Page 50 - Environment: The Science Behind the Stories

CO 2 Figure 2.10 The burning of
Light firewood demonstrates energy
conversion from a more-ordered to
H O Heat a less-ordered state. This increase
2
in entropy reflects the second law of
thermodynamics.

Potential energy Kinetic energy Increase in entropy
(stored in the molecular (released as heat and light)
bonds of wood)

the flame (Figure 2.10). With the help of oxygen, the complex However, because this energy is spread across such vast areas,
biological polymers that make up the wood are converted it is difficult to harness efficiently.
into a disorganized assortment of rudimentary molecules In each attempt we make to harness energy, some portion
and heat and light energy. When energy transforms from a escapes. We can express our degree of success in capturing
more-ordered state to less-ordered state, it cannot accom- energy in terms of the energy conversion efficiency, the ratio
plish tasks as efficiently. For example, the level of energy of the useful output of energy to the amount we need to input.
available in ash (a less-ordered state of wood) is far lower When we burn gasoline in an automobile engine, only about
than that available in a log of firewood (the more-ordered 16% of the energy released is used to power the automobile,
state of wood). and the rest of the energy is converted to heat and escapes
If the second law of thermodynamics specifies that sys- without being used (p. 526). Incandescent light bulbs are even
tems tend to move toward disorder, then how does any sys- less efficient; only 5% of their energy is converted to light,
tem ever hold together? The order of an object or system can while the remainder escapes as heat.
be increased by the input of energy from outside the system.
Living organisms, for example, maintain their highly ordered
structure and function by consuming energy. When they die Light energy from the sun powers
and these inputs of energy cease, the organisms undergo most living systems
decomposition and attain a less-ordered state.
The energy that powers Earth’s biological systems comes
primarily from the sun. The sun releases radiation from
Some energy sources are easier large portions of the electromagnetic spectrum, although our
to harness than others atmosphere filters much of this out and we see only some of CHAPTER 2 • E ART h’s Physi CAL
this radiation as visible light (Figure 2.11). Most of the sun’s
The nature of an energy source helps determine how easily energy is reflected, or else absorbed and re-emitted, by the
people can harness it. Sources such as fossil fuels and the atmosphere, land, or water (p. 503). Solar energy drives winds,
electricity we produce in power plants contain concentrated ocean currents, weather, and climate patterns. A small amount
energy that we can readily release. It is relatively easy for us to (less than 1% of the total) powers plant growth, and a still
gain large amounts of energy efficiently from such sources. In smaller amount flows from plants into the organisms that eat
contrast, sunlight and the heat stored in ocean water are more them and the organisms that decompose dead organic matter.
diffuse. Each day the world’s oceans absorb heat energy from A minuscule percentage of this energy is eventually deposited
the sun equivalent to that of 250 billion barrels of oil—more below ground in the chemical bonds in fossil fuels (because
than 3000 times as much as our global society uses in a year. fossil fuels are derived from ancient plants; pp. 542–544).

Microwaves Visible light s ys TE m s: mATTER , E NER gy, AN d
Radio Ultra- Gamma
waves Infrared violet X-rays rays
Low energy, High energy,
longer shorter
wavelength wavelength
Non-ionizing Ionizing

1 10 –2 10 –4 10 –6 10 –8 10 –10 10 –12 10 –14 gE o L ogy
Wavelength (meters)
Figure 2.11 The sun emits radiation from many portions of the electromagnetic spectrum. Visible light
makes up only a small proportion of this energy. Some radiation that reaches our planet is reflected back; some is
absorbed by air, land, and water; and a small amount powers photosynthesis. 49

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