One way of achieving such a price is through carbon markets, which put an overall limit on emissions but allow participants busting their caps to buy rights to emit greenhouse gases from those within their limits.

A carbon market already exists through the Kyoto Protocol, which caps 36 industrialised countries emissions -- but it does not set caps on three of the world's top four culprits: the United States, China and India.

Fears that emissions caps constrain industry and so competitiveness are hampering global agreement on a new deal after present Kyoto rules expire in 2012, a deal which would allow industry to estimate the future price of carbon and invest accordingly.

"If we don't make a set of numbers by at least 2009 then the chances of the (carbon) market functioning in 2012 will be very slim indeed," said Henry Derwent, director of Climate, Energy and Environmental Risk at Britain's environment ministry, speaking at a Euromoney-backed energy conference in London.

But 2009 is not soon enough for some.

"I think 2009 is two years too late," said Neil Eckert, Chief Executive of Climate Exchange PLC, which wholly owns the European Climate Exchange and the Chicago Climate Exchange.

URGENT

Policymakers want industry to direct some of the vast investment in new energy supplies now needed -- some US$20 trillion by 2030 according to the International Energy Agency -- into clean energy like renewables.

"The world needs to act quicker than the UN can change its rules," Eckert told Reuters, pointing to the voluntary commitment of some US cities and corporates to cut their emissions, even though the United States pulled out of Kyoto-style national cuts in 2001.

Last week Britain pledged to put into law its goal of cutting carbon emissions by 60 percent by 2050, seen as a way of showing industry carbon limits were here to stay regardless of UN deals.

At U.N talks last week in Nairobi some 189 countries and over 70 environment ministers could not agree to a deadline to reach a global climate deal, only agreeing to complete necessary analysis by 2008, hinting at a deal in 2009.

"What kind of ambition levels governments are likely to have is what matters (to industry)," said Kirsty Hamilton, consultant to the Business Council for Sustainable Energy and author of a survey of business views on Kyoto.

"It would have been better if they'd firmed up a deadline."

PROGRESS

The United States reiterated in Nairobi its preference to invest in clean energy technologies than sign up to legally binding emissions caps, a view that discourages carbon market advocates.

"We must have the United States in, and we must have an agreement in 2008 or 2009," said Janos Pasztor, the UN official who oversees the bulk of carbon trading under Kyoto.

On the positive side at Nairobi, Canada did not rule out meeting its Kyoto goals, which it had previously said were unachieveable, potentially unleashing a big source of demand for emissions rights.

And Australia said it wanted to form a nationwide carbon market which it could plug into similar schemes.