* Reluctance to take on more ambitious CO2 cut targets
* Pressure is on as climate risks grow
By Nina Chestney
BONN, Germany, May 21 (Reuters) - Reluctance to raise ambitions to cut greenhouse gas emissions due to economic constraints is threatening progress towards limiting global warming, delegates at United Nations' climate talks in Germany warned on Monday.
The talks in Bonn, which end on May 25, are partly to discuss ways of raising the level of ambition on cuts but the worsening eurozone crisis and battered global economy have increased reluctance to commit to more financially onerous cuts by the end of the decade, delegates told Reuters.
Last year's U.N. climate talks in Durban, South Africa, agreed to develop a new protocol, legal instrument or legally binding deal by 2015 which would apply to all parties under the U.N.'s climate convention and would come into force no later than 2020.
Countries had already agreed in 2010 that deep greenhouse gas emissions cuts had to be made to keep a rise in global average temperature below two degrees Celsius above pre-industrial levels this century to avoid more extreme weather, glacier melts, ocean acidification and other harmful impacts.
But efforts so far to cut emissions are not seen as sufficient to stop a rise beyond two degrees this century.
"The ambition gap must be closed..in Doha," said Sai Navoti, lead negotiator for the Alliance of Small Island States, referring to talks scheduled for November-December in Qatar.
"Failing to close the gap immediately will lead to sginificant risks across various tipping points and global average temperature exceeding 3.5 degrees," he added.
Last November, the U.N. Environment Programme issued a report showing that the gap between current emissions cut pledges and what is needed to limit global warming is wider than ever, growing from 5-9 gigatonnes of CO2-equivalent in 2010 to 6-11 gigatonnes in 2011.
Current pledges cover around 80 to 85 percent of greenhouse gas emissions and nine economies among the world's top 30 emitters in 2005 have not yet tabled cuts, said Justin Lee, head of Australia's climate delegation.
"The shared collective efforts are not enough to meet the two degree goal. Countries that haven't yet pledged, should."
The European Union has said it would cut emissions by 30 percent from 1990 levels by 2020 from the current 20 percent if other large emitters take on equally ambitious pledges but none have yet done so and the EU is now grappling with the rapid deterioration of the euro zone economy.
"People clearly do not want to talk about raising pledges with the global recession and euro zone about to collapse under its own weight," said a source who requested anonymity.
Less developed countries are also under pressure to define domestic measures to cut emissions through so-called Nationally Appropriate Mitigation Actions (NAMAs) but progress there too is slow due to lack of finance.
Such actions could include programmes to develop renewable energy, improve energy efficiency, or the uptake of electric vehicles, for example.
Although the number of NAMA initiatives has grown to 52 from 30 last year, less than five have been implemented, said a report on Monday by the German ministry for the Environment, Nature Conservation and Nature Safety and consultancy Ecofys.
The greenhouse gas emissions cuts from just 13 such programmes is expected to total around 23.6 million tonnes of carbon dioxide equivalent per year by 2020, the report showed.
"More nations should come forward with NAMAs. It is time to ask what can be done. Nothing at all is not the right answer," said Kaminaga Kaminaga, negotiator for the Marshall Islands, in the Pacific Ocean.
People's current ways of life on those islands, which are only 2 metres above sea level, could be under threat even if seas rose a metre this century as glaciers and ice caps melt due to global warming.
"There is no higher ground and nowhere to relocate," Kaminaga warned. (additional reporting by Ben Garside, editing by William Hardy)