1. The Greenhouse Effect & Global Warming The earth’s energy balance & radiation

2. Objectives Understand and apply the blackbody radiation law; Understand the meaning of the term emissivity;

3. Use the Phet applet to answer the following questions & lab activity. https://phet.colorado.edu/en/simulation/blac kbody-spectrum Describe what happens to the blackbody spectrum as you increase the temperature. What happens to the shape of the curve and the peak of this curve? What happens to the blackbody spectrum as you decrease the temperature? Set the temperature to that of a light bulb (around 3000 K). Based on this information, do light bulbs seem efficient? Why do light bulbs get hot? Imagine that you see 2 hot, glowing objects--one is glowing orange and the other is glowing blue. Which one is hotter?

4. The Black Body Law

5. The Black Body Emissivity = 1 A ‘perfect’ emitter Good real approximation: charcoal, soda can opening Black, dull surface e closer to 1 Light shiny surface e closer to 0 SurfaceEmissivity Black body1 Ocean water0.8 Ice0.1 Dry land0.7 Land with vegetation 0.6

6. The Black Body

7. Surfaces that are black and dull are also good absorbers of radiation (wear dark colors when cold). Light colored surfaces are good reflectors of radiation (wear light colors when hot).

8. Black Body Radiation The energy radiated by a body is distributed over an infinite range of wavelengths, however, most of the energy is radiated at a specific wavelength determined by the temperature of the body – the higher the temperature the shorter the wavelength. Room temp (20°C, 293 K) – infrared – hence the “heat” association.

9. Black Body Radiation

10. Example: By what factor does the power emitted by a body increase when the temperature is increased from 100°C to 200°C?

11. Black Body Radiation Example: The emissivity of the naked human body may be estimated to be 0.90. Assuming a body temperature of 37°C and a surface area of 1.60 m2, calculate the amount of energy lost by the body when exposed to a temperature of 0.0°C for 30 mins.

12. Assignment 1-3

13. Objectives Understand the meaning of the term albedo; Work with a simple energy balance equation;

14. Solar Radiation The sun may be considered to radiate as a perfect emitter (i.e. as a black body). The sun emits a total power of P=3.9x10 26 W. The average earth-sun distance is d=1.5x10 11 m. So, at the distance of the Earth, we may imagine that the power radiated by the sun is distributed uniformly on the surface of a sphere centered at the sun of radius d.

15. Solar Radiation

16. Albedo

17. Snow has a high albedo (0.85) indicating that snow reflects most of the radiation incident on it, whereas charcoal has an albedo of only 0.04, meaning that it reflects very little of the light incident on it. The Earth as a whole has an average global albedo of about 0.3 and varies based on: Time of year (many/few clouds) Latitude (how much snow/ice) Desert land (high albedo 0.3-0.4) Forests or water (low albedo 0.1) Etc.

18. Albedo

19. Energy Balance

20. Example

21. a)Write down an equation expressing the fact that the power received by the earth equals the power radiated by the earth into space (an energy balance equation) b)Solve the equation to calculate the constant earth temperature c)Comment on your answer.

22. Example

24. Energy Balance Another drawback of the simple model presented above is that the model is essentially a zero-dimensional model. The earth is treated as a point without interactions between the surface and the atmosphere. (Latent heat flows, thermal energy flow in oceans through currents, thermal energy transfer between the surface and the atmosphere are all ignored) Realistic models must take all these factors and many others into account, and so are very complex.

25. Assignment 4, 5, 6, 8

26. Objectives Engage: Watch this videoWatch this video Explore: Complete this activityComplete this activity Understand the meaning of the term greenhouse effect; Name the main greenhouse gases and their natural & anthropogenic sources & sinks; Understand the molecular mechanism for infrared radiation absorption; Understand the definition of surface heat capacity and apply it in simple situations;

27. The greenhouse effect This effect applies to any planet with an atmosphere. Earth assumed here. Most solar radiation in visible region (w/ small amounts in UV and IR). About 30 % reflected back into space, rest warms surface & atmosphere. Earths avg surface temperature = 288 K (Earth radiates in IR) IR radiation is strongly absorbed by various gases in the atmosphere – greenhouse gases

28. The greenhouse effect Greenhouse gases re-radiate the absorbed IR radiation in all directions -> some reabsorbed by earth’s surface (additional warming), would otherwise be lost in space Without this greenhouse effect, the earth’s temperature would be 32K lower. No atmosphere – no greenhouse effect

29. The greenhouse effect

30. The greenhouse effect may be described as the warming of the earth caused by infrared radiation emitted by the earth’s surface, which is then absorbed by various gases in the earth’s atmosphere and then partly re-radiated back toward the surface. The gases primarily responsible for this absorption (the greenhouse gases) are water vapor, carbon dioxide, methane, and nitrous oxide.

