"It's been a rapid expansion... We're starting to say where are the future projects -- and with post-2012 uncertainty maybe there won't be too many."

China already provides the majority of credits sold worldwide since its rapid growth, large industrial base and heavy reliance on coal make it a natural destination for investors seeking credits and for firms providing technology. Many credits have come from cutting potent industrial gas hydrofluorocarbon (HFC).

"Buyers are coming to us and saying: we don't want China and we don't want HFC," Godson said.

Reducing methane and nitrous oxide are now among the most attractive sectors, as they generate a large number of credits. Despite China'a stated goal to improve energy efficiency, the potential in this sector has not been realised yet.

"China is low on biogas and energy efficiency -- those projects are small," Godson added. "The minimum price requirements mean if you're going after a small project you don't get any incentive to do that."

China has set a minimum price of around 8 euros (US$10.65) a tonne for credits, which it sees as a national asset, stopping firms from getting a bargain but also guaranteeing steady project revenues.

But the lack of efficiency projects may hamper China's efforts to reduce the energy it uses to generate each dollar of income by 20 percent between 2006 and the end of the decade.

It has abandoned yearly targets: in 2006 it aimed for a 4 percent improvement but managed just over 1 percent.

Wind projects, which could cut emissions from the country's coal-dominated power production, also commanded a premium for credit buyers because of low risk, the conference heard.

Western companies are not willing to transfer technology to China if they cannot control its use, while China's limit on foreign equity ownership was also a deterrent.

Investors are wary of working with small coal mines to cut methane because projects require considerable upfront investment in power generation as well as gas capture and storage infrastructure that is not well enough protected by current laws.

However, Asia's large population and fast growth is likely to keep it the top region for emissions-cutting projects, with executives pointing to heavy-emitting countries such as South Korea as still having a lot of potential.