The American Association for the Advancement of Science came as close as such a respectable institution can to screaming an alarm last week. "As scientists, it is not our role to tell people what they should do," it said as it began one of those sentences that you know will build to a "but". "But human-caused climate risks abrupt, unpredictable and potentially irreversible changes."

In other words, the most distinguished scientists from the country with the world's pre-eminent educational institutions were trying to shake humanity out of its complacency. Why weren't their warnings leading the news?

In one sense, the association's appeal was not new. The Royal Society, the Royal Institution, Nasa, the US National Academy of Sciences, the US Geological Survey, the IPCC and the national science bodies of 30 or so other countries have said that man-made climate change is on the march. A survey of 2,000 peer-reviewed papers on global warming published in the last 20 years found that 97% said that humans were causing it.

When the glib talk about the "scientific debate on global warming", they either don't know or will not accept that there is no scientific debate. The suggestion first made by Eugene F Stoermer that the planet has moved from the Holocene, which began at the end of the last ice age, to the manmade Anthropocene, in which we now live, is everywhere gaining support. Man-made global warming and the man-made mass extinction of species define this hot, bloody and (let us hope) brief epoch in the world's history.

If global warming is not new, it is urgent: a subject that should never be far from our thoughts. Yet within 24 hours of the American association's warning the British government's budget confirmed that it no longer wanted to fight it.

David Cameron, who once promised that if you voted blue you would go green, now appoints Owen Paterson, a man who is not just ignorant of environmental science but proud of his ignorance, as his environment secretary. George Osborne, who once promised that his Treasury would be "at the heart of this historic fight against climate change", now gives billions in tax concessions to the oil and gas industry, cuts the funds for onshore wind farms and strips the Green Investment Bank of the ability to borrow and lend

All of which is a long way of saying that the global warming deniers have won. And please, can I have no emails from bed-wetting kidults blubbing that you can't call us "global warming deniers " because "denier" makes us sound like "Holocaust deniers", and that means you are comparing us to Nazis? The evidence for man-made global warming is as final as the evidence of Auschwitz. No other word will do.

Tempting though it is to blame cowardly politicians, the abuse comes too easily. The question remains: what turned them into cowards? Rightwing billionaires in the United States and the oil companies have spent fortunes on blocking action on climate change. A part of the answer may therefore be that conservative politicians in London, Washington and Canberra are doing their richest supporters' bidding. There's truth in the bribery hypothesis. In my own little world of journalism, I have seen rightwing hacks realise the financial potential of denial and turn from reasonable men and women into beetle-browed conspiracy theorists.

But the right is also going along with an eruption of know-nothing populism. Just as there are leftish greens, who will never accept that GM foods are safe, so an ever-growing element on the right becomes more militant as the temperature rises.

Clive Hamilton, the Australian author of Requiem for a Species, made the essential point a few years ago that climate change denial was no longer just a corporate lobbying campaign. The opponents of science would say what they said unbribed. The movement was in the grip of "cognitive dissonance", a condition first defined by Leon Festinger and his colleagues in the 1950s . They examined a cult that had attached itself to a Chicago housewife called Dorothy Martin. She convinced her followers to resign from their jobs and sell their possessions because a great flood was to engulf the earth on 21 December 1954. They would be the only survivors. Aliens in a flying saucer would swoop down and save the chosen few.

When 21 December came and went, and the Earth carried on as before, the group did not despair. Martin announced that the aliens had sent her a message saying that they had decided at the last minute not to flood the planet after all. Her followers believed her. They had given up so much for their faith that they would believe anything rather than admit their sacrifices had been pointless.

Climate change deniers are as committed. Their denial fits perfectly with their support for free market economics, opposition to state intervention and hatred of all those latte-slurping, quinoa-munching liberals, with their arrogant manners and dainty hybrid cars, who presume to tell honest men and women how to live. If they admitted they were wrong on climate change, they might have to admit that they were wrong on everything else and their whole political identity would unravel.

The politicians know too well that beyond the corporations and the cultish fanatics in their grass roots lies the great mass of people, whose influence matters most. They accept at some level that manmade climate change is happening but don't want to think about it.

I am no better than them. I could write about the environment every week. No editor would stop me. But the task feels as hopeless as arguing against growing old. Whatever you do or say, it is going to happen. How can you persuade countries to accept huge reductions in their living standards to limit (not stop) the rise in temperatures? How can you persuade the human race to put the future ahead of the present?

The American historians of science Naomi Oreskes and Eril M Conway quoted a researcher, who was asked in the 1970s what his country's leaders said when he warned them that C02 levels would double in 50 years. "They tell me to come back in 49 years," he replied.

Most of the rest of us think like the Washington politicians of the Carter era. And most of us have no right to sneer at Dorothy Martin and her cult either. We cannot admit it, but like them, we need a miracle to save us from the floods.