Leaders from the Group of 20 major economies are split over phasing out coal and limiting global warming to 1.5 degrees Celsius, officials said, throwing into doubt whether ambitious climate change targets can be hit.

The gathering of world leaders in Rome this weekend is expected to set the tone for talks at the nearly two-week United Nations climate summit in Glasgow, slated to follow immediately afterward.

G-20 nations, including the U.S., China, Russia, India and Saudi Arabia, will attempt to forge a common position on how best to adhere to the 2015 Paris climate agreement, which asks countries to start reducing their emissions as soon as possible and achieve a climate-neutral world by midcentury.

Officials said forging consensus on policies to achieve this remains difficult given the G-20’s competing interests and that few concrete proposals are likely to come out of the summit.

Recent energy crises have also spurred leaders to rethink their stance on fossil fuels. In China, a coal supply shortage has led to major revisions of the country’s carbon roadmap, elevating the importance of energy security and creating wiggle room for adding more coal plants, a person familiar with the discussions said.

Without a positive signal from G-20 leaders, agreement at COP26—as the Glasgow climate summit is known—will be even harder to achieve, climate activists fear.

The G-20 and COP26 could be “mutually reinforcing or mutually weakening,” said one senior official involved in the talks.

Italian Prime Minister Mario Draghi told Italy’s Parliament earlier this month that his country, which holds the G-20 presidency this year, hoped to achieve consensus among the group’s leaders before the Glasgow conference.

“The climate crisis can only be managed if all major global players decide to act in an incisive, coordinated and simultaneous manner.” Mr. Draghi said, noting that G-20 members account for about three-quarters of the world’s carbon emissions.

The issue of coal will be a litmus test of G-20 leaders’ political resolve. The group includes several heavy users and producers of the fossil fuel, including China, the U.S. and Australia. In July, G-20 environment ministers meeting in Naples couldn’t agree to set dates for phasing out the use of coal and ending the building of new coal-fired power stations.

Coal-rich countries such as China, India and Australia emerged as vocal opponents of such targets, said people familiar with the negotiations, adding that Turkey, Russia and Saudi Arabia were also part of the camp.

Some countries fear that an agreement to phase out coal would quickly lead to pressure to wind down the use of other fossil fuels such as gas or oil, said Chris Littlecott, an associate director at climate consulting firm E3G.

A surge in fossil-fuel prices as economies reopened after lockdowns has led several countries, including China and the U.K., to lean on coal to power their industries and electricity supply.

G-20 climate officials are meeting face-to-face late this week, immediately before their leaders come together at the weekend, to discuss these issues as well as try to fix a deadline for ending fossil-fuel subsidies.

Chinese President Xi Jinping said in April that China would begin “phasing down” its coal consumption in 2026. But neither China nor India, the second-most populous country in the world, are willing to commit to an end date or use the phrase “phase out” in relation to coal.

The action plan on how China plans to reach its carbon-dioxide peak before 2030, which was released by the State Council on Tuesday, said new constructions of coal plants needed to adhere to international energy efficiency standards. An earlier version of the plan made no mention of new coal-fired power plants, said the person familiar with the discussions, adding that a few renewable-energy targets had also been dropped from the final version, while a greater emphasis was placed on energy security.

Coal powers around 56% of China’s industry-heavy economy and is regarded as vital for the country’s energy security. It is unlikely China will even start considering this politically sensitive question until after the twice-a-decade Communist Party congress in fall 2022, the person said.