1. 1 MET 112 Global Climate Change MET 112 Global Climate Change - Lecture 3 The Earth’s Energy Balance Dr. Eugene Cordero San Jose State University Outline  Energy  Solar and terrestrial radiation  Absorption and scattering  Global energy balance

2. 2 MET 112 Global Climate Change Earth’s Energy Balance  Energy entering top of atmosphere  Energy entering the Earth’s surface

3. 3 MET 112 Global Climate Change Earth’s Energy Balance  Energy entering top of atmosphere  Energy entering the Earth’s surface = Energy leaving top of atmosphere = Energy leaving Earth’s surface

4. 4 MET 112 Global Climate Change There are three modes of energy transmission in the atmosphere.  Conduction:  Convection: the transfer of energy by mass motions within a fluid or gas, resulting in actual transport of energy.  Radiation: Energy transmission

5. 5 MET 112 Global Climate Change There are three modes of energy transmission in the atmosphere.  Conduction: the transfer of energy in a substance by means of molecular excitation without any net external motion.  Convection: the transfer of energy by mass motions within a fluid or gas, resulting in actual transport of energy.  Radiation: the propagation of electromagnetic waves through space. Energy transmission

7. 7 MET 112 Global Climate Change Convection

8. Electromagnetic radiation  Radiation is the transfer of energy by rapid oscillations of electromagnetic fields.  The most important general characteristic is its wavelength ( ), ____________________________.  Radiation travels through space at the speed of light (3 x 10 8 m s -1 ).

9. Electromagnetic radiation  Radiation is the transfer of energy by rapid oscillations of electromagnetic fields.  The most important general characteristic is its wavelength ( ), ____________________________.  Radiation travels through space at the speed of light (3 x 10 8 m s -1 ). Defined as the crest-to-crest distance

10. 10 MET 112 Global Climate Change

11. 11 MET 112 Global Climate Change Radiation  What emits radiation? –  Examples:  Radiation laws: –Warmer objects emit more _________ than cold objects. (Stefan-Boltzmann Law) –Warmer objects emit a ________proportion of their energy at short wavelengths than cold objects. (Wien’s Law)

12. 12 MET 112 Global Climate Change Radiation  What emits radiation? –All objects with a temperature greater than 0°K emit some type of radiation (energy)  Examples:  Radiation laws: –Warmer objects emit more intensely than cold objects. (Stefan-Boltzmann Law) –Warmer objects emit a higher proportion of their energy at short wavelengths than cold objects. (Wien’s Law)

13. 13 MET 112 Global Climate Change Review questions  Considering the previous discussion –Which object would emit more (intensity) radiation: Earth or Sun? –If you were examining the radiation emitted by both the Sun and Earth, which would have a longer wavelength? –What wavelength radiation are you emitting right now?

14. 14 MET 112 Global Climate Change Review questions  Considering the previous discussion –Which object would emit more (intensity) radiation: Earth or Sun? –If you were examining the radiation emitted by both the Sun and Earth, which would have a longer wavelength? –What wavelength radiation are you emitting right now? Sun Earth infrared

15. 15 MET 112 Global Climate Change Solar Radiation (Sunlight)  Sunlight is primarily made up of the following: – – – Unit: 1  m = 0.000001 m

16. 16 MET 112 Global Climate Change Solar Radiation (Sunlight)  Sunlight is primarily made up of the following: –Visible Light (44%) –Infrared Radiation (48%) –Ultraviolet Radiation (7%) Unit: 1  m = 0.000001 m

17. 17 MET 112 Global Climate Change Terrestrial or Longwave Radiation  Planets mainly emit  Radiation emitted by planets occurs mainly at wavelengths ______ than those contained in solar radiation

18. 18 MET 112 Global Climate Change Terrestrial or Longwave Radiation  Planets mainly emit infrared radiation  Radiation emitted by planets occurs mainly at wavelengths _____ than those contained in solar radiation Solar Radiation (“Shortwave”) Planetary Radiation (“Longwave”) longer

19. 19 MET 112 Global Climate Change Solar vs. Terrestrial Radiation  The sun is much hotter than planets; therefore, sunlight consists of shorter wavelengths than planetary radiation ;  Thus …

20. 20 MET 112 Global Climate Change Recap  ______________ radiation comes from the sun and is composed of both ultraviolet and visible radiation  ______________ radiation comes from the Earth and is composed of infrared radiation  Recall that everything (above a temperature of 0K) emits some type of radiation (energy) with a particular wavelength.

