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INTRODUCTION

Threw the last 2 million years has the climate changed several times between cold periods, called ice ages, and warm periods, between ice ages. While the ice ages ruled, enormous amounts of water where transformed to ice into glaciers that formed an ice
sheets on the northern hemisphere. The ice sheets spread over large parts of the continents where it was created. One doesn’t know exactly how many ice ages there has been, but in Northern Europe there has been at least seven ice ages, where the glaciers in the Scandinavian mountains grew and united to an enormous ice sheets, the ice sheets of Northern Europe.

Glaciers
Today, 11 % of the earths land masses are covered by glaciers. Of these, 84 % is constituted of the Antarctic ice shield, while the mainland ice on Greenland consists of 11 %. To compare, you can say that under the last ice age, 31 % of the land was covered by ice and sea level lied 150 m below today’s sea level. To understand how a glacier is born, there are some concepts to be mentioned first.

To mention the climate, the normal condition on earth is the ice age. We are just lucky to live in between ice ages, in a warm period. But this condition never lasts very long. The last between ice age period, called “Eem”, lasted only about 30.000 years, after an ice age, called “Saale”, that lasted about 100.000 years. Other ice ages has easily lasted up to 200.000 years. The period we are living in now has for the time being lasted 17.000 years, but it hasn’t have to last very much longer.

Milutin Milankovitch's theory
The ex. Yugoslavian mathematic professor Milankovitch, finished in 1930 a book "Mathematical climatology and the Astronomic Theory of Climate changes", where he writes, there are 3 things that have a final decision on the earths climate.

1) The way the earth rotates around the sun.

2) The earth’s inclination.

3) Time of the year, and how close the earth is to the sun.

Table over the earth’s cycles
         

1) The earth's course around the sun is like an ellipse (oval). The form of the ellipse changes from being almost a circle to become a more oval from again. In a cycle of 95.000 years the ellipse changes its form. That means that every 47.500 years the course turns in to a almost circle and then in an other 47.500 years back to an ova. Look at the figure.

2) The earths axis inclines compared to the sun. It is this phenomenon that gives us the change in seasons. If the axis had been strait, we wouldn’t have the seasons we know. The axis always inclines between 22.1° and 24.5°. It takes 21.000 years for the earth to move from 22.1° to 24.5°, and another 21.000 to come back where it started. The less the inclination is the less variations in seasons we can se, and the other way around. This means that variations in season goes through a cycles of 42.000 years. See figure.

3) As the earths course is in a ellipse form, it has some importance, when in the year the sun is closest to the sun. It takes the earth 1 year to rotate around the sun. All together it means that the earth is closest to the sun the 3rd of January and farthest away from the sun the 4th of July, meaning warmer winters and colder summers. In about 10.500 years the earth will be farthest away the 3rd of January and closest to the sun the 4th of July. This will give colder winters and warmer summers. This cycle takes about 21.000 years.

The interplay/correlation of these 3 factors, does that the difference in temperature in Scandinavia will swing with 2-3°. While the middle temperature, in the last ice age, for the month of July was 8-10° lower than today, other factors must have had some influence on the climate as well. Milankovitch thought that the fall in temperature could double from 2-3° to 4-6°, alone only because of the effect of the albedo. Albedo is a way of measuring how many % of the suns rays are reflected back from a surface. While both ice and the snows albedo is quite bigger than earth and plants. would areas covered by ice and snow reflect a big % of the suns rays and would double the drop in temperature. The could temperature in Northern Europe during an ice age, would force sea streams further south and Norway would miss its vital warm Golf stream.

From Milankovitch theories we can expect the warm temperatures from today to continue another 40.000 year. Still some scientists think that it will get colder during the next 1000 years.

Perspectives
Why do we worry about the ice age? It happened so long ago and what ever we know about the ice age is very uncertain. Yes that is true… but that is what makes the ice age so exciting and interesting. Many geologists still disagree about many aspects concerning the ice ages. That way we all the time need new knowledge to understand the changes in climate of the past. It is only when we understand the weather of the past that we can predict the future weather more precisely. Denmark is an interesting study, because the Danish landscape has during the last ice age been the border area for the enormous ice shield. Denmark is full of remains from the last ice age, and there are big economic and environmental interests in these remains.


 

 


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