Understanding energy flow is vital to many environmental issues. One can describe the way ecosystems function by saying that matter cycles and energy flows. This is based on the laws of conservation of matter and energy and the second law of thermodynamics, or the law of energy degradation.

Energy flow is strictly one way, such as from higher to lower or from hotter to colder. Objects cool only by loss of heat. All cooling units, such as refrigerators and air conditioners, are based on this principle: they are essentially heat pumps, absorbing heat in one place and expelling it to another.

This heat flow is explained by the laws of radiation, as seen in fire and the color wheel. All objects emit radiation, or heat loss, but the hotter the object the greater the amount of radiation, and the shorter and more energetic the wavelength. As...