On the northern edge of a vast Chinese factory city, welding torches gleam as workers finish construction on a gas-fired power plant to replace one that burned coal and blanketed the surrounding neighborhood in a sooty pall.

It’s one of several huge gas-fired plants being built to pump more electricity throughout this sprawling industrial city of about 10 million, where rising demand for power has led to rationing and blackouts that are now rippling across eastern China and threaten international supply chains.

This archipelago of power plants underlines an unsettling reality in the global fight to slow climate change. China burns more fossil fuels than any other nation, making it the planet’s top source of the greenhouse gases that are warming the Earth. And its voracious appetite for electricity is only growing.

Xi Jinping, China’s top leader, has promised his country will start reducing carbon dioxide and other gases generated by burning coal, gas and oil by 2030 and then stop adding them to the atmosphere altogether by 2060. But climate scientists warn that nations must make a sharp turn away from fossil fuels now, in order to avert the most catastrophic consequences of climate change.

Just weeks before a critical United Nations climate summit in Glasgow, attention is riveted on China and whether it will do more to cut emissions. The world’s top energy agency said last week that China “has the means and capacity” to reduce its pollution. Its actions could be consequential for the planet’s climate, already at a pivotal moment.

“We want to see ambition from China,” said Alok Sharma, a member of the U.K. Parliament who is overseeing the international climate negotiations. “China is responsible for almost a quarter of all global emissions right now. And they are going to be a critical part of making sure that we get success.”

China has taken some important steps this year to begin to curb its use of coal, the dirtiest of fossil fuels. In April, Mr. Xi vowed that China would “strictly control coal-fired power generation projects.” He added that the country would reach peak coal consumption by 2025, and then reduce it over the following five years.

Following Mr. Xi’s promise, local governments slowed approvals for new coal power projects within China, after a big surge in 2020. Some provinces, like coastal Shandong, mandated over the summer that some of their oldest, least efficient coal-fired plants be closed.

IN September, Mr. Xi announced at the United Nations that China would stop financing new coal power plants in other countries. Several U.S. experts said that was an important step, but not enough.

“The main event is for China to pledge a major cut in its emissions now, in this decade, as U.S., E.U. and others have,” Todd Stern, the climate envoy under former President Barack Obama, wrote on Twitter.

John Kerry, President Biden’s international climate envoy, noted while he was in the city of Tianjin a month ago that China still plans to build 247 gigawatts of new coal power. That is nearly six times Germany’s entire coal power capacity. China’s plan “would actually undo the ability of the rest of the world” to restrain global warming to a relatively safe level, he said.

“Can the world afford to have China, as already the No. 1 emitter, continuing to grow in those emissions over the next 10 years?” Mr. Kerry said in an interview. “No.”

Over the past three decades, China’s growth in energy use has been explosive. Each year, China burns more coal than the rest of the world combined and almost as much oil as the United States.