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Global Warming Made Visible

Rhône Glacier Retreat

Rhône Glacier in southwestern Switzerland, retreating
The Rhône Glacier in southwestern Switzerland is retreating due to Global Warming.
View from the mountain west of the glacier, October 2011

Rhône Glacier Retreat and Ice Ages

From these photographs it is evident that the local climate in the Valais region has been continously warming since the end of the 19th century. Similar observations have been made throughout the Swiss Alps.

Within the last 500000 years, Switzerland has been covered almost completely by glaciers for four periods lasting several 10000 years each:

Ice Age from (year) to (year) duration (years)
Günz -600000 -550000 50000
Mindel -480000 -420000 60000
Riss -230000 -180000 50000
Würm -120000  -10000 110000

But even within a relatively warm period, there are periods of glacier growth and periods of glacier retreat. The reasons for these natural cycles are less obvious than one might assume.

Milancovich Cycles

In the middle of the 20th century Joseph-Alphonse Adhémar, James Croll und Milutin Milankovitch proposed a theory that the ice-ages correspond to the combined effects of three astronomical cycles.
1. The earth's orbit around the sun is not a perfect circle but rather elliptical and even that not in a perfect way,
    it changes in a cycle of some 100000 years.
2. The (imaginary) axis of the rotation of the earth around itself (responsible for day and night) is not rectangular to the orbit plane,
    but oscillates in a cycle of some 41000 years.
3. The axis is not perfectly stable either, but describes a circle within some 24000 years.
As a consequence the effective radiation power of the sun on the earth's surface is not constant but varies considerably.

More precise measurements made in the last 100 years show, however, that though the Milankovitch cycles are an important factor they cannot fully explain the temperature changes during the warmer and colder periods of the Ice Ages.

Other effects like vulcano eruptions can have massive, sometimes even catastrophic effects for smaller periods, but they are not predictable in the same way as astronomical cycles are. For example, a vulcano eruption in Indonesia in 1815 (Mount Tambora) led to very cold summers in the northern hemisphere resulting in reduced crops and famine for a few years.

Rhône Glacier Retreat and Global Warming

While a detailed prediction of ice-age cycles remains difficult, there is obviously a close correlation between carbon dioxide concentration and temperature. (For the detailed graph, see wikipedia)

But while the maximum natural carbon dioxide concentration used to be some 300 ppmv during the last three warm periods 200, 120000, 230000 and 320000 years ago, the carbon dioxide concentration has steeply risen to 375 ppmv since the beginning of the industrial age 200 years ago. This corresponds to an accelerated melting of glaciers in many regions of the world.

For a more detailed analysis, with facts and figures from the Bernina region (eastern Swiss Alps) see
Reasons for and Consequences of Global Warming

Rhône Glacier panoramic view
Rhône Glacier panoramic view
click to enlarge

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