Arguably no other area of research yields a sharper contrast between a steady stream of "eureka!" moments, and the sometimes terrifying implications of those discoveries for the future of the planet.

"Science is exciting when you make such findings," said Konrad Steffen, who heads the Cooperative Institute for Research in Environmental Sciences (CIRES) in Boulder, Colorado.

"But if you stop and look at the implications of what is coming down the road for humanity, it is rather scary. I have kids in college -- what do they have to look forward to in 50 years?"

And that's not the worst of it, said top researchers gathered here last week for a climate change conference which heard, among other bits of bad news, that global sea levels are set to rise at least twice as fast over the next century as previously thought, putting hundreds of millions of people at risk.

What haunts scientists most, many said, is the feeling that -- despite an overwhelming consensus on the science -- they are not able to convey to a wider public just how close Earth is to climate catastrophe.

That audience includes world leaders who have pledged to craft, by year's end, a global climate treaty to slash the world's output of dangerous greenhouse gases.

It's as if scientists know a bomb will go off, but can't find the right words to warn the people who might be able to defuse it.

French glaciologist Claude Lorius, one of the first scientists to publish, in 1987, evidence that global warming was real, has despaired of getting the message across.

"At first, I thought that we could convince people. But there is a terrible inertia," he told AFP. "I fear that society is not up to the challenge of a crisis like this. Today, as a human being I am pessimistic."

John Church, an expert on sea levels at the Antarctic Climate and Ecosystem Cooperative Research Centre in Hobart, Tasmania, takes an equally dim view of our collective capacity for denial.

"Perhaps society has realised the seriousness, but it certainly hasn't realised the urgency," he said.

"But even if you are pessimistic -- and sometimes I am -- it does not help. What are you going to do? Chop off your hands and give up? That's not a solution either," he said.

Most scientists, while no less alarmed by snowballing evidence of a planet out of kilter, still think there is time to act.

"We are actually going to have to decrease the amount of carbon dioxide in the atmosphere if we want to stabilise climate and avoid some highly undesirable effects," said James Hansen, director since 1981 of NASA's Goddard Institute for Space Studies. "It is still possible to do that."

Some of those undesirable effects include massive droughts, more intense hurricanes and a panoply of human misery including expanded disease and tens of millions of climate refugees.

Even gloomier scenarios see a world map redrawn by sea levels rising tens of metres and a planet able to sustain only a fraction of the nine billion people projected to become, as of 2050, Earth's stable population.

But even if it is urgent to let the world know just how bad it could be, there is also a danger of frightening people into inaction, said other scientists.

"I do worry that people just can't deal, psychologically, with the enormity of the problem, and that they may revert to doing nothing," said William Howard, a researcher at the University of Tasmania.

"As a scientist, I deal with climate change on a time scale of hundreds of thousands of years, and even I have a hard time dealing with it," added Howard, who reported last week that tiny marine animals called forams are losing their capacity to absorb huge amounts of carbon pollution from the atmosphere.

"The risk is that when science pumps out more and more evidence that we are facing dangerous tipping points" -- triggers that would make climate change irreversible -- "that you put your head in the sand and move from denial to despair," said Johan Rockstrom, director of the Stockholm Environment Institute.

Hanging over the conference proceedings like an invisible cloud were the apocalyptic predictions of the monstre sacre of Earth sciences, 90-year-old British scientist James Lovelock.

A true iconoclast, Lovelock commands respect because he understood decades before his peers that Earth behaves as a single, self-regulating system composed of physical, chemical and biological components, a concept he dubbed the Gaia principle.

In his just-released book "The Vanishing Face of Gaia", he basically says we have already passed a point of no return, and that it is now impossible "to save the planet as we know it."

"Efforts to stabilise carbon dioxide and temperature are no better than planetary alternative medicine," he wrote.

It is perhaps telling that more than a dozen scientists interviewed could only say that they hoped Lovelock was wrong.

None could say -- based on the science -- that they knew he was wrong.

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