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OCR for page 31
4
THE EARTH SYSTEM
Digby J. McLaren
Our ideas about the earth have changed since James Hutton first gave
us a model 200 years ago. He recognized the existence of an earth system
and correctly outlined a model of ongoing change through small increments
over an enormous time period. He thus paved the way for Darwin's still
broader biological conceptions on the same basis. Hutton's model, how-
ever, was not evolutionary, and he really did make the oft-quoted re-
mark, "We find no vestige of a beginning, no prospect of an end.' It is
ironical today, when we are at last approaching an approximation to a
new model of the earth, that we are faced with the very real prospect of
an end.
We now see the earth as a small planet in space that is inherently
changeable. Its liquid core and mantle are heated by radioactive ele-
ments that still remain from its origins some 4.5 billion years ago.
This heat induces ongoing crustal and mantle movement described under the
general term "plate tectonics." Within this system there are many sub-
systems of change at present acting at different rates, some rhythmic
and others episodic. As a consequence, it is beyond our capacity to
predict future changes accurately. Some are manifest in earthquake and
volcanic activity on land and at the ocean ridges. They are linked to
change in the relative position of the plates leading, in turn, to
changes in climate and ocean circulation and in the ambient life forms at
or near the surface of the planet. All are ongoing and currently unpre-
dictable.
The planet, with its life forms, is part of the solar system and is
thus influenced by the sun and by variations in earth tilt and orbit
round the sun. These induce further changes in atmospheric and ocean
circulation, and therefore climate. Finally, the planet has been con-
stantly bombarded by material in the form of meteorites and comets, some
large enough to cause further massive changes in the earth system and its
biomass. We are far from being able to tie all these variables together
into a coherent model.
Life has played an important role in shaping the physical and chem-
ical nature of the planetary surface. Life developed in balance with the
changing environment as a result of an evolutionary process driven by
those changes. In the very recent past, the emergence of the human race
has begun to cause change in the environmental flux more rapidly than,
31
OCR for page 32
32
and in a different manner from, the established system. With essen-
tially free energy supplied by fossil fuels, our species has become,
during the last 2 centuries, a dominant force for change on earth by any
measure we may apply.
We are now able to chart past and current environmental changes, and
techniques recently developed enable us to view the land, oceans, and
atmosphere from space, and to measure secular changes in climate, cloud
and ice cover, soil moisture, and marine and land big-productivity. Ice
cores have furnished an accurate record as far back as 160,000 years of
global temperature, levels of atmospheric carbon dioxide, and variations
year by year in wind-borne sediments, including volcanic events. Other
techniques allow us to penetrate more deeply into the past.
Direct measurement may now be made of the accelerating effects of
quarrying by humans of soils, forests, and ground water, encouraged by an
economic system not yet adjusted to evaluating the sustainability of a
resource. Quarrying here implies reducing the capacity of a resource,
commonly assumed to be renewable, by overuse to such a degree that
recovery will not occur on a human time scale, if at all.
The scientist may point out and measure many of the changes that are
taking place in our immediate environment and in the time scale of our
own lives. But it will take very much more than science to change our
current system and persuade us to learn to live in balance with the
earth's ecosystem. It seems to me that three major forces are at work to
prevent this from happening. The following remarks are neither scien-
tific nor social; they are the kind of observations that an intelligent
martian, newly arrived on earth, might make, unhampered by axiom or
belief.
1. Population growth seems to be the single most important factor in
increasing environmental stress, including depletion of materials and
energy resources and a runaway increase in solid, liquid, gaseous, and
heat waste. We are currently adding 1 billion people to the population
of the world every 11 years. And we must remember that most of the re-
sources and most of the waste produced are due to the activities of a
relatively small proportion of the total population. In certain areas of
the world people are reproducing much more rapidly than in the West, but
a Western baby will drive a car when he or she grows up and will use re-
sources and produce waste at a rate 100 to 500 times greater than that
of many of the babies being born in the Third World.
2. Nonrenewable energy consumption is another significant cause of
environmental stress. Fossil fuel use continues to grow; as the use of
petroleum products as fuel continues to decline relatively, it will be
more than offset by an increase in coal burning and a concomitant
increase in greenhouse gases and particulates in the atmosphere. The
warming effect appears to have started: how much shall we accept,
bearing in mind the inevitable change in climate and rise in sea level?
3. Global military expenditures now total nearly $1 trillion per
year. In the light of problems facing the world today, these figures
represent an enormous, almost unimaginable waste of resources and human
. .
1ngenulty.
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33
We are all in this together, and so we must find a joint solution.
It is too late to build walls around or put roofs over regions of the
world. The problems are exclusively global and the solutions must be
also. We find we are now faced with a task that
anything we have ever contemplated: ~ ~~ ~
Is more difficult than
to decide how we may continue to
~ ~ ,
live on this small planet. For if we depart from ecological balance to
the extent that we destroy most of the remaining life on earth--and the
big killing is under way--then surely we are dooming ourselves to a
similar fate. In other words, we must learn to live in balance with
the world we find ourselves in.
The human being is an animal that has moved out of ecological
balance with its environment. Humankind is a wasteful killer and
despoiler of other life on the planet. This normal and apparently
acceptable behavior is licensed by a belief in God-given resources and
encouraged by an economic system that emphasizes short-term profit as
a benefit and has not learned to put a real cost on the resources we
consume.
the ~~ r~~~
to decide how to run this planet
the ~~~ ~ ~ ~
the
human species has taken over. I
-
I believe, therefore, that it is perfectly proper, as a scientist,
to appeal for an inductive approach in looking at our present condition
on earth, to draw empirical conclusions, including constructing some
worst-case scenarios, and to attempt to assign probabilities to them.
I began these remarks by focusing on the earth system, and I find that
~ - suggest that we do not know enough
We are forcing our will upon it, using
steadily depleting resources and increasing waste discharge, while at
same time claiming that we must aim for sustainability. May we
attain this globally, or have we passed the limits within which it may be
achieved?
Representative terms from entire chapter:
time scale
