How big a role should carbon capture play in climate efforts?

World leaders at the annual United Nations climate talks have battled for years over whether they should “phase out” fossil fuels like coal or just phase them “down.”

Now, another phrase has taken center stage at this year’s summit in Dubai: Should countries agree to end the use of “unabated” fossil fuels?

That peculiar word choice might allow nations to continue to burn coal, natural gas, or oil as long as they trap and bury the resulting carbon dioxide, and stop the gas from heating the planet.

One big dispute is over how big a role this technology, known as carbon capture and storage, should play in the fight against global warming. Some oil and gas producers say it should be central in planning for the future. Others, including many activists and world leaders, dismiss carbon capture as too unproven and too risky.

A few recent studies have found that carbon capture can be a valuable tool for curbing emissions from certain activities, like cement manufacturing. But its use is likely to be limited: It would be nearly impossible for countries to keep burning fossil fuels at current rates and capture or offset every last bit of carbon dioxide that goes into the air. The technology is expensive, and in many cases there are better alternatives.

Despite billions of dollars in investment, countries and industries have also struggled to get carbon capture projects up and running. Unless that changes quickly, experts say, the technology might not play more than a marginal role in climate efforts.

“Carbon capture and storage definitely could be a critical technology,” said Fatih Birol, executive director of the International Energy Agency. “But the history of carbon capture to date has largely been a disappointment.”

In September, the IEA published a detailed road map for what it would take to slash the world’s energy-related emissions to nearly zero by midcentury in order to lessen the risk of catastrophic climate disruptions.

In that road map, carbon capture accounted for just 8 percent of the world’s total emissions cuts between today and 2050. By contrast, the vast majority of reductions would come from countries shifting away from fossil fuels entirely: relying more heavily on wind and solar power for electricity and swapping out gasolinepowered cars for electric ones.

Cost is one reason. In theory, companies could attach a carbon capture device onto almost any factory or power plant that burns fossil fuels today. But in practice, it’s often cheaper to shut down a coal plant and replace it with some combination of wind, solar, and batteries, or to swap out a gas boiler for an electric heat pump.

Still, there are cases where carbon capture might be the best option. One of them might be cement kilns, which release huge amounts of carbon dioxide as they transform limestone into cement. Some steel producers are exploring carbon capture as a way to reduce their emissions. Electric utilities might use gas plants with carbon capture to backstop intermittent wind and solar power.

Many researchers differ in their estimates of how much carbon capture is likely needed, but they all broadly agree on one thing: Total fossil fuel use will have to fall sharply no matter what to keep global warming at relatively low levels.