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Energy in Nature
THE WORD "ENERGY" is used widely, but often in ways that inadequately reflect its deeper scientific meaning. For the moment, let us regard it as a property of matter that enables us to describe why physical and chemical transformations occur. (I discuss its meaning in more detail in chapter 3.)
The word "nature" has a number of meanings, but most people see nature as that which is living: soil, plants, trees, animals, birds, fishes, and so on. In the Western tradition, the word's connotations derive from the idea that "man" is separate from the rest of the environment. Nature is that which is alive, but not human, and of no "value" until man takes hold of its resources and transforms them into usable things. This ideology has been a powerful force behind the dominance of the Western tradition over the past few centuries. Most other cultures see humans as an integral, inseparable part of the natural environment.
In this book, I use "nature" to encompass everything in the environment of planet Earth, but with particular reference to the domain of living organisms in the sea, land, and air. In this perception, humankind is obviously part of nature, not apart from her.
EARTH AND SUN
The sun is the source of energy for almost everything that happens on earth. The nonrenewable stocks of fossil fuels, coal, oil, and gas in most economies come from the remains of plants and animals that lived millions of years ago, absorbing solar energy as they grew and reproduced. Renewable energy sources, such as water in mountain lakes and rivers, wind, and waves, result directly from the action of the sun on the earth's atmosphere.
To put the sun and the earth into their wider context—the physical universe—let us look briefly at current ideas of how they came into being.
HOW IT ALL BEGAN
Theories as to the origin of the universe—like many scientific theories—have gone through major changes over the past hundred years. The main impetus for the changes has been the realization that creation accounts, common to many cultural and religious traditions, need to be reinterpreted in the light of the scientific discoveries of this century. The reason why the biblical accounts of creation (Genesis 1 and 2, for example) have been reinterpreted is not that these ideas are wrong. Rather, they were written as part of a cultural-historical framework of belief, expressed in the language of imagery. They should not be seen as scientific explanations of a cosmic physical process. Thus, the truth of accounts of creation, from no matter which great religious tradition, should not be judged by the methodology of science; they are myths with spiritual and religious meaning. As such, they stand separate from scientific theories and should not be compared with them.
Currently, the most widely accepted scientific theory is that the physical universe originated in a cataclysmic event (the "big bang") some 10 to 20 billion years ago. The primeval building blocks of all the matter-energy of the universe started off concentrated into an unbelievably small, super-hot "fireball." This then exploded, flinging its contents out into space.
In the sense in which the terms are used here, matter and energy are not really distinguishable from each other. This is why we use the term "matter-energy." Under the extreme conditions of a big bang, temperatures would be of the order of a million million degrees: so hot that even electrons, protons, and other elementary particles could not exist independently. Although that initial state lasted for only a small fraction of a second, these conditions indicate that in the beginning the universe could be regarded, in a sense, as pure energy, much of which subsequently changed into matter.
Subsequent cooling then produced gases, which over billions of years aggregated into condensed masses and eventually formed the first stars. Many of these stars generated so much heat (from gravitational collapse and their own radioactivity) that they exploded again. This process may have occurred several times and may be going on today in some distant part of the universe. It is believed, for example, that our sun is probably a fourth- generation star.
The physical universe owes its nature and structure to that initial process. The theory tells us nothing, however, about what happened before the big bang. Indeed, the question of whether even time and space existed before that event cannot be answered unequivocally
Stars are usually too hot for simple molecules to form in them—their high energy levels ensure that atoms that come together to form molecules are immediately flung apart again. Formation of a variety of stable molecules results from cooler conditions that may be found in regions some distance away from the stars. Our solar system was probably formed around 4.5 to 5 billion years ago from a huge cloud of interstellar dust that came together as a result of gravitational attraction. The earth is thought to have condensed out of a part of the cloud that contained a diversity of elements, especially those necessary for the development of life.
LIFE ON EARTH
It is not known how life began on earth. One hypothesis is that spontaneous generation of simple life forms occurred in a "primeval soup" of hydrogen, ammonia, methane, carbon dioxide, hydrogen sulfide, water vapor, and other simple gases formed from combinations of the lighter atoms. These could have been present soon after the earth cooled enough for them to be formed. Lightning discharges could have provided the energy needed to trigger chemical combinations, giving rise to elementary life forms.
Another hypothesis is that on the tiny dust grains in interstellar clouds, conditions may have been conducive to the formation of the building blocks of life. These grains, diffused over the universe and aggregated into meteorites and comets, may have served as "seeds" for the generation of life here. If correct, this theory also suggests that such a process may have occurred elsewhere in this galaxy and others.
Yet another hypothesis suggests that in some situations, there were minerals (probably clays) with complex surfaces to which simple molecules may have become attached. Under certain circumstances, the attached molecules could undergo reactions with adjacent ones to form larger, more complex molecules, which could have been precursors of the first simple organisms.
Whichever hypothesis eventually turns out to be correct, the important thing is that life has apparently existed on earth for several billion years and that over this time there has been a process of evolution, with more and more complex forms of life coming into existence.
The initial life forms came into being around 3.5 billion years ago. They were probably one-celled bacteria existing in water, perhaps close to seashores. Single-celled algae came on the scene about 2 billion years ago. These organisms did not "breathe" oxygen, because free oxygen was not present in the atmosphere in those early days. However, they produced oxygen as a result of their activities, excreting it as a waste product into the water in which they lived. Over millions of years, oxygen built up in the seas and in the atmosphere until, about 1 to 2 billion years ago, it reached today's level of 21 percent, at which it has stayed reasonably constant.
After the oxygen level settled down, evolution quickened. Simple cells gave rise to more complex cells and multicellular organisms. Sexual reproduction introduced a vastly greater range of genetic combinations, in turn increasing the likelihood of successful development of new organisms. In time, life forms came into existence that were able to feed off other life forms. Instead of having to make their nutrients from minerals and gases via the photosynthesis process driven by light energy, these more advanced forms could obtain them ready-formed into the amino acids, carbohydrates, and so on manufactured by simpler organisms. They then had a competitive edge and were able to develop faster as species.
Over time, more and more specialization occurred. Plants developed from simple organisms and in turn provided a food source for animals. About 450 million years ago, plants began to colonize the land. Animals followed them about 50 million years later.
The processes of evolution did not take place in a continuous manner. Evolution apparently occurred in jumps, with long periods of relative stability in between. Sudden transitions after long periods of stability may have occurred due to changes in the environment, perhaps from climatic factors (ice ages, for example), volcanic activity, or meteorite impact.
The awesome complexity of life on earth is the result of hundreds of millions of years of development. How the process started is a matter of great interest, but in some respects it is largely irrelevant to the questions that face us today. The most important group of questions relates to the power of humanity to make choices (especially about survival), not only for itself as a species but for virtually all other life forms as well. In order to understand more about where we humans are going, we need to know not only where we have come from but also where we are now. We do this by looking first at the place of energy in the natural environment.
ENERGY FLOWS TO EARTH
In the general sense, life on earth (including virtually all activities of human societies) stems, directly or indirectly, from the sun. The sun is the source of effectively all of the energy available to the solar system. The earth is a "consumer" of some of the sun's energy in that energy absorbed from the sun is used to drive atmospheric and life processes before being rejected to the cosmic "heat sink" of outer space. The radiant energy received from the sun supplies heat to the earth's surface and light for the processes of photosynthesis in plants. The complex hierarchy of animal life depends on these flows of energy, from the simplest organisms to the giants of the forest, from bacteria to humans.
Energy from the sun heats the sea and the land, thereby creating convection currents in the atmosphere that result in air movements, evaporation of water from the sea, and rain. Table 1.1 gives data on some of the paths taken by incident solar radiation in the earth's atmosphere. It also shows the approximate percentages of the total incident solar energy traveling along each path.
From these data, for each solar constant joule (SCJ) (units of energy are described in chapter 3) of solar radiation that reaches the outer atmosphere, 53 percent never reaches the earth's surface. Of the remaining 48 percent, 34 percent falls on the oceans and 14 percent falls on the land.
When energy takes part in activities at the earth's surface, some of it is always degraded into low-temperature heat. This heat is ultimately lost from the earth's system by long-wavelength (infrared) radiation into space. A small part of that energy may be stored for a time, either as plants and animals or as fossil fuels. Eventually, even these will be degraded into low-grade heat, but modern societies are accelerating the process by using the reserves at a rate vastly greater than their formation by natural and geological processes. In this context, accelerated global warming, forest death, and damage to the ozone layer testify to the limited ability of the earth's ecosystem to absorb wastes.
ENERGY AS THE BASIS FOR LIFE
The main energy pathways shown in table 1.1 are the energy supply for the environment within which life exists, but they do not directly involve living things as such. To incorporate the activities of living organisms into our picture, we need to look in more detail at solar radiation as the energy source for biological photosynthesis in plants.
The majority of plants obtain most of their energy from the sun in the form of light. Together with chlorophyll, light energy enables the manufacture of food and other materials needed for plant maintenance and growth, from the carbon dioxide in the air and from other nutrients obtained from the soil via root structures. In a sense, energy is "embodied" in plant tissue as it grows, in that energy and matter combine to create more complex structures than those of the food taken in. Figure 1.1 shows this process in diagrammatic "systems" form, with a store of plant matter (biomass) being built up as a result of interaction between incoming energy from the sun and existing plant matter, such as leaves. Energy is continually being degraded to low-temperature heat.
Figure 1.1, which shows only the energy flows involved in overall plant growth, is, of course, heavily simplified. Nevertheless, energy flow is a critical element in such systems, and a great deal of important information and deep insight may be gained by consideration of flows of direct and embodied energy. Embodied energy flows provide a unique means of following processes and systems in nature and in society.
The growth process depicted in figure 1.1 may also be represented on a graph to show how the size of the embodied energy store (the biomass) changes with time. Figure 1.2 shows how the size of a plant increases slowly at first, then at an accelerating rate. Known as exponential growth, this pattern is typical of the early stages of growth in many systems (see chapter 7). It is an example of a positive feedback system, in which growth reinforces itself (see also chapter 5). Such processes cannot go on forever, of course, since they will in time be limited by the rate of energy flow available (usually from the sun). Eventually, after the plant's essential needs for its own maintenance have been met, a stage is reached at which no surplus energy is available for growth. The system then settles down to a more or less constant level (represented by the dashed section of the growth curve). The growth curve as a whole, known as a logistic curve, is typical of the long-term behavior of all ecosystems and many other systems.
Plants, on land and in the sea, are food for many animals (herbivores) and small fish, which in turn are food for flesh-eating animals and larger fish (carnivores). The energy flows that enable plants to grow are the basis for the whole web of life. Although a large quantity of plant matter is needed to feed one herbivore and a large quantity of herbivores is needed to feed each carnivore, only part of the solar energy embodied in each kilogram of plant matter eventually ends up in the carnivore as tissue (muscle, bone, etc.). This is because energy is always "lost" at each stage in the process (more correctly, it is degraded into an unavailable form—see chapter 3) and is rejected into the surrounding environment. When animals die, their remains decompose and fertilize the growth of biomass. Animal dung has a similar function.
In such a chain, embodied sunlight is progressively "concentrated" through each successive transformation process. At each step in the chain, the output can be described as being of energetically higher quality, because it has more embodied energy per unit of organism. In short, more embodied energy is required to keep a carnivore alive than to keep an herbivore alive. This is not surprising, since a consequence of this increase in embodied energy is that the total quantity of organisms in each stage is very much less than in the previous one. Thus, a very large quantity of soil is required to support a large quantity of plants, which in turn support a much smaller number of insects, a yet smaller number of birds and rodents, and so on, up to the level of the higher carnivores. This way of looking at things uses the image of the pyramid. Lines of dependence for food and other services within the pyramid are what we have already referred to as food chains. The pyramid as a whole is a tangle of food chains—the higher and more complex the pyramid, the more evolved is the ecosystem that it models.
An example is a food chain comprising grass, grasshoppers, frogs, trout, and humans. At each stage of the chain—when the grasshopper eats the grass, the frog eats the grasshopper, and so on—there is a "loss" of energy. In the process of consuming food, most animals lose about 90 percent of the food energy to their surrounding environment as low-temperature heat and as dung. Only around 10 percent of the food energy remains embodied in the tissue of the eater, for transfer to the next stage of the food chain. In our example, the pyramid involves around 1,000 tons of grass to feed 27 million grasshoppers, which feed 90,000 frogs, which feed 300 trout, all to sustain 1 human for a year.
Excerpted from Energy and the Ecological Economics of Sustainability by John Peet. Copyright © 1992 John Peet. Excerpted by permission of ISLAND PRESS.
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PART I. Nature
Chapter 1. Energy In Nature
Chapter 2. The Scientific World View
Chapter 3. Energy'"a Scientific Perspective
Chapter 4. The Political-economic World View
Chapter 5. The Systems Approach
Chapter 6. The Biophysical Systems World View
PART II. Limits
Chapter 7. The Physics And Morality Of Growth
Chapter 8. Feedbacks And Externalities
Chapter 9. Myths Of The Political-economic World View
Chapter 10. Myths Of Science And Energy
Chapter 11. Ecology Versus Exemptionalism
Chapter 12. Humanity Separated From Nature
PART III. Choices
Chapter 13. Values For A Sustainable Future
Chapter 14. Energy For A Sustainable Future
Chapter 15. Sustainable Development
Chapter 16. Ecological Economics
Chapter 17. With People's Wisdom: Stewardship And Sufficiency
Appendix: The Venice Declaration