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.
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