The United States and China have announced an action plan on greenhouse emissions as part of a "historic" pact acclaimed by climate scientists and denounced by US Republicans as a job-killer.
The leaders of the world's two biggest polluters have put their stamp on attempts to breathe new life into action against global warming ahead of international talks in Paris next year.
US President Barack Obama said Wednesday's joint announcement on the two countries' emissions targets was a "historic agreement" and a "major milestone in the US-China relationship".
Attempts to deal with climate change, which scientists warn is approaching a potentially catastrophic point of no return, have long been stymied by the unwillingness of the United States and China to work together on the problem.
But China set a target for its greenhouse gas output to peak "around 2030", which Obama commended as an effort to "slow, peak and reverse the course" of its emissions.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
And Obama, who faces scepticism as well as outright denial about climate change in the US Congress, set a goal for the United States to cut its own emissions of greenhouse gases by 26 to 28 per cent from 2005 levels by 2025.
"We have a special responsibility to lead the worldwide effort against climate change," Obama said at a joint news conference with Chinese President Xi Jinping said.
"We hope to encourage all economies to be more ambitious."
China and the US, which together produce around 45 per cent of the world's carbon dioxide, will be key to ensuring a global deal on reducing emissions after 2020 is reached next year.
The two countries have long been at loggerheads over global targets, with each saying the other should bear more responsibility for cutting emissions of gases blamed for heating up the atmosphere.
But after the 2009 Copenhagen Summit nearly ended in fiasco, salvaged only by a last-minute deal brokered by Obama and China's then premier, Washington and Beijing have started to move closer towards agreement.
The World Resources Institute, a US-based environmental group, hailed the Obama-Xi pact as a breakthrough.
"It's a new day to have the leaders of the US and China stand shoulder-to-shoulder and make significant commitments to curb their country's emissions," the institute's president Andrew Steer said.
"They have both clearly acknowledged the mounting threat of climate change and the urgency of action."
But while it was the first time China agreed to a target date for emissions to peak, the commitment was qualified, leaving considerable room for manoeuvre.
The US Senate's new Republican leader was quick to slam Obama's proposed greenhouse gas reductions.
"This unrealistic plan, that the president would dump on his successor, would ensure higher utility rates and far fewer jobs," Senator Mitch McConnell said.
The European Union pledged last month to reduce emissions by at least 40 per cent by 2030 compared with 1990 levels.
But efforts to make meaningful progress on climate change will by stymied unless the US sets "a concrete and ambitious" goal to reduce its greenhouse gas emissions, Connie Hedegaard, EU climate commissioner, said in October.
The EU accounts for 11 per cent of the world's greenhouse gas emissions, compared to 16 per cent for the United States and 29 per cent for China.
