WASHINGTON/BEIJING - The United States and China have pledged to fight climate change together, a surprising move from the keen rivals that gave the global climate talks in Glasgow a much-needed boost.

But whether the world's two largest emitters of planet-warming greenhouse gases can achieve their aim will be a test of their commitment to the cause, said experts.

"The pledge prevented the worst from happening, which is a decoupling on climate action," Greenpeace China global policy adviser Li Shuo told The Straits Times yesterday. But, given the "life-threatening stakes if climate change continues to worsen", both countries must put their words into action and stay the course despite geopolitical tensions, he added.

The US and China said on Wednesday they will do more to cut methane emissions and phase out coal this decade.

United Nations Secretary-General Antonio Guterres and the European Union's climate policy chief Frans Timmermans welcomed the news.

Mr Guterres wrote on Twitter that "tackling the climate crisis requires international collaboration and solidarity, and this is an important step in the right direction".

Mr Timmermans also wrote on Twitter that "bilateral cooperation between the two biggest global emitters should boost negotiations at COP26. Now we must find the global deal that keeps 1.5 degrees alive". He was referring to the UN climate conference and the push to limit global warming to 1.5 deg C above pre-industrial levels.

The deal was a surprise amid strained ties over human rights, trade and Taiwan, which China views as a renegade province, to be reunified by force, if necessary. The US said last month it will come to Taiwan's defence if Beijing attacks.

The latest pledge on climate action was announced by American climate czar John Kerry and his Chinese counterpart Xie Zhenhua in a move that experts say is the necessary push for a more robust agreement at the end of COP26 in Glasgow. It has been the only point of agreement between the US and China recently.

Both countries recognised that the world had so far fallen short of the 2015 Paris Agreement targets to limit global warming, and they stressed "the vital importance of closing that gap as soon as possible".

Methane emissions, in particular, must be reduced in the current decade given their role in increasing temperatures, said Washington and Beijing.

The statement said China will develop a national plan "aiming to achieve a significant effect on methane emissions control and reductions in the 2020s".

This follows the Biden administration's recently released national action plan to reduce America's methane emissions.

The US and China also committed to a meeting in the first half of next year to discuss how to better tackle such emissions. This could include standards to reduce methane from the fossil fuel and waste sectors, and incentives to cut it from the agricultural sector.

Mr Ma Jun, director of the Institute of Public and Environmental Affairs in Beijing, said the pledge was a bright spot during the summit, given its rocky start.

President Joe Biden had accused Chinese President Xi Jinping and Russian President Vladimir Putin of failing to show leadership on climate change when they did not attend the summit in Glasgow.

In response, Chinese Foreign Ministry spokesman Wang Wenbin said China has been putting to practice its commitment to fight climate change.

"What we need in order to deal with climate change is concrete action rather than empty words," he said.