Simmering tensions around the decision to hold a global climate summit in a petrostate burst into the open Monday when Sultan al-Jaber, the Emirati oil executive who is leading the conference, launched into an angry public defense of his position on ending fossil fuel use.

Al-Jaber, who runs the state-owned oil company, ADNOC, was under fire for a video that surfaced in which he said 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 over preindustrial levels.

That’s the threshold beyond which scientists say humans would struggle to adapt to increasingly severe storms, drought, heat and rising sea levels caused by global warming.

Climate experts convened by the United Nations have said that nations must cut the emissions from fossil fuels 43% by the end of this decade, compared with 2019 levels, if the world has any hope of limiting warming to 1.5 degrees Celsius.

Many diplomats and scientists say that would be impossible without phasing out fossil fuels and want governments to emerge from the climate talks being held in Dubai with a pledge to end the use of coal, oil and gas.

“The 1.5-degree limit is only possible if we ultimately stop burning all fossil fuels,” U.N. Secretary-General António Guterres said Friday. “Not reduce. Not abate. Phase out. With a clear time frame aligned with 1.5 degrees.”

But al-Jaber, who is supposed to be guiding nearly 200 nations toward an ambitious plan to tackle global warming, framed things differently in his comments two weeks ago.

“There is no science out there, or no scenario out there, that says the phaseout of fossil fuel is what’s going to achieve 1.5,” al-Jaber said during a panel discussion called She Changes Climate that featured Mary Robinson, the former president of Ireland who is now a prominent climate advocate.

Robinson asked al-Jaber if he would lead a global effort to taper down and then end the burning of fossil fuels. He chastised her for asking the question, saying he had expected a “sober and mature conversation” not an “alarmist” one.

The panel discussion took place two weeks ago, but only came to light Sunday when al-Jaber’s comments were reported by The Guardian.

“Please, help me, show me a road map for a phaseout of fossil fuels that will allow for sustainable socioeconomic development, unless you want to take the world back into caves,” he told the panel.

His remarks set off a firestorm at the climate talks known as COP28.

Former Vice President Al Gore, who has called for fossil fuels to be replaced with wind, solar and other renewable energy, assailed al-Jaber.

“From the moment this absurd masquerade began, it was only a matter of time before his preposterous disguise no longer concealed the reality of the most brazen conflict of interest in the history of climate negotiations,” Gore said in an email. “Obviously, the world needs to phase out fossil fuels as quickly as possible.”

But on Monday, a defiant al-Jaber suggested he did not say what he can be heard saying on the video. And he indicated that anyone who claimed otherwise was trying to undermine his leadership of COP28.

The planet has already warmed about 1.2 degrees since the industrial revolution, driven by the burning of coal, oil and gas.

Jim Skea, the chair of the U.N.’s Intergovernmental Panel on Climate Change, said Monday while sitting next to al-Jaber that fossil fuels would need to be “greatly reduced” by 2050 in order to limit global warming to 1.5 degrees.

The fossil fuel industry has responded to suggestions of a phaseout by saying that technology could capture and store carbon emissions, which would allow it to continue to operate.