At the end of the APEC trade summit in China, Obama announced a climate change agreement with President Xi.
Under the deal, the United States would cut its carbon emissions between 26-28 per cent -- from levels established in 2005 -- by 2025.
China would peak its carbon emissions no later than 2030 and would also increase the use of non-fossil fuels to 20 per cent by 2030.
"As the world's two largest economies, energy consumers and emitters of greenhouse gases, we have a special responsibility to lead the global effort against climate change," Obama said in a joint press conference with Xi.
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Obama said he hopes the announcement will spur other nations to tackle climate change.
"We hope to encourage all major economies to be ambitious -- all countries, developing and developed -- to work across some of the old divides, so we can conclude a strong global climate agreement next year," he said.
Chinese President Xi said: "We agreed to make sure that international climate change negotiations will reach an agreement in Paris."
The White House said the ultimate target is to "achieve deep economy-wide reductions on the order of 80 per cent by 2050."
It said the announcement marks the first time China has agreed to cut its carbon emissions, and said the Chinese are calling for "an energy revolution" that would include a broad economic reform programme that would address air pollution."
Last evening, the two heads of state held a meeting at the Zhongnanhai leadership compound.
After that meeting, the two leaders pledged to push forward a new type of major-country relations between the two countries.