Global Energy Balance: The Greenhouse Effect

1. Global Energy Balance:The Greenhouse Effect Geos 110 Lectures: Earth System Science Chapter 3: Kump et al 3rd ed. Dr. Tark Hamilton, Camosun College

2. 3 Inner Rocky Planets with Atmospheres Venus -------------Earth----------------Mars The Goldilocks Zone

3. Then Goldilocks tried Baby Bear’s porridge and it was just right, so she ate it all up!

4. Venus: South Pole > 460°C, CO2 SO2UV Image: Pioneer Venus Orbiter, Feb, 5, 1979 Greenschist Facies Metamorphism, No Clays Supercritical Fluids, No Liquid Water

5. Earth: The Blue Planet (Ice, Water, Steam) Earth ~ 15°C average, Seasons, abundant liquid water Transparent N2 – O2 – Ar Atmosphere, minor GHS’s

6. Mars: -55°C, CO2millibar atmosphere Colder than a Polar winter, hydrated minerals, no H2O(l) • Less atmosphere than a Bar in Nanaimo, Dry Ice Caps

7. Electromagnetic Radiation - Waves • E and B vary as wave passes at speed of light • E-field interacts with matter through its electrons

8. Energy, Frequency & Wavelength • E = h ν, Higher Frequency  Higher Energy • E = h c/λ, Lower energy  Longer Wave • Whats nu? ……. ν = c/ λ • Or • λν = c , c = 3x108 m/s

9. 400 nm < Visible Light < 700 nm • Longer wave infra-red and microwaves are “heat” for greenhouse • Shorter wavelength hard UV & X-rays are ionizing radiation

10. Flux: Energy per unit area per unit timeNormal Incidence Minimizes Area • Heat or Light per unit area decreases w/ Sun Angle • The Sun heats less at Dawn, Dusk & Winter than 12pm

11. Normal Incidence = Circular FootprintMaximum Flux!

12. Inclined Incidence Increases Area but Decreases Heating  Decreased Flux

13. Inverse Square Law Intensity of light/heat decreases w/ square of distance e.g. 2X distance = ¼ power, 1/3 distance = 9 x power

14. Temperatures of Water Phase Changes Celsius based on freezing & boiling or H2O Kelvins Absolute (no offset), same size as Celsius Farenheit Freezing & Coagulation of Human Blood…eeew!

15. Temperature Scales • Celsius: 0° Freezing, 100° Boiling • T°F = [T°C + 1.8] + 32° or • T°C = [T°F – 32] / 1.8 where 1.8 = 9/5 • T K = T°C + 273.15 (Kelvins, not degrees K)

16. A Cold Black Body absorbs at all wavelengths Cold = Black Hot = emits Red Hotter = emits White

17. The Planck Function • The Planck Function: variation of blackbody radiation & λ • Wein’s Law: λmax ~ 2898/T (Kelvins) • Stefan-Boltzmann Law: Sum of All Flux ~ σ T4

18. The Planck Function: variation of blackbody radiation & λ (wavelength)

19. Wein’s Law: λ max ~ 2898/T (Kelvins) • The Sun’s Photosphere is ~ 5780 Kelvins

20. Stefan-Boltzmann Law: Sum of All Flux ~ σ T4Emission goes up as temperature to the 4th power!

21. Blackbody Emission Spectra for Sun & Earth • Ultraviolet.…Visible………………………..Infrared • The Sun emits more at all wavelengths λ (energies) • The Earth absorbs in visible light (0.4-0.7) μm & emits in infrared ( λ > 1μm)

22. Solar Energy FluxStefan Boltzmann Law • Fsun = σ (5780 K)4 ~ 6.3 x 107 W/m2 • If some other star were twice as hot: • Fstar = σ (2 x 5780 K)4 • = (2)4 x σ (5780 K)4 = 16 Fsun ! • Sooo… this must be a real rock star?

23. Earth’s Global Energy Balance • For Earth’s Energy Budget to Balance • Flux inmust = Flux out • if true T°C = Constant, One climate, No weather • but Flux in > Flux out so Earth is Warming • 3 Factors Control Earth’s Energy Budget & Climate: • Solar Flux at any particular distance • Earth’s reflectivity (albedo) • Greenhouse Gas Effects

24. A Closer Look at Global Energy Balance

25. Earth’s Energy Balance Energy emitted = Energy absorbed : • Energy emitted = 4π REarth2 x σTEarth4 • This follows from Stefan-Boltzmann & Spherical Shape E absorbed = E intercepted – E reflected: • E absorbed = πREarth2S - πREarth2SA = πREarth2 S(1-A) • Where : S = Solar Flux & SA = Earth’s Projected Area Therefore: 4π REarth2 x σTEarth4 = πREarth2 S(1-A) or: σTEarth4 = S(1-A)/4

26. The Greenhouse EffectOne-Layer Atmosphere • ~33°C net surface warming = Tmean sT - Tradiating • Atmosphere radiates IR down & absorbs IR up

27. The Greenhouse EffectOne-Layer Atmosphere Flux up from ground = Net Solar input + Flux down from air For Earth’s Surface: solar input + atmospheric heat • σTSurface4 = S(1-A)/4 + σTEarth’s Air4 For Earth’s Air: atmosphere radiates 2 ways • σTSurface4 = 2σTEarth’s Air4 Equate, subtract σTEarth’s Air4 & divide by σ to obtain: • TS = 2 ¼ TEA this is hotter with Air by 1.19 • or ΔTg = TS – TEA = 303 – 255 = 48K, Really ~15 K

28. Was 387, CO2 now = 390.02 ppm August 2011 Increasing ~ 2 ppm/yr, N2, O2 & Ar are “inert”

29. Trace Greenhouse Gases CFC’s from blowing gas, refrigerants & burned plastic H2O 4% = 40,000 ppm, 1.7 ppm CH4 ~ 63 ppm CO2

30. Thermal Layers in Earth’s AtmosphereDominate the Atmospheric Structure • The Pressure gradient is log-linear, decreasing 6 orders of magnitude over the 1st 100 km • Earth’s surface & Stratopause are warmest • The Tropopause and Mesopause are coldest

31. The Log-Linear Pressure Gradient Decreases by 6 orders in 100 km • Barometric Law: Pressure decreases with altitude by a factor of 10 for each 16 km altitude -0.625 bar/km • Deviation from Log-Linearity is due to temperature gradients within layers • At Jet airplane heights ~11 km the pressure 618 mb

32. Atmospheric Thermal LayeringTroposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere • Earth’s surface & Stratopause are warmest • The Tropopause and Mesopause are coldest

33. Atmospheric Thermal Layering • Exosphere: gas rarely collides, can escape to space • Thermosphere: (85 to 120 - 500 km) > Δ~1.3°/km • Mesopause = minimum in thermal profile ~ -95°C • Mesosphere: (50 to 60 – 85 to 120 km) Δ-2.3°/km • Stratopause = maximum in thermal profile ~ 0°C • Stratosphere: (8 to 15 – 50 to 60 km), Δ~1.4°/km • Tropopause = minimum in thermal profile ~ -65°C • Troposphere: (0- 8 or 15 km), densest, warmest, lowest layer, thick in Tropics, thin at Poles, Δ-6°/km • Clouds, Rain, Snow; well mixed by convection • Earth & Ocean surface is base of Troposphere

34. Modes of Heat Transport & Storage • How is each one of these important in the Atmosphere and at Earth’s Surface? • Where and when is each of these important?

35. Heat Storage and Transfer • Sensible Heat cal/g°C is proportional to density • You can stand hot or cold air better than water of same T • Latent Heat  depends on condensable H2O • Radiation = emission of photons by excited electons • Convection = Heat, Mass & Momentum transfer in a fluid, via fluid motion w/ density currents/gradients • Conduction = Heat transfer by direct contact of molecules (significant only in solids, not fluid or gas). Hot rocks, sand, hot asphalt, hot tin roof

36. Heat Storage and Transfer • Sensible Heat You can stand hot or cold air better than water of same T, more mass or density, more heat capacity • Latent Heat  Evaporated H2O carries heat to atmosphere, condensed/crystallized H2O leaves heat • Radiation = The hotter the atmosphere, the more radiation to the air, ground and space • Convection = Heating unevenly or from below in gravity field drives convection

37. Heat Storage & Transfer: Troposphere • Earth & Ocean are heated ~ equally by sun’s radiation • The Earth’s surface re-radiates in IR • This IR and that of the Sun, heats GHG’s in the Troposphere or is reflected downwards by clouds, especially near the Earth’s surface unstable lower density air rises & convects, thus we get weather • Troposphere re-radiates IR up into less dense atmosphere layers where it can be lost to space • There is also sensible, latent and convected heat

38. Most of the O3Ozone is in the Stratosphere • < 5ppm H2O vapour, usually no clouds, stratified Exception is Antarctic Winter, thin Stratospheric Clouds

39. Why is there such a wavy T° Profile Earth’s surface heats lower Troposphere which convects O3 in Stratosphere is heated above by UV, stable stratification O2 absorbs short wave UV in Thermosphere for uppermost atmospheric heating

40. Water’s Big Dipole MomentMakes it rotate when it absorbs IR • IR λ > 12 μm is virtually all absorbed by water’s rotation band • CO2 has 2 perpendicular π bonds which also absorb

41. Molecular Absorption Spectrum: GHG’s • Molecules can: rotate, or vibrate atoms changing bond lengths and bend changing dipole moments • CO2 at λ > 15 μm is a bending mode for O=C=O

42. CO2’s bending mode of vibration • Alternating planes of π bonds C=O and lone pairs on end oxygens experience polarizations & bending

43. Other Greenhouse GasesReduce Outgoing IR • N2O Nitrous Oxide - several bands between 530-760/cm & between 1585-4000/cm • O3 Ozone – 9.6 μm in window between H20 & CO2 • CH4 Methane = 37x the value of 1 CO2 for GHG, many absorption bands in 1.16 μm region • Freons – CHClF2 , CCl2F2 , substituted lopsided polar methanes absorb in 8-12 μm window! More GHC power than a CO2 molecule

44. So Wazzup with N2 & O2 ? • N2 & O2 are highly symmetric w/ short strong bonds • They absorb in UV & don’t affect IR heating

45. Clouds Have Variable Effects on IR • Clouds & lower concentration aerosols block heat • Different types: Stratus, Cumulus, Cirrus • Can raise albedo blocking Sun or hold heat in

46. Low Level Stratus are Water Droplets

47. High Level Cirrus are Ice Crystals

48. Tall Cumulonimbus have all 3 Phases • Vertical Convection, Thunderstorms • Water-Ice (sleet/hail)-Steam

49. Radiation Flux versus Cloud Type • Cirrus are high thin, pass more light, lower IR flux • Stratus-Cumulus: low dense, reflect more, high IR

50. General Circulation Model  Climate • OK, so quantify this, match it to the Earth System • Now build a Computer model-change it-see an effect, conclude, change something else, map it out