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| CHAPTER 02 - ENVIRONMENTAL CHANGES AND HUMAN DEVELOPMENT |
Environmental change occurs as a result of both natural and human
processes. Environmental systems and human activities contribute to environmental changes through the transformation and transportation of large quantities of
energy and materials. Natural systems transform the sun's energy into
living matter and cause changes by cycling materials through geological, biological, oceanic and atmospheric processes (the biogeochemical cycles described
below). Human activities, on the other hand, transform materials and
energy into products and services to meet human needs and aspirations.
Compared with natural processes, human transformation of materials
and energy has for the most of human history been relatively small. Nowadays, human activities are altering these flows at unprecedented scales;
human-induced consumption and transformation of net primary productivity
is estimated to be about 40 per cent of that carried out by the Earth's terrestrial
ecosystems (Vitousek et al, 1986). Humans fix almost as much nitrogen and sulphur in the
environment as does nature (Graedel and Crutzen, 1989). We are also altering the carbon
cycle by releasing large quantities to the atmosphere from the burning of
fossil fuels. Human emissions of trace metals such as lead exceed natural flows by a factor of 17. The human contribution of other metals such as
cadmium, zinc, mercury, nickel, arsenic and vanadium is twice or more
than that of natural sources (Nriagu and Pacyna, 1988).
The scale of planetary changes induced by human activities is also
evident in the modification of the physical landscape. Since the eighteenth century, the
planet has lost 6 million km2 of forests an area larger
than Europe (Clark, 1989). In addition, the degradation of land to the
point that its biotic function is damaged has increased. According to a recent study from
the United Nations Environment Programme (UNEP) the extent of vegetated
soil degradation has reached 1964.4 million hectares (17 per cent of the
Earth's land area) in the last 45 years, due to overgrazing, deforestation,
overexploitation, and improper agricultural and industrial practices
(UNEP, 1993). In Europe, the portion of degraded vegetated land reached
about 23 per cent of the total over the same period (Oldeman, et al, 1991).
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