If the evidence is overwhelming that man-made climate change is already upon us and set to wreak planetary havoc, why do so many people refuse to believe it?
The UN's panel of climate scientists, in a landmark report, described the proof of global warming as "unequivocal".
That was two years ago, and since then hundreds of other studies have pointed to an ever-bleaker future, with a potential loss of life numbering in the tens of millions, if not more.
Yet survey after survey from around world reveals deep-seated doubt among the public.
A poll published in Britain on November 14, to cite but one example, found that only 41 per cent of respondents accepted as an established fact that human activity was largely responsible for current global warming.
The majority said the link was not proven, that green propaganda was to blame or the world was not heating up at all.
Last week, a private exchange of emails among climate scientists stoked a firestorm of scepticism after it was hacked and posted on the web.
The memos expressed frustration at the scientists' inability to explain what they described as a temporary slowdown in warming, and discussed ways to counter the campaigns of climate naysayers.
Experts see several explanations for the eagerness with which so many dismiss climate change as overblown or a hoax.
"There is the individual reluctance to give up our comfortable lifestyles - to travel less, consume less," said Anthony Grayling, a philosophy professor at the University of London and a bestselling author in Britain.
While deeply anchored in the West, this resistance also extends to emerging economies such as China, India and Brazil where a burgeoning middle class is only today tasting the fruits of a lifestyle they have waited so long and worked so hard to obtain.
For Tim Kasser, a professor of psychology at Knox University in Galesburg, Illinois, the reality of climate change impinges on core aspects of our identity.
"We are told a thousand times a day, notably through advertising, that the way to a happy, successful and meaningful life is through consumption," he said.
"But now scientists and environmentalists come along and say part of the problem is that we are consuming too much or in the wrong way."
Yet there may also be a darker explanation. It is the human instinct to shut out or modify a terrifying truth: that the world as we know it is heading for a smash.
"It's a paradox: when it comes to disasters, people do not allow themselves to believe what they know," explained Jean-Pierre Dupuy, a professor of social philosophy at the Ecole Polytechnique in Paris.
"Because everybody is in denial - or would like to be in denial - and would prefer to not shoulder too much of the responsibility for dealing with the problem, you have a kind of disconnect here," Grayling said.
Even scientists reluctantly pushed by their growing sense of alarm into launching public appeals for action have trouble coping.
When Clive Hamilton, a professor of public ethics at Australian National University, attended a September climate conference at Oxford tasked with imagining a world warmed by 4 degrees Celsius, he was struck by how researchers spoke among themselves.
"It was very revealing. As they relaxed somewhat, they began to speak about their fears, about losing sleep, not wanting to think about the implications of what they do," he recalled.
Under such circumstances, people are resourceful in finding ways to reassure themselves or turn their backs on the threat posed by climate change.
Some applaud their own environmental virtue: "Changing to compact fluorescent bulbs makes people feel good - 'I've done my bit for today,'" said Kasser, describing a common attitude in the United States.
"Blaming China and India is another great psychological defence mechanism."
A more sophisticated variant is to conclude, with a sigh of resignation. that individual action isn't enough.
"Even if all of us were at our most maximally green, it probably wouldn't make much more than about a 0.5 per cent difference," said Grayling in characterising this mentality.
At some point, however, reality may bite.
Hamilton, who is running for Parliament in Australia, said more and more people he meets are having what he calls an "Oh shit!" moment.
"It's that moment when you really get it, when you understand not just intellectually but emotionally that climate change is really happening. I think we will see a rush of that over the next couple of years," he said.
It may take one or more terrible shocks - national bankruptcies, a major environmental disaster in a vulnerable country like Bangladesh - for that to happen, said Grayling.
Once it does, "it will be impossible to look back over your shoulder and think, 'it's not true,' or 'there will be a scientific fix, it will all go away'."
