phy392_lecture07_web_2011

Phy392_lecture07_web - PHY392S Physics of Climate Lecture 7 Web Notes The Greenhouse Effect The Earths Greenhouse Effect Radiative Forcing Global

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PHY392S Physics of Climate Lecture 7 - Web Notes The Greenhouse Effect The Earth’s Greenhouse Effect Radiative Forcing Global Warming Potentials Fourier, Arrhenius, and Callendar PHY392 - Physics of Climate Lecture 7, Page 1
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The Greenhouse Effect - 1 CO 2 , H 2 O, CH 4 , O 3 naturally radiatively active gases The fundamental reason for the existence of the greenhouse effect is that the temperature decreases with altitude in the troposphere. Radiatively active gases, as well as clouds, absorb the radiation emitted by the warmer surface, while their emission of radiation to space occurs at cooler atmospheric temperatures. The trapping of the radiation by radiatively active molecules produces an increase in the surface temperature of about 33 degrees Celsius (assuming no change in albedo when atmosphere is removed…). Recall: This gives T e ~255 K (-18°C) (with F sun =1367 W m -2 , A=0.3, ε =1) Using T S ~288 K (15°C), the atmosphere traps ~33°C. 4 e infrared T 4 ) A 1 ( F σ ε = PHY392 - Physics of Climate Lecture 7, Page 2
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Increase in CO 2 leads to a decrease in the infrared transparency of the atmosphere Increase in the surface temperature NOT LINEAR! CO 2 is active in the infrared spectral region 342 Wm -2 107 Wm -2 235 Wm -2 390 Wm -2 155 Wm -2 The Greenhouse Effect - 2 155 W m -2 is trapped in the atmosphere represents the greenhouse effect Major players water vapour, CO 2 , N 2 O, O 3 , CFCs, CH 4 , HCFCs, HFCs, … PHY392 - Physics of Climate Lecture 7, Page 3
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Of the incoming solar radiation, 49% is absorbed by the surface. This is returned to the atmosphere as sensible heat, latent heat, and infrared radiation. Most of this radiation is absorbed by the atmosphere, which in turn emits radiation. Radiation lost to space comes from cloud tops and regions much colder than the surface. Result = greenhouse effect. (IPCC 2001, Fig. 1.2) Earth’s Annual Global Energy Budget PHY392 - Physics of Climate Lecture 7, Page 4
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Atmospheric Windows What happens if you add a more of a gas which absorbs in an atmospheric window? (e.g., the 8 to 12 µ m spectral region) The effect can be large because there is no “competition” for the photons Gases that absorb in the atmospheric window are potent greenhouse gases (e.g., CH 4 , N 2 O, CFCs). Adding more CO 2 or another gas that absorbs in the same region as CO 2 or H 2 O has a smaller effect because there is already strong absorption there. PHY392 - Physics of Climate Lecture 7, Page 5
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Clouds: absorb and emit infrared radiation increase planetary albedo high-altitude cirrus clouds cause warming low-level stratus clouds cause cooling The Role of Clouds and Aerosols Overall clouds and aerosols tend to cool the Earth system
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This note was uploaded on 02/19/2011 for the course PHYSICS 392 taught by Professor Weak during the Spring '11 term at Toledo.

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Phy392_lecture07_web - PHY392S Physics of Climate Lecture 7 Web Notes The Greenhouse Effect The Earths Greenhouse Effect Radiative Forcing Global

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