(Written for Unesco by Dr. Gerald Wendt.)
Canadian scientists are looking for a new site for the town of Aklavik, centre of a region extending some 50,000 square miles in the extreme north of Canada’s North-West Territory.
The ground on which Aklavik stands, on the delta of the Mackenzie River within the Arctic Circle, is composed largely of ice particles. If a thaw occurs, due to an unusual rise in the temperature, the land may subside as much as 6 ft., bringing it to the river level it has been found impossible to dig satisfactory building foundations, or to lay down proper drainage systems in this soil.
A project has, therefore, been approved by the Canadian Parliament for the removal of the town to another site, where it will be safe. The changes in climate that people think they experience are seldom real. Extremes of heat or cold, of drought or rainfall, occur at intervals, many years apart. Because those of childhood seem most dramatic, they are longest remembered, and we are easily tempted to compare present average weather with the remembered extremes. These extremes, however, can be expected to recur, and do not constitute a lasting change.
Nevertheless, it is now quite certain that the average temperature of the inhabited parts of the earth has risen about 2 deg. F. within the past 100 years, with most of that change since 1890.
This seems a very small change, but it is important. If the average temperature of the earth should drop by only 4 deg. the glaciers would again advance from the Poles and eventually cover large parts of Canada, Northern Europe, and Asia on the other hand, if the present process of warming continues to the end of this century, the melting of Arctic ice will cause a rise in the sea level that may be troublesome on many sea coasts. Over a longer course of time, this slow rate of change would transform the earth.
It has happened often in past ages. The earth is at least 2,000 million years old and in that time the temperature has gone up and down repeatedly. For about 95 per cent of its existence the earth was much warmer than now and tropical conditions prevailed over most of the surface. The coal deposits in England, in Siberia, and Alaska, and even on the Antarctic continent, are the remains of luxuriant tropical vegetation, long since extinct. At intervals of about 250 million years there have been relatively short periods, only a few million years long, of intense cold when glaciers covered a large portion of the continents of the earth. Only 10 to 20 thousand years ago vast sheets of ice extended from the North Pole, into Germany and France, and covered all of Canada and the northern part of the United States.
STILL WARMING UP
We are still in the period of warming up after the last glacial age. In Greenland, in Alaska, and in the Alps and elsewhere the glaciers are still receding because the snow that falls in the short and relatively mild winters does not make up for the melting of ice during the long, warm summers. In Spitzbergen the average winter temperature has risen 19 deg. since 1910, and the harbour is now open 200 days a year. Where records have been kept the facts are beyond question. In Philadelphia, United States of America, the rise in temperature has been 4 deg. in the past century. In Montreal, Canada, in Britain, and in Scandinavia, the increase has been about 2 deg. since 1850.
The future of many lands depends on whether this change will go on and for how long it will continue. No-one knows because no one can be sure of the reason for the changes. They may be due to conditions on the sun and a change in the amount of heat that reaches the earth. They may be due to a shift in the tilt of the earth’s axis. But there is evidence for either of these two possibilities. Most experts agree that they are caused by changes in the earth’s atmosphere, for which two principal possibilities have been suggested.
One of these is a change in the activity of the earth’s volcanoes. A really large volcanic eruption, such as that of the island of Krakatoa in the East Indies in August, 1883, throws enormous quantities of fine ash many miles into the sky and winds carry the ash to all parts of the earth to dim the sunlight. After the eruption of Krakatoa, astronomers at the Montpellier Observatory in France noted a 10 per cent. decrease in the amount of sunshine. For about three years the thin cloud of volcanic ash apparently prevented the full strength of the sun from reaching the earth’s surface. The eruption of Krakatoa, however, was the last of the great eruptions. So the air may be clearer now and the sunshine brighter and hotter. It is possible, though not very probable, that volcanic ash in the air is the cause of periods of cooler weather.
CARBON DIOXIDE GAS
Nearly a century ago the British scientist John Tyndall suggested that the cause is to be found in the increase or decrease of carbon dioxide gas in the atmosphere.
Normally, the air contains 0.03 per cent. of this gas. It acts somewhat like the glass roof of a greenhouse because it is transparent to the direct rays of the sun and lets them strike the earth and there change into radiant heat waves. These rays are absorbed by the carbon dioxide just as they are by a greenhouse roof. They do not escape into empty space, but remain to warm the air and thus the earth itself.
Any increase in the amount of carbon dioxide in the air would, therefore, result in a warmer climate. The fact is that direct measurements of the carbon dioxide content of the atmosphere tend to show that the amount has increased by about 10 per cent. during the past 50 years. That would nicely account for the increase in the average temperature.
But the question then becomes: What causes the carbon dioxide to vary? There are several possibilities. Green plants absorb carbon dioxide from the air and water from the earth and under the action of sunshine combine them to make sugars, starches and cellulose and thus to build their structures. About a million million tons of carbon dioxide are thus taken out of the atmosphere every year in the life process of growing plants. But this is not a total loss because the plants, and the animals that feed upon them, eventually die and decay, and in decaying the carbon dioxide is reformed and escapes back to the atmosphere. If this decay does not occur, as in the formation of coal where the plants are buried and protected from decay then the growth of plants results in a gradual loss of carbon dioxide from the air. But only some 10,000,000 tons of carbon dioxide are thus buried in the earth each year and lost to the atmosphere. It is a comparatively small amount and cannot be an important factor.
Another influence on the carbon dioxide content of the air is geological. The weathering of rocks and their conversion into soil are to a large extent an attack upon the rocks by carbonic acid, the weak acid that forms when carbon dioxide dissolves in water. The result is a slow change of the rocks from silicates to carbonates. This process takes about 100,000,000 tons of carbon dioxide from the air every year. But this process is balanced by another geological process. Hot springs and volcanoes pour large quantities of carbon dioxide into the air, approximately 100,000,000 tons a year. Thus the two geological processes normally counteract each other. It is interesting that this change in the carbon dioxide content would also affect the amount of rainfall. A cloud sheds its rain when there is a considerable difference of temperature between its lower and upper surfaces. With less carbon dioxide, the upper surface of the cloud cools more quickly and thus increases the rainfall. Periods of low carbon dioxide are both cooler and wetter. Periods of high carbon dioxide are hotter and dryer.
But there is one new factor that would increase the carbon dioxide content of the air. It is an effect of man’s activity, the burning of coal and oil. The carbon dioxide produced by combustion is much larger than is generally realised. Burning a ton of coal produces about two and a half tons of carbon dioxide. It is estimated that each year 6,000,000,000 tons of carbon dioxide are poured into the atmosphere, chiefly in industrial plants. This is a much larger amount than from any other cause. If all this additional carbon dioxide stays in the atmosphere it alone could account for a temperature rise of 2 deg. in a century. Strange as it may seem, this is very close to the rate at which the temperature is actually rising now. Thus man himself may be responsible for the changing climate.
If this is so, and if no other process appears to counterbalance it, then the climate of the earth will become continually warmer and possibly also dryer for the next few centuries. This, in turn, means that crops such as grain, or grapes which could formerly be grown only in southern areas, will become available much nearer to the Arctic. Already in Finland and Scandinavia, farmers are ploughing fields that had lain under the ice for centuries. In Canada and Siberia, the area of permanently frozen ground is retreating toward the Pole at the rate of a hundred yards to several miles a year. Time was when Greenland and Iceland supported a flourishing culture and grapes could be cultivated in England. Such times are likely to return, and vast areas of Canada, Alaska, and Siberia may become available for food production.
Source: The Queensland Times