Johann Hari: The last gasp of the global warming deniers

They are beached on the shores of the wrong side of history, now abandoned even by Bush

And so, at last and at least, the words come. The evidence is now so thuddingly inescapable that even George W. Bush - a man who, when pricked, bleeds oil - has acknowledged "the serious challenge of global climate change" in his State of the Union address. It is only a rhetorical concession, another excuse to fiddle as the West Antarctic ice-sheet melts - but it is also a crux moment in the history of global warming denial.

Today, the small, lingering band of global warming "sceptics" are beached on the farthest shores of the wrong side of history. They are alone, abandoned even by Global Warming Bush and the oil industry.

Yet this is not a time to gloat. It is time to appeal to them to join the fight for survival. Deniers, I am sure some of you were sincere. Man-made global warming is such a horrifying event, it is natural to want to scramble for scraps of evidence suggesting it can't be true. And there are some small misanthropic parts of the environmentalist movement it is perfectly natural to recoil from. The direct action group Earth First! famously made the vile statement that "the Aids epidemic, rather than being a scourge, is a welcome development in the inevitable reduction of human population ... If [it] didn't exist, radical environmentalists would have to invent [it]." Maybe you wrongly thought all environmentalists were like this. Maybe that's why you were so eager to disprove our core issue.

I know it's painful to give up on something you have passionately believed. So let's - for one last time - go through your arguments.

Deniers' Myth Number One: Scientists are divided on whether man is causing global warming. In 2004, the universally-respected journal Science studied 928 randomly selected scientific papers containing the words "global climate change". None of them - not one - disagreed with the view that global warming is being caused to a significant degree by burning fossil fuels. As Jim Baker, who was head of one of the leading scientific organisations in the US, explains, "There is a better scientific consensus on this issue than any other, with the possible exception of Newton's Law of Dynamics."

Deniers' Myth Number Two: The current warming of the world is simply part of the planet's natural cycle. After all, there were no carbon emissions when the last ice age ended - why should the current warming be due to them? There is a sliver of truth in this: natural climate change has not stopped, and it never will. But we have superimposed onto it a great blast of greenhouse gases of our own, with far stronger effect.

To understand this, you only have to grasp some basic 19th-century physics. As Professor Chris Rapley of the British Antarctic Survey explains, "There are natural greenhouse gases in the earth's atmosphere which trap heat on the planet, keeping the surface temperature 30 degrees warmer than it otherwise would be. Since the start of the industrial revolution, we have released lots more greenhouse gases - around 1,000 billion tonnes of them. This has enhanced the natural greenhouse effect, and trapped more heat - currently 0.6 degrees. The more greenhouse gases we add, the warmer we'll be. It's not rocket science."

Deniers' Myth Number Three: The current warming in the world is all due to changes in the energy output of the Sun. In 1991, the Danish scientists Knud Lassen and Eigil Friis-Christensen found a correlation between temperature changes on Earth from 1850 onwards and sunspot activity, which usually indicate changes in the intensity of solar radiation. As the sun warmed, we warmed.

Other scientists studied this closely, and found out that they were partly right: up to 40 per cent of the planet's warming is indeed due to solar activity. But since 1980, sunspot activity has been declining - yet temperatures down here have been soaring to the highest levels ever recorded. So while the Sun can take some of the flak, the world's scientists agree: the other 60 per cent remains with us.

Deniers' Myth Number Four: In the 1970s, scientists were warning about "global cooling" and a looming Ice Age. How can we now trust these warnings of global warming? In fact, in the 1970s two - literally two - scientists tentatively suggested that cooling could occur over millennia. To compare that meek, misreported suggestion by two people to the overwhelming scientific consensus from tens of thousands of climatologists is, I am sure you deniers can see now, dishonest.

Denier's Myth Number Five: Global warming is a religion. People have always had an innate psychological need to believe in a looming apocalypse - this is just the latest version.

Precisely the opposite is the truth. Global warming is based on very close empirical observation of the real world, and deductions based on reason. If its conclusions fall into one particular niche in intellectual history, that doesn't change the fact they are true. It is you, the deniers clinging to myths, who resemble the faithful. Far from being Galileos, you have been siding with the fossil fuel Vatican.

Last year, there was an extraordinary exchange on the BBC's Newsnight between the environmentalist George Monbiot and the global warming denier Melanie Phillips. Monbiot pointed out that virtually all the "evidence" Phillips cites stems from people funded by Exxon-Mobil, a Big Oil corporation that has dedicated tens of millions of dollars to promoting denialist myths so they can carry on pumping carbon dioxide into the atmosphere. "Could it be," Monbiot asked, "that you are an unwitting dupe of Exxon-Mobil?" Phillips replied, "It could be, it could be. I have no idea who funds the people I read and listen to."

No idea. She had lauded Ross McKittrick, funded by Exxon, for debunking" environmentalist graphs. She had lauded, as invaluable experts, Dr Roy Spencer, Dr Richard Lindzen, the Cato Institute, the Tech Central Science Foundation and the George C. Marshall Institute - every one funded by Exxon. She has not yet recanted.

Deniers, the war is over. You still have time to come in from the cold and join the warming world on which the rest of us live. There is no shame in making an honest mistake. But if you have any respect for evidence and for human survival, you must begin today to redeploy all that energy you have spent furiously claiming that the world's climatologists are idiots into arguing for a drastic reduction in the world's carbon emissions. These necessary cuts are still, despite George Bush's measly admission, a less likely prospect than global ecocidal disaster. Join us as we try to reverse those odds and there may - just - be a chance you could be remembered with something other than contempt.

j.hari@independent.co.uk