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 U.N. pact to fight climate change.

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

Aviation is responsible for about two percent of global greenhouse gas pollution and that share is expected to rise, as leading green groups and the European Union demand the sector clean up its act.

Air France/KLM, British Airways, Cathay Pacific, Virgin Atlantic, airport operator BAA and international NGO The Climate Group have proposed a deal that covers all carbon pollution from the international aviation sector.

This would ensure equal treatment for airlines and open the way to global emissions trading within the sector and possibly with other industries and countries.

There are some airlines that still think we're only 2 pct of global emissions therefore let us get on with our job in peace, said Mark Kenber, policy director of The Climate Group, which advises businesses and governments on how to cut carbon pollution.

That in Europe, not least as a PR pitch, doesn't work anymore, he told Reuters by telephone from London.

If airlines don't propose something credible environmentally but also that works well for them economically, then they will get saddled with some other option.

The proposal by the six-member aviation deal group is to be presented to climate change negotiators later on Monday in Bonn in Germany, where representatives from 175 nations are meeting to work on a broader climate pact to replace the Kyoto Protocol.

Negotiations for the post-Kyoto pact are due to be wrapped up in December in Copenhagen.

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Conservation groups such as WWF say aviation has not been doing enough to tackle the sector's growing share of greenhouse gas pollution and must pay for its emissions like many other industries.

Emissions from global aviation are about 650 million tons of CO2 annually, according to the Association of Asia-Pacific Airlines.

Many airlines say only a global approach is fair and criticize the European Union's decision to include aviation in the bloc's emissions trading scheme from 2012.

Kenber says the Aviation Global Deal Group is hoping other major carriers will join and were talking to several other airlines in the Asia-Pacific, Middle East and the United States.

The scheme to be outlined later on Monday recommends that nations agree to a global cap on aviation emissions and that any scheme agreed must be integrated within a post-Kyoto climate pact set to take effect from 2013.

According to the 43-point proposal, individual carriers would surrender allowances in proportion to the carbon content of their annual fuel purchases. A U.N. body should administer the system, including the auction of permits.

Auction proceeds would be split between the Kyoto Protocol's adaptation fund for developing nations, help fund development of sustainable biofuels for use in aviation and toward a U.N.-backed initiative that aims to save forests in poorer nations in return for tradable carbon credits.

Kenber said the group's next step was to conduct a deeper analysis of what the aviation cap might be as well as how best to integrate the scheme into the carbon market.

The ultimate aim was to have the scheme adopted as one of the proposals on the table when U.N. climate negotiators meet again in June in Bonn.

Germany Climate change