* Kyoto extension could be flexible to enable deeper targets

* Could help raise ambitions when economy better

* Decision on second Kyoto length not seen until end of Doha

By Nina Chestney

BONN, May 23 (Reuters) - A yearly review of countries' greenhouse gas emissions cut pledges under an extension to the global climate pact the Kyoto Protocol could be a way to raise climate ambitions, the European Union's lead climate negotiator said on Wednesday.

Negotiators from over 180 countries are meeting in Bonn, Germany, until Friday to work towards getting a new global climate pact signed by 2015 and to ensure ambitious emissions cuts are made after the Kyoto Protocol expires at the end of this year.

United Nations' climate talks in South Africa last year agreed to extend Kyoto for five or eight years from 2013 into a second commitment period and to get all countries in 2015 to sign a new deal that would force them to cut emissions no later than 2020.

Nations are under increasing pressure to put emissions cut pledges for Kyoto's second phase on the table or deepen existing ones before the current commitment period ends on Dec. 31.

The EU, which pledges to cut emissions by 20 percent from 1990 levels by 2020, has said it would move to a deeper target of 30 percent if other big emitters made similar moves.

However, the worsening eurozone crisis and flagging global economy have increased reluctance to commit to more financially onerous cuts by the end of the decade.

"It is difficult to see under current circumstances that we would move away from the current 20 percent (target)," Artur Runge-Metzger, the EU Commission's director of EU and international climate strategy, told Reuters.

"We have made some proposals to bring some new flexibility into the Kyoto Protocol so we can raise the level of ambition a year or two later when conditions for other parties are also right to make the move forward," he added.

"Every year we could look at where we stand in terms of implementation on all the pledges that have been made (previously) and see if there is a possibility to do new actions in the coming years."


EXTENDING KYOTO

Another impetus to ramping up ambitions could come from nations who have not yet made any pledges to do so this year, particularly developing countries.

"That includes countries like the Philippines, Egypt and Malaysia who haven't made any pledges right now. That could be an important contribution to close the (emissions) gap," Runge-Metzger said.

Some countries want the length of Kyoto's second phase to be defined before they will commit to it and/or offer pledges.

The EU, among others, favours an eight-year duration so that the end of Kyoto could coincide with the start of a new climate deal.

But some smaller countries, which are more vulnerable to climate change, want a shorter, five-year period so that there is a greater chance of limiting global warming and avoiding devastating effects like sea level rise and ocean acidification.

Although there have been "constructive discussions" in Bonn this week, a decision on the duration issue will probably not be taken until the final nights of a meeting in Doha, Qatar, in November-December, Runge-Metzger said.

The EU and some smaller nations covering around 15 percent of global emissions have pledged to continue to be bound by Kyoto after it expires but Japan, Russia and Canada have refused and the United States has never had a Kyoto target.

Australia and New Zealand have put off a decision until later this year.

"My impression is that New Zealand and Australia really want to continue under the Kyoto framework. They have said there are a number of internal issues to sort out. This might take until Doha," he added. (Editing by William Hardy)

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