(For other news from the Reuters Environment Summit, click on http://www.reuters.com/summit/GlobalEnvironment07?pid=500)

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By Alister Doyle and Gerard Wynn

LONDON, Oct 3 (Reuters) - Governments may need to step up the fight against global warming to a level beyond even the toughest existing goals to help safeguard the planet, the head of the U.N. climate panel said on Wednesday.

Risks ranging from extinctions of animals and plants to rising sea levels meant that even a strict European Union target of limiting global warming to 2 Celsius (3.6 Fahrenheit) over pre-industrial levels might be too lax.

"People are actually questioning if the 2 degrees Centigrade benchmark that has been set is safe enough," Rajendra Pachauri, head of the Intergovernmental Panel on Climate Change (IPCC), told a Reuters Environment Summit.

"There are some responsible voices that are raising this question. I expect that this will multiply," he said, adding the issue was starting to be discussed by scientists and policymakers.

Many experts reckon the 2 Celsius goal, seen by the EU as a limit to avoid "dangerous" change, is fast getting out of reach because of a rapid build-up of greenhouse gases mainly from burning fossil fuels in cars, factories and power plants.

The IPCC, drawing on the work of 2,500 top climate scientists, said in May that emissions of greenhouse gases would have to peak by 2015 to limit warming to 2 to 2.4 Celsius. Emissions are surging, especially in developing countries led by China.

EXTINCTIONS

Pachauri, an Indian scientist, said that rising temperatures this century could bring risks for the extinction of up to 30 percent of the world's species. A creeping rise in sea levels could threaten Pacific islands and many coastlines.

And fighting climate change would force tough choices.

"If you take the extreme view of some people -- 'let's just grow economically, if a few islands are submerged it's cheaper to move people than try to save them' -- that's the kind of value judgment that's involved.

"Can we be so insensitive?" he asked. Facing a range of threats which could include food shortages after droughts or floods, poor coastal states such as Bangladesh or the Maldives could not simply adapt by building walls against rising seas.

"You cannot build a wall and then start chewing a wall if there is going to be inadequate food supply. It's not just sea level rise. There are a whole range of other impacts (such as) hurricanes, extreme precipitation."

Pachauri said temperatures have already risen by 0.7 Celsius since the Industrial Revolution and would edge up by a further 0.5 or 0.6 Celsius this century even if surging emissions were capped now.

Still, he said there was reason for optimism that the world would start to take action to work out a long-term international plan to fight climate change at a U.N. meeting in Bali, Indonesia, in December.

"There are healthy signs and reason for cautious optimism that things will start happening at long last," he said.

Countries are seeking a way to expand the U.N.'s Kyoto Protocol beyond 2012. Kyoto sets caps on emissions for 36 industrial nations and Bali will seek to engage outsiders led by the United States and China.

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