Four of the world's top airlines have backed a global scheme to curb carbon emissions and hope the proposal will be included in a broader UN pact to fight climate change.

It is the first time airline firms have banded together to make recommendations to UN climate change officials on how to tackle the sector's carbon emissions.

It will be hard work getting rich nations to agree cuts in greenhouse gases that are deep enough to satisfy the demands of developing countries at climate talks, UN's climate chief told Reuters on Monday.

Some 175 nations are meeting this week in Bonn in one of a series of UN-led meetings meant to forge a deal in Copenhagen in December to replace or extend the Kyoto Protocol.

A hydropower plant on the upper reaches of China's Yellow River was this week approved by the United Nations to sell carbon credits, making it the biggest hydro project to do so, Xinhua reported on Friday.

The United States is ready to take a leading role in tackling climate change, President Barack Obama said on Sunday, receiving a cautious welcome from European Union hosts at talks in the Czech capital Prague.

OPEC said oil was not to blame for climate change and consuming countries should pay to fight the threat, while the CEO of Royal Dutch Shell said drivers could help by not buying Hummer sports utility vehicles.

"Oil is not responsible," the producer group's Secretary General, Abdullah al-Badri, told reporters on Thursday on the sidelines of the International Oil Summit in Paris.

Developing nations must adopt targets for cutting greenhouse gas emissions and they need to do their share to reduce global warming, Mexican President Felipe Calderon said on Wednesday.

Aviation leaders called on Monday for a global carbon emissions scheme for their industry, arguing that an emerging patchwork of regional and national systems could bring more, not less, environmental damage.

The world is striving for a new U.N. climate "treaty" in December to succeed Kyoto. Or perhaps it will be a vaguer "agreement," "deal" or "decision."