More research needed to understand level that might cause tipping points, says head of UN climate science panel

* Multiple lines of evidence suggest earth is warming

* More work needed to understand tipping points

By Nina Chestney

PARIS, Dec 8 (Reuters) - Global warming has not paused, but more research is needed to understand the level that might cause tipping points, or irreversible damage to the earth's climate system, the chair of the U.N. panel of climate scientists told Reuters on Tuesday.

In 2013, the panel reported a slowdown or "hiatus" in warming since about 1998, despite rising man-made emissions of greenhouse gases, heartening sceptics who said the risks of climate change had been exaggerated. However, more recent research by the U.S. National Oceanic and Atmospheric Administration (NOAA) has suggested this hiatus is an illusion.

"There is no hiatus (in global warming). Multiple lines of evidence suggest that the earth is warming," said Hoesung Lee, the 69-year-old South Korean economics professor named chair of the U.N. Intergovernmental Panel on Climate Change (IPCC) in October.

"For instance, the atmospheric concentration of CO2 is rising, sea levels have been rising and the temperature of the ocean has also been rising," he said in an interview. "The important point is we need to look at the trend, not just one year of data."

But Lee, attending the U.N. climate summit in Paris, said more work was needed, based on a number of years of observations, to establish a "clear understanding of the relationship between carbon emissions and economic growth".

Lee will oversee the next cycle of reports from the IPCC, whose most recent findings in 2013-14 concluded that global warming meant risks of "severe, pervasive and irreversible impacts".

He said more study was also needed to understand the importance of tipping points, where, for instance, ice melt becomes irreversible.

"Clearly the most dangerous impacts will be related to crossing over the tipping points," he said.

Any deal done in Paris is almost certain to fall short of a U.N. goal of limiting global temperature rise to below 2 degrees Celsius (3.6 Fahrenheit), which many scientists see as the threshold for avoiding dangerous climate change.

Some countries that are more vulnerable to global warming, such as low-lying island nations, say the temperature rise needs to be limited even further, to 1.5 C (2.7 F).

(Editing by Kevin Liffey)

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