Conspiracy theorists are often the subject of scorn or mockery; rejected and ridiculed by the rest of us, they hide away on internet chat forums where they blather on about the collapse of 7 World Trade Center, the rise of the Illuminati or the omnipresence of Mossad. Not the climate-change deniers. Unlike Israel's intelligence agency, they really do seem to be omnipresent these days. Indeed, unlike the Illuminati, they even control national governments.
For instance, Australia's new prime minister, Tony Abbott, has called the science on climate change "absolute crap" and already abolished the country's Climate Commission. In 2012, Mitt Romney, the Republican nominee for the most important job in the world, was of the view that "we don't know what's causing climate change on this planet". Here in the UK, the Environment Secretary, Owen Paterson, a Conservative, is, in the words of the Financial Times, a "known climate change sceptic". So, too, is a Conservative member of the Commons energy and climate change committee, Peter Lilley.
Denialism abounds. In March, a YouGov poll found that only 39% of the British public believed human activity was making the world warmer, down from 55% in 2008, while the proportion of Brits who believed that the world wasn't getting warmer had quadrupled - up from 7% in 2008 to 28%.
Depressingly, you can draw no other conclusion from these facts than that the conspiracy theorists are winning. The deniers of global warming have come in from the cold. The "merchants of doubt", to borrow a phrase from the science historians Naomi Oreskes and Erik Conway, seem to have perfected the dark art of "keeping the controversy alive", sowing seeds of doubt and confusion in the minds of politicians, journalists and voters, in spite of the scientific consensus.
Thus, I use both the terms "denier" (rather than "sceptic") and "conspiracy theorist" advisedly. After all, they either deny that the world is warming or deny that mankind is responsible for this warming. Remember: 97% of climate scientists agree the world is warming and that mankind is responsible. Consider also: a survey by Oreskes of every peer-reviewed abstract on the subject "global climate change" published between 1993 and 2003 - 928 in total - couldn't find a single paper that rejected the consensus position on human-induced climate change.
The real sceptics are the cautious scientists of the Intergovernmental Panel on Climate Change who, year after year, assess and reassess the new data and go through thousands of peer-reviewed studies, forming groups and committees to check and doublecheck the results.
As for the "conspiracy theorist" tag, let me be blunt: climate-change deniers are the biggest conspiracy theorists of all. In order to embrace the delusions of the deniers, you have to adopt the belief that tens of thousands of researchers, some of them awardwinning scientists, from across the world (not to mention the political spectrum) have conducted behind the scenes, undetected by the media, a campaign of peer-reviewed deceit in defiance of empirical data. How else to explain what the US Republican senator James Inhofe, a darling of the deniers, calls "the greatest hoax ever perpetrated against the American people"?
Yet it isn't just barmy GOP politicians. Or the gaffe-prone prime minister of Australia. Take Richard Lindzen, the doyen of the selfstyled "climate sceptics" and a tenured professor of meteorology at the Massachusetts Institute of Technology. Earlier this year, I interviewed him for my al-Jazeera TV series Head to Head; unlike the vast majority of his fellow deniers, Lindzen has the advantage of being a trained scientist who has bothered to study our planet's climate.
Why, I asked the softly-spoken professor, did he think national academies of science from 34 different countries - including the United States, the United Kingdom, China, India, Russia, France, Germany, Japan, Mexico, Canada, Brazil and South Africa - had all signed up to the IPCC consensus position on man-made climate change?
Richard Lindzen: "They've been told: 'Issue a statement on this.'"
Me: "Told by who?"
RL: "Well, I'd rather not say, to be honest."
Me: "Why not?"
RL: "Because in each case, it would be in some ways embarrassing - I mean, each of them are dependent [sic] on the goodwill of the government. And if they're told 'sign on', they'll sign on."
Huh? Are we expected to believe that 34 different national academies of science are all working hand in glove with their country governments to exaggerate the impact of carbon-dioxide emissions on the climate and cover up the supposed evidence of global cooling? To what end - and on whose orders? Greenpeace? Al Gore?
To be honest, I don't have a problem with most conspiracy theorists. If they want to believe that the 9/11 attacks were an "inside job" or that the Nasa moon landings were "faked", so be it. Each to his own. In any case, most of these cranks and clowns do no harm to anything, other than their own reputation (or non-reputation).
But the climate-change deniers of today, with their astonishing combination of manufactured doubt, faux outrage, mass paranoia and evidence-free pseudoscience, are endangering our planet. According to the World Health Organisation, "climatic changes already are estimated to cause over 150,000 deaths annually". The poorest countries, incidentally, bear the brunt of these preventable fatalities.
It's no laughing matter. This particular conspiracy theory costs lives.
Mehdi Hasan is the political director of the Huffington Post UK and a contributing writer for the New Statesman, where this article is cross-posted