Global Change and the Earth System: A planet under pressure Page: 15
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7":
& ...Reverberations of Change
Human changes to the Earth System do not operate in simple cause-effect
relationships. A single type of change triggers a large number of responses in
the Earth System, which then reverberate or cascade through the System, often
interacting with natural variability to become feedbacks for further change.Long-term perspectives
THE LEGACY OF PAST human changes to the Earth
System provides the backdrop on which the present,
much more significant, suite of human changes will
be played out. To understand and project what is
happening now and in the future, it is essential
to understand the long-term cumulative effects
of past human impact and the nature of specific
environmental thresholds, particularly those that
lead to reduced resilience.
The degradation of terrestrial ecosystems by
human activities is often linked to a shift beyond a
threshold in a critical function, such as productivity.
In parts of the New Guinea Highlands, for example,
intensification of subsistence farming has led to the
conversion of a productive forest-garden mosaic,based on a cycle of forest clearance, subsistence
horticulture and woody regeneration, into a stable
but much less productive grassland ecosystem.
The Baltic Sea has undergone similar reverbera-
tions of change due to human activities around its
shores; over the past two centuries dense human
populations have sufficiently increased nutrient
supplies to the sea to cause a threshold to be passed.
Eutrophication occurred, the depth to which light
can penetrate decreased and the balance in diatom
productivity shifted from benthic (bottom-dwelling)
to planktonic communities. To understand future
global change-related impacts on contemporary
systems like the New Guinea Highlands and the
Baltic Sea, the cascading effects of past human-driven
changes must be understood.Reverberations of Change
:
.IGBP SCIENCE No. 4
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Global Environmental Change Programmes. Global Change and the Earth System: A planet under pressure, text, 2001; Stockholm, Sweden. (https://digital.library.unt.edu/ark:/67531/metadc12041/m1/17/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .