GLASGOW, Scotland—Leaders from more than 100 nations kicked off COP26 climate talks here, confronting still-large gaps over how to slash emissions quickly enough to avoid the most destructive effects of global warming.

The United Nations summit opened Monday, a day after leaders of the Group of 20 major economies made little progress over the weekend hammering out specific climate goals many had hoped would ease discussions in Glasgow. Leaders reached a deal to end financing of coal-burning power plants overseas that aren’t...

GLASGOW, Scotland—Leaders from more than 100 nations kicked off COP26 climate talks here, confronting still-large gaps over how to slash emissions quickly enough to avoid the most destructive effects of global warming.

The United Nations summit opened Monday, a day after leaders of the Group of 20 major economies made little progress over the weekend hammering out specific climate goals many had hoped would ease discussions in Glasgow. Leaders reached a deal to end financing of coal-burning power plants overseas that aren’t equipped with technology to capture and store carbon dioxide emissions. But they didn’t agree on targets for phasing out fossil fuel subsidies or their dependence on coal, one of the biggest sources of carbon-dioxide emissions.

The negotiations have pitted developed nations against developing ones, with the two sides arguing over which countries should shoulder the burden for further emissions reductions. The U.S. and Europe want large developing nations to cut emissions more quickly. China, the biggest emitter of greenhouse gases, has said it would begin to reduce emissions before 2030, while Western officials have called on China to accelerate that plan.

President Biden arriving at the COP26 climate talks in Glasgow on Monday.

Photo: KEVIN LAMARQUE/REUTERS

That divide didn’t get significantly narrower following the G-20 summit in Rome. Late Sunday, U.S. officials ratcheted up pressure on China and other holdouts, while also taking steps to convince participants the Biden administration had the ability to make good on its own emissions-cutting efforts, despite its checkered history in previous climate deals and a deeply divided Congress back in Washington.

The Biden administration unveiled a fresh strategy outline Monday detailing how the U.S. will reach its net-zero emissions target by 2050. “We’re stepping forward in ways that are going to make it extremely difficult for people not to raise their ambition,” said U.S. climate envoy John Kerry.

Speaking to reporters on Air Force One as President Biden flew from Italy to Scotland, U.S. national security adviser Jake Sullivan said there had been progress at the G-20 but cited China as a “significant outlier.” He said China and other countries have an obligation to do more.

“The U.S. is stepping up to do its part,” Mr. Sullivan said. “Key U.S. allies: Japan, Korea, the European Union, Canada, others are stepping up to do their part. And now the question is, Will some of the remaining countries step up to do theirs?” Mr. Biden had earlier singled out Saudi Arabia and Russia as needing to do more as well.

The goal of the Glasgow summit is to hammer out a plan to cut emissions to levels scientists hope will limit global warming to well-under 2 degrees Celsius, and preferably 1.5 degrees, above pre industrial era temperatures. The U.N. says governments’ current emissions reduction plans put the world on track for 2.7 degrees of warming, and that some of the biggest economies, including the U.S., haven’t put in place the policies needed to meet their emissions reduction targets.

Leaders from more than 100 nations kicked off COP26 climate talks in Glasgow on Monday.

Photo: YVES HERMAN/REUTERS

Developing countries counter that developed nations—in particular the —are responsible for the most of carbon dioxide emissions, which accumulate in the atmosphere and cause warming over decades. They want the U.S., Europe, Japan and a few other nations to cut their emissions faster. To meet their targets for adopting renewable energy, developing countries are preparing to ask for a big increase in financial support from wealthy nations. African nations have already made their demand public: more than $1.3 trillion annually starting in 2030.

—U.S.

Negotiators from developing countries worry about the U.S. commitment to fighting climate change over the long term. The U.S. has twice backed out of U.N. climate change deals—first the Kyoto Protocol under President George W. Bush and then the Paris agreement of 2015 under President Donald Trump. After signing the U.S. back up to the Paris deal, Mr. Biden is now struggling to pass his own climate plans through Congress.

After meeting with Mr. Kerry in mid-April, members of China’s climate team expressed skepticism in private toward Mr. Biden’s pledge to reduce U.S. greenhouse-gas emissions by 50% to 52% from their 2005 levels by 2030, according to people familiar with the discussion. The Chinese didn’t believe the goal was realistic and said the Americans had no concrete road map in place, according to these people.

Some other key nations that are big producers of fossil fuels are opposing a rapid shift away from fossil fuels. Saudi Arabia’s strategy during the COP26 talks will rest entirely on what it calls the carbon circular economy, or CCE, according to people familiar with the matter. The country’s energy minister

Prince Abdulaziz bin Salman believes the kingdom should continue investing in hydrocarbons along with reforestation and carbon capture technology.

Another flashpoint is India, the third biggest emitter after the U.S. and China. It hasn’t presented an updated emissions plan, as required every five years under the Paris accord. Nor has the Indian government taken a step that scientists say is crucial: setting a target for net-zero greenhouse gases, meaning that emissions have been slashed enough to be completely offset by natural and other means of absorbing them from the atmosphere.

—Andrew Restuccia and Summer Said contributed to this article.

Write to Matthew Dalton at Matthew.Dalton@wsj.com, Catherine Lucey at catherine.lucey@wsj.com and Sha Hua at sha.hua@wsj.com