The Group of 20 rich countries are divided over phasing out coal and committing to limit global warming to 1.5 degrees Celsius as they prepare for a crucial summit in Rome next week, sources familiar with the negotiations said.

The need to curb greenhouse gases will be high on the agenda of the Rome G20 gathering on Oct. 30-31, seen as a key stepping stone immediately ahead of broader United Nations climate talks, called COP26, to be held in Glasgow, Scotland.

COP26 president, Britain's Alok Sharma, said in a speech this month the G20, which accounts for 80% of global emissions, would be "make or break" for achieving success in Glasgow.

Big polluters such as China and India have so far dug in their heels, however, and little progress has been made since G20 energy and environment ministers met in Naples in July, said three sources, asking not to be named due to the sensitivity of the talks.

"Countries are not moving, at the moment they are still just making sure their positions are heard loud and clear," said one of the sources.

But he added that such intransigence was normal at this stage and that any concessions were unlikely to come before G20 climate sherpas meet face-to-face next Thursday and Friday, immediately before their leaders' weekend meeting.

"Where I see the problem is in the commitment to 1.5 degrees and in the phase out of coal and fossil fuels by China, India and Russia," said another source, a G20 minister.

In a letter to G20 president, Italy's Mario Draghi, nine countries including Grenada and the Marshall Islands, both vulnerable to storms and rising seas, urged G20 nations to hike their climate pledges to "set the tone" for COP26. 

Climate scientists say capping global warming at 1.5 degrees compared with pre-industrial levels is vital to limit environmental disasters, but a broad and clear commitment to achieve the goal is proving elusive.

The landmark UN Paris Agreement signed in 2015 aimed to limit global warming to "well below 2 degrees" and "preferably" to 1.5 degrees, and since then international gatherings have tried with difficulty to toughen up the language.

In Naples, energy and environment ministers recognised that environmental risks were lower at 1.5 degrees than at 2, but again fell short of clearly stating 1.5 must not be breached.

They also failed to reach unanimous agreement on fixing dates to end fossil fuel subsidies, halt international financing of coal projects and phase out coal power altogether, asking leaders to bridge the gaps at the upcoming Rome summit.

Coal still powers more than half the electricity generated by China, the world's largest energy producer and also the largest greenhouse gas emitter.

The country has pledged to become carbon neutral by 2060 but has not committed to a date for halting domestic coal production.

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At least four G20 leaders are not expected to come to Rome, including China's Xi Jinping and Vladimir Putin of Russia, another major oil and gas producer.

One source said while such absences were "not a great political signal," they would not necessarily prevent progress.

Indian Prime Minister Narendra Modi will be coming to Rome, officials said, and New Delhi confirmed on Thursday that he will also be at the COP26 in Glasgow. read more

Neither Russia, China nor India have committed to achieving net zero carbon emissions by 2050, considered a vital goal in limiting global warming to 1.5 degrees.

So far China is proving most reluctant to commit to the 1.5 degree ceiling, while India is most intransigent in not pledging net zero emissions by 2050, one of the sources said.

China and India are also among a group of countries that have not yet presented new national plans, known as Nationally Determined Contributions (NDCs) ahead of COP26, on how they will help curb climate change.

A number of countries including the two Asian giants this week criticised rich nations that have broken their own promises to cut CO2 and deliver financial help to weaker countries to battle climate change. In this situation it is unfair to expect poorer peers to commit to tougher emissions targets, they said.

One of the sources said breakthroughs were more likely in Glasgow than in Rome.

Big emitters like China, India and Russia tend to feel pressured and hectored by the Western countries at the G20, he said, making them defensive and reluctant to concede ground.

The much larger UN forum was more "neutral" and conducive to compromise, he said.

The Rome G20 will also focus on the coronavirus pandemic and how to foster global economic recovery, Italian Prime Minister Mario Draghi, who will chair the meeting, said on Wednesday.