* Blow to sceptics arguing natural variations to blame
* Nations hoping to get greenhouse gas deal in Doha
* Experts have more data on Greenland, Antarctica, sea levels
By Environment Correspondent Alister Doyle
DOHA, Nov 29 (Reuters) - Evidence that global warming is man-made is getting stronger, the head of a U.N. panel of climate scientists said, in a further blow to sceptics who argue rising temperatures can be explained by natural variations.
Rajendra Pachauri spoke on the sidelines of a conference in Qatar where 200 nations are trying to reach a deal to cut emissions of greenhouse gases to avert floods, droughts, heatwaves and mounting sea levels.
The influential U.N. climate panel said the probability human activity was the main cause of climate change was "at least 90 percent" in its last report in 2007.
Pachauri told Reuters late on Wednesday he expected the panel would raise the level of that likelihood even higher in its next report, due in 2013.
"We certainly have a substantial amount of information available by which I hope we can narrow the gaps, increase the level of certainty of our findings," he said.
"We will have a lot more information this time around on the melting of Greenland and Antarctica. I hope we will get a little more information on sea level rise," he added.
Rising sea levels pose a particular threat to people living in low-lying areas, from Bangladesh to the cities of New York, London and Buenos Aires. They open up the risk of storm surges, coastal erosion and, in the worst case scenario, complete swamping of large areas of land.
The last report by the U.N.'s Intergovernmental Panel on Climate Change (IPCC) gave a wide range for sea levels, saying they could rise by between 18 and 59 cm (7-24 inches) by 2100.
Those numbers did not take account of a possible acceleration of a melt of Antarctic or Greenland ice, due to big uncertainties.
"KYOTO THE ONLY SHOW IN TOWN"
Some scientists and organisations have questioned whether gases released by industry and other human activity are the main causes of global warming, pointing instead to natural climactic variations and events like shifts in the sun's output.
They have also suggested warming may have flattened out, citing data showing 1998, 2005 and 2010 are tied as the warmest years since records began in the mid-19th century.
But a study released during the Qatar talks study backed IPCC projections that temperatures were creeping higher, and sea levels were rising even faster than predicted.
Pachauri said the panel would also gain wider understanding of the formation of clouds. The white tops of clouds at low altitudes tend to bounce heat back into space, cooling the planet, while high-altitude clouds often trap heat.
The Doha talks are struggling to extend the U.N.'s troubled Kyoto Protocol, which binds most developed nations to cut emissions by at least 5.2 percent below 1990 levels by 2008-12.
Russia, Canada and Japan are pulling out, saying it is now time for fast-growing emerging nations led by China and India to take on commitments. Under current plans, a new global deal is meant to be agreed in 2015 and enter into force by 2020.
Pachauri said that Kyoto still seemed a good idea. "It's the only show in town. Why give it up?" he said.
A U.N. conference two years ago agreed to limit any rise in temperatures to less than 2 degrees Celsius (3.6F) above pre-industrial times. But greenhouse gas levels hit a new record in 2011, despite the world economic slowdown.