WATCH: Biden delivers remarks at U.N. climate summit

GLASGOW, Scotland — In a marked change of tone for U.S. leaders, President Joe Biden acknowledged at a U.N. summit Monday that the United States and other developed nations bore much of the responsibility for climate change, and said actions taken this decade to contain global warming will be decisive in preventing future generations from suffering.

“None of us can escape the worst that is yet to come if we fail to seize this moment,” Biden declared.

The president treated the already visible crisis for the planet — flooding, volatile weather, droughts and wildfires — as a unique opportunity to reinvent the global economy. Standing before world leaders gathered in Scotland, he sought to portray the enormous costs of limiting carbon emissions as a chance to create jobs by transitioning to renewable energy and electric automobiles.

Yet he also apologized for former President Donald Trump’s decision to leave the Paris Agreement and the role the U.S. and other wealthy countries played in contributing to climate change.

“Those of us who are responsible for much of the deforestation and all of the problems we have so far,” Biden said, have “overwhelming obligations” to the poorer nations that account for few of the emissions yet are paying a price as the planet has grown hotter.

As for Trump’s action, he said: “I shouldn’t apologize, but I do apologize for the fact the United States, the last administration, pulled out of the Paris Accords and put us sort of behind the eight ball a little bit.”

The magnitude of the moment is crashing head-first into complicated global and domestic politics. Biden administration officials have scolded China for failing to commit more to curbing carbon emissions, as China’s efforts could be crucial in any success against climate change. But the president is still trying to nail down his own climate investments with Congress.

The summit is often billed as essential to putting into action the landmark 2015 Paris climate accord, which Biden rejoined after becoming president this year. The Trump administration largely withdrew from hands-on diplomacy, such that part of Biden’s efforts at the climate summit and the gathering of the Group of 20 nations in Rome this weekend was to reestablish the U.S. as a partner.

But Biden and his administration face obstacles in prodding the U.S. and other nations to act fast enough on climate, abroad as at home. In the runup to the climate summit, the administration has tried hard to temper expectations that two weeks of talks involving more than 100 world leaders will produce major breakthroughs.

Rather than a quick fix, “Glasgow is the beginning of this decade race, if you will,” Biden’s climate envoy, John Kerry, told reporters Sunday.

As the summit opens, the U.S. is still struggling to get some of the world’s biggest climate polluters — China, Russia and India — to make stronger pledges to burn far less coal, gas and oil and to move to cleaner energy.

Major polluters including China and Russia have made clear they had no immediate intention of following the U.S. and its European and Asian allies to zero out all fossil fuel pollution by 2050. Scientists say massive, fast cuts in fossil fuel pollution are essential to having any hope of keeping global warming at or below the limits set in the Paris climate accord.

The G-20 meeting was supposed to create some momentum for more climate progress in Glasgow. The leaders at the Italy summit did agree on a series of measures, including formalizing a pledge to cut off international subsidies for dirty-burning, coal-fired power plants.

Biden also announced at the G-20 a separate U.S.-European Union steel agreement as a chance to curb imports of “dirty” Chinese steel forged by coal power. It’s another step toward potentially using Western markets as leverage to persuade China, the world’s top climate polluter, to ease up in its enthusiasm for coal power.

But the world currently is on track for a level of warming that would melt much of the planet’s ice, raise global sea levels and greatly increase the likelihood and intensity of extreme weather, experts say.

Biden told reporters Sunday night he personally found the climate outcomes from the Rome summit “disappointing,” countering the positive assessments of his aides. And he put the blame on two rivals of the U.S.

“The disappointment relates to the fact that Russia, and ... not only Russia but China basically didn’t show up in terms of any commitments to deal with climate changes,” Biden said.

The Biden administration on Monday released its strategy for transforming the U.S. into an entirely clean energy nation by 2050. The long-term plan, filed in compliance with the Paris agreement, would increasingly run the world’s largest economy on wind, solar and other clean energy. More Americans would zip around in electric vehicles and on mass transit. And state-of-the-art technology and wide open spaces carefully preserved could soak up carbon dioxide from the air.

The Biden administration has succeeded, over 10 months of diplomacy leading up to the Glasgow summit, in helping win significant new climate pledges from allies. That includes persuading many foreign governments to set more ambitious targets for emissions cuts, promoting a global pledge to cut emissions of methane, and the promise from leading economies to end funding for coal energy abroad.

Neither Russian President Vladimir Putin nor Chinese President Xi Jinping is attending the Glasgow summit, although they are sending senior officials. Their refusals, and India’s, to move substantially faster to cut their reliance on coal and petroleum threaten to frustrate hopes of reaching the target cuts set in the Paris climate accord.

China under Xi has firmed up commitments to cut emissions but at a slower pace than the U.S. has encouraged.

U.S. national security adviser Jake Sullivan told reporters traveling with the president that climate change should not viewed as a rivalry between the U.S. and China, as China, the world’s second largest economy, could act on its own.

“Nothing about the nature of the relationship between the U.S. and China, structurally or otherwise, impedes or stands in the way of them doing their part,” Sullivan said.

Biden arrived at the international climate summit with the fate of his own climate package still uncertain in Congress. Objections from holdouts within Biden’s own Democratic Party have compelled him to back away from one bill that would have prodded the United States’ own move away from coal and natural gas and to cleaner energy for generating electricity.

Hundreds of billions of dollars of climate measures remain in Biden’s package before Congress, however.

“The largest investment in the history of the world” on climate, Biden told reporters Sunday. “And it’s gonna pass.”