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Global climate now on a knife-edge - Brendan McWilliams

19 Jan 2006

Weather Eye - Irish Times

By Brendan McWilliams

Geologists of the early 19th century were mystified by the existence all over Europe of gigantic boulders which differed in composition from their surroundings and had obviously been transported from a distant spot.

The accepted explanation was that these erratics, as they were called, were carried to their destinations by great currents of water and mud associated with Noah's flood.

The theory neatly accounted for the fossilised remains being unearthed by inquisitive geologists and had the convenient advantage that it did not undermine the word of God, as set forth in considerable detail in the Old Testament.

"How daft they were, how daft!" we think nowadays, in our generationally chauvinistic way. We know now, of course, that over the millenniums there have been dramatic and sometimes very rapid shifts in the earth's climate, as it swings from relatively benign conditions, such as we enjoy at present, to the much colder interludes that we call "ice ages".

Each time the earth became colder, the advancing ice gouged deep grooves in the underlying rock and swallowed up large chunks of rock in its path; then as the climate warmed, the retreating ice deposited these rocks in splendid isolation many miles away from their point of origin. It is a chilling thought in more ways than one, moreover, that in the past 750,000 years, the global climate has been in "ice age" mode for more than 90 per cent of the time.

In the past, these massive swings in Earth's climate were mainly a consequence of eccentricities of the Earth's orbit and the idiosyncrasies of the way in which it revolves on its own axis. More recently, as we know, of more immediate concern is the likely effect of increasing amounts of atmospheric carbon dioxide and other greenhouse gases on global temperatures.

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