21. 21 MET 112 Global Climate Change Recap  ______________ radiation comes from the sun and is composed of both ultraviolet and visible radiation  ______________ radiation comes from the Earth and is composed of infrared radiation  Recall that everything (above a temperature of 0K) emits some type of radiation (energy) with a particular wavelength. Shortwave or solar Longwave or terrestrial

22. 22 MET 112 Global Climate Change Energy from the Sun  Obviously, the Sun provides the Earth with it’s energy. The question is, how much of the Sun’s energy does the Earth get?  Sun’s energy is either – –  Scattering happens by bouncing off –Particles in the atmosphere –  Absorption happens when certain gases absorb the energy –

23. 23 MET 112 Global Climate Change Energy from the Sun  Obviously, the Sun provides the Earth with it’s energy. The question is, how much of the Sun’s energy does the Earth get?  Sun’s energy is either –Scattered (reflected away) or –Absorbed  Scattering happens by bouncing off –Particles in the atmosphere –Earth’s surface  Absorption happens when certain gases absorb the energy –The reality is the only certain gases absorb certain wavelengths.

24. 24 MET 112 Global Climate Change Absorption of radiation  Absorption of shortwave radiation by atmospheric gas molecules is small; –most absorption of shortwave radiation occurs at the Earth’s surface.  Most gases do not interact strongly with longwave radiation, however –

25. 25 MET 112 Global Climate Change Absorption of radiation  Absorption of shortwave radiation by atmospheric gas molecules is fairly weak; –most absorption of shortwave radiation occurs at the Earth’s surface.  Most gases do not interact strongly with longwave radiation, however –Greenhouse gas molecules absorb certain wavelengths of longwave radiation.

27. Absorption of Radiation in the Earth’s Atmosphere

28. 28 MET 112 Global Climate Change Incoming solar radiation  Each ‘beam’ of incoming sunlight can be either: –Reflected back to space:  –Or absorbed; either by atmosphere (e.g. clouds or ozone) or Earth’s surface.

29. 29 MET 112 Global Climate Change Incoming solar radiation  Each ‘beam’ of incoming sunlight can be either: –Reflected back to space:  Clouds  Atmosphere  Surface –Or absorbed; either by atmosphere (e.g. clouds or ozone) or Earth’s surface. Albedo

30. 30 MET 112 Global Climate Change

33. Longwave radiation is emitted from surface. Some surface radiation escapes to space Most outgoing longwave is absorbed in atmosphere (by greenhouse gases) Greenhouse gases emit longwave upward and downward Some atmospheric radiation escapes to space Some atmospheric radiation is absorbed at the surface

34. 34 MET 112 Global Climate Change Greenhouse Effect Sequence of steps: 1. 2. 3. 4. 5. Result: warmer surface temperature

35. 35 MET 112 Global Climate Change Greenhouse Effect Sequence of steps: 1.Solar radiation absorbed by earth’s surface. 2.Earth gives off infrared radiation. 3.Greenhouse gases absorb some of the Earth’s infrared radiation. 4.Greenhouse gases (water and CO 2 ) give off infrared radiation in all directions. 5.Earth absorbs downward directed infrared radiation Result: warmer surface temperature

36. 36 MET 112 Global Climate Change Energy Balance  Assume that the Earth’s surface is in thermodynamic equilibrium:  Thermodynamic Equilibirum: –

37. 37 MET 112 Global Climate Change Energy Balance  Assume that the Earth’s surface is in thermodynamic equilibrium:  Thermodynamic Equilibrium: –The flow of energy away the surface equals the flow of energy toward the surface Surface Average surface temperature = 15°C

38. 38 MET 112 