Many delegates among 166 nations attending exploratory talks in Bonn this week say they have become gloomier about the chance of formal negotiations starting in Bali, Indonesia.

Without decisive progress it would be necessary to look for fall-back options, Artur Runge-Metzger, head of the European Commission's Climate Change Unit, told Reuters.

"That would be triggered if you would really see that Bali would be a failure: if in Bali you would not know how to proceed forward on the negotiations," he said.

"There are a vast number of meetings planned. To say now Bali will be a failure would be completely wrong."

What is needed is a clear plan of action, he said.

"A kind of programme of work, whatever you want to call it, that outlines what needs to be done. Some part of this programme has already been decided last year in Nairobi," he added, referring to agreement to review the Kyoto Protocol and for rich nations which already have emissions caps to negotiate new ones.

But analysts are already looking at strategies to bridge the gap between 2012 and when a successor Kyoto deal is in place.

"We do need to think about bridging strategies between Kyoto commitment periods," said Elliot Diringer, director of international strategies at the US-based Pew Centre on Global Climate Change.

"While it would be preferable to have a new set of mandates from 2012 we should prepare alternatives. We could have an agreement from 2015 and in the meantime maintain existing caps."

Diringer felt even 2009 may be too early to launch formal Kyoto extension talks, as a new US administration beds in. The United States pulled out of the present Kyoto pact in 2001.

Businesses globally say they need clarity on the shape of future climate policy, in order to make investments now in infrastructure that could last 40-plus years.

One such policy is a carbon market that requires big polluters to buy permits to produce greenhouse gases, and so puts a price on carbon emissions.

The European Union recently adopted emissions targets to 2020 which will guarantee its carbon market until then, regardless of any successor to Kyoto.