The Earth is flat. At least that used to be the universal view until about the fourth century BC. By medieval times, most Europeans accepted that it was spherical but old ideas die hard.
So it was that just 40 years ago members of the International Flat Earth Society dismissed the Apollo Moon landing as a hoax, staged by Hollywood and based on an Arthur C Clarke script.
What is the explanation for such triumphs of wishful-thinking over evidence-based belief? What drives an apparently intelligent rational human being to deny the link between, say, HIV and Aids or smoking and lung cancer long after the case has been proven beyond doubt for everyone else?
It's an interesting question in the context of climate change deniers. I refuse to call them sceptics because that word implies someone who is searching for the truth. There are lots of them out there and they are very well-organised.
I know this because every time I write about the issue, it provokes a deluge of letters telling me the Earth is cooling, not warming; the ice-caps are growing, not melting; and sea levels are falling. All untrue (or derived from such selective or subjective data as to be extremely misleading). Nothing I say will convince them because I am an "eco-Nazi", or what Ryanair's Michael O'Leary would label a "hairy, dungaree and sandal-wearing climate change alarmist" (despite appearances to the contrary).
They have their own champions: Czech President Vaclav Klaus says climate campaigners "challenge our freedom"; Sarah Palin denies that polar bears are endangered; David Bellamy has described global warming as "poppycock". Significantly, Britain's best known denier is former Tory Chancellor Nigel Lawson, who admits he doesn't understand the science.
Typically, deniers are right-wing, distrustful of government interference and admirers of free-market capitalism. They regard the climate campaign as a left-wing conspiracy to defraud the public through green taxes. Only yesterday senior Tory David Davis was complaining about "the ferocious determination to impose hair-shirt policies", suggesting David Cameron's green makeover of the Conservative Party may be unfinished business. The belief in the fossil-fuelled status quo would be laughable if that whole mindset wasn't so potentially catastrophic.
Climate change deniers include a few scientists with relevant credentials, though not many. Best known is Professor Pat Michaels of the Cato Institute, who starred in the infamous Channel 4 documentary The Great Global Warming Swindle. Yesterday, one of the tabloids splashed an Australian academic, Professor Ian Plimer, dismissing the scientific consensus on man-made climate change as a "load of hot air underpinned by fraud".
This is a reference to "Climategate", the row over leaked emails to and from Professor Phil Jones of the University of East Anglia, suggesting a conspiracy to suppress data that called into question man-made climate change. UEA handled this row badly. Probably Jones got too emotionally involved with his work but this doesn't completely invalidate it. Instead of hiding away, Jones should have been giving interviews telling anyone who would listen that his results on surface temperature reconstruction are confirmed independently by the National Oceanic and Atmospheric Administration and Nasa.
The irony of this story is that climate change deniers are notorious for their dirty tricks. During the Bush administration, satellite images showing the shrinking ice cover in the Arctic - an emblem of the damage done by climate change - were kept secret. In 2007, a committee on US government reform criticised systematic efforts "to censor climate scientists by controlling their access to the press and editing testimony to Congress".
The book Climate Cover-up by James Hoggan and Richard Littlemore documents minutely how naysayers manipulated and fabricated data to support their position. A case in point is the way one relatively cool year (2008) - a widely predicted blip - has been used to suggest that the world is cooling when, as Ed Miliband keeps reminding us, we have had nine of the 10 warmest years on record in the past 15 years.
Much of the denial industry is driven by the oil and coal industries. A conference in New York in March, entitled "Global warming: was it ever really a crisis?", was organised by the Heartland Institute, funded by Exxon Mobil until three years ago. And a leaked memo recently revealed the much-quoted Professor Michaels is funded by an electricity company running coal-fired power stations.
This lobby has succeeded in confusing the public. A recent poll in Britain suggests around one-third think the link between climate change and man-made emissions remains unproven, and 15% do not believe global warming is happening at all. The instinct for balance in the serious media is partly to blame for this because of the platform these titles give to climate change creationists and the way analysis often treats both sides equally. Meanwhile, several of the right-inclined tabloids are overtly sceptical. Recently Sir Nicholas Stern, the government adviser on the economics of climate change, compared the naysayers to "flat-earthers". "If you look at all the serious scientists in the world, there is no big disagreement on the basics of this," he said.
Nil desperandum, however. It is easy to forget how far the climate change lobby has come. In early 1990, I interviewed Bill McKibben, a charming, lanky, tweed-suited American who had just written the first book for a general audience that warned about climate change. "We have built a greenhouse where once there bloomed a sweet and wild garden," he warned. The End of Nature was a surprise bestseller (still in print).
A dozen more followed and then Step It Up, a grassroots environmental campaign drawing climate change to the attention of the US Congress. Now he runs 350.org , a global campaign based on peer-reviewed Nasa climate scientist James Hansen's contention that any atmospheric concentration of carbon dioxide above 350 parts per million will lead to environmental catastrophe.
There's work to do because it's currently 390ppm. It's possible to get it down but we need Copenhagen to come up with a solution, not just an agreement, says McKibben. We shouldn't bet against him because, if he's right and we've done nothing, our children's children will be sunk. There's no place for flat-earthers in this argument.