After Rome all roads lead to Glasgow, where nearly 200 nations will gather for United Nations climate talks (COP26) on Sunday following the climate-centric G-20 summit.

Never has climate change figured so prominently on the G-20 agenda, and never have leaders hopped straight from a G-20 to a climate summit: more than 120 heads of state and government are expected at the outset of COP26 in Scotland. The G-20 summit ending the same day will signal how committed the world's major economies are to curbing global warming.

The G-20 – including China, the United States, India, the European Union and Russia – accounts for 80% of the global GDP and nearly 80% of greenhouse gas emissions.

"The G-20 is going to be very important for COP26," said Helen Mountford, VP for climate and economics at the World Resources Institute.

"The idea is to get very clear and strong pressure signals from the leaders on what they plan to do, both individually and collectively," she told Agence France-Presse (AFP).

Climate negotiators, CEOs, policy wonks and nongovernmental organizations (NGOS) at the 13-day climate talks will parse the G-20 communique for signs of where COP26 might break down or see breakthroughs.

Keeping 1.5C in play

No measure of success at COP26 looms larger than capping global warming at 1.5 degrees Celsius (2.7 degrees Fahrenheit) below pre-industrial levels, a threshold only a few tenths of a degree away.

"We want to be able to say with credibility coming out of Glasgow that we have kept 1.5C within reach," United Kingdom minister and COP President Alok Sharma told journalists by Zoom this week.

But that means slashing global emissions nearly in half by 2030 and to "net-zero" by 2050.

We are far from the mark. Recently updated carbon-cutting pledges – known as nationally determined contributions, or NDCs – would still see global temperatures rise a "catastrophic" 2.7 degrees Celsius, according to the U.N.

"We need sharp emissions cuts within this decade," said Rachel Cleetus, policy director for climate and energy at the Union of Concerned Scientists.

G-20 countries that have not stepped up with stronger near-term carbon cutting pledges – Australia, Japan, Brazil, Russia, Saudi Arabia – "are likely to be among those least enthusiastic" about a strongly worded commitment to 1.5 degrees Celsius, she told AFP.

Cool on near-term action

China – by far the world's biggest carbon polluter – plans to make its economy carbon neutral before 2060, but has also resisted pressure to deepen near-term ambition.

The cornerstone temperature goal in the 2015 Paris Agreement, China points out, is "well below 2C" – the 1.5 degrees Celsius goal was purely aspirational, even if it has since become the de facto target.

Beijing's revised climate plan, submitted to the U.N. Thursday, repeats a long-standing goal of peaking emissions by 2030.

"There's no way to be on a trajectory that's consistent with 1.5C by 2030 unless China does a lot more in this decade," said Alden Meyer, a senior associate at climate and energy think tank E3G.

India, meanwhile, argues that if net-zero by 2050 is the global goal, then rich countries should be carbon neutral 10 years earlier to allow poorer, emerging nations a larger carbon allowance and more time to develop.

A best-case scenario, experts say, would be a G-20 communique that calls for ramping up emissions reductions in the coming decade, setting 2023 – when a Paris Agreement "stocktake" is to take place – as a deadline for hard numbers.

These issues call for not only fast, decisive action, but also considerations of climate finance and the importance of long-term thinking with regards to climate change.

"Worst case would be something squishy that doesn't emphasize near-term 2030 action, but focuses more on long-term net-zero goals," said Cleetus.

Fossil fuels

G-20 finance ministers this summer gave a nod for the first time to carbon pricing as a potentially useful tool in the fight against climate change, but going beyond that has proved hard.

"A major breakthrough is unlikely, the political will is not really there," said Meyer.

In 2009, the G-20 pledged to "phase out over the medium term inefficient fossil fuel subsidies" that encourage wasteful consumption.

Twelve years later, however, subsidy levels remain in the hundreds of billions of dollars per year.

Proposals by Italy and the United States to set up timetables for action have met stiff resistance, notably from Russia and Saudi Arabia, according to observers.

When it comes phasing out coal, the picture is mixed.

Chinese President Xi Jinping's announcement in September that China would stop financing new coal-fired power plants abroad was widely welcomed, and deepens a global trend that the G-20 could endorse.

But when it comes to winding down domestic use of coal, positions are sharply divided, which means a forceful call in the communique to end coal is highly unlikely.

The U.S., Canada and European Union nations favor a rapid phase-out. China, India and Indonesia, however, continue to expand coal-fired energy capacity.

The G-20 also includes Argentina, Canada, France, Germany, Italy, Mexico, South Africa, South Korea, Turkey and the United Kingdom.