WASHINGTON (AP) — The leaders of Russia and China put aside their raw-worded disputes with U.S. President Joe Biden on Thursday long enough to pledge international cooperation on cutting climate-wrecking coal and petroleum emissions in a livestreamed summit showcasing America's return to the fight against global warming.

Neither Vladimir Putin nor Xi Jinping immediately followed the United States and some of its developed allies in making specific new pledges to reduce damaging fossil fuel pollution during the first day of the two-day U.S.-hosted summit. But climate advocates hoped the high-profile — if glitch-ridden — virtual gathering would kickstart new action by major polluters, paving the way for a November U.N. meeting in Glasgow critical to drastically slowing climate change over the coming decade.

The entire world faces "a moment of peril" but also "a moment of opportunity," Biden declared, speaking from a TV-style chrome-blue set for the virtual summit of 40 world leaders. Participants appeared one after the other onscreen for what appeared to be a mix of live and recorded addresses.

"The signs are unmistakable," Biden said. "The science is undeniable. The cost of inaction keeps mounting."

Biden's new U.S. commitment, timed to the summit, would cut America's fossil fuel emissions as much as 52% by 2030. It comes after four years of international withdrawal from the issue under President Donald Trump, who mocked the science of climate change and pulled the U.S. out of the landmark 2015 Paris climate accord.

Biden's administration this week is sketching out a vision of a prosperous, clean-energy United States where factories churn out cutting-edge batteries and electric cars for export, line workers re-lay an efficient national electrical grid and crews cap abandoned oil and gas rigs and coal mines.

But Senate Republican leader Mitch McConnell dismissed the administration's plans as costly and ineffective.

"This is quite the one-two punch," McConnell said in a Senate speech Thursday. "Toothless requests of our foreign adversaries ... and maximum pain for American citizens."

At the summit, Japan announced its own new 46% emissions reduction target and South Korea said it would stop public financing of new coal-fired power plants, potentially an important step toward persuading China and other coal-reliant nations to curb building and funding of new ones as well.

Canadian Prime Minister Justin Trudeau, one of the leaders shown watching summit proceedings in the coronavirus pandemic's familiar Brady Bunch-style multibox conference screen, said his nation would up its fossil fuel pollution cuts from 30% to at least 40%.

Travel precautions under the pandemic compelled the summit to play out on livestream, limiting opportunities for spontaneous interaction and negotiation. Its opening hours were sometimes marked by electronic echoes, random beeps and off-screen voices.

But the summit also marshaled an impressive display of the world's most powerful leaders speaking on the single cause of climate change.

China's Xi, whose country is the world's biggest emissions culprit, followed by the United States, spoke first among the other global figures. He made no reference to disputes over territorial claims, trade and other matters that had made it uncertain until Wednesday that he would even take part in the U.S. summit. And he said China would work with America in cutting emissions.

"To protect the environment is to protect productivity, and to boost the environment is to boost productivity. It's as simple as that," Xi said.

Putin and his government have been irate over Biden's characterization of him as a "killer" for Russia's aggressive moves against its opponents, and he is under pressure this week over the declining health of jailed opposition figure Alexei Navalny. But he made no mention of those disputes in his own climate remarks.

"Russia is genuinely interested in galvanizing international cooperation so as to look further for effective solutions to climate change as well as to all other vital challenges," Putin said. Russia by some measures is the world's fourth-biggest emitter of climate-damaging fossil fuel fumes.

Climate efforts in recent years have proved a forum where even rival world leaders want to be seen as putting aside disputes to serve as international statesmen and women, even though the cumulative output of fossil fuel emissions is still hurtling the Earth toward disastrous temperature rises.

The pandemic made gathering world leaders for the climate summit too risky. So Biden's staff built a small set in the East Room that looked like it was taken from a daytime talk show.

Biden and Vice President Kamala Harris joined Secretary of State Antony Blinken and White House climate envoy John Kerry at a horseshoe-shaped table set up around a giant potted plant to watch fellow leaders' speeches.

The format meant a cavalcade of short speeches by world leaders, some scripted, some not. "This is not bunny-hugging," British Prime Minister Boris Johnson said of the climate efforts. "This is about growth and jobs."

The Biden administration's pledge would require by far the most ambitious U.S. climate effort ever, nearly doubling the reductions that the Obama administration had committed to in the Paris climate accord.

German Chancellor Angela Merkel was one of many allies welcoming the U.S. return after Trump..

"I'm delighted to see that the United States is back, is back to work together with us in climate politics," Merkel declared in her virtual appearance. "Because there can be no doubt about the world needing your contribution if we really want to fulfill our ambitious goals."

Pope Francis contributed a video from the Vatican, saying, "I wish you success in this beautiful decision to meet, walk together going forward and I am with you all the way."

The new urgency comes as scientists say that climate change caused by coal plants, car engines and other fossil fuel use is worsening droughts, floods, hurricanes, wildfires and other disasters and that humans are running out of time to stave off catastrophic extremes of global warming.

Leaders of smaller states and island nations buffeted by rising seas and worsening hurricanes appealed for aid and fast emissions cuts from world powers.

"We are the least contributors to greenhouse gas emissions, but the most affected by climate change," said Gaston Alfonso Browne, prime minister of Antigua and Barbuda. He called for debt relief and more international assistance to recover from storms and the pandemic to prevent a flow of climate refugees. His people he said, are "teetering on the edge of despair."

Longtime climate policy experts, no strangers to climate summits with solemn pledges, watched some speeches with skepticism. After Brazil's President Jair Bolsonaro promised an end to clearcutting in the Amazon, Dan Wilkinson of Human Rights Watch's environmental programs noted, "It is going to be hard for anyone to take it seriously until they actually start taking steps."

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Knickmeyer reported from Oklahoma City. Associated Press writers Ashok Sharma in New Delhi, Joe McDonald in Beijing, Vladimir Isachenkov in Moscow, David Biller in Rio de Janeiro, Nicole Winfield in Vatican City, Mari Yamaguchi in Tokyo and Aamer Madhani, Seth Borenstein, Lisa Mascaro and Alexandra Jaffe in Washington contributed to this report.