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Global Warming Made Visible
Rhône Glacier Retreat
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:
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.
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.
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
click to enlarge
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