18
Numerous similar processes can be observed
in nature as well (Fig. 2.4). For example, warming atmosphere causes evaporation and thus
cloud formation. Growing clouds reflect more
radiation back to space resulting in a loss of radiation on the surface of Earth therefore the atmosphere starts to cool down. Decreasing
temperature reduces evaporation and thus cloud
formation resulting in increasing solar radiation
on the surface therefore the decrease of
temperature stops in a while and then it starts to
rise again. As a result of the two negative feedbacks the temperature of the atmosphere becomes
stable within a certain interval. (Of course, this
process would be this regular if no disturbing
events occurred. In case, for example, a strong
front appears in the given area its effects do not
let the process happen as normal.)
Since negative feedbacks stabilise the system,
they are also called stabilising feedback. One of
the basic conditions of ecological systems is that
they can regulate their material and energy flow
via negative feedbacks thus they remain selfsustaining in the long term. Such systems are also
called cybernetic system. In living organisms
negative feedback based cybernetic regulation
results
in
steady
internal
conditions
(homeostasis).
Positive feedbacks are the opposite. Using
again the example from climatology, due to the
cooling of the atmosphere in a certain area the
surface of snow and ice increases (Fig. 2.4d). The
reflection of solar radiation (albedo) from a white
surface is much greater than that from the soil
surface therefore the radiation loss of the surface
is great resulting in further cooling. This mechanism therefore intensifies the already started
cooling process making the system instable. In
the case of a warming process, darker soil patches
appear from below the melting snow cover. The
albedo of the darker soil patches is smaller causing greater energy intake resulting in further
warming and intensified snowmelt. The process
lasts until the total snow cover is melted.
Similar positive feedbacks are active during ice
melt in the Arctic Ocean. Satellite images show
that ice around the North Pole has a gradually
decreasing area at summer while the area of seawater with small albedo freed from the ice cover is
increasing. Therefore the ocean water absorbs
more and more heat intensifying the rate of ice
melt. The effects of this process are of global level
as it contributes to global warming. In general, the
dominance of positive feedbacks can be very dangerous from environmental points of view since
they could result in quality changes in the system
and finally in total destruction. Fortunately, in
natural conditions negative feedbacks dominate in
the global Earth system making its operation
rather stable. For the time being we do not know
where the limits of this stability are.
2.2.2 Behaviour of Systems
Regarding External or Internal
Effects: Chaos Theory
and Adaptive Systems
First of all, external and internal effects in the
case of systems have to be defined. We have
declared before that natural systems generally
have natural boundaries. This natural boundary
can be defined easier in certain cases while their
identification is more difficult in others. For
example, the boundary of the water ecological
system of a lake can be delineated relatively
accurately, even though the boundary would be
rather a zone of beach than a sharp boundary line.
Natural landscape boundaries are much more
uncertain. Identifying the boundary between two
neighbouring landscapes is still under scientific
debates. In the case of landscape boundaries
again rather zones can be identified based on
exact studies. In cases like these—when a single
boundary line is to be defined as system boundary—the central line of the boundary belt is
regarded the system boundary.
In case the boundary of a system is known,
any effect on the system arriving outside the
boundary is considered an external effect.
Identifying external effects it has to be analysed
whether the reason triggering the effect exists
outside the system (form) and the system has no
or very slight feedback on the triggering reason.
Considering the climate system such external
effect is solar radiation.
2 Structure and Operation of Systems, Models of the Global Earth System
Numerous similar processes can be observed
in nature as well (Fig. 2.4). For example, warming atmosphere causes evaporation and thus
cloud formation. Growing clouds reflect more
radiation back to space resulting in a loss of radiation on the surface of Earth therefore the atmosphere starts to cool down. Decreasing
temperature reduces evaporation and thus cloud
formation resulting in increasing solar radiation
on the surface therefore the decrease of
temperature stops in a while and then it starts to
rise again. As a result of the two negative feedbacks the temperature of the atmosphere becomes
stable within a certain interval. (Of course, this
process would be this regular if no disturbing
events occurred. In case, for example, a strong
front appears in the given area its effects do not
let the process happen as normal.)
Since negative feedbacks stabilise the system,
they are also called stabilising feedback. One of
the basic conditions of ecological systems is that
they can regulate their material and energy flow
via negative feedbacks thus they remain selfsustaining in the long term. Such systems are also
called cybernetic system. In living organisms
negative feedback based cybernetic regulation
results
in
steady
internal
conditions
(homeostasis).
Positive feedbacks are the opposite. Using
again the example from climatology, due to the
cooling of the atmosphere in a certain area the
surface of snow and ice increases (Fig. 2.4d). The
reflection of solar radiation (albedo) from a white
surface is much greater than that from the soil
surface therefore the radiation loss of the surface
is great resulting in further cooling. This mechanism therefore intensifies the already started
cooling process making the system instable. In
the case of a warming process, darker soil patches
appear from below the melting snow cover. The
albedo of the darker soil patches is smaller causing greater energy intake resulting in further
warming and intensified snowmelt. The process
lasts until the total snow cover is melted.
Similar positive feedbacks are active during ice
melt in the Arctic Ocean. Satellite images show
that ice around the North Pole has a gradually
decreasing area at summer while the area of seawater with small albedo freed from the ice cover is
increasing. Therefore the ocean water absorbs
more and more heat intensifying the rate of ice
melt. The effects of this process are of global level
as it contributes to global warming. In general, the
dominance of positive feedbacks can be very dangerous from environmental points of view since
they could result in quality changes in the system
and finally in total destruction. Fortunately, in
natural conditions negative feedbacks dominate in
the global Earth system making its operation
rather stable. For the time being we do not know
where the limits of this stability are.
2.2.2 Behaviour of Systems
Regarding External or Internal
Effects: Chaos Theory
and Adaptive Systems
First of all, external and internal effects in the
case of systems have to be defined. We have
declared before that natural systems generally
have natural boundaries. This natural boundary
can be defined easier in certain cases while their
identification is more difficult in others. For
example, the boundary of the water ecological
system of a lake can be delineated relatively
accurately, even though the boundary would be
rather a zone of beach than a sharp boundary line.
Natural landscape boundaries are much more
uncertain. Identifying the boundary between two
neighbouring landscapes is still under scientific
debates. In the case of landscape boundaries
again rather zones can be identified based on
exact studies. In cases like these—when a single
boundary line is to be defined as system boundary—the central line of the boundary belt is
regarded the system boundary.
In case the boundary of a system is known,
any effect on the system arriving outside the
boundary is considered an external effect.
Identifying external effects it has to be analysed
whether the reason triggering the effect exists
outside the system (form) and the system has no
or very slight feedback on the triggering reason.
Considering the climate system such external
effect is solar radiation.
2 Structure and Operation of Systems, Models of the Global Earth System