How an Ice Age Begins

The idea that climatic warming can induce climatic cooling may seem counterintuitive, but that process of warming leading to cooling is a basic part of the "orbital theory" of an insolation-driven (sunlight-driven) Ice Age cycle. The orbital theory, also known as the Milankovitch theory, is based on the fact that cyclic changes in the earth's orbit of the sun alter the amount of sunlight that reaches the earth, and it is the most widely-accepted theory of Ice Age causation.

The next Ice Age will be precipitated by -- quite literally -- an upward trend in summer temperatures and summer warming of the oceans in the Northern Hemisphere, which will increase oceanic evaporation and cause an increase in precipitation, some of which will fall as snow that will feed the growth of glaciers at high elevations and at high latitudes.

An Ice Age is characterized by the formation of vast glaciers on top of large continental land masses. Since there are much larger continental land masses located in the high latitudes of the Northern Hemisphere than in the Southern Hemisphere, it is in the Northern Hemisphere that the Ice Age cycle is most obviously manifested. At the peak of the last Ice Age glacial maximum, about 18,000 years ago, vast glaciers up to two miles thick covered all of Canada, all of Scandinavia, and most of the British Isles.

The astronomical phenomenon known as the Precession of the Equinoxes causes a gradual rotation of the earth's axial tilt, which changes the seasons during which the Northern and Southern Hemispheres make their nearest approach to the sun (at perihelion) and their farthest excursion from the sun (at aphelion).

For the past 11,000 years perihelion -- the earth's nearest approach to the sun -- has occured during the Northern Hemisphere's winter, and aphelion -- the earth's farthest excursion from the sun -- has occured during the Northern Hemisphere's summer.

When perihelion -- the earth's nearest approach to the sun -- occurs during the winter and aphelion -- the earth's farthest excursion from the sun -- occurs during the summer, there is a reduction in the temperature extremes of the seasons. That is because at perihelion the nearness of the earth to the sun reduces the cold of winter and at aphelion the increased distance of the earth from the sun reduces the warmth of summer. Furthermore, a winter perihelion shortens the duration of the winter and a summer aphelion lengthens the duration of the summer.

But the short, mild winters and long, mild summers which the Northern Hemisphere has enjoyed for the past 11,000 years have come to an end. During the next 11,000 years the winters in the Northern Hemisphere will become longer and colder, and the summers will become shorter and hotter.

During the next 11,000 years the Northern Hemisphere will experience short, hot summers and long, cold winters. The blazing hot summers will warm the oceans and cause increased precipitation, much of which will be deposited as snow at high elevations and in the high latitudes, facilitating the genesis and growth of glaciers. The long, cold winters will further facilitate the growth and maintenance of glaciers in the high latitudes and high elevations of the Northern Hemisphere.

Research has shown that during the previous Ice Age glacial maximum, the first 5,000 years of the glacial advance was characterized by the conditions described by the above paragraph. After 5,000 years, the continental glaciers became well established at their full extent and the Northern Hemisphere remained in full Ice Age conditions for another 5,000 years before the ice began to retreat about 11,000 years ago.

In recent years we have seen record-breaking high summer temperatures recorded in many parts of the Northern Hemisphere, and we have also seen record-breaking low winter temperatures recorded in many parts of the Northern Hemisphere. The winters of 2007-8 and 2008-9 broke many records for low temperatures and the depth of snowfall, and in early October of 2009 we are already seeing an early onset of wintry-cold conditions in the Northern Hemisphere.

The increasing extremes of summer and winter temperatures in the Northern Hemisphere that we have seen in recent years are consistent with what we should expect to see as the Northern Hemisphere moves into another 11,000 year period of extreme summers and winters.

And that is how an Ice Age begins.

Gregory Fegel

Published on October 7, 2009 at Pravda.ru.