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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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. • R
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This note was uploaded on 11/03/2009 for the course PHYSICS PHYS 100 taught by Professor Lioudmila during the Spring '09 term at UBC.

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Topic5 Greenhouse Effect and Global Warmin gpdf -...

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