L’AQUILA, Italy (Reuters) - The G8 agreed on Wednesday to try to limit global warming to 2 degrees Celsius and cut its greenhouse gas emissions by 80 percent, but it failed to persuade China and India to join a bid to halve world emissions.

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With only five months until a new U.N. climate pact is due to be agreed in Copenhagen, climate change organizations said the G8 had left much work to be done and ducked key issues.

China and India resisted signing up for a global goal of halving greenhouse gas emissions by 2050. Developing economies demanded rich nations commit to steeper short term reductions.

And while the 2 Celsius goal was adopted for the first time by the United States, Russia, Japan and Canada, it had already been agreed in 1996 by the European Union and its G8 members Germany, Britain, France and Italy.

The G8 statement also failed to pinpoint a base year for the 80 percent reduction -- saying it should be “compared to 1990 or more recent years” -- meaning the target was open to interpretation. “The world will recognize that today in Italy werecognize have laid the foundations for a Copenhagen deal that is ambitious, fair and effective,” said British Prime Minister Gordon Brown.

German Chancellor Angela Merkel said the 2 Celsius (3.6 Fahrenheit) target, since pre-industrial times, was “clear progress” for the G8.

The G8 backed the creation of a global carbon trading market and a fund financed by rich nations to pay for technological change, but it fell short of the $100 billion a year advocated by Britain’s Brown and non-governmental groups.

“While agreeing to keep temperature rise to below 2 degrees rise Celsius, without a clear plan, money and targets on how to do this the G8 leaders will not have helped to break the deadlock in the UN climate negotiations,” said Tobias Muenchmeyer, Greenpeace International political adviser.

CHINA’S ABSENCE KEY

Temperatures have already risen by about 0.7 Celsius since the start of the Industrial Revolution ushered in widespread burning of fossil fuels, the main cause of warming according to the U.N. Climate Panel.

Many developing nations also view two degrees as the threshold beyond which climate change will reach danger levels, with rising seas and more heatwaves, floods and droughts.

The temperature target was due to be included in a statement from the 17-member Major Economies Forum (MEF), which groups the G8 plus major developing economies, which will meet on Thursday.

Last minute talks to convince MEF members to sign up to the goal of cutting world greenhouse gases by at least 50 percent by 2050 -- adopted by the G8 last year -- unraveled on Tuesday.

Delegates said the absence of Chinese leader Hu Jintao, who flew home to deal with an outbreak of ethnic violence in western China, dashed hopes of an eleventh hour breakthrough.

“China’s not here so they cannot move anywhere: there will be no agreement tomorrow in the MEF text on 50 percent. We will take this up again at the G20 when China is present,” said a senior European G8 source involved in the talks.

German Chancellor Angela Merkel said emerging countries appeared willing to sign up to long-term emissions goals if rich nations would agree to tough targets by 2020. The G8 statement called for “robust” medium-target cutbacks, but gave no details.