Environmental Engineering Reference
In-Depth Information
state when a critical point has been reached. The human body is another example
of this. On its own the human body is able to keep its body temperature quite con-
stant at 37 °C, even during major changes in ambient temperature. However, if a
person becomes seriously hypothermic, the body temperature quickly drops at a
certain point.
The Sahara is an example of very erratic climate change. Several thousand years
ago the Sahara was green. The vegetation there absorbed moist air from the Atlantic
and monsoon rains. Due to very minor changes in the earth's orbit and in the incli-
nation of the earth's axis, the conditions for the monsoon rains deteriorated over a
period of thousands of years. The vegetation managed to survive until a certain point
around 5500 years ago. But then within a short period the vegetation died and the
Sahara turned into a dry desert. A new stable state then developed, which continues
until today. The populations of large areas had to fl ee due to the dryness of the
terrain. The Nile valley in Egypt became a place of refuge for the environmental
refugees of the day. This contributed towards the creation of the Pharaonic high
culture and was perhaps even the basis for the biblical stories that have been passed
down through the ages.
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http://www.pik-potsdam.de/%7Estefan
Internet page of climate researcher
Stefan Rahmstorf at the Potsdam
Institute for Climate Impact
Research
The origins of the erratic climate changes that occurred many years ago are sus-
pected to lie in changes in ocean currents, which continue to have a major effect on
our climate even today. For example, Berlin and London are located further north
than Quebec in Canada. A comparison of temperatures shows that Western Europe
is about fi ve degrees warmer than it should be considering its latitude. The reason
for this is a gigantic self-regulating heat transport machine: the Gulf Stream.
In Central America the sun heats the water masses of the Caribbean Sea and the
Atlantic. The Antilles Current and the currents from the Caribbean merge together
to become the Gulf Stream, which is 50 km wide and transports enormous masses
of warm saltwater northwards along the American coast. These currents are so large
they can be seen from space. From North America the current then moves straight
across the Atlantic, continues along the European coast to Norway and ends in the
European part of the North Sea (Figure 2.11). Some of the heat is absorbed by the
air beforehand, and this air then moves with westerly winds towards Europe. This
explains why winds from the west always promise relatively mild temperatures to
some parts of Europe.
In the North Sea between Norway, Iceland and Greenland the warm saltwater comes
together with colder, less salty water and cools off quickly. This water increases in
density, becomes heavier and consequently sinks to the bottom quickly. In the North
Sea 17 million cubic metres of water sink to a depth of 3000-4000 m per second.
This corresponds to around 20 times the entire capacity of all rivers on earth. The
