BEIJING - China and the US agreed ambitious greenhouse gas emission targets on Wednesday, the White House said in a statement, with Beijing setting a goal for its emissions to peak "around 2030".
It is the first time China - the world's biggest polluter - has set a date, even approximate, for its emissions to stop increasing, and the White House said China would "try to peak early".
At the same time the US set a goal to cut its own emissions of the gases blamed for climate change by 26-28 per cent from 2005 levels by 2025.
The declaration came as President Barack Obama met his Chinese counterpart Xi Jinping for talks in Beijing.
China will look to "increase the non-fossil fuel share of all energy to around 20 per cent by 2030", the White House said. The proportion stood at 10 per cent last year, Chinese officials have previously said.
Scientists argue that drastic measures must be taken if the world is to limit global warming to the UN's target of two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels, and failing to do so could have disastrous results.
China and the US, which together produce around 45 per cent of the world's carbon dioxide, will be key to ensuring that a global deal on reducing emissions after 2020 is reached in Paris 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.
Wednesday's promises are equally fraught with challenges.
While the US - which never ratified the Kyoto Protocol on climate change - has pledged to cut emissions in the past, goals have shifted or been missed altogether.
Its greenhouse gas emissions increased last year, despite Washington setting emissions reduction goals during a climate summit in 2009.
The deadline for Obama's new pledge is in more than a decade's time but he only has two years left in his presidency and faces a Congress controlled by opposition Republicans in both houses, which will make passing crucial environmental legislation more difficult.
Much of his action on climate change so far has been done with executive orders rather than co-operation from an often confrontational legislature.
While it was the first time China agreed to a target date for emissions to peak - officials have previously only spoken of doing so "as soon as possible" - the commitment was qualified, leaving considerable room for manoeuvre.
China has trumpeted its efforts to reduce dependence on coal and oil in the past, and is the world's largest hydropower producer, with a growing nuclear sector.
But economic growth remains a vitally important priority and has seen demand for energy soar.
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.