Energy Reserves and Usage

Ever since the Industrial Revolution, the worldwide use of commercial energy—that sold to users and usually derived on a large scale from fossil-fuel combustion, hydroelectricity, and nuclear power, as opposed to the biomass collected and used by individual families—has risen almost every year; the current annual global growth rate is about 2%. The period of the most rapid increase began after World War II, when global commercial energy consumption was only about one-tenth the current level.

Because the amounts are so huge, it is useful to discuss global quantities of energy in terms of the large energy unit EJ, an exajoule, which is 1018 joules. The total amount of commercial energy consumed by humans currently amounts to about 400 E] annually, with the United States consuming about 100 EJ of that total.

Determinants of Growth in Energy Use

Although increases in energy usage are sometimes thought to be mainly tied to population growth, this is a dominant factor only for less developed countries, for which energy use per capita is small anyway. The usage of commercial energy by a country depends on many factors, including its population, geography, and climate, as well as on the cost of energy. However, the most important factor in total energy usage appears to be the gross domestic product (GDP) of the country. In industrialized societies, about 11 megajoules (11 million joules) of energy are currently needed on average to produce one (U.S.) dollar's worth of goods and services. Interestingly, the energy-to-GDP ratio for many developing countries, including China, has about the same value. The ratio for India is somewhat less than those for developed countries, and those for nondeveloped countries are lower still.

In the past, it has been found that although the energy-to-GDP ratio usually rises when a country begins to industrialize, it then drops gradually as the infrastructure becomes more substantial and efficient. For example, the ratio for the United States dropped by 44% from 1970 to 2000.

The fantastic rise in global energy usage in the second half of the twentieth century was due mainly to industrial expansion and to increases in the standard of living in the now-developed countries. The energy consumption in these countries continues to expand, though now only slowly. Per capita energy use in the United States currently amounts to 10,000 J/sec {i.e., 10,000 watts, the equivalent of one hundred 100-W light bulbs burning continuously), about twice that in the European Union and Japan, and about five times the world average.

However, economic growth in the developing countries—which contain three-quarters of the world's population—is rising more quickly and with it their total energy consumption. Thus, although per capita energy usage in China is only half the global average, it is rising. The developing countries collectively used only 30% of the world's commercial energy in 1993, but they are expected to consume more than half of it starting sometime in the next decade. According to the International Energy Agency, between 1994 and 2010 the rate of increase for the developing countries collectively is expected to be 4% annually, which, if compounded, would produce a doubling over that period. For developed countries, the annual rise over the same period is expected to be 1.5%, amounting to 2?% if compounded over that period. The overall global increase is expected to continue to be about 2% annually over the next few decades.

PROBLEM 7-1

Any quantity V whose value increases in a time period t by a percentage of its previous value exhibits exponential growth according to the equation

V = V0ekt where V0 is the initial value and k is the fractional increase in each time period. Given that this equation will apply to the growth in energy usage if it increases by the same percentage each year, derive a general formula relating the number of years required for energy usage to double as a function of the annual fractional increase k. What is the doubling time when 4% annual growth (i.e., k = 0.04) is in operation? What about 3%, 1.5%, and 1.0% annual growth rates? If k = 0.02, how many years does it take for the energy use to increase 10-fold? If energy usage grew by a factor of 10 over 50 years, what was the annual compounded rate of growth in this period?

The usage of energy involves its transformation from one form to another, eventually resulting in its degradation to waste heat; as such, it does not pose any global environmental problem per se. However, there are usually side effects associated with energy production and/or consumption that are serious environmental issues, as we shall see in the rest of this chapter and in the next.

The most serious long-range global environmental problem associated with energy use is the release into the atmosphere of carbon dioxide, C02, when fossil fuels are combusted to produce heat. Indeed, the rest of this chapter

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Coping with Asthma

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