Environmental Physics PHYS 1149
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This 19 page Class Notes was uploaded by Maudie Larkin on Monday October 12, 2015. The Class Notes belongs to PHYS 1149 at Georgia Southern University taught by Anand Balaraman in Fall. Since its upload, it has received 47 views. For similar materials see /class/222053/phys-1149-georgia-southern-university in Physics 2 at Georgia Southern University.
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Date Created: 10/12/15
Chapter 12 Keeping Warm The Science of Climate CapHg a 2mm Peavsan Euunmm inc pubiishing as Pearson Addisonrwesiey 121 Keeping a House Warm Keeping a house warm in the winter involves a balance between Energy input from the heating system Insulation Energy loss through the walls For a house at constant temperature the rate of I energy input must equal the rate of energy loss 121 Keeping a House Warm If your thermostat broke the temperature would notjust get higher without limit Insulation Instead the temp would rise until the rate of energy input from the heater equaled the rate of energy loss through the walls 122 Keeping a Planet Warm Energy out l v ii r Sunlight 39 quot energy in Keeping a planet warm involves a balance between Incoming solar energy Outgoing infrared radiation to space For a planet at constant temperature the rate of energy input must equal the rate of energy loss 122 Keeping a Planet Warm Since the rate of energy loss increases with increasing temperature a planet naturally achieves this state of energy balance through temperature adjustments Energy out Sunlight energy in FIGURE 12039 122 Keeping a Planet Warm Solar constant S 1368 Earth s albedo reflectivity is about 31 Clouds Land Solar energy absorbed Sa 2 940 122 Keeping a Planet Warm Zero Dimensional Energy Balance Model Rate at which Earth absorbs energy R Sa Rate at which Earth emits energy 60AT4 6047IR T4 Setting the two rates equal to each other R Sa 6047IR T4 yx 122 Keeping a Planet Warm Zero Dimensional Energy Balance Model Our model predicts an average Earth temp of 4 S 235 40 567gtlt10 8 W m2K4 Earth s actual average temperature is 287 K 59 F warmer than our estimate 414gtlt109K4 123 In the Greenhouse The zero dimensional energy balance model doesn t take the warming effect of Earth s atmosphere into account The greenhouse effect l simply refers to the cowlghfgl lll ylll l tilifl e atmosphere 123 In the Greenhouse Earth s atmosphere is mostly transparent to visible light Certain gases in the atmosphere greenhouse gases absorb the infrared radiation emitted by the planet s surface 123 In the Greenhouse These greenhouse gases inhibit outgoing infrared radiation making it difficult for the Earth to shed the energy it gains from the Sun Sunlight We will consider three complementary ways to understand the greenhouse effect 123 In the Greenhouse An Insulating Blanket Atmospheric greenhouse gases have somewhat the same effect as an insulating blanket or the insulation in a house More effective insulation lower k requires a higher temperature to achieve the same loss rate Temperature rises with increased insulation Recall that the heat loss rate through a slab of conductivity k is szAm Tc Th T 123 In the Greenhouse An Insulating Blanket The presence of insulating atmospheric greenhouse gases makes Earth s surface temperature higher than it would be otherwise d 123 In the Greenhouse Infrared Up and Down The atmosphere is warmed by infrared radiation from the surface Since it is at a finite Atmosphere temperature the atmosphere emits its own infrared radiation P eo AT4 123 In the Greenhouse Infrared Up and Down As a result the surface is warmed by both Visible light from the Sun Infrared radiation from the atmosphere Atmosphere The surface must get rid of all this energy so the surface temperature must go up P eo AT4 123 In the Greenhouse Warm Below Cool Above 0 The power radiated to Solar energy Infrared to space 235W w MW space IS P e 0T4 1 e O39T4 space a a a s Atmosphere P 0T4 e T4 space s a s a 0 An increase in atmospheric infrared absorption can mean Surface FIGURE 1203 Energy Elwimnmenh and Climate Copyright ww Norton amp Compsny zoos Lower atmospheric temp Higher surface temp 124 Earth s Energy Balance Earth s complete energy balance involves additional complex processes including Reflection of sunlight from the clouds and surface Convection Evaporation Evapotranspiration Clouds which play a complex role 124 Earth s Energy Balance 107 Reflected solar mooming 235 UtQOing radiation solar radiation infrared radiation 107 Wm2 42 wm 235 Wm2 Reflected by clouds 4o aerosols and Em39md by Atmospheric atmosphere atmosphere window 77 Greenhouse ases i 324 Infrared radiation Convection aPO Surface 324quot transpiration radiation Absorbed by su n aoe 39 r Absorbed by surface FIGURE 1204 Energy Environment and Climate Copyright WW Norton amp Company 2008 125 A Tale of Three Planets FIGURE 1205 Energy Environment and Climate Copyright WW Norton amp Company 2008
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