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.
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.
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.
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