As negotiators work to agree on a final text, attention has turned to a fundamental question: Will the talks call for a phaseout of fossil fuels?

With fresh promises to cut methane and billions of dollars in new commitments to help poor countries adapt to a warming planet, a sense of momentum and optimism pervaded the first days of the United Nations climate summit in Dubai.

Now comes the hard part.

Five days into the two-week conference, known as COP28, the talks have become consumed by an intense debate over the future of fossil fuels.

The president of the event is under fire for having suggested that it is not necessary to phase out oil, gas and coal, the burning of which is dangerously heating the planet. At least 1,300 fossil fuels lobbyists, a record, are participating in the talks. And Saudi Arabia has said it opposes any agreement that calls for an end to fossil fuels — significant because, under U.N. rules, any single country can scuttle a deal.

At the same time, scientists, activists and dozens of world leaders are growing more adamant in their calls for a rapid reduction in oil, gas and coal, arguing that, without a pivot away from fossil fuels, the planet is destined for catastrophe. Agreement on a phaseout would be historic; Past U.N. climate deals have shied away from even including the words “fossil fuels.”

Against this backdrop, negotiators from more than 170 countries are frantically working to hash out an agreement that can be approved by every nation by next Tuesday.

“The COP presidency has brought baggage to this process, and far too many oil lobbyists,” said Tzeporah Berman, a Canadian activist who is chairwoman of the Fossil Fuel Non-Proliferation Treaty Initiative. “He has also brought a chance for a real conversation on how to phase out fossil fuels.”

Tensions over the decision to hold of the event in the Emirates have swirled for months and burst into view on Monday, when Sultan Al Jaber, the oil executive presiding over the climate talks, came under fire for saying there is “no science” behind the idea that fossil fuels must be phased out in order to keep average global temperatures from rising above 1.5 degrees Celsius above preindustrial levels.

That’s the threshold beyond which scientists say humans will struggle to adapt to increasingly severe storms, heat, drought and fire. The planet has already warmed by about 1.2 degrees Celsius.

On Tuesday, a group of more than 100 leading climate scientists issued a response, reiterating the consensus that nations must rapidly phase out fossil fuels to keep global temperatures from rising more than 1.5 degrees Celsius.

“There seems to be, in the corridors of the negotiations, some uncertainty of where the science stands,” said Johan Rockstrom, the director of the Potsdam Institute for Climate Impact Research in Germany and one of the authors of the letter. “So we wanted to provide a very solid summary of the overwhelming evidence we have.”

Send In The Lobbyists:

Mr. Al Jaber has sought to walk back his remarks, but the debate has highlighted the influence of oil-producing countries and the fossil fuel lobby.

Mary Robinson, the former president of Ireland who tried unsuccessfully to press Mr. Al Jaber to support an end to fossil fuels, said the COP28 president was “compromised.” But she added, “He said to judge him by results, and we will.”

The rancorous debate over the future of fossil fuels is playing out in a country built with a fortune made from oil. After long days of frenetic meetings at a sprawling convention center, diplomats and executives retreat to the luxury hotels of Dubai for poolside receptions and private dinners on manmade islands.

Yet time for consensus is running short.

Many scientists and activists want the final agreement, which is due in a week, to include unambiguous language that calls for the rapid phaseout of fossil fuels.

“I don’t think we are going to leave Dubai without some clear language and clear direction about moving away from fossil fuels,” said David Waskow, director of the international climate initiative at the World Resources Institute, an environmental research group.

But several Gulf state leaders and top oil executives have indicated they are not open to such language.

“Absolutely not,” the Saudi energy minister, Prince Abdulaziz bin Salman, said when asked during a television interview in Riyadh whether his country would support an agreement that called for the phase-down or phaseout of fossil fuels.

Aaron Padilla, the vice president of corporate policy at the American Petroleum Institute, which represents some of the biggest oil and gas companies in the United States, called the effort to demand a fossil fuel phaseout “misguided.”

Earlier at the conference, Darren Woods, the chief executive of Exxon Mobil, told the Financial Times that the discussions had “put way too much emphasis on getting rid of fossil fuels, oil and gas” and not enough on “dealing with the emissions associated with them.”

In Dubai, Mr. Woods has had plenty of company from the fossil fuel industry. For the first time, the United Nations required attendees to disclose their affiliations, and The Associated Press counted at least 1,300 attendees working on behalf of oil, gas and coal interests. That is three times the number of fossil fuel lobbyists thought to have attended last year’s climate summit, the A.P. reported.

While the summit organizers declared Tuesday ‘Energy Transition Day,’ activists renamed it “Fossil Fuel Phaseout Day” and held a series of actions to make their case.

At one point, a protester dressed in a lengthy cape covered with images of a burning forest walked toward the crowd of about 100, waving arms like a butterfly, to the beat of a drum that grew faster and faster.

Demonstrators carried a silver model of an oil pipeline high in the air, displaying a message on its side that said “Make Polluters Pay.”

“The world is burning, do you not see!” one climate activist, Amalen Sathanathar, part of a group called the Artivist Network, shouted into a megaphone. “We’re still fanning the flames.”

Late on Monday, negotiators issued a 24-page draft of an agreement that gave some indication of the distance that remains between nations on the question of a phaseout. It offered a number of different options, ranging from a clearly-stated “orderly and just phaseout of fossil fuels” to no mention whatsoever.

Many nations and fossil companies are advocating for the end of “unabated fossil fuels,” which broadly means that any new coal, oil and gas plants must incorporate technology that captures emissions before they can enter the atmosphere. That nascent technology is expensive and not available on a commercial scale. It currently removes just 0.1 percent of the carbon dioxide in the atmosphere.

David Tong of Oil Change International, an advocacy group, argued that abatement would “serve as escape hatches for the industry” because it would allow companies to continue to drill oil and gas. Mr. Tong also noted that there was no agreed-upon definition of “unabated” in the U.N. climate body and said “if the word gets into the text, it’s the Wild West.”

But some scientists said they were less concerned about the specific language around fossil fuels, and more focused on the whether or not the final text would include detailed plans for achieving real emissions reductions.

“It’s pointless to have endless debates about phasing out or phasing down,” Mr. Rockstrom said. “You need paragraphs of accountable, specific, science-based pathways for emissions reductions over the coming decades.”

The New York Times

David Gelles is a correspondent on the Climate desk, covering the intersection of public policy and the private sector.

Lisa Friedman reports on federal climate and environmental policy from Washington. She has broken multiple stories about the Trump administration’s efforts to repeal climate change regulations and limit the use of science in policymaking

Vivian Nereim is the lead reporter for The Times covering the countries of the Arabian Peninsula. She is based in Riyadh, Saudi Arabia.