Geoscience Reference
In-Depth Information
Portugal, Spain, France, Italy and Greece. There has also been a significant increase
in deaths from heat stress among the poor and elderly in Europe and North America.
Another major issue is a change in the incidence of climate-related diseases, such
as malaria, dengue fever and meningitis, with expansion of these diseases into areas
that were previously exempt, as in the highlands of Ethiopia and Kenya. On a more
positive note, if the early Holocene can be used as a guide to what might happen as
sea surface temperatures become warmer, there is likely to be a strengthening of the
summer monsoon across Asia and Africa, leading to a longer summer wet season
with more intense rains. This should lead to an increase in plant cover along the
southern margins of the tropical deserts, such as the Sahara and Thar deserts, but it
will also depend on human pressure in the form of deforestation and overgrazing, as
discussed in
Chapter 24
. When confronted with extreme climatic events in the past,
human societies have responded in one of three ways: they migrated (Clark,
1980
),
adapted (Macklin et al.,
2013
) or became extinct (Diamond,
2005
). Those societies
with flexible patterns of resource use were the ones that survived best.
Chapter 26
outlines some key prerequisites for achieving sustainable use of the natural resources
of our desert regions. In a world of uncertainty, conservative use of water, energy,
plants and animals is essential, as are flexible forms of land use. The most adaptable
communities are the ones that will fare best in coping with the uncertainty inherent
in future climatic change.
25.6 Conclusion
The earth's climate is governed by energy from the sun. About half of all incoming
short-wave solar radiation reaches the surface of the earth and is then emitted back
to space as outgoing long-wave (infrared) terrestrial radiation. Roughly half of all
solar radiation is received at the earth's surface, with some reflected back to space
and the rest absorbed by the atmosphere. If there were no atmosphere around the
earth, the average temperature at the surface of the earth would be
−
18
°
C rather than
the present
C. This is because certain gases in the atmosphere absorb infrared
radiation and cause the lower atmosphere to become warmer. Such gases include
water vapour, carbon dioxide, methane and nitrous oxide. These gases are popularly
known as greenhouse gases.
At any given time, there is a balance between energy inputs to the earth's surface
from short-wave solar radiation and energy losses from the surface of the earth in
the form of long-wave terrestrial radiation. Any factor that disturbs this equilibrium
will lead to either cooling or warming at the earth's surface, depending on whether
it causes a net increase or decrease in the solar energy that reaches the surface of
the earth. For example, an increase in sulphur dioxide can lead to localised cooling,
while an increase in any of the greenhouse gases has the reverse effect. At the present
time, there is a steady increase in the atmospheric concentration of carbon dioxide,
+
14
°
