Physical basis of the Greenhouse Effect -The “wavelength shift”- 1.Black body radiation, 2.Absorption spectra 3.Conservation of energy Energy & Environment 263

Black body radiation Continuous spectra Wavelength [nm, nanometers] ColorScience.htm

Black body radiation Continuous spectra – we see as white light Wavelength [nm, nanometers] ColorScience.htm

Black body radiation Continuous spectra & human cones, rods Wavelength [nm, nanometers] ColorScience.htm Warning: shows range of three types of cones, but not relative sensitivities (green has ~ 10x sensitivity of red).

Black body radiation Continuous visible spectra – higher temp Wavelength [nm, nanometers] ColorScience.htm

Black body radiation Continuous visible spectra -- lower temperature Wavelength [nm, nanometers] ColorScience.htm Note peak shift   And flatter shape with lower Temperature

Black body radiation Continuous visible spectra -- lower temperature 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

Black body vs. atomic line spectra Continuous spectra – from bulk solids with complex modes Atomic line spectra – discrete energy levels Wavelength [nm, nanometers] ColorScience.htm Hydrogen EMISSION line spectra

Solar black body radiation Solar spectra … ~5800 K at surface Yellow-green at middle. Combo ~ white. But, some parts missing … Wavelength [nm, nanometers] ColorScience.htm

Blackbody radiation Wavelength [nm, nanometers] ColorScience.htm Hydrogen ABSORPTION spectra But, what we actually get from the sun is:

ColorScience.htm Hydrogen EMISSION line spectra Hydrogen ABSORPTION spectra Hydrogen emits/absorbs same energies. Atomic physics: ATOMISTIC and QUANTUM view of micro-world Larger jump  more energy  bluer color

ColorScience.htm Hydrogen EMISSION line spectra Hydrogen ABSORPTION spectra Hydrogen emits/absorbs same energies. Atomic physics: ATOMISTIC and QUANTUM view of micro-world

Greenhouse: Black body radiation Three concepts crucial to understand greenhouse effect: 1)Blackbody radiation is E&M radiation a) Continuous spectra b) Shifts with temperature Physics of radiant energy

Greenhouse: Black body radiation Three concepts crucial to understand greenhouse effect: 1)Blackbody radiation is E&M radiation a) Continuous spectra b) 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

Greenhouse: Black body radiation Three concepts crucial to understand greenhouse effect: 1)Blackbody radiation is E&M radiation a) Continuous spectra b) 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

Greenhouse: and “Wavelength shift” Fourth issue: CO2 emissions and H2O already in atmosphere Look in detail now Physics of radiant energy …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 

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

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

Fourth issue: CO2 emissions, and H2O already in atmosphere Source: Earth shine

Fourth issue: CO2 emissions, and H2O already in atmosphere Source: Earth shine 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 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. “

Greenhouse: and “Wavelength shift”