Phasing out fossil fuels completely is not a realistic goal, according to China’s climate envoy and the world’s top greenhouse emitter’s representative to the United Nations’ climate talks in November.

Fossil fuels are essential to maintain grid stability and energy security given the sometimes unreliable nature of renewables, Xie Zhenhua said, according to a video recording of a speech at a conference in Beijing.

“Completely phasing out fossil fuel is unrealistic,” Xie said. “We should build the new before discarding the old,” he said, calling for an understanding of the challenges faced by individual countries.

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Xie’s comments highlight the challenges ahead of the COP28 climate conference in Dubai in November, where the exact nature of a fossil-fuel “phase-out” will be a topic of conversation. China’s approvals for new coal power plants has surged in recent years after a series of power shortages, raising questions about its promises to consign the fuel to a supporting role to its fast-expanding renewables.

Read more: China’s Coal Build-Out Raises Questions on Future Power Plans

Xie said he’s been in regular contact with his US counterpart, John Kerry, in preparation for the summit and was willing to travel to a third country or even the US to take those discussions forward. The two sides resumed climate talks in July after nearly a yearlong freeze in ties that followed then-US House Speaker Nancy Pelosi’s high profile visit to Taiwan.

The Chinese climate negotiator also urged countries to eliminate barriers to trade in renewable energy products and technology cooperation. Major Chinese solar manufacturers dominate the industry globally but have suffered from shipping disruptions in the US due to customs curbs designed to tackle alleged human rights abuses.