- The document discusses the greenhouse effect and the Earth's energy budget. It explains that the Earth's surface absorbs around 48% of incoming solar radiation and that the remaining 52% is either reflected or absorbed by the atmosphere. - It describes the three main types of atmospheric scattering - Rayleigh, Mie, and non-selective scattering - and explains that Rayleigh scattering causes the blue color of the sky and reddish-orange sunsets. - The greenhouse effect is caused by gases like CO2, CH4, and H2O that absorb outgoing longwave radiation. Methane is an important greenhouse gas because it is 23 times more potent than CO2 and livestock are a major source.

1. What is the Greenhouse Effect?

2. Review of last lectureReview of last lecture
– The two basic motions of the EarthThe two basic motions of the Earth
– What causes the four seasons: the Earth’s tiltWhat causes the four seasons: the Earth’s tilt
and the 3 ways it affects the solar insolationand the 3 ways it affects the solar insolation
(change of length of the day, beam spreading,(change of length of the day, beam spreading,
beam depletion)beam depletion)
– Change of the Earth’s orbit at longer timeChange of the Earth’s orbit at longer time
scales (Milankovitch cycles): eccentricity, axialscales (Milankovitch cycles): eccentricity, axial
tilt, and precessiontilt, and precession

3. Satellite Measurements of the Earth’sSatellite Measurements of the Earth’s
Radiation BudgetRadiation Budget
NASA’s Earth
Radiation Budget
Satellite (ERBS) 1985-
1989

4. Earth’s energy budget (averaged over theEarth’s energy budget (averaged over the
whole globe and over a long time)whole globe and over a long time)
• At the top of the atmosphere:At the top of the atmosphere:
Incoming shortwave = Reflected Shortwave + Emitted longwaveIncoming shortwave = Reflected Shortwave + Emitted longwave
• At the surface:At the surface:
Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming)Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming)
+ Latent heat flux + sensible heat flux+ Latent heat flux + sensible heat flux
Sensible
heat 7%
Latent heat
23%
Net Longwave 21%
Yellow:
shortwave
Red:
longwave

5. Atmospheric influences on radiationAtmospheric influences on radiation
ReflectionReflection ScatteringScattering AbsorptionAbsorption
(absorber(absorber
warms)warms)

6. ReflectionReflection
• reflectionreflection – redirection of energy w/o– redirection of energy w/o
absorptionabsorption
• all objects reflect visible lightall objects reflect visible light 
effectiveness varieseffectiveness varies
• albedo –albedo – % of visible light reflected% of visible light reflected
• There are two types of reflection (solidThere are two types of reflection (solid
surface):surface):
– SpecularSpecular: light is reflected with: light is reflected with
equal intensity (e.g. mirror)equal intensity (e.g. mirror)
– Diffuse reflectionDiffuse reflection OROR scatteringscattering::
light is reflected in multiple directions,light is reflected in multiple directions,
weakly (e.g. snow)weakly (e.g. snow)

8. 3 Types of Scattering:3 Types of Scattering:
1.1. RaleighRaleigh
2.2. MieMie
3.3. Non-SelectiveNon-Selective
Atmospheric ScatteringAtmospheric Scattering
A discussion of each type follows…A discussion of each type follows…

9. • involves gases smaller than insolation wavelength
• scatters light in all directions
• most effective at short wavelengths (violet, blue)… hence,
blue sky
Rayleigh ScatteringRayleigh Scattering
The Earth has an atmosphere. So it has
Rayleigh scattering and its sky appears
blue
The Moon has no atmosphere. So it
has no Rayleigh scattering and its sky
appears dark

10. • Rayleigh scattering also explains reddish-orange
sunsets when light travels through thick slice of
atmosphere

11. Monet: Impressions, SunriseMonet: Impressions, Sunrise

12. Grainstacks at differentGrainstacks at different
time of the daytime of the day

13. 2) Mie scattering2) Mie scattering
– involves aerosols (e.g. dust, smoke) larger thaninvolves aerosols (e.g. dust, smoke) larger than
gas moleculesgas molecules
– forward scatterforward scatter
– equally effective across visible spectrumequally effective across visible spectrum
– explains hazy, gray daysexplains hazy, gray days

14. 3) Non-selective scattering3) Non-selective scattering
– Happens when atmospheric particles are much largerHappens when atmospheric particles are much larger
than the wavelength of incoming radiation (e.g. waterthan the wavelength of incoming radiation (e.g. water
droplets in clouds)droplets in clouds)
– Act like lenses; scatter all wavelengths equally toAct like lenses; scatter all wavelengths equally to
create a white appearancecreate a white appearance
– That’s why clouds appear whiteThat’s why clouds appear white

