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# Greenhouse Effect

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This powerpoint shows the radiation from the sun and what happens to it at the Earth's surface and in the atmosphere. The effect of greenhouse gases is included.

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### Greenhouse Effect

1. 1. 1. 342 W/m2 is the intensity absorbed when averaged over the entire surface of the Earth where 1370 W/m2 is the solar constant that strikes a circular area of the Earth. (4x342 W/m2 = 1370 W/m2) 2. 168 W/m2 is absorbed by the Earth, but the energy being radiated from the Earth is 24 W/m2 (thermals) + 78 W/m2 (evapo-transpiration) + 390 W/m2 (surface radiation) = 492 W/m2. How can this be? 3. Notice 324 W/m2 is absorbed by the Earth after being absorbed by greenhouse gases and re-emitted to the Earth. 4. The total intensity escaping to outer space is 235 W/m2 (infrared) and 107 W/m2 (reflected solar) = 342 W/m2.
2. 2. Different books use the terms quot;greenhouse effectquot; and quot;global warmingquot; differently. In this course, greenhouse effect means the warming of the earth's surface beyond a 255 K average temperature by greenhouse gases that occur naturally in the earth's atmosphere. Global warming means the warming of the earth's surface beyond a 288 K average temperature because of greenhouse gases from anthropogenic (human) sources. That the greenhouse effect makes the earth habitable for humans has been known in the scientific community for over a 100 years.
3. 3. The next slide is the spectrum of incoming sunlight again
4. 4. The next slide is the spectrum of infrared radiated from the Earth at the Sahara Desert
5. 5. 400 wave numbers = 25 m = 25,000 nm 1000 wave numbers = 10 m = 10,000 nm. Ultraviolet light has wavelengths between 200 and 400 nm. Radiance is almost the same as intensity.
6. 6. The next slide shows infrared from the Earth being absorbed by greenhouse gases instead of infrared emitted through the atmosphere. The dark bands are infrared wavelengths that are being absorbed.