31. The greenhouse effect

32. MechanismIntensity IN (arbitrary units) Radiation from sun100 Total for entire earth100 MechanismIntensity OUT (arbitrary units) Reflected from surface5 Reflected from atmosphere25 Radiation from clouds and atmosphere 65 Radiation from surface with no atmospheric absorption (the IR ‘window’) 5 Total for entire earth100

33. The greenhouse effect MechanismIntensity IN (arbitrary units) Transmitted to surface from sun30 Absorbed IR radiation re- radiated back to Earth (greenhouse effect) 96 Total for earth’s surface146 MechanismIntensity OUT (arbitrary units) Reflected from surface5 Convection & evaporation30 IR radiation from surface106 Radiation from surface with no atmospheric absorption (the IR ‘window’) 5 Total for earth’s surface146

34. The greenhouse effect

36. The Greenhouse effect The radiation incident on the earth is mainly visible light. Photons of visible light, unlike photons of IR radiation are not absorbed by the gases of the atmosphere The incident radiation passes through the atmosphere and arrives at earth’s surface (having had about 25% of the radiation reflected back into space from the upper atmosphere).

37. The greenhouse effect – sources & sinks Sources: Carbon dioxide (CO 2 ) methane (CH 4 ) water vapor (H 2 O) nitrous oxide (N 2 O) chlorofluorocarbons (cfcs) Sinks: CO 2 absorbed by plants during photosynthesis methane destroyed in lower atmosphere by chemical rxns involving free hydroxyl radicals (- OH) nitrous oxide destroyed in atmosphere by photochemical rxns Natural & anthropogenic (man-made) origins

38. The greenhouse effect Greenhouse Gas Natural SourcesAnthropogenic Sources H2OH2OEvaporation of water from oceans, rivers, & lakes CO 2 Forest fires, volcanic eruptions, evaporation of water from oceans Burning fossil fuels in power plants and cars, burning forests CH 4 Wetlands, oceans, lakes & rivers Flooded rice fields, farm animals, termites, processing of coal, natural gas, and oil, and burning biomass N20N20Forests, oceans, soil & grasslands Burning fossil fuels, manufacture of cement, fertilizers, deforestation (reduction of nitrogen fixation in plants)

39. Mechanism of photon absorption Consider a molecule of carbon dioxide. Remember energy is quantized in electrons in atoms. The same principle of quantized energy states applies to molecules due to their vibrational & rotational motion.

40. Mechanism of photon absorption The big difference between the two kinds over energy level (vibrational/rotational vs atomic) is that the difference in energy levels is approximately the same as the energies of infrared photons (less than atomic).

41. Mechanism of photon absorption This means IR photons travelling through these gases will be absorbed (exciting the molecules to a higher energy level), then re-emitted as the molecule transitions back to a lower energy level. Re-emission back to earth or to space.

42. Mechanism of photon absorption

44. Transmittance curves As IR radiation passes through the atmosphere, some of it is absorbed so that by the time it hits the surface, it’s intensity will be less than the incident intensity. We may then make a transmittance curve that shows the variation with wavelength of the percentage of radiation that actually gets through the gas.

45. Transmittance curves This figure shows the theoretical blackbody spectrum of the sun and the actual spectrum due to absorption by gases in the atmosphere. This figure shows a realistic transmittance curve for earth’s atmosphere at sea level for IR radiation.

46. Surface heat capacity

47. Surface heat capacity - Example

48. Surface heat capacity

49. Example Radiation of intensity 340 W m -2 is incident on the surface of a lake of surface heat capacity C s = 4.2 x 10 8 J m -2 K -1. Calculate the time t requires to increase the temperature by 2.0 K. Comment on your answer.

50. Surface heat capacity

51. Assignment 9 & 11

52. Objectives State the evidence linking global warming to the increased concentrations of greenhouse gases in the atmosphere; Discuss the expected trends on climate caused by changes in various factors and appreciate that these are interrelated; State possible solutions to the enhanced greenhouse effect and international efforts to counter global warming.

53. Global Warming The greenhouse effect keeps Earth’s temperature at 288K, making life as we know it on earth possible. Human activity has caused the concentration of greenhouse gases in the atmosphere to increase, leading to additional warming. The variation of the deviations of the Earth’s average temperature from the expected long- term average since 1880. The deviations are positive and increasing.

54. Global Warming Variation with time of the concentrations of the main greenhouse gases over geological, recent, and present time periods. All increasing. CO 2 almost double pre- industrial.

55. Global Warming The previous 2 figures on global temperature and greenhouse gas concentrations are strong evidence of a connection. Criticism: not long enough time span Counter: ice cores in Antarctica & Greenland – analyze very old ice core samples gives info about gas concentrations & atmospheric temp & time of freezing. Results – very close link between global warming & greenhouse gases.

56. Global Warming: Antarctic Ice Cores

57. Extracted from 3600 m deep over (frozen) lake Vostok in East Antarctica in 1998 have been thoroughly analyzed to reveal a connection btwn temp changes & changes in concentrations of CO 2 & CH 4. Can give detailed accounts of global climate over 42,000 years!

