In December this year, parties to the United Nations Framework Convention on Climate Change (UNFCCC) will descend on Copenhagen to wrangle over the details of a new global climate deal — a potential successor to the Kyoto Protocol. See Nature’s Road to Copenhagen special for more coverage.

China has announced it will reduce its carbon dioxide emissions per unit of GDP by between 40 and 45% of 2005 levels by 2020.

“Appropriate handling of the climate change issue is of vital interest to China’s social and economic development and people’s fundamental interests, as well as the welfare of all the people in the world and the world’s long-term development,” says the country’s State Council (Xinhua).

The Chinese announcement came barely hours after US President Barack Obama announced he would put a 17% below 2005 levels by 2020 offer on the table at the forthcoming Copenhagen climate talks. However, Obama’s offer on emissions was for absolute emissions, not the ‘carbon intensity’ measure linked to GDP levels that China prefers.

China’s pledge doesn’t actually mean that they will have to cut their carbon emissions. If the country’s economy grows enough then the target could be hit, provided industry becomes more efficient in its use of fossil fuel produced power, even if total carbon emissions actually rise.

“In 2020, the country’s GDP will at least double that of now, so will the emissions of greenhouse gases. But the required reduction of emissions intensity by 40 to 45 percent in 2020 compared with the level of 2005 means the emissions of [greenhouse gases] in 2020 has to be roughly the same as emissions now,” Qi Jianguo, of the Chinese Academy of Social Sciences, told Xinhua.

Still, the UN’s top climate official Yvo de Boer said the moves by America and China “can unlock two of the last doors to a comprehensive agreement” (AP, Bloomberg).