* Cambridge climate expert to win $2,830 after record heat

* Record heat in 2015 supports wagers on long-term warming

OSLO, Jan 20 (Reuters) - For British climate expert Chris Hope, new data showing that 2015 was the hottest year ever recorded is not just confirmation he’s been right all along that the planet is getting warmer.

It also won the Cambridge University researcher a 2,000 pound sterling ($2,830) wager made five years ago against a pair of scientists who reject man-made global warming and bet Hope that the Earth would be cooling by now.

NASA, the U.S. National Oceanic and Atmospheric Administration (NOAA) and the British Met Office said on Wednesday that 2015 was the warmest year recorded since 1880, boosted by a long-term build-up of greenhouse gases and a natural El Nino event warming the Pacific Ocean.

That puts last year ahead of 2014, the previous warmest, as well as 2010, 2005 and 1998, when a strong El Nino marked, for a time, a peak in temperature rises.

A slowdown in temperature increases after 1998 - described by most climate experts as a hiatus in a long-term rise - has been invoked by a small band of sceptics who say mainstream science has exaggerated the risks.

Hope agreed wagers of 1,000 pounds each with two of them: British engineer Alan Rudge and Australian geologist Ian Plimer. Hope bet average global temperatures in 2015 would be no more than 0.1 degree Celsius (0.18 Fahrenheit) cooler than 2008.

He said it was good to test theories with cash. “Of course, one side ends up happier than the other,” he said. Neither Rudge nor Plimer were immediately available to comment.

“You win some, you lose some,” said Benny Peiser, director of the Global Warming Policy Foundation, for which Rudge is an adviser. Peiser said the pace of warming “is not something that people ... need to be greatly concerned about”.

Among other wagers, in 2005 British climate modeller James Annan bet $10,000 against two Russian solar physicists that average global temperatures from 2013-17 would be warmer than 2003-07.

“Things are looking good for my bet,” Annan said, noting the U.N.’s weather agency has said 2016 could be as warm as 2015. If so, Annan reckons that his bet is safe unless 2017 is the coldest year since about 1929.

His Russian opponents are not conceding yet.

Galina Mashnich, an expert at the Institute of Solar-Terrestrial Physics in Irkutsk, Russia, who made the bet with her colleague Vladimir Bashkirtsev, said the new temperature data is not definitive.

“2015 is not the warmest year, according to some sources,” she wrote in an e-mail to Reuters. In recent years, she said, it was “most likely temperature increases are caused by El Nino”.

The Russian solar experts predicted a decade ago that a decline in energy output from the sun, linked to the Earth’s changing orbit, will depress temperatures.

Annan did lose one bet, of 100 pounds in 2011, linked to the pace of global warming.

Hope said he made his wager partly to show a potential for a financial market in temperatures, allowing investors to hedge long-term climate risks, for instance of rising sea levels or damage to crops linked to differing rates of warming.

After the spur of El Nino fades, global temperatures are likely to be slightly cooler in 2017, said Myles Allen, a climate expert at Oxford University.

He predicts any drop will revive doubters’ claims of an end to warming.

“I bet you in a few years’ time they will say global warming stopped in 2015 or 2016,” Allen, who is not a sceptic and is senior author of U.N. climate reports, said. (Reporting By Alister Doyle, editing by Bruce Wallace/Jeremy Gaunt)