Physical basis of the Greenhouse Effect

-The “wavelength shift”-

1. Solar insolation calculation (doc file)

2. Blackbody radiation, 3. Absorption spectra4. Conservation of energy

Energy & Environment 263

Online at: http://www.umich.edu/~twod/energy/resources/greenhouse_lecture

2

Black body radiation

• Continuous spectra

400 500 600 700 Wavelength [nm, nanometers]

ColorScience.htm

3

Black body radiation

• Continuous spectra – we see as white light

400 500 600 700 Wavelength [nm, nanometers]

ColorScience.htm

4

Black body radiation

• Continuous spectra & human cones, rods

400 500 600 700 Wavelength [nm, nanometers]

ColorScience.htm

Warning:shows range

of three types of cones,

but notrelative

sensitivities(green

has ~ 10xsensitivity

of red).

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Black body radiation

• Continuous visible spectra – higher temp.

400 500 600 700 Wavelength [nm, nanometers]

ColorScience.htm

6

Black body radiation

• Continuous visible spectra -- lower temperature

400 500 600 700 Wavelength [nm, nanometers]

ColorScience.htm

Note peak shift And flatter shapewith lower Temperature

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Black body radiation

• Continuous visible spectra -- lower temperature

400 500 600 700 Wavelength [nm, nanometers]

ColorScience.htm

-- Wavelength vs. temp is Stephan-Boltzmann law

-- Peak is Wein’s law

-- Shape or ‘distribution’ of intensity with frequency is Plank’s Readiation Law … A big deal in Quantum Mechanics’ history (Einstein, Plank, et al)

-More on this & math later

8

Black body vs. atomic line spectra

• Continuous spectra – from bulk solids with complex modes

• Atomic line spectra – discrete energy levels

400 500 600 700 Wavelength [nm, nanometers]

ColorScience.htm

Hydrogen EMISSION line spectra

9

Solar black body radiation

• Solar spectra … ~5800 K at surface • Yellow-green at middle. Combo ~ white.

But, some parts missing …

400 500 600 700 Wavelength [nm, nanometers]

ColorScience.htm

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Blackbody radiation

400 500 600 700 Wavelength [nm, nanometers]

ColorScience.htm

Hydrogen ABSORPTION spectra

But, what we actually get from the sun is:

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400 500 600 700

ColorScience.htm

Hydrogen EMISSION line spectra

Hydrogen ABSORPTION spectra

Hydrogen emits/absorbs same energies.

electron

neutron

proton

Atomic physics:ATOMISTICand QUANTUMview of micro-world

Larger jumpmore energy bluer color

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400 500 600 700

ColorScience.htm

Hydrogen EMISSION line spectra

Hydrogen ABSORPTION spectra

Hydrogen emits/absorbs same energies.

electron

neutron

proton

Atomic physics:ATOMISTICand QUANTUMview of micro-world

13

Greenhouse: Black body radiation

Three concepts crucial to understand greenhouse effect:

1) Blackbody radiation is E&M radiation a) Continuous spectrab) Shifts with temperature

• Physics of radiant energy

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Greenhouse: Black body radiation

Three concepts crucial to understand greenhouse effect:

1) Blackbody radiation is E&M radiation a) Continuous spectrab) Shifts with temperature

2) Line Spectra of atoms (or bands of molecules)a) Discrete lines (bands)b) Emission and absorption at same energies

• Physics of radiant energy

15

Greenhouse: Black body radiation

Three concepts crucial to understand greenhouse effect:

1) Blackbody radiation is E&M radiation a) Continuous spectrab) Shifts with temperature

2) Line Spectra of atoms (or bands of molecules)a) Discrete lines (bands)b) Emission and absorption at same energies

3) Equilibrium temperature reached when earth’s emission = earth’s absorption.- Slight change in either -> colder or hotter earth

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Greenhouse: and “Wavelength shift”

• Fourth issue: CO2 emissions and H2O already in atmosphere

• Look in detail now Physics of radiant energy …

• We’ll need couple students with calculators … (And remember Sun = 6000 K, earth = 288 K, sigma = 5.67 x 10-8 Watts m-2)

Later: solar-earth spectra compared

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• Fourth issue: CO2 emissions, and H2O already in atmosphere

Source: http://www.lenntech.com/The-greenhouse-effect.htm

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• Fourth issue: CO2 emissions, and H2O already in atmosphere

Source: http://www.lenntech.com/The-greenhouse-effect.htm

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• Fourth issue: CO2 emissions, and H2O already in atmosphere

Source: http://www.lenntech.com/The-greenhouse-effect.htm

Earthshine

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• Fourth issue: CO2 emissions, and H2O already in atmosphere

Source: http://www.lenntech.com/The-greenhouse-effect.htm

Earthshine

WATER VAPOR “Water molecules, always abundant I air, absorb thermal IR light due to the H-O-H bending vibration, the peak in the spectrum for this absorption occurs at about 6.3 µm. Thus almost all the relatively small amount of outgoing IR in the 5.5-7.5 µm regions is intercepted by water vapor. There are other water vibrations the remove thermal infrared light of wavelength 12 µm and longer. In fact the water is the most important greenhouse gas in the earth’s atmosphere, though on a per molecule basis it is a less efficient absorber than is CO2. ““The equilibrium vapor pressure of liquid water, and consequently the maximum concentration of water vapor in air, increases exponentially with temperature. Thus the amount of thermal IR redirected by water vapor will rise as a result of any global warming induced by the other greenhouse gases and will amplify the temperature increase. Since it comes about as an indirect effect of increasing the levels of other gases. Consequently, water is not usually listed explicity among gases whose increasing concentrations are enhancing the greenhouse effect.  Water in the liquid form droplets in clouds also absorbs thermal IR. “

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Greenhouse: and

“Wavelength shift”