UN-led study, due to be published in 2018, will look into ways of cutting emissions to cap temperature rise at 1.5C
* 1.5C limit for global warming risks slipping out of reach
* Report due in 2018 to guide global climate accord
By Alister Doyle
OSLO, Aug 18 (Reuters) - Scientists on Thursday set the outlines of a report on how to restrict global warming to a limit agreed last year by world leaders - even though the temperature threshold is at risk of being breached already.
The U.N.-led study, due to be published in 2018 as a guide for governments, will look into ways of cutting greenhouse gas emissions to cap the rise at 1.5 degrees Celsius (2.7 Fahrenheit) above pre-industrial levels.
It will examine impacts of a 1.5C rise on vulnerable parts of the world including Greenland's ice sheet and coral reefs.
Thelma Krug, a Brazilian scientist who led the four-day meeting in Geneva, said it will also cast the fight against climate change as part of a wider struggle to end poverty and ensure sustainable growth.
"Rapid changes are needed for (no rise above) 1.5C," she told Reuters.
World leaders agreed to work towards that target at a meeting in Paris in December, also requesting the report as part of a global agreement to phase out greenhouse gas emissions, mainly from burning fossil fuels, in the second half the century.
The global rise reached 1.3C in the first half of 2016, which is almost certain to be the warmest year since records began in the 19th century, beating 2015.
Some studies indicate emissions could breach levels consistent with 1.5C within about five years. Many show temperatures overshooting that limit and then being reduced later by extracting greenhouse gases from the atmosphere with yet-to-be developed technology.
"It will be difficult, but there are also opportunities," said Sabine Fuss, a delegate at the Geneva meeting from the Mercator Institute on Global Commons and Climate Change.
Costly action now could help avert even more expensive damage from floods, heat waves, extinctions and rising ocean levels, she said.
The Geneva talks of experts from the Intergovernmental Panel on Climate Change agreed the chapters in the report and sketched out the content. Their conclusions will have to be formally approved by a wider IPCC meeting in October.
Almost all scientific research has been into less stringent temperature targets. But the Paris meeting took scientists by surprise by seeking to limit temperature rises to "well below" 2C (3.6F) while "pursuing efforts" for 1.5C.
Nebojsa Nakicenovic, deputy director general of the International Institute for Applied Systems Analysis, said 1.5C would be possible only if combined with sweeping U.N. goals for sustainable development by 2030 agreed last year, including ending hunger and poverty.
Taken together, that would mark "a fundamental transformation" of the world economy, he said.
(Reporting By Alister Doyle; editing by John Stonestreet)
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