1. GLOBAL ENERGY BUDGET The Greenhouse Effect

2. Earth’ Surface Temperature Amount of incident sunlight Reflectivity of planet Greenhouse Effect – Absorb outgoing radiation, reradiate back to surface Clouds Feedback loops – Atmospheric water vapor – Extent of snow and ice cover

3. The “Goldilocks Problem” Venus – 460  C (860  F)- TOO HOT Earth – 15  C (59  F)- JUST RIGHT Mars – -55  C (-67  F)- TOO COLD

4. The “Goldilocks Problem” Temperature depends on – Distance from the Sun AND – Greenhouse effect of its atmosphere Without Greenhouse effect – Earth’ surface temperature 0  C (32  F)

5. Global Energy Balance - Overview How the Greenhouse Effect works Nature of EMR – Why does the Sun emit visible light? – Why does Earth emit infrared light? Energy Balance – incoming & outgoing – Calculate magnitude of greenhouse effect Effect of atmospheric gases & clouds on energy Why are greenhouse gases greenhouse gases?

6. Global Energy Balance - Overview Understand real climate feedback mechanisms – estimate the climate changes that occur Current Future

7. ELECTROMAGNETIC RADIATION 50% of Sun’s energy in the form of visible light

8. EMR Self-propagating electric and magnetic wave – similar to a wave that moves on the surface of a pond Moves at a fixed speed – 3.00 x 10 8 m/s

9. ELECTROMAGNETIC WAVE 3 characteristics – speed – wavelength – frequency = c or = c / The longer the wavelength, the lower the frequency The shorter the wavelength, the higher the frequency

10. PHOTONS EMR behaves as both a wave and a particle – General characteristic of matter Photon – a single particle or pulse of EMR – Smallest amount of energy able to be transported by an electromagnetic wave of a given frequency – Energy (E) of a photon is proportional to frequency E = h = hc / where h is Plank’s constant and h =6.626 x 10 -34 J-s (joule-seconds)

11. PLANK’S CONSTANT E = h = hc / High-frequency (short-wavelength) photons have high energy – Break molecules apart, cause chemical reactions Low-frequency (long-wavelength) photons have low energy – Cause molecules to rotate or vibrate more

12. ELECTROMAGNETIC SPECTRUM

15. Infrared (IR) Radiation – 40% of Sun’s energy – 0.7-1000  m (1  m = 1 x 10 -6 m) Visible Radiation / Visible Light / Visible Spectrum – 50% of Sun’s energy – 400-700 nm (1nm = 1 x 10 -9 m) red longest, violet shortest Ultraviolet (UV) Radiation – 10% of Sun’s energy – 400-10 nm X-Rays & Gamma Rays – affect upper atmosphere chemistry

16. EMR & CLIMATE Visible & Infrared most important – Why? Sun? Earth? Ultraviolet – Drives atmospheric chemistry – Lethal to most life forms

17. FLUX Flux (F) – the amount of energy (or number of photons) in an electromagnetic wave that passes  through a unit surface are per unit time

18. Flux & Earth’s Climate

19. The Inverse-Square Law If we double the distance from the source to the observer, the intensity of the radiation decreases by a factor of (½) 2 or ¼

20. The Inverse-Square Law S = S 0 (r 0 / r) 2 where S = solar flux r = distance from source S 0 = flux at some reference distance r 0

21. Solar Flux The solar flux at Earth’s orbit = 1366 W/m 2 1AU = 149,600,000 km (average distance from Earth to Sun) Venus and Mars orbit the Sun at average distances of 0.72 and 1.52 AU, respectively. What is the solar flux at each planet?

22. The Inverse-Square Law Small changes in earth’s orbital shape + inverse-square law + solar flux CAN CAUSE LARGE CHANGES IN EARTH’S CLIMATE

23. TEMPERATURE SCALES Temperature – a measure of the internal heat energy of a substance – Determined by the average rate of motion of individual molecules in that substance – The faster the molecules move, the higher the temperature

24. TEMPERATURE SCALES Celsius - °C – boiling and freezing points of water Fahrenheit - °F – mixture of snow & salt and human body Kelvin (absolute) – K – The heat energy of a substance relative to the energy it would have at absolute zero Absolute zero – molecules at lowest possible energy state

25. TEMPERATURE SCALES

26. TEMPERATURE CONVERSIONS T (°C) = [T(°F) – 32] / 1.8 T(°F) = [T (°C) x 1.8] + 32.

27. TEMPERATURE CONVERSIONS Convert the following:  98.6 °F to °C  20 °C to °F  90 °C to °F  100 °F to °C

28. ABSOLUTE TEMPERATURE T(K) = T (°C) + 273.15 0 K (absolute zero) = -273.15 °C Convert the following:  98.6 °F to K  20 °C to K  90 °C to K  100 °F to K

