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Greenhouse Effect: the context

The three planets

Energy balance

Albedo

Introduction

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Four billion years ago Earth, Venus and Mars

had similar CO2atmospheres

Mars Thin atmosphereAlmost all CO2in ground Increase in temperature: +6C

Earth0.03% CO2in atmosphereIncrease in temperature: +31C

Venus Thick atmosphere 96% CO2Increase in temperature: +510C

Temperature increase due to Greenhouse effect

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Tenuous gases of the atmosphere

Steam emissions from coal burning electric power stations

Hydrocarbon powered aircraft engine

Snowy mountains

Image from aircraft over Victoria, Australia, Credit: David Jamieson

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Energy must balance

Energy input = energy reflected + energy absorbed& re-radiated

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Albedo determines how much energy is reflected

Albedo

Cloud up to 0.7

Snow 0.8-0.9Water 0.2 to 1

(depends on angle)Bare Ground 0.17

Road 0.04

Charcoal (soot) 0.04

Earth Average

0.31

Black Body 0

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white

light yellow

lemon

orange

dark orange

salmon

bright cherry

cherry

mediumcherrydark cherry

blood red

faint red

1205C (2200F)

1080C (1975F)

990C (1830F)

940C (1725F)

915C (1680F)

845C (1550F)

790C (1450F)

745C (1375F)

690C (1275F)

635C (1175F)

580C (1075F)

500C (930F)

Emission of energy: colour depends on temperatureThese are the colours of an ideal black body

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The Stefan Bolzmann Law

SUN T= 5780 K

E*= 6.34#

107

Wm-2

EARTHT= 290 K

E*= 400 Wm-2

Total black body irradiance:

where = 5.67#10-8W m-2K-4

(temperature T is measured in Kelvin)

E* =

T

4

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a simple approximation to get started.

Sun Power Input = Earth Heat output

(1 A) S(rE)2=(TE)

44(rE)2

A=Earth Albedo, S=Sun input rate on Earth (W/m2), rE=Earth Radius, TE=Earth surface temperature

Gives TE= 255 K or 18oC

But the average temperature is actually +15o

C

Clearly we are missing something!

It is the Greenhouse effect!

Let us apply black body physics to the Earth

Moon seen through the atmosphere, Credit: NASA;

(1 0.31) 1,370 = 5.67#108(TE)44

1,370 W/m2

at 12 noon

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Greenhouse Effect: the context

Summary

Mars and Venus can teach us about planetary energetics

Energy in must balance Energy out

Albedo affects reflected energy

Simple physics tells us how much a body radiates

The surface of the Earth is warmed by the Sun AND the atmosphere (the

Greenhouse effect)

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Image Credits

Slide

Details

2 Mars (http://hubblesite.org/newscenter/archive/releases/2005/34/image/h/) by NASA $(http://www.nasa.gov/),ESA $(http://www.spacetelescope.org/), and The Hubble Heritage $

Team (http://heritage.stsci.edu/) (STScI /AURA ) (http://www.stsci.edu/|http://www.aura-astronomy.org/)

The Blue Marble : Western Hempishpere(http://eoimages.gsfc.nasa.gov/images/imagerecords/57000/57723/globe_west_2048.jpg) byNASA [Public Domain]

Venus Cloud Tops (http://hubblesite.org/gallery/album/solar_system/venus/pr1995016g) by L. Esposito (University of Colorado,

Boulder), and NASA $(http://www.nasa.gov/)

3 David Jamieson

4

Swirling Maelstrom (http://sdo.gsfc.nasa.gov/assets/gallery/preview/Swirling_304_Sept2010.jpg) by NASA [Public Domain]$Full Earth (http://www.nasa.gov/images/content/115334main_image_feature_329_ys_full.jpg) by NASA/Apollo 17 [Public Domain]

5 South Pole frame (SouthPole_1920x108060fps.0001.tif ) from Pulse of Snow and Sea Ice(SVS Animation 3944 http://svs.gsfc.nasa.gov/goto?3944) by NASA/Goddard Space FlightCenter Scientific Visualization Studio

6 (partial) Swirling Maelstrom (http://sdo.gsfc.nasa.gov/assets/gallery/preview/Swirling_304_Sept2010.jpg) by NASA [Public Domain]pt2010.jpg

Adaptation: David Jamieson

7 Swirling Maelstrom (http://sdo.gsfc.nasa.gov/assets/gallery/preview/Swirling_304_Sept2010.jpg) by NASA [Public Domain]Full Earth (http://www.nasa.gov/images/content/115334main_image_feature_329_ys_full.jpg) by NASA/Apollo 17 [Public Domain]

8 (partial) Swirling Maelstrom (http://sdo.gsfc.nasa.gov/assets/gallery/preview/Swirling_304_Sept2010.jpg) by NASA [Public Domain]$View of the crescent moon through the top of the earth's atmosphere (

http://commons.wikimedia.org/wiki/File:Top_of_Atmosphere.jpg) By NASA Earth Observatory [Public domain], via WikimediaCommons