PES » Global Warming » The Earth’s Energy Balance
	Practice Questions Movie Transcript Earth’s energy balance will enable you to understand radiative equilibrium. You will also be able to recognize that the temperature of earth depends on the amount of solar energy that it absorbs. The temperature of earth depends largely on the total radiation received form the sun. The earth reflects about 30% of the solar energy radiation reaching it and absorbs the remaining 70%. The absorbed solar radiation heats up the earth. While the earth continually absorbs solar radiation, it will not simply continue to heat up. In response to this heating, the earth emits longwave radiation into space. The emission of longwave radiation cools the earth. As the earth cools, it emits less radiation to space, but because it is still continually absorbing solar radiation, it still heats up. As it heats up, the earth emits more radiation to space and so it cools. This dynamic physical process of absorption and emission and resultant heating and cooling creates what is knows as a state of equilibrium. The term equilibrium describes a stable condition where all of the influencing factors are in balance and so cancel each other out. Because of this equilibrium, the temperature of the earth has been relatively constant over time. For scientists, this balance between the amount of solar radiation absorbed, and the amount of longwave radiation emitted by the earth is known as radiative equilibrium. Radiative equilibrium tells us that the longwave radiation emitted by the earth will equal the amount of solar radiation that is absorbed by the earth. In fact, we can determine the temperature of the earth by knowing the amount of longwave radiation it emits. If one of the components of the earth’s energy balance changes the amount of longwave radiation the earth emits the temperature of the earth will also change and the earth will arrive at a new radiative equilibrium. For example, if the amount of solar radiation absorbed were to suddenly increase, the amount of longwave radiation emitted would also increase. The temperature of the earth would then increase but a new radiative equilibrium would be reached so the earth would not continue to become hotter. In summary, the earth’s radiative equilibrium describes the balance between the incoming shortwave and the outgoing longwave radiation. The temperature of the earth can be determined by the amount of outgoing longwave radiation which is equal to the amount of incoming solar radiation absorbed by the earth.		forward: The Greenhouse Effect back: Radiation from the Sun and Earth browse: Table of Contents
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