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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

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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?