Geoscience Reference
In-Depth Information
Sometimes the change may be gradual and progressive,
causing a gradual decrease in resistance rather than a
dramatic increase in driving forces. Global warming is a
good example of this. The melting of the permafrost in
arctic lands will cause a thermokarst landscape to form
which will not be able to return to its original state, even
if the climate returned to its original condition. The
second case of non-equilibrium occurs when positive
feedback prevents a return to equilibrium
(
Figure 1.10b
).
Examples of this can be found in many soil systems, in
coastal systems and in fluvial systems.
A third cause of nonequilibrium is chaos, or completely
unpredictable and unstructured behaviour. As turbulent
flow is chaotic, examples of chaotic behaviour in systems
have been proposed for some fluvial features and for
overland flow on hill slopes. However, it is difficult to
separate the effects of thresholds, positive feedback and
chaos in many non-equilibrium systems. Such is the
complexity of the real world that instability is likely to
result from differing combinations of them. Chaos theory
is proving to be a stimulus to re-evaluating systems in
physical geography, however. Other systems which are
being looked at to see whether chaos theory is applicable
include tropical storms, earthquakes, volcanic eruptions,
convection cells driving plate tectonics, glaciers and Ice
Ages, mass movements, and periglacial patterned ground.
moist soil. The African Sahel is a biome where many large
weather systems, like Atlantic hurricanes, have their
genesis. Huge amounts of solar radiation interact with the
water cycle to evaporate water into the atmosphere to
drive these weather systems. It has been discovered that
soils in this region have exceptional speeds of drainage,
due to underlying geology, and surface water is not
exposed to the atmosphere for long, usually disappearing
deep underground within a day of falling. When these
high infiltration rates were recognized and added to the
climate model, predicted timings of subsequent rainfall
were a month later than previous predictions, and close
to actual observations. Rainfall also came in the afternoon
rather than at night, also reflecting reality. Therefore
small-scale soil moisture processes control the large-scale
climate processes, which in turn change soil moisture. We
have here the combination of the small scale to the large,
with feedback from the large to the small, making the
world interconnected (Blyth 2007).
SYSTEM SCIENCE
The twenty-first century brings with it further develop-
ments of the systems approach, driven by awareness of
rapid climate change and international concern for its
impacts on global physical environments and human
activities. The study of global biogeochemical cycles and
biogeophysical processes by Bolin, Lovelock and others
integrated large parts of the newly-emergent environ-
mental sciences during the 1970s and 1980s. Focusing on
environmental chemistry and physics, rather than
geographically-based studies of climate, geomorphology
and biogeography, it reinforced rather than revolution-
ized the general systems paradigm. However, by 1990
NASA's developing space shuttle programme of Earth-
atmosphere investigations, the recovery of intriguing
environmental data by drilling through deep ocean
sediments and ice sheets, and measurable shifts in climate
and sea level, galvanized the international scientific and
political communities.
It is now accepted that human activity is forcing rapid
global environmental changes, particularly through fossil
fuel combustion and other industrial and agricultural
interventions in the very biogeochemical cycles on which
humans and climate depend. In addition to anthro-
pogenically-disturbed gas sinks and exchange processes,
the biogeophysical state of Earth's ocean and landsurfaces
also strongly influence the constituents and behaviour
of the atmosphere. This led to the modified paradigm of
Accommodating scale in physical
geography
Scale has always been a major concern in geography.
Studying and modelling the Earth as a whole, or studying
and modelling a single river meander, are both common
scales of study in modern physical geography. In the past,
work at these two scales tended to be in isolation, but it
is now realized that both approaches are not only
important to understanding the environment, but also
act in a complementary manner to each other, being
connected by feedback at very contrasting scales. The
multi-scale, multi-process approach (or 'small affects big'
theory) emphasizes the many connections across different
scales, with one scale altering another. The more we study
real ecosystems, the more we appreciate how soils and
plants at the small-scale are closely bound to weather and
climate at the large scale.
Blyth (2007) discusses the land-modelling work of the
UK's Natural Environment Research Council (NERC)
and its research centres (the Centre for Ecology and
Hydrology (CEH) and the Climate and Land Surface
Systems Interaction Centre (CLASSIC)). An example of
small-affects-big theory is that rain clouds develop above
