China has unveiled its first firm target for limiting greenhouse gas emissions¹, two weeks before a global summit on climate change in Copenhagen.

哥本哈根全球气候变化峰会召开前两周之际，中国首次宣布了限制温室气体排放的坚定目标。

 Beijing said it would aim to reduce its "carbon intensity²" by 40-45% by the year 2020, compared with 2005 levels.

Carbon intensity, China's preferred measurement, is the amount of carbon dioxide emitted for each unit of GDP.

But our correspondent says it does not mean China's overall levels of carbon dioxide will start falling.

Its economy is still growing and is mostly fuelled by polluting coal, says the BBC's Quentin Sommerville in Beijing.

It will be at least a couple of decades before China's emissions peak, so it is likely to remain the largest polluter for some time to come, he adds.

But greenhouse gas emissions in China have not been rising as fast as its economy has been growing.

The Copenhagen UN summit - between 7-18 December - aims to draw up a treaty to succeed the 1997 Kyoto Protocol³, although observers say this is unlikely.

Beijing also said on Thursday that Chinese Prime Minister Wen Jiabao would attend the talks.

That confirmation⁴（确认） came a day after US President Barack Obama said he would go to the summit.

The US - the second largest polluter after China - said President Obama would offer to cut US emissions by 17% from 2005 levels by 2020.

But the offer was less than hoped for by the EU, Japan and UN scientists - most other countries' targets are given in comparison with 1990 figures.

BBC environment correspondent Richard Black says that on that basis the US figure amounts to just a few percentage points, as its emissions have risen by about 15% since 1990.

This is much less than the EU's pledge of a 20% cut over the same period, or a 30% cut if there is a global deal; and much less than the 25-40% figure that developing countries are demanding.

President Obama's offer reflects figures in a bill narrowly passed by the House of Representatives in June, but yet to be confirmed by the Senate.

He will arrive at the summit after it opens and will not stay until the end, when delegates hope to stitch together（缝合，凝聚） a deal. While in Europe, he will also collect his Nobel Peace Prize in Oslo.

Thursday's announcement by China marks the first time it has issued numerical targets for plans to curb⁵（抑制，束缚） the growth of greenhouse gas emissions.

A statement from Beijing's State Council, or cabinet, said: "This is a voluntary action taken by the Chinese government based on its own national conditions and is a major contribution to the global effort in tackling climate change," Xinhua news agency reported.