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Emissivity Our conservation of Energy equation tells us that energy absorbed = energy released. We can't forget that Earth has a "blanket" of gases held to the surface by its gravity. These atmospheric gases help "trap" the radiated heat and keep it close to the surface of the Earth. The "greenhouse gases ", like water vapor, carbon dioxide, methane ...) This heating of the Earth's due to its atmospheric gases is often referred to as the "greenhouse effect". High energy, shortwave radiation from the sun passes through earth's atmosphere fairly unimpeded. However, when the earth absorbs this energy and radiates its longwave radiation out, the atmospheric gases absorb specific wavelenghts of this outgoing radiation and re - emit some of this radiation back to Earth. The effect of the atmospheric gases in trapping heat is often related to terms such as "opacity" and "emissivity". Therefore, we will include "emissivity" or "e" in our energy budget equation for Earth. A planet with an "e" value = 1.0 implies that the planet has little or no atmosphere, and 100% of the radiation emitted is released to space. Would an emissivity level of 1.0 more likely describe Venus, Earth, or Mars? Why? A planet with an "e" value = 0.70 implies that the planet has an atmosphere capable of emitting 70% of Earth's radiation to space, the other 30% being "trapped" close to the Earth's surface. One of the most difficult variables for climate models to predict is the effect of clouds on the absorption and emission of heat energy. Since Stefan-Boltzman tells us that the Energy of longwave radiation decreases with temperature. The radiation emitted at the top of clouds has a lower energy than at the bottom of clouds. Different types of clouds: cumulus, stratus... have a different "heat trapping", emissivity effect on the atmosphere. Scientists who work on computer climate modeling agree with the old lyrics, "I've looked at clouds from both sides now, from in and out, and still somehow, it's cloud's illusions I recall. I really don't know clouds at all." (Joni Mitchell). Terms: Vocabulary /Concept Map :
use as is, or, add some of your own terms and construct a concept map.
Challenge Formula Worksheet:
Explain the challenge equation and complete the short essay questions.
Global Warming Activity: Calculate
and graph the "e" value for Earth at its given mean average
temperature, and then for doubling of the CO2 concentration.
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