Topic5 Greenhouse Effect and Global Warmin gpdf

# Topic5 Greenhouse Effect and Global Warmin gpdf -...

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1 Greenhouse Effect and Global Warming Greenhouse Effect Atmosphere Model Greenhouse Gases Refined Earth Energy Balance Climate Feedback Loops Global Warming Greenhouse Effect ; Atmosphere Model ; Greenhouse Gases; Refined Earth Energy Balance; Climate Feedback Loops; Global Warming Our energy balance model describes the main heat gain and loss mechanism of the Earth but fails to predict the surface temperature accurately. We obtained a temperature of the Earth as seen from space: The effective Earth temperature – some average temperature of the atmosphere, not the temperature of the surface of the Earth. We need to include the atmosphere more explicitly. The albedo describes the total reflection of the cloud cover but we also need to include the wavelength-dependent absorption and transmission of the atmosphere: Greenhouse effect . Greenhouse Effect ; Atmosphere Model ; Greenhouse Gases; Refined Earth Energy Balance; Climate Feedback Loops; Global Warming Energy from the sun in form of visible light passes easily through the atmosphere (or glass). The energy is absorbed on the surface of Earth (or things inside a greenhouse). The warm surface (or objects) emits longer infrared (IR) wavelengths. The atmosphere (glass) is not transparent for IR wavelength. The energy is absorbed in the atmosphere (glass). The heated atmosphere (glass) re-emits the IR radiation back onto the Earth’s surface and into space. Simulation.

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2 Greenhouse Effect ; Atmosphere Model ; Greenhouse Gases; Refined Earth Energy Balance; Climate Feedback Loops; Global Warming The portion of IR radiation that is radiated back onto the surface Earth is in addition to the power from the Sun’s radiation. It is like being in a warm room: Your body gets some radiation energy back from the warm walls. So how do we have to modify our energy balance equation? Previously, without greenhouse effect: P in = P out P in = (1- A ) S π R Earth 2 P out = 4π R Earth 2 σ T Earth 4 Now with greenhouse effect? ( ) K T T S A T A Earth Earth 255 4 1 4 = = σ Greenhouse Effect; Atmosphere Model ; Greenhouse Gases; Refined Earth Energy Balance; Climate Feedback Loops; Global Warming Like a window in a greenhouse, the atmosphere is transparent for visible part of sunlight but absorbs some of the infrared radiation that is emitted by the Earth surface This absorbed energy is than re-emitted in all directions, so a half is radiated back onto the Earth’s surface . σ T A 4 σ T A 4 Greenhouse Effect; Atmosphere Model ; Greenhouse Gases; Refined Earth Energy Balance; Climate Feedback Loops; Global Warming P in = (1- A ) S π R Earth 2 + e σ T A 4 4π R Atm 2 P out = e σ T s 4 4π R Earth 2 (Since we consider the surface, we treat the radiation from the atmosphere as incoming portion.) S: Solar constant, T A : Atmospheric temperature, T S : Surface temperature.
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