The European Commission said Monday it would look at broadening the scope of its innovative carbon emissions trading scheme to include more countries, industries and gases.

A commission spokeswoman said "advanced discussions" were already underway with Norway, Liechtenstein and Iceland about including them in the programme, under which industrial polluters can buy and sell emissions quotas. However, even more promising, California, the northeastern US states and Australian states were also looking at ways of linking up to the system, she said.

The United States has refused to ratify the Kyoto Protocol, a United Nations treaty that requires industrialised nations to curb their emissions of six gases blamed for global warming. Currently, the EU trading scheme only covers big energy-intensive industrial plants and power generators, but in the future the commission would also like to bring in smaller industrial energy users. It also plans to propose including aviation in the scheme in the coming months. Among other ideas under consideration, the commission was looking at the possibility of including nitrus oxide (N2O) from ammonia production and methane from coal mines.

The ideas are being floated as part of a review of the emissions trading scheme in order to make revisions in the second half of 2007 for the third trading period starting in 2013. The scheme got off the ground in 2005 and an initial trial phase runs until next year. The commission is currently studying member states' plans to allocate emissions quotas to industry for the second period running from 2008 to 2012.