A critical climate conference that began with world leaders acknowledging an Earth in crisis was set for a second day of leaders' speeches on Saturday that organizers hope will set the stage for concrete action in coming days.

The annual United Nations conference, known as COP28, was dominated Friday by presidents, prime ministers and royals laying out their plans to reduce heat-trapping emissions and urging each other to come together to avert climate catastrophe that seemed to draw closer than ever in 2023 .

With about 150 of the planet's top decision-makers in attendance, opening speeches spilled into Saturday where some 60 nations had yet to speak before the major work of the conference, which runs through Dec. 12, begins.

Missing from the conference are the heads of the top two polluting nations — Presidents Joe Biden of the U.S. and Xi Jinping of China. Vice President Kamala Harris was set to stand in Saturday for Biden.

Harris’ appearance at COP28 in Dubai marks the first time since COP3 in Kyoto, Japan, that a vice president has led America’s delegation. COP3 in 1997 saw then-Vice President Al Gore speak. Intervening COP summits through President George W. Bush’s tenure saw lower-level.

COPs have grown in prominence in recent years. President Barack Obama attended some summits during his eight years. President Donald Trump saw lower-level involvement at COP as he withdrew the U.S. from the Paris Accords. And President Joe Biden attended COP26 in Glasgow, Scotland, and COP27 in Sharm el-Sheikh, Egypt.

In a fire-and-brimstone kickoff Friday, U.N. Secretary-General Antonio Guterres, fresh from viewing melting glaciers in Antarctica and Nepal , said "Earth's vital signs are failing" and told leaders, “you can prevent planetary crash and burn.”

He referred to inequality and conflicts, mentioning the return of fighting between Israel and Hamas on Friday.

“Climate chaos is fanning the flames of injustice,” Guterres said. “Global heating is busting budgets, ballooning food prices, upending energy markets, and feeding a cost-of-living crisis. Climate action can flip the switch.”

Jordan's King Abdullah said it was impossible to separate climate change from the war in Gaza .

“Climate threats magnify the devastation of war,’’ the king said. “Let’s be inclusive of the most vulnerable Palestinians severely impacted by the war.”

Kenya President William Ruto called climate change “the defining issue of our era” and joined many leaders who repeated major goals of conference organizers: to triple renewable energy and double energy efficiency.

Those goals aren't controversial, but what to do about fossil fuels is.

Guterres, a long-time critic of oil, gas and coal use that is causing climate change, fired his strongest shots yet against the industry, which includes COP28 host country United Arab Emirates, saying, “We cannot save a burning planet with a firehose of fossil fuels.”

In a direct challenge to fossil fuel-aligned nations, the U.N. chief said the only way to limit warming to the goal set in 2015 in Paris — 1.5 degrees Celsius (2.7 Fahrenheit) since the start of the industrial era — requires eliminating oil, coal and gas use. “Not reduce, not abate. Phase out," he said.

The conference president on Friday issued a document calling for a “phase-down” of fossil fuels , which experts say is less than a phase-out. But 106 nations in Africa, Europe, the Caribbean and in the Pacific signed a statement calling for a full exit. It's up to the more than 190 countries in the talks to come up with an agreement everyone can be happy with, said conference Director General Majid Al Suwaidi. (AP)