29. BLACKBODY RADIATION Blackbody – something that emits/absorbs EMR with 100% efficiency at all wavelengths

30. BLACKBODY RADIATION Radiation emitted by a blackbody Characteristic wavelength distribution that depends on the absolute temperature of the body Plank Function – relates the intensity of the radiation from a blackbody to its wavelength or frequency

31. BLACKBODY RADIATION CURVE

32. Blackbody Simulation

33. WIEN’S LAW The flux of radiation emitted by a blackbody reaches its peak value at wavelength λ max, which depends on the body’s absolute temperature – Hotter bodies emit radiation at shorter wavelengths λ max ≈ 2898, where T is temperature in kelvins T λ max is the max radiation flux in μm

34. WIEN’S LAW

35. Sun’s radiation peaks in the visible part of EMR 2898 / 5780 K ≈ 0.5 μm Earth’s radiation peaks in the infrared range 2898 / 288 K ≈ 10 μm

36. WIEN’S LAW

37. ELECTROMAGNETIC SPECTRUM

38. THE STEFAN-BOLTZMANN LAW The energy flux emitted by a black body is related to the fourth power of a body’s absolute temperature F = σ T 4, where T is the temperature in kelvins and σ is a constant equal to 5.67 x 10 -8 W/m 2 /K 4 The total energy flux per unit are is proportional to the area under the blackbody radiation curve

39. THE STEFAN-BOLTZMANN LAW

40. Example a hypothetical star with a surface temperature 3x that of the Sun F sun = σ T 4 = (5.67 x 10 -8 W/m 2 /K 4 ) (5780 K) 4 = 6.3 x 10 7 W/m 2 F star = σ T 4 = (5.67 x 10 -8 W/m 2 /K 4 ) (3x5780 K) 4 = 3 4 x σ (5780 K) 4 = 81 F sun

41. THE NATURE OF EMITTED RADIATION Wien’s Law – hotter bodies emit radiation at shorter wavelengths Stefan-Boltzmann – energy flux emitted by a blackbody is proportional the fourth power of the body’s absolute temperature SO – the color of a star (wavelength) indicates temperature, temperature indicates energy flux

42. EARTH’S ENERGY BALANCE The amount of energy emitted by Earth must equal to amount of energy absorbed – The average surface temperature is getting warmer – Imbalance caused by increase in CO 2 and other greenhouse gases OR – Imbalance caused by natural fluctuations in the climate system

43. EARTH’S SURFACE TEMPERATURE Depends on: 1.The solar flux (S) available at the distance of Earth’s orbit (30% of incident energy reflected) 2.Earth’s reflectivity or albedo (A) – the fraction of the total incident sunlight that is reflected from the planet as a whole 3.The amount of warming provided by the atmosphere (magnitude of the greenhouse effect)

45. PLANETARY ENERGY BALANCE energy emitted by Earth = energy absorbed by Earth

46. Effective Radiating Temperature (T e ) The temperature that a true blackbody would need to radiate the same amount of energy that Earth radiates Use Stefan-Boltzmann law to calculate energy emitted by Earth Energy emitted = σ T e 4 x 4  R 2

47. Energy Absorbed by Earth energy absorbed = energy intercepted – energy reflected Energy Intercepted (Incident Energy)- the product of Earth’s projected area and the solar flux =  R 2 S Energy Reflected - the product of Earth’s incident energy and albedo =  R 2 S x A

48. ENERGY ABSORBED energy absorbed = energy intercepted – energy reflected energy absorbed =  R 2 S -  R 2 S x A =  R 2 S (1 – A)

49. PLANETARY ENERGY BALANCE energy emitted by Earth = energy absorbed by Earth σ T e 4 x 4  R 2 =  R 2 S (1 – A) σ T e 4 = (S/4) (1 – A) where σ is 5.67 x 10 -8 W/m 2 /K 4, T is temperature in kelvin, S is solar flux, and A is albedo The planetary energy balance between outgoing infrared energy and incoming solar energy

50. MAGNITUDE OF THE GREENHOUSE EFFECT Effective Radiating Temperature – Atmospheric temperature at which most outgoing infrared radiation derives – Average temperature that Earth’s surface would reach with no atmosphere – Using planetary energy balance equation - Earth’ s effective radiating temperature = -18  C or 0  F

