(Bloomberg) -- The world needs to phase out some fossil fuels — while employing carbon capture technology — to reach net zero climate targets by mid-century, US climate envoy John Kerry said, even as negotiators haggled over the best approach.

The future of oil, gas and coal has become a major hurdle for countries wrapping an initial week of talks at the COP28 climate summit in Dubai, where final decisions must be agreed unanimously. While the EU and US are pushing for some kind of commitment to phase out fossil fuels, China, India and others have balked at the approach. Saudi Arabia’s energy minister told Bloomberg the kingdom wouldn’t agree to phase down language in a final accord.

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“If you’re going to reduce the emissions and you’re actually going to hit the target of net zero by 2050, you have to do some phasing out. There’s no other way to get to that target,” Kerry said at a news conference Wednesday. “You’ve got to have largely a phase out of fossil fuels in our energy system,” while focusing carbon capture technologies on steel, cement and other hard-to-abate sectors.

An endorsement of carbon capture is unpopular with some countries and activists at the UN summit. COP28 President Sultan Al Jaber drew fire for resurfaced remarks he says were misunderstood asserting that the phase out of fossil fuel is not what’s going to keep global warming to 1.5C, a critical tipping point. 

Read More: COP28 President’s Fossil Fuel Phase Out Talk Draws Condemnation

Kerry said carbon capture, utilization and storage — or CCUS — is an essential part of the mix. While “you can raise some very legitimate questions about CCUS,” it still is working in certain ways, he said. 

“Science says we have to reduce the emissions. It doesn’t prescribe some particular discipline that has to be done; it says reduce the emissions,” Kerry said. And “the science says we cannot get to net zero 2050 without some” carbon capture.

Read More: What Is COP28 and Why Is It Important?

The clash over possible language on fossil fuels, renewable energy and efficiency set up a difficult second week of climate talks in Dubai, following a flurry of voluntary emissions-cutting commitments unveiled in recent days.

“We’ve had a pretty damn good week here in Dubai already,” even if there are “tough issues” looming, Kerry said. 

“I’m not telling you that everybody’s going to come kumbaya to the table, but I am telling you we’re going to make our best effort to get the best agreement we can to move as far as we can as fast as we can,” Kerry said. “That’s what people in the world want us to do. It’s time for adults to behave like adults and get the job done.”

(Updates with further Kerry comments from seventh paragraph.)

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