GLASGOW - Dozens of nations signed up to deals to phase out coal and end fossil fuel finance at UN climate talks in Scotland on Thursday (Nov 4), as pressure grows to halt the expansion of polluting energy that is warming up the planet.

But some of the agreements failed to attract key nations, raising questions about the true impact of the deals.

One of the key aims of Britain, the host of the COP26 climate talks, is to spell the end of coal, the most carbon-intensive fossil fuel and the single largest source of carbon dioxide (CO2). The gas traps heat in the atmosphere, disrupting the climate and causing greater weather extremes, as well as the melting of glaciers and polar ice caps that is raising sea levels.

In one of the key deals announced on Thursday, Indonesia, Poland, Vietnam and other nations pledged to phase out the use of coal-fired power stations and stop building new plants. But the United States and large coal consumers such as China declined to join.

Signatories agreed to phase out coal-fuelled power generation in the 2030s in richer countries, and the 2040s for poorer nations.

A majority also committed to shun investment in new coal plants at home and abroad. But China, India and Australia threw a shadow over the attempt to win global backing for an exit from coal.

Indonesia also did not agree to the part of the deal on ending finance for new coal plants.

"Today I think we can say that the end of coal is in sight," COP26 president Alok Sharma of Britain told the Glasgow meeting. He later told a news conference it had been a personal priority since becoming COP26 president to consign coal to history and that now "I think you can say with confidence that coal is no longer king".

Thursday's agreement has 77 signatories, including 46 countries, 23 of which are making commitments on ending coal for the first time, he said.

A separate announcement by the Powering Past Coal Alliance, an international campaign, on Thursday said it had secured 28 new members, including Singapore, to pledge to quit coal.

By joining the alliance, Singapore has committed to continue phasing out the use of unabated coal in its electricity mix by 2050, and to restrict direct government finance of unabated coal power internationally, said the National Climate Change Secretariat and ministries of Sustainability and the Environment as well as Trade and Industry.

Unabated coal refers to power plants that do not have equipment to capture and store the CO2 emissions.

And in another announcement, 25 countries, development banks and national groupings - including the United States, Canada and Costa Rica - pledged to end public finance for new fossil fuel exploration and production overseas by the end of 2022. Instead the money would go towards green energy finance.

If implemented, the landmark pledge could push close to US$18 billion (S$24.4 billion) a year in international funding not just out of coal but also the oil and gas sector in developing countries, according to campaign group Oil Change International.

Ms Jean Su, director of the energy justice programme at the Centre for Biological Diversity in Washington DC, told media at the Glasgow talks that it was "the first political commitment to phase out oil and gas", Reuters reported.

Ending public finance is a key part of the puzzle in phasing out support for fossil fuels.

The Group of 20 (G-20) countries spent at least US$63 billion per year financing oil, gas and coal projects through their development finance institutions, export credit agencies and the multilateral development banks compared with about US$26 billion per year for renewables, said a report last month by non-governmental organisations Friends of the Earth US and Oil Change International.

Public finance is important because it helps reduce the financial risks for specific projects. But ultimately it undermines efforts to ramp up investment in cleaner energy because governments typically also subsidise fossil fuels through myriad other means, such as tax breaks.

Public finance, though, is dwarfed by the total value of subsidies for fossil fuels.

A report by BloombergNEF and Bloomberg Philanthropies earlier this year found that G-20 countries have provided more than US$3.3 trillion in subsidies for fossil fuels between 2015 and 2019, or just over US$600 billion a year. This is despite the landmark Paris climate agreement being sealed in 2015 in which nations pledged to limit global warming - and ultimately fossil fuel use.

The G-20 nations, which collectively are responsible for about 80 per cent of humanity's annual CO2 emissions, are under pressure to end fossil fuel subsidies and instead redirect the money to green energy investments and support for poorer developing nations.

While the announcements on the phase-out of coal by countries are important, the key is how nations enact policies to guide that transition to green energy as well as access to financing, said Ms Jennifer Layke, global director, energy programme, at the World Resources Institute in Washington.

"It's a pretty significant list of countries that committed today to phasing out coal power," she told a media briefing.

She said steps to revamp electricity grids and thinking about long-term energy storage technologies such as hydrogen are key initiatives that will help the green transition.

But finance is vital. At COP26, funds pledged by wealthier countries and philanthropies to help developing nations make the green switch are important. But the question is whether they can move fast enough, she said.

One additional initiative announced earlier this week by the US government, called the Clean Energy Demand Initiative, creates a platform to connect countries with companies seeking to rapidly deploy clean energy to offset electricity demand in their sectors, including health, manufacturing, retail, technology, and transportation.

More than 75 companies have indicated investment interest in 14 countries, which could drive up to US$67 billion in renewable energy infrastructure, the White House said in a statement about the programme.