The climate is changing. But it always has

By Dr. David Whitehouse, Astronomer and Author

The global climate is changing. It always has. Fifteen thousand years ago the place where I am writing this (Hampshire, England) was Arctic tundra on which almost nothing could live. The glaciers reached not far north of here, and places that were to become Manchester, Liverpool and Glasgow were under a kilometer of ice. When the ice receded Britain was completely covered in trees. That the trees are fewer was due to early man. That the ice is no longer here was due to natural climatic cycles.

Few doubt that the world has warmed in the past thirty years. We have reasonably good global temperature records for the past 150 years and, in general, they show a gradual warming, possibly from the cold spell in the 17th century some call the ‘Little Ice Age.’

Temperatures at a plateau

From 1850 to about 1910, the temperature did not change very much at a time when the world was somewhat colder than it is today. Between 1910 and 1940 there was a sustained warming, 0.4 deg C in 30 years. Then there was a period of 40 years when again the temperature did not change much. Just before1980 it started rising again, 0.4 deg C in 25 years, but this rise ceased in 2000. We live in the warmest decade for at least 150 years, probably longer, but in the last decade the global average annual temperature has remained at a plateau.

On the face of it, today’s warm spell isn’t anything unusual. There is growing evidence that there was a so-called Medieval Warm Period about 800 years ago. In a recent research paper, Professor Michael Mann of Penn State University – of now discredited ‘hockey stick’ graph fame – admitted that the temperatures then could well be higher than today. It used to be thought that the Medieval Warm Period was confined to Europe, but there is now evidence it was more global.

There is also some evidence that a thousand years before the Medieval Warm Period, the so-called Roman Warm Period was just as warm, possibly warmer, as was possibly the Minoan Warm Period a 1,000 years before that. So, in absolute terms the recent warm spell is not historically extraordinary.

Some argue that the rate of increase of global temperature in the past 30 years has been more rapid than in the past. This is not so. The IPCC (International Panel on Climate Change) says that the year when mankind’s influence on the global climate was first apparent was 1960. Before that time, it maintains, all changes can be explained as natural. It is curious, then, that the rate of temperature increase seen before that date (1910 to 1940) is statistically identical to the recent rate of temperature increase (1980 to 2000).

So neither the warmth of the past few years, nor the temperature increase leading up to it is unusual.


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