No one can deny that in recent years the need to "save the planet" from global warming has become one of the most pervasive issues of our time. As Tony Blair's chief scientific adviser, Sir David King, claimed in 2004, it poses "a far greater threat to the world than international terrorism", warning that by the end of this century the only habitable continent left will be Antarctica.
Inevitably, many people have been bemused by this somewhat one-sided debate, imagining that if so many experts are agreed, then there must be something in it. But if we set the story of how this fear was promoted in the context of other scares before it, the parallels which emerge might leave any honest believer in global warming feeling uncomfortable.
The story of how the panic over climate change was pushed to the top of the international agenda falls into five main stages. Stage one came in the 1970s when many scientists expressed alarm over what they saw as a disastrous change in the earth's climate. Their fear was not of warming but global cooling, of "a new Ice Age".
For three decades, after a sharp rise in the interwar years up to 1940, global temperatures had been falling. The one thing certain about climate is that it is always changing. Since we began to emerge from the last Ice Age 20,000 years ago, temperatures have been through significant swings several times. The hottest period occurred around 8,000 years ago and was followed by a long cooling. Then came what is known as the "Roman Warming", coinciding with the Roman empire. Three centuries of cooling in the Dark Ages were followed by the "Mediaeval Warming", when the evidence agrees the world was hotter than today.
Around 1300 began "the Little Ice Age", that did not end until 200 years ago, when we entered what is known as the "Modern Warming". But even this has been chequered by colder periods, such as the "Little Cooling" between 1940 and 1975. Then, in the late 1970s, the world began warming again.
A scare is often set off - as we show in our book with other examples - when two things are observed together and scientists suggest one must have been caused by the other. In this case, thanks to readings commissioned by Dr Roger Revelle, a distinguished American oceanographer, it was observed that since the late 1950s levels of carbon dioxide in the earth's atmosphere had been rising. Perhaps it was this increase that was causing the new warming in the 1980s?
Stage two of the story began in 1988 when, with remarkable speed, the global warming story was elevated into a ruling orthodoxy, partly due to hearings in Washington chaired by a youngish senator, Al Gore, who had studied under Dr Revelle in the 1960s.
But more importantly global warming hit centre stage because in 1988 the UN set up its Intergovernmental Panel on Climate Change (the IPCC). Through a series of reports, the IPCC was to advance its cause in a rather unusual fashion. First it would commission as many as 1,500 experts to produce a huge scientific report, which might include all sorts of doubts and reservations. But this was to be prefaced by a Summary for Policymakers, drafted in consultation with governments and officials - essentially a political document - in which most of the caveats contained in the experts' report would not appear.
This contradiction was obvious in the first report in 1991, which led to the Rio conference on climate change in 1992. The second report in 1996 gave particular prominence to a study by an obscure US government scientist claiming that the evidence for a connection between global warming and rising CO2 levels was now firmly established. This study came under heavy fire from various leading climate experts for the way it manipulated the evidence. But this was not allowed to stand in the way of the claim that there was now complete scientific consensus behind the CO2 thesis, and the Summary for Policy-makers, heavily influenced from behind the scenes by Al Gore, by this time US Vice-President, paved the way in 1997 for the famous Kyoto Protocol.
Kyoto initiated stage three of the story, by formally committing governments to drastic reductions in their CO2 emissions. But the treaty still had to be ratified and this seemed a good way off, not least thanks to its rejection in 1997 by the US Senate, despite the best attempts of Mr Gore.
Not the least of his efforts was his bid to suppress an article co-authored by Dr Revelle just before his death. Gore didn't want it to be known that his guru had urged that the global warming thesis should be viewed with more caution.
One of the greatest problems Gore and his allies faced at this time was the mass of evidence showing that in the past, global temperatures had been higher than in the late 20th century.
In 1998 came the answer they were looking for: a new temperature chart, devised by a young American physicist, Michael Mann. This became known as the "hockey stick" because it showed historic temperatures running in an almost flat line over the past 1,000 years, then suddenly flicking up at the end to record levels.
Mann's hockey stick was just what the IPCC wanted. When its 2001 report came out it was given pride of place at the top of page 1. The Mediaeval Warming, the Little Ice Age, the 20th century Little Cooling, when CO2 had already been rising, all had been wiped away.
But then a growing number of academics began to raise doubts about Mann and his graph. This culminated in 2003 with a devastating study by two Canadians showing how Mann had not only ignored most of the evidence before him but had used an algorithm that would produce a hockey stick graph whatever evidence was fed into the computer. When this was removed, the graph re-emerged just as it had looked before, showing the Middle Ages as hotter than today.
It is hard to recall any scientific thesis ever being so comprehensively discredited as the "hockey stick". Yet the global warming juggernaut rolled on regardless, now led by the European Union. In 2004, thanks to a highly dubious deal between the EU and Putin's Russia, stage four of the story began when the Kyoto treaty was finally ratified.
In the past three years, we have seen the EU announcing every kind of measure geared to fighting climate change, from building ever more highly-subsidised wind turbines, to a commitment that by 2050 it will have reduced carbon emissions by 60 per cent. This is a pledge that could only be met by such a massive reduction in living standards that it is impossible to see the peoples of Europe accepting it.
All this frenzy has rested on the assumption that global temperatures will continue to rise in tandem with CO2 and that, unless mankind takes drastic action, our planet is faced with the apocalypse so vividly described by Al Gore in his Oscar-winning film An Inconvenient Truth.
Yet recently, stage five of the story has seen all sorts of question marks being raised over Gore's alleged consensus. For instance, he claimed that by the end of this century world sea levels will have risen by 20 ft when even the IPCC in its latest report, only predicts a rise of between four and 17 inches.There is also of course the harsh reality that, wholly unaffected by Kyoto, the economies of China and India are now expanding at nearly 10 per cent a year, with China likely to be emitting more CO2 than the US within two years.
More serious, however, has been all the evidence accumulating to show that, despite the continuing rise in CO2 levels, global temperatures in the years since 1998 have no longer been rising and may soon even be falling.
It was a telling moment when, in August, Gore's closest scientific ally, James Hansen of the Goddard Institute for Space Studies, was forced to revise his influential record of US surface temperatures showing that the past decade has seen the hottest years on record. His graph now concedes that the hottest year of the 20th century was not 1998 but 1934, and that four of the 10 warmest years in the past 100 were in the 1930s.
Furthermore, scientists and academics have recently been queuing up to point out that fluctuations in global temperatures correlate more consistently with patterns of radiation from the sun than with any rise in CO2 levels, and that after a century of high solar activity, the sun's effect is now weakening, presaging a likely drop in temperatures.
If global warming does turn out to have been a scare like all the others, it will certainly represent as great a collective flight from reality as history has ever recorded. The evidence of the next 10 years will be very interesting.
• Scared to Death: From BSE To Global Warming - How Scares Are Costing Us The Earth by Christopher Booker and Richard North (Continuum, £16.99) is available for £14.99 + £1.25 p&p. To order call Telegraph Books on 0870 428 4115 or go to books.telegraph.co.uk .
