Historical evidence shows that the climate of the world since the planet was formed more than 4,000 million years ago has fluctuated greatly, and on many occasions has borne little resemblance to what we experience today.
The Climate Shapes Mans Destiny
For example, we are currently in the middle of an ice epoch (longer than an ice age) which has lasted millions of years and is likely to continue for millions more. Yet, in the context of the history of the planet, this is not a normal period. More average conditions would be significantly warmer, producing the lush vegetation and hot conditions that prevailed aeons ago when dinosaurs walked the Earth for millions of years.
The reason why we are in the middle of such a cold epoch has a great deal to do with the positioning of the land masses. Almost imperceptibly, the great continents are constantly moving and changing location. Throughout the history of the Earth it has been unusual to have one polar ice-cap; it is unique for us now to have two of them.
Normally the circulation of the warm currents of the oceans, as I mentioned earlier, helps distribute the heat and ensure a general uniformity of temperatures. However, the land mass that has become known to us as Antarctica has temporarily (in global terms!) positioned itself over the South Pole thereby blocking off warm currents. This has allowed ice some 1,800 metres (6,000 feet) thick to form a sheet over that now most inhospitable of continents.
Similarly, by another quirk of the slow drift of the continents, land has encircled the North pole, causing the waters there to be largely cut off from the worldwide drift of oceanic currents. This too has allowed an ice-cap to develop at the North Pole. Eventually – and by this I mean in tens of millions of years – the land masses of North America and Europe, which are moving away from each other, will be far enough apart to allow the warmer currents from the Atlantic to warm up the Arctic and melt the ice-cap. However, as far as humans are concerned at present the existence of two polar ice-caps is, for all practical purposes, a permanent one. Within an ice epoch there are ice ages which alternate with shorter warmer periods known as interglacials. At the moment the Earth is passing through an interglacial which has lasted for around 10,000 years following the last Ice Age, which in turn went on for some 100,000 years. It would appear from historical climatic evidence that this ice age/interglacial pattern was established at the beginning of this ice epoch. Perhaps ominously for man, the pattern suggests that ice ages last around 100,000 years on average and the shorter, warmer interglacials around 10,000 – so we are nearing the end of our current warmer period. However, there is no need for any alarm at this thought. The next ice age could be up to 1,000 years or more away – a short period in climatology but a comfortingly lengthy one for us. And in any case no one can yet predict what effect the greenhouse effect may have on the overall pattern of global cooling and in arresting a return to glacial conditions.
What does seem apparent is that within the current interglacial, starting some 10,000 years ago, there have been smaller patterns emerging – periods of warmer weather, followed by colder weather and so on. These have been broken down by climatologists into four main periods. The first followed the end of the last Ice Age, indeed it caused it to end, and probably reached its warmest about 5,000 or 6,000 years ago. At this time the temperature would have been on average about 2C (3.6F) warmer than the present day. This period has acquired the name the Optimum period as a result, and was followed by a much colder spell which more or less coincides with the historical period called the Iron Age, which reached its coldest around 2,500 years ago. (It should be remembered that these changes are gradual and do not occur overnight). The next period, one less well known but much closer to our own time and therefore much better documented, was the so-called Little Optimum. This period of warming peaked in western Europe around 1100 AD and coincided with a period of growth and agricultural and technological advance during what we call the Middle Ages. On average temperatures were around 1C (1.8F) lower than now. Vineyards flourished in England and generally cultivation was possible on higher and more northerly ground than at present, crops also grew on Greenland.
However, the Little Optimum gave way by the late Middle Ages to a gradual cooling of the Earth that led to the Little Ice Age, which reached its peak 200 to 300 years ago. It was during this period that the Great Frost Fairs took place on the Thames as the river froze sufficiently to allow people – and even elephants! – to walk on it safely. (In the winter of 1683/4 a whole ox was roasted on the ice). The water did freeze again in the 1890’s but was not hard enough to support people. Again it should be remembered that even within this colder period there were some hot, dry spells, such as 1666, the year of the Great Fire of London. Although it is widely accepted that the last Little Ice Age ended around 1850 there has been some speculation as to whether we are still in it and that our present warmer period could be but a brief respite. There is certainly evidence that the first half of this century was unusually warm compared with the last few hundred years and that, the greenhouse effect aside, we are heading for a cooler period. In any case, all historical climatic trends point to us nearing the end of our interglacial and gradually approaching the next age of ice.