who can watch presentations by Chinese officials and executives from the world's biggest renewable energy companies.

"Let's honor the legacy and fulfill the Paris vision guided by the vision of shared future," Meng Xiangfeng, vice president of China's CATL, the world's largest battery maker, told an audience on Thursday.

"Let's advance climate cooperation and build a clean, beautiful world together."

The battery giant already supplies one-third of batteries for EV makers including Tesla (TSLA.O), Ford (F.N) and Volkswagen (VOWG.DE). It was CATL's first time hosting an event at a COP, seeking to reach an audience of governments and NGOs.

Earlier that afternoon, China's vice minister of ecology Li Gao told a packed audience that China's status as the world's leading producer of renewable energy "brings benefits to countries, particularly in the Global South".

China's State Grid, the world's largest electric utility, and solar giants Trina and Longi also made presentations.

Chinese electric auto giant BYD introduced a fleet of plug-in hybrid vehicles compatible with biofuel manufactured at its plant in Bahia, Brazil, for use at COP30.

Both COP President Andre Correa do Lago and COP30 CEO Ana de Toni have praised China's role as a clean energy technology leader.

"China has shown leadership not only by carrying out its own energy revolution, but with China's scale capacity, we can now also buy low-carbon... at competitive prices," de Toni told Reuters.

"China is very determined not only to continue to be a very stable leader in the Paris Agreement, strengthening climate governance, but also to take very practical actions to support other countries."

BEHIND THE SCENES

China is playing a more subtle role behind the scenes in the negotiations by filling a void left by the United States, which was known for rallying governments toward agreement, according to current and former diplomats involved in negotiations.

"Little by little, China is acting as a guarantor of the climate regime," said one senior diplomat from an emerging economy. "They invested a lot on the green economy. If there's any kind of involution, they will lose."

One Brazilian diplomat said China played a key role in helping reach an agreement over the COP30 agenda before negotiations even began, whereas in previous years its diplomats would not get involved unless there was some key issue for them.

Sue Biniaz, who served as US deputy climate envoy under John Kerry and was a key architect of the Paris Agreement, said China had the ability to bring together the wide-ranging interests of the developing world, from major emerging economies like the BRICS to small developing nations. She worked closely with Chinese counterparts on four bilateral climate agreements, including the one that unlocked the Paris deal.

"They tend to be very tough, take on tough positions like the U.S. did, but then be pragmatic towards the end," she told Reuters. "They have to come up with an outcome that nobody thinks is bad enough to block."

Biniaz said she was not yet convinced that China was playing a leadership role beyond the pavilions.

"If they had wanted to, they would have put in a more ambitious emission reduction target," she said, referring to China’s announcement in September that it would cut emissions at least 7% from their peak by 2035.

Li Shuo, a veteran observer of China at UN climate talks who heads the China Climate Hub at the Asia Society Policy Institute, countered that China's technology position was already a show of political leadership because its companies were making UN pledges achievable.

"The most powerful country isn’t the one with the loudest microphone at COP," he said, "but the one actually producing and investing in low-carbon technologies."