Geoscience Reference
In-Depth Information
28
In
Chapter 9
we explained how our present climate is far
from constant and has shown signs of change over the
recent and distant geological past. At times, much of
the temperate latitudes have been covered by ice with
polar deserts extending across much of Europe and North
America. At other extremes, temperatures have been
comparable or even slightly warmer than those of the
present, and in more distant geological times the climate
of areas which are now temperate or polar may have been
tropical.
Without doubt, therefore, the climate at any point on
Earth's surface undergoes fluctuations. Some of these
changes are part of the movement of continental plates
across Earth's surface (see
Chapter 10),
but many are the
result of long- and short-term processes that act on our
atmosphere, as outlined in
Chapter 9.
This aspect of
climate is stressed again here to emphasize the importance
of natural climatic fluctuations that are nothing to do with
human activities. We know our atmosphere and climate
are the result of a complex interplay of factors that give
rise to changes over time. What we are not sure about is
the relative importance of these factors and the feedbacks
that can cause dampening or enhancement of the changes.
About fifty years ago, some climatologists were predicting
the onset of the next glacial phase because the present
interglacial period had lasted about as long as previous
ones. Therefore it was reasonable to expect natural forces
working on Earth's system to trigger off cooling again. As
we are still uncertain about the precise trends of these
natural changes of climate, it is not surprising that it is
difficult to isolate the impact of human activities on
Earth's climate superimposed on these natural changes.
Nevertheless as climate interacts with most other aspects
of the physical environment, from mass movements to soil
formation, it is important to attempt to predict what may
happen to our climate. This is what we shall be doing in
this chapter by first illustrating what predictions have
been made about future climate and then the impacts this
will have on certain aspects of the physical environment.
Space prevents a fuller discussion.
The approach taken by scientists to predict future climate
is through modelling (see
Chapter 6).
This is a very
complex process that involves identifying those processes
which control our climate and then trying to model what
happens, using basic mathematical and physical equa-
tions. The complexity is partly derived from the wide
range of scale involved, from soil and vegetation charac-
teristics, where responses can be rapid, to the extremely
slow interchange that occurs in the deep-oceanic circu-
lations and the orbital variations influencing the input of
solar radiation over thousands of years. Modelling does
have weaknesses, as argued by critics of anthropogenic
global warming, but it does represent the best way of
producing predictions as long as we are aware of its
