The world's two largest carbon polluters, China and the United States, sat on the sidelines during the world's very first efforts to keep Earth cool.
But on Friday, looking ahead to December talks in Paris to hammer out a new climate change agreement, presidents Xi Jinping and Barack Obama signalled they were in lock step behind an ambitious deal.
The world's two largest economies flexed their muscles with a joint agreement to increase their commitments above and beyond the breakthrough agreement the two leaders sealed in Beijing nearly a year ago.
Xi for the first time pledged to help finance poorer countries deal with global warming, and he confirmed 2017 as the target to launch a long-expected plan to take its localised carbon trading system to the national level.
Obama signalled that his push to get US power plants to reduce emissions blamed for global warming would get one step tougher next year. Those states that have not submitted a plan would be subjected to an imposed federal plan, the joint statement said.
The two presidents also agreed to implement new fuel efficiency standards for heavy-duty vehicles by 2019 - a sector of the transport branch that has not yet been widely addressed.
On some of the many pledges in the agreement, China is following in US footsteps.
Its $US3.1 billion ($A4.41 billion) finance pledge matches the $US3 billion US commitment to help poorer countries on the climate issue.
And Beijing agreed to restrict its public investments in projects with high carbon emission, a step the US took in 2013.
"That's a big deal," Athena Ballesteros, director of sustainable finance at the private World Resources Institute (WRI) in Washington, told dpa.
She said China's move was "already sending some ripples" through countries such as Brazil and South Africa, which could follow suit.
