COPENHAGEN - A 20 percent cut in greenhouse gases by rich nations would be a pretty good result for a U.N. climate summit even though it falls short of developing nations' hopes, the head of the U.N. climate panel said on Tuesday.

Rajendra Pachauri, chairman of the Intergovernmental Panel on Climate Change (IPCC), said a U.S. reduction offer of 3 percent below 1990 levels by 2020 made it hard to reach more ambitious cuts by 2020 for industrialized nations as a group.

If we can get something like that it would be a pretty good outcome, Pachauri told Reuters, when asked if he would be satisfied with cuts of 20 percent below 1990 levels by 2020 at a summit at the end of the December 7-18 conference.

Pachauri's panel in 2007 outlined a scenario of cuts of 25 to 40 percent below 1990 levels by 2020 to avoid the worst of climate change such as wildfires, droughts, floods and rising sea levels.

An Indian citizen, Pachauri has often urged far tougher action by the rich, especially to help developing nations threatened by rising sea levels.

Many developing nations want cuts of at least 40 percent, the toughest end of the IPCC range. But offers by recession-hit developed nations so far total about 14 to 18 percent below 1990 levels by 2020.

Pachauri said it was now important to get a forward-looking agreement to be adjusted over time. He said he was giving a personal opinion and that negotiators would have to decide.

OBAMA

U.S. President Barack Obama aims to come to Copenhagen for a closing summit. He has said he will offer a U.S. cut of 3 percent below 1990 levels by 2020, or a reduction of 17 percent from 2005 levels after sharp rises in recent years.

The United States is the only developed nation with no caps on emissions under the existing Kyoto Protocol. I would hope that some of the other countries will fill the gap by doing a little more and perhaps get the Americans to move further, Pachauri said.

Pachauri told a seminar that he hoped the IPCC would learn from a scandal over leaked emails from a British University that skeptics say raises questions about the IPCC's conclusions that mankind is causing global warming.

We have decided to look into this issue just to see if there are any lessons for us to take on board. That's not an investigation of anybody, he said. He said that the University of East Anglia and the police were making formal probes.

He expressed sympathy for scientists expressing personal opinions critical of skeptics in internal mails.

There are times that I've said 'I'll murder so and so' but I don't carry out the act. These were friends ... expressing anger, expressing anguish and I think we should leave it at that. We often say things we don't mean.

(Editing by Robin Pomeroy)

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