The need to curb emissions will be high on the agenda of the Rome G20 gathering on October 30-31, seen as a key stepping stone immediately ahead of broader United Nations climate talks, called COP 26, to be held in Glasgow, Scotland.

So far big polluters such as China and India have dug in their heels 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.

However he added that such intransigence was normal at this stage and 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 Naples, energy and environment ministers recognised the desirability of limiting global warming to 1.5 degrees but fell short of a clear commitment to achieve the goal.

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.

At least four G20 leaders are not expected to come to Rome, including China's Xi Jinping, at the helm of the world's biggest greenhouse gas emitter, and Russia's Vladimir Putin, head of the largest energy producer.

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

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 COP 26, on how they will help curb climate change.

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

However, 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.

Australian Associated Press