15. Video: The greenhouse effectVideo: The greenhouse effect
• http://www.youtube.com/watch?v=ZzCA60WnoMkhttp://www.youtube.com/watch?v=ZzCA60WnoMk

16. Atmospheric Absorption - The Greenhouse EffectAtmospheric Absorption - The Greenhouse Effect
TransparentTransparent
to solarto solar
(shortwave)(shortwave)
radiationradiation
Opaque toOpaque to
earth’searth’s
(longwave)(longwave)
radiationradiation
Major GH gases:
CO2, H20(v), CH4

17. The importance of methane (CHThe importance of methane (CH44))
• 23 times more powerful as a greenhouse gas than23 times more powerful as a greenhouse gas than
COCO22
• The livestock sector is a major player, whichThe livestock sector is a major player, which
accounts for 35-40% global anthropogenicaccounts for 35-40% global anthropogenic
emissions of methane (their burps!)emissions of methane (their burps!)
• The livestock sector is responsible for 18% of totalThe livestock sector is responsible for 18% of total
greenhouse gas emissionsgreenhouse gas emissions
• Therefore, consuming less meat can helpTherefore, consuming less meat can help
reducing global warming than not driving cars.reducing global warming than not driving cars.

18. Seasonal variation of surface radiationSeasonal variation of surface radiation

19. Surface “Sensible” andSurface “Sensible” and
“Latent” heat transfers“Latent” heat transfers
1.1. ConductionConduction
– This is how excess heat in ground isThis is how excess heat in ground is
transferred to the atmosphere via antransferred to the atmosphere via an
extremely thin layer of air in contactextremely thin layer of air in contact
with the surfacewith the surface
1.1. ConvectionConvection
– Once the heat is transferred from theOnce the heat is transferred from the
surface to the air via conduction,surface to the air via conduction,
convection takes over from here viaconvection takes over from here via
“sensible” and “latent” heat transfers“sensible” and “latent” heat transfers
First, recall 2 other methods ofFirst, recall 2 other methods of
energy transfer in addition toenergy transfer in addition to
radiation:radiation:

20. Sensible HeatSensible Heat
• Heat energy which is readily detectedHeat energy which is readily detected
• Magnitude is related to an object’s specific heatMagnitude is related to an object’s specific heat
– The amount of energy needed to change the temperature ofThe amount of energy needed to change the temperature of
an object a particular amount in J/kg/Kan object a particular amount in J/kg/K
• Related to massRelated to mass
– Higher mass requires more energy for heatingHigher mass requires more energy for heating
• Sensible heat transfer occurs from warmer to coolerSensible heat transfer occurs from warmer to cooler
areas (i.e., from ground upward)areas (i.e., from ground upward)

21. Latent HeatLatent Heat
• Energy required to induce changes of stateEnergy required to induce changes of state
in a substancein a substance
• In atmospheric processes, invariablyIn atmospheric processes, invariably
involves waterinvolves water
• When water is present, latent heat ofWhen water is present, latent heat of
evaporation redirects some energy whichevaporation redirects some energy which
would be used for sensible heatwould be used for sensible heat
– Wet environments are cooler relative toWet environments are cooler relative to
their insolation amountstheir insolation amounts
• Latent heat of evaporation is stored in waterLatent heat of evaporation is stored in water
vaporvapor
– Released as latent heat of condensationReleased as latent heat of condensation
when that change of state is inducedwhen that change of state is induced
• Latent heat transfer occurs from regions ofLatent heat transfer occurs from regions of

22. Seasonal variation of surface energy budgetSeasonal variation of surface energy budget
Storage change = net radiation - latent heat flux -
sensible heat flux

23. SummarySummary
• Earth’s energy balance at the top of the atmosphere and at theEarth’s energy balance at the top of the atmosphere and at the
surface. What percentage of solar energy is absorbed by thesurface. What percentage of solar energy is absorbed by the
surface?surface?
• Atmospheric influences on radiation (3 ways)Atmospheric influences on radiation (3 ways)
• The three types of atmospheric scattering. What causes theThe three types of atmospheric scattering. What causes the
blue sky? Why causes the reddish-orange sunsets?blue sky? Why causes the reddish-orange sunsets?
• What cause the greenhouse effect? What are the majorWhat cause the greenhouse effect? What are the major
greenhouse gases? Why is methane important?greenhouse gases? Why is methane important?
• Sensible heat flux (dry flux from warm to cold regions) andSensible heat flux (dry flux from warm to cold regions) and
latent heat flux (wet flux from wet to dry regions)latent heat flux (wet flux from wet to dry regions)