58. Global Warming Variation with time of temperature & CO 2 concentration over the last 400,000 yrs.

59. Global Warming: ? That need ! Best estimate for temperature increase over a given time period? Effects of a higher temperature on the amount of rainfall? How much ice will melt? What will be the rise in sea level? Will there be areas of extra dryness and drought and, if so, where will they be? Will the temperature of the oceans be affected and, if so, by how much? Will there be periods of extreme climate variability? Will the frequency & intensity of tropical storms increase? What is the effect of sulfate aerosols in the atmosphere? Do they offset global warming? What are the feedback mechanisms affecting global climate? Can the observed temperature increase be blamed on greenhouse gases exclusively? Can the process of global warming be reversed even if present emissions are drastically reduced? Ecological implications of the expected changes in the habitat? Effects on agriculture? More diseases? Social & economic effects?

60. Global Warming: Other theories Increased solar activity? General consensus: GW patterns not consistent w/ changes in solar activity. Increased concentrations of greenhouse gases due to volcanic activity& changes in Earth’s orbit around the sun. Changes in eccentricity (how oval/circular) & tilt causing variations in received energy Occur over huge timescales (20,000 – 100,000 yrs) Probably not relevant for the climate changes of the last 200 yrs.

61. Global Warming: Sea level Sea level always varies Atmospheric pressure Plate tectonics Wind Tides Flow of large rivers Changes in salinity Temp determines how much ice melts/water freezes Ice age (18,000 ya) – 100 m lower than present Changes in sea level affect the amount of water that can evaporate and the amount of thermal energy that can be exchanged with the atmosphere. Affect ocean currents – transfer thermal energy from warm tropics to colder regions.

62. Sea level: melting of ice Melting a mass m of ice at 0°C requires thermal energy Q = mL, where L is the specific latent heat of fusion of ice -> removes energy from surroundings (cooling) Land ice: increases sea level when melted Sea ice: does not change sea level (Archimedes principle – weight of ice = weight of displaced water)

63. Sea level: estimating sea level changes

64. Sea level: estimating sea level changes EXAMPLE The area of the oceans of the Earth is about 3.6x10 8 km 2 and the average depth of water is about 3.7 km. using a coefficient of volume expansion of water of 2x10 -4 K -1, estimate the expected rise in sea level after a temperature increase of 2 K. Comment on your answer.

65. Effects of global warming on climate Higher than average earth temp implies rise in sea level Changes albedo – more water, less dry land

66. Effects of global warming: EXAMPLE About 50% of the area of a certain large region of the earth’s surface was covered by water. As a result of ice melting, 60% of this region is now covered by water. Estimate the change in the albedo of the region. Take the albedo of sea water to be α s =0.20 and that of land to be α l =0.40.

67. Effects of global warming on climate Expected changes in temp due to change in albedo b/c of more water covering land are actually small More significant – more water + higher temp = increased rate of evaporation = more water vapor in atmosphere. Cools earth’s surface More cloud cover More precipitation (not necessarily in region of interest) CO2 solubility in oceans decreases – more in atmosphere

68. Example Large areas of rainforests are being destroyed by cutting down (and burning) trees. Discuss the possible effects of this on the energy balance of the region.

69. Deforestation Rainforests must be preserved to maintain the existing habitat & prevent extinction of many plant & animal species Effect on climate uncertain b/c rainforests do produce methane & contribute to increased concentrations of greenhouse gases Absorb carbon dioxide but returned to atmosphere when trees die & decompose

70. Measures to reduce global warming Using fuel-efficient cars & further developing hybrid cars Increase efficiency of coal-burning power plants Replacing coal-burning power plants w/natural gas fired power plants Consider methods of capturing & storing carbon dioxide produced in power plants (CCS) Increase in wind & solar power production Consider nuclear power Being energy conscious w/ buildings, appliances, transportation, industrial processes & entertainment Stopping deforestation

71. The Kyoto Protocol & the IPCC 1997 in Kyoto, Japan – industrial nations agreed to reduce their emissions of greenhouse gases by 5.2% from 1990 levels over the period 2008- 2012 Allowed mechanisms for developed nations to use projects aimed at reducing emissions in developing nations as part of their own reduction targets Endorsed by 160 countries – legally binding at 55 – not signed by US or Australia

72. The Kyoto Protocol & the IPCC Kyoto protocol – mandatory limits on greenhouse gas emissions 2005: Asia-Pacific Partnership on Clean Development and Climate (APPCDC or AP6) – voluntary reductions Signed by US, Australia, India, the People’s Republic of China, Japan & South Korea Agree to cooperate in reducing emissions Criticized as worthless b/c reductions are voluntary Defended b/sc it includes major GH gas producers not bound by Kyoto protocol.

73. The Kyoto Protocol & the IPCC Intergovernmental Panel on Climate Change (IPCC) - Major, detailed, comprehensive, scientifically impartial analysis of global climate Created by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in 1988. Conducts no research of its own, but reports on technical, scientific, and socio-economic aspects of climate change using assessments of existing published scientific material. Four reports (1990, 1997, 2001, 2007) – instrumental in providing accurate analysis of the global situation.

74. Assignment 23-26 & 28-31