Hopes that a deal may be possible have increased since the election of what many see as a "green" U.S. president and business is increasingly enthusiastic about the opportunities thrown up by climate change.

"It is essential to engage heads of state and government stronger in the whole process to ensure a positive result in Copenhagen," Anders Fogh Rasmussen told the annual meeting of the World Economic Forum in Davos Friday.

Business leaders meeting in the Swiss ski resort this week have called on governments to create certainty on the climate issue, so they can plan for the future.

"What I hear business leaders here in Davos say is: We want clarity from governments on where they intend to go with climate change. We need a clear investment perspective," the U.N.'s top climate official, Yvo de Boer, said.

In a statement released Thursday, the forum said clean energy investment needs to more than triple to $515 billion a year to stop planet-warming emissions reaching levels deemed unsustainable by scientists.

This changing business environment would create opportunities for firms, said Royal Dutch Shell Chief Executive Jeroen van der Veer.

"This is the best opportunity that could come for Shell because we claim to be good at technology, we have an international mindset, we can invest in it and we happen to know something about it," he said.

However, some have warned the temptation is to switch to cheap, polluting fuels, notably coal, in times of economic hardship and there was a risk that would offset the effects of lower industrial energy use.

"It's bad news for the long term. Many renewable, nuclear and efficiency projects are being postponed," said Fatih Birol, chief economist of the International Energy Agency, which advises 28 industrialized nations.

"The long-term impact is that emissions will go up if governments don't do something," he told Reuters.

European Energy Commissioner Andris Piebalgs agreed that recession potentially made it difficult to push through the EU's ambitious environmental

plans, and could complicate the process of getting a deal in Copenhagen this year, but said events this month had made him feel more optimistic.

The European Commission this week announced funding on carbon capture and storage and, in addition to the boost provided by Obama's backing for the environment, he said more unlikely supporters had included Russia and China.

"I am optimistic about what I have heard from leaders... There is a new chance for green growth. It is important to see the silver lining," he said.