51. MAGNITUDE OF THE GREENHOUSE EFFECT Actual surface temperature or Earth = 15  C Difference between effective and actual caused by greenhouse effect ∆ T g = T s – T e For Earth ∆ T g = 15  C –(–18  C) = 33  C By absorbing part of the infrared radiation radiated upward from the surface and reemitting it in both upward and downward directions, the atmosphere allows the surface to be warmer that it would be if no atmosphere were present

52. THE GOLDLOCKS PROBLEM A planet’s greenhouse effect is at least as important in determining a planet’s surface temperature as is its distance from the Sun For homework – Critical Thinking #2

53. FAINT YOUNG SUN PARADOX Solar luminosity, and flux (S), is estimated to be 30% lower early in Earth’s history – Earth’s average surface temperature would have been below freezing (if albedo & greenhouse effect unchanged) – The early Earth had liquid water and life HOMEWORK – Critical Thinking #5

54. ATMOSPHERIC COMPOSITON

55. ABUNDANT NON-GREENHOUSE GASES Nitrogen – Inert – As N important role in biological cycles Oxygen – Reactive – Respiration Argon – Inert – Byproduct of potassium decay

58. ATMOSPHERIC PRESSURE Influences climate & radiation budget Force per unit area Pressure at Sea Level – 1 atmosphere (1 atm) – 14.7 lbs/in 2 – 1.013 bar – 1013 millibars

59. ATMOSPHERIC PRESSURE Barometric Law – the pressure decreases exponentially with altitude – a factor of 10 for every 16 km increase in altitude Pressure decreases faster with increasing altitude when the air is colder

60. ATMOSPHERIC TEMPERATURE THERMOSPHERE MESOSPHERE STRATOSPHERE TROPOSPHERE

61. Lowest layer Temperature decreases rapidly with altitude 0 - ±15 km Important in climatic studies Where weather occurs Well mixed by convection

63. METHODS OF HEAT TRANSFER Convection – transfer of heat energy by moving fluids – Generated when fluid heated from below Conduction – transfer of heat energy by direct contact between molecules Radiation – transfer of heat energy by electromagnetic waves emitted from a body

64. METHODS OF HEAT TRANSFER

65. TROPOSPHERE Incoming solar energy absorbed by surface (land and water) Energy reradiated as IR radiation IR radiation absorbed by greenhouse gases and clouds Energy transported by convection instead Where atmosphere more transparent to IR, the energy radiated from Earth

66. LATENT HEAT Heat energy absorbed or released by the transition form one phase to another – solid, liquid, gas

67. STRATOSPHERE ±15 – 50 km Temperature increases with altitude Pressure much lower Contains most of Earth’s ozone Very dry - <5 ppm water vapor Non-convective, less well mixed

68. MESOSPHERE 50 – 90 km Temperature decreases

69. THERMOSPHERE 90+ km Temperature increases Aurora Borealis

70. EXOSPHERE Outermost fringe of the atmosphere Infrequent molecular collisions

71. ATMOSPHERIC TEMPERATURE THERMOSPHERE MESOSPHERE STRATOSPHERE TROPOSPHERE

72. VERTICAL TEMPERATURE PROFILE Troposphere -  – Ground absorbs sunlight, heats atmosphere above Stratosphere -  – Ozone absorbs solar radiation – Maximum heating occurs at top of layer Mesosphere -  – Ozone & heating rate decline Thermosphere -  – O & N absorb shortwave UV radiation

73. WHY DO SAME GASES CONTRIBUTE TO THE GREENHOUSE EFFECT & OTHERS DO NOT? Gas molecules absorb/emit radiation in two ways 1.Changing the rate at which the molecule rotates 2.Changing the amplitude with which a molecule vibrates

74. CHANGE IN ROTATION Molecules rotate at discreet frequencies If the frequency of the incoming wave is just right, the molecule absorbs the photon The molecule emits the photon when the rotation slows down Depends on structure of molecule

76. H 2 O ROTATION BAND Strong absorption feature of Earth’s atmosphere – H 2 O molecule absorbs IR radiation of 12μm or longer – Virtually 100% of infrared radiation > 12μm absorbed

77. H 2 O ROTATION BAND

78. CHANGE IN AMPLITUDE OF VIBRATION If the frequency at which the molecule vibrates matches frequency of incoming wave, molecule absorbs photon and vibrates more Bending mode of CO 2 allows molecule to absorb IR radiation about 15 μm λ

79. CHANGE IN AMPLITUDE OF VIBRATION

80. 15 μm CO 2 BAND Strong absorption feature of Earth’s atmosphere Important to climate because it occurs near peak of Earth’s outgoing radiation – very little of Earth’s outgoing radiation can escape because it is absorbed by CO 2

81. OTHER GREENHOUSE GASES CH 4, N 2 O, O 3 and freons – More effect on outgoing radiation than low concentrations would suggest – Absorb at different wavelengths than H 2 O & CO 2

82. O 2 & N 2 Poor absorbers of IR radiation Perfectly symmetrical molecules Electromagnetic fields unable to interact with symmetrical molecules

83. EFFFECT OF CLOUD ON RADIATION BUDGET Quantification of effect difficult Many types of clouds – Cumulus – water – Cumulonimbus – water – Stratus – water – Cirrus – ice

84. CLOUD TYPES

85. CLOUD EFFECTS Day – cool Earth by reflecting sunlight back to space – Without clouds albedo would be ~0.1 – At 0.1 T e would increase 17  C Night – warm Earth – reemit outgoing IR radiation

86. CLOUD EFFECTS Stratus – low, thick – Increase albedo – Reflect incoming solar radiation – Radiate at higher temperature, and according to Stefan- Boltzmann law radiate more energy to space Cirrus – high, thin – Increase greenhouse effect – Ice crystals more transparent to incoming solar radiation – Radiate at lower temperatures and according to Stefan- Boltzmann law radiate less energy to space

87. CON TRAILS FROM JETS?

88. EARTH’S GLOBAL ENERGY BUDGET

89. PRINCIPLE OF PLANETARY ENERGY BALANCE At the top of the atmosphere, the net downward solar radiation flux (incoming minus reflected), must equal the outgoing infrared flux

90. CLIMATE MODELING Climate system complex Computer models based on data used to simulate climate systems GCM – General Circulation Model aka global climate model - include – 3-d representation of atmosphere (winds, moisture, energy) – Weather (clouds, precipitation – Require huge amounts of computer power

91. One Dimensional Climate Model Radiative-Convective Model (RCM) – Climate system approximated by averaging incoming solar and outgoing IR over Earth’s entire surface – Vertical dimension divided into layers – Temperature of each layer calculated Energy received or emitted Convection Latent heat release

92. RCMs Allow estimation of greenhouse effect magnitude – uses concentrations of greenhouse gases in atmosphere – Models accurately predict ∆T g (33  C) – Allow prediction of temperature increase due to GHG Doubling CO 2 from 300ppm to 600ppm would produce a 1.2  C increase The temperature change ∆T 0 in the absence of any climate system feed back loops

93. CLIMATE FEEDBACKS Amplify or moderate radiative effect due to GHG concentrations – Water Vapor Feedback – Snow and Ice Albedo Feedback – The IR Flux/Temperature Feedback – The Cloud Feedback (Uncertain)

94. THE WATER VAPOR FEEDBACK If Earth’s surface temperature , then water vapor  (precipitation) If water vapor , then greenhouse effect , and surface temp  If Earth’s surface temperature , then water vapor  (evaporation) If water vapor , then greenhouse effect , and surface temp 

95. THE WATER VAPOR FEEDBACK

96. Incorporated into RCM by assuming fixed relative humidity in troposphere RCM predicts equilibrium change in surface temperature for CO 2 doubling is 2X effect without water vapor

97. Mathematically Speaking... Comparing equilibrium temperature with and without water vapor feedback (from Ch 2) ∆T eq = ∆T 0 + ∆T f ∆T eq = 1.2  C+ 1.2  C  2.4  C 97

98. The Feedback Factor The ratio of the equilibrium response to forcing (the response with feedback) to the response without feedback  = temperature change with feedback = 2.4  C  2 temperature change w/out feedback 1.2  C Negative feedback loop if 0 <  < 1 Positive feedback loop if 1 <  STRONGLY POSITIVE 98

99. SNOW & ICE ALBEDO FEEDBACK Snow & ice have higher albedo than land & water Increases in snow and ice coverage should decrease surface temperature Positive feedback loop Snow & ice restricted to middle & high latitudes, 2- or 3-d models are required

100. SNOW & ICE ALBEDO FEEDBACK

101. THE IR FLUX/TEMPERATURE FEEDBACK Strong negative feedback loops Stabilizes Earth’s climate on short time scales If Earth’ surface temperature , outgoing IR flux , if outgoing flux , surface temperature would  – More energy is lost from the system System can fail if the atmosphere contains too much water vapor – Venus – runaway greenhouse

102. THE IR FLUX/TEMPERATURE FEEDBACK

103. THE CLOUD FEEDBACK (UNCERTAIN) Adds significant uncertainty to climate models – Clouds can warm or cool, depending on height – Form at some locations and not others Most current GCMs – Net positive feedback for doubled CO 2 Increase in cirrus clouds (warming) outweighs any increase in stratus clouds (cooling)