Most human endeavors demand large amounts of energy to be spent in a short time scale (i.e., are energy-intensive). This energy is presently available largely from fossil fuels or from a secondary source derived from them. Since the industrial revolution, we have invented machinery allowing a single person to extract and control far more energy than he or she could individually generate or even consume. (The human body can barely produce about 100 W of energy.) From then on we have been drilling out millions of barrels of oil a day, tapping natural gas reserves, and mining increasingly large amounts of coal. This is a consequence of both the population increases and societal change tending toward increasingly energy-intensive life-styles. These fossil fuel reserves built up over millions of years are of course nonrenewable within the short time scale of their use. The coal reserves are fossilized land plants that lived 300 million or more years ago, while oil is formed from the phytoplankton sediments deposited 100 million years ago in the bottom of prehistoric oceans. These fossil fuels are currently being depleted at a rate that is 100,000 times faster than they are formed and with alarming inefficiency. The conversion efficiency of the extracted fossil fuel into useful heat, electricity, or mechanical energy to power the automobiles are ridiculously low.
The world consumption of fossil fuels was around 7600 million tons of oil equivalent in 1999. The United States with only about 5% of the world's population accounts for about 21% of the global use of fossil fuel (but also accounts for 26% of the global gross domestic product, GDP11). High energy intensities are generally associated with high standards of living. The disparity in living standards in the developing and developed nations is appallingly large and continues to widen. Yet, achieving parity in living standards worldwide is prohibitively expensive in terms of both energy and material requirements. The aggregate area of ecologically productive land needed to provide the entire population of Earth with the present North American life-style is estimated to take two additional Earths ! The present paradigm of development is clearly not sustainable in the long term.
There is little doubt that a major shift toward sustainable growth12 is inevitable in all parts of the world and will likely include changes in technology as well as in life-styles. Defining "sustainable development" has not been easy; the UN World Commission on Environment and Development offers a working definition as, "meeting the needs of the present without compromising the ability of future generations to meet their own needs." This implies a long-term perspective and even an appreciation of the demands by future generations on the limited energy and material resources. Sustainability can only be achieved when environmental concerns become an integral part of the economic process and is paid the same close scrutiny devoted to economic competitiveness and profitability. The difficulty in its implementation lies in the fact that the major beneficiaries of the altruism demanded of the present generation in adopting these goals are the as-yet nonexistent future generations. Strictly speaking, any sustainable functioning demands that fossil energy be used only at the rate it can be replenished, maintaining the net pool of potential reserves at about the same level. This is clearly an impractical goal. In practical terms it translates into using fossil fuel reserves more efficiently, only for the more worthwhile of the human
11 The gross domestic product of a country is the sum of goods and services produced in the country or, in this instance, in the whole world.
12 Growth on Earth is presently driven by the finite reserves of fossil energy and materials. As such, growth cannot be sustainable in the long run; strictly speaking the term "sustainable growth" is a misnomer.
endeavors and that too at only a minimal rate. Accelerating technological breakthroughs that improve energy efficiency and deliver alternative energy options should be a crucial component of any long-term strategy on ensuring energy for the future.
In the developing countries in Africa or Latin America it is not uncommon for renewable resources to meet as much as 60-70% of the demand for energy. Worldwide, however, the renewable sources accounted for only 18% of the energy consumed in 1995. Renewed interest in non-fossil-fuel technologies has encouraged the development of modern, biomass-based plants as well as innovative solar or wind technologies. Given the present scale of their development, the energy produced by these will probably remain a small fraction of that from conventional renewable resources (such as straw, firewood, or small-scale hydroelectric plants) in the foreseeable future.
The gloomy scenario of possible energy and raw material limitations applies only to the long-term rather than to the immediate future. Even if we assume that the remaining global oil potential of about 2 trillion barrels13 was all that was available, this still allows about 100 years of use at present rates of energy consumption. Assuming that technologies to recover estimated but unproven oil reserves and including coal14 and natural gas reserves become available, this time frame can be as long as a few centuries.15 The estimated "reserves" are continually upgraded, as new information becomes available, making the numerical values of reserves woeful underestimates. Potential fuel reserves in the United States that are more difficult to access — such as the western shale, eastern shale, and tar sands—can and will be exploited as the rising price of crude oil makes these explorations cost competitive. A reasonable window of time is therefore available for this transition of the global economy from uncontrolled energy-driven growth to a sustainable mode of development16. How wide this window is depends on the optimism of the analyst; the most optimistic expect 1000 years worth of oil, and about 5 millennia worth of oil from the exploitation of shale oil reserves . Figure 1.3 shows the past and future course of world reliance on different primary energy resources. The heavy line starting at the bottom of the graph shows the evolution of energy use from 1850 to the present time. The set of lines starting in the 1990s and trending downward shows the expected paths of energy resource use in the future. The labels A, A1, B, C1, and C2 refer
13 Estimate of the proven reserves of conventional oil in the world is about 140,200 million tons at this time. However, this estimate increases with time as additional reserves are discovered and because of advances in recovery techniques that makes more of the reserve exploitable.
14 Estimated coal reserves in the world at the end of 1998 amounted to 984,211 million tons, sufficient to last for the next 200 years. The natural gas supplies in the United States alone is estimated to be sufficient for 60-120 years of consumption at the present rate.
15 The Department of Energy estimates of U.S. crude reserves accessible with existing technology is about 99 billion barrels. Using a higher cost of $27/barrel that allows the use of advanced technologies to be used in extraction, the reserves can be as high as 575 billion barrels .
16 At the UN Conference on Environment and Development in Rio de Janeiro in 1992 an agenda for sustainable development, the Agenda 21, was laid out.
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