China and the United States are expected to give the Paris climate change agreement a big push forward as the world's largest economies gather for the G20 Summit this weekend, experts say.

With China－which has shown growing international leadership on climate change－hosting the summit for the first time, "we can expect climate and energy to be front and center", said Joanna Lewis, a specialist at Georgetown University on energy and environmental issues in China.

The summit on Sunday and Monday is also the last for US President Barack Obama, who hopes to cement action on climate change as one of his legacy issues, experts say.

China and the United States, the world's two biggest contributors to climate change, have made a joint political push to drive action on the problem since 2014, when they made their targets for the Paris agreement public at the same time.

"The US and China are poised to lead the way in the G20 (on climate action) so other countries will follow," Lewis told journalists by telephone.

But G20 members so far have committed to only a sixth of the emissions cuts needed to hold global temperature increases to "well below 2 C", as agreed to in Paris, so much more needs to be done, said Lutz Weischer, head of international climate policy at Germanwatch, an advocacy group that tracks climate action.

In particular, planned new coal-fired power plants within the G20 would nearly double coal capacity if built, and would make it "virtually impossible" to limit warming even to 2 degrees, said a report issued on Thursday by the Climate Transparency consortium.

"In the real world, there is still a long way to go, particularly for the G20, and they need to reflect that in a more serious way," Weischer told journalists.

G20 economies produce about 80 percent of climate-changing greenhouse gas emissions, with China and the United States taking the lead, noted Andrew Steer, president of the World Resources Institute.

Getting more G20 members to ratify the Paris climate deal could boost momentum for it to take effect early, perhaps even by the end of this year or early next, he added.

That is considered increasingly important as the world continues to break temperature records on an almost monthly basis and struggles with more extreme weather, worsening coral bleaching, and other impacts that suggest climate change is advancing faster than anticipated.

For the Paris climate agreement to come into effect, 55 countries representing 55 percent of the world's emissions must ratify it.

So far 23 countries have done so, but 55 nations accounting for 58 percent of emissions have indicated they will approve the deal by the end of the year, said Andrew Light, a senior fellow at World Resources Institute and a former US State Department climate adviser.