Geoscience Reference
In-Depth Information
CHAPTER TWENTY-THREE
Environmental
reconstruction
Environmental change over time is a recurring theme
throughout the topic. Many changes, especially diurnal,
seasonal and annual fluctuations associated with solar
radiation and ocean tides are taken for granted and
commonly regarded as 'constants' to which the biosphere
and our human lives are well adjusted. Appreciation of
their constancy lies in the very short-term, cyclic nature
of these changes and expectations they will always return
to broadly the same point. We can also conceptualize time
scales far longer than our own lives, such as alternating
Quaternary cold and temperate climates linked with
Milankovich cycles (over 10
4-5
yr) and even supercon-
tinental cycles of continental break-up and reformation
(10
8-9
yr). However, we are aware that these cycles produce
quite different outcomes in terms of the character and
geographical distribution of resultant environments, even
if the process remains constant.
So much for cyclic environmental changes, long-term
stability and dynamic equilibrium. It is also apparent that
many events lead to irreversible, catastrophic, non-linear
and chaotic changes, caused typically by dramatic, short-
lived and high-energy events but varying in their
environmental implications. The materials and landform
of a landslide clearly cannot be restored to their original
state and position. It is irreversible and potentially
catastrophic in human terms, through loss of life or
buildings. As a common, constituent process of conti-
nental denudation it is not a
geological
catastrophe, unlike
the asteroid impact which probably created the Chicxulub
crater in southern Mexico 65 Ma ago - triggering major
climatic, oceanic and geological disturbances held
responsible for the extinction of perhaps 70 per cent of
living species.
The significance of predictability and uncertainty in
environmental change is heightened by the dramatic rise
in concern for global climate change, its causes and
impacts. Some assert that change is a natural, cyclical
phenomenon, immune to human disturbance and that an
equable climate equilibrium will return without our
intervention. These
environmental sceptics
are primarily
government lobbyists representing political and business
interests challenged by climate and environmental change.
The global scientific community overwhelmingly believes
that natural variability alone cannot explain the rate and
magnitude of contemporary change and hence human
society itself is the principal cause, threatening global
economic and political security.
We are persuaded of this by reconstructing past
environments - Earth system history - as a key to pre-
dicting environmental futures, together with increasing
understanding of holistic Earth systems and acceptance
that environmental change can be neither simply cyclic
nor unpredictably catastrophic. Why worry about forecast
sea level rise of 1 m over the next century when parts of
the British coast experience tidal ranges exceeding 10 m
twice daily; and vanishing permafrost, which might
beneficially extend the northern limits of boreal forest and
cultivation? Answers lie in our appreciation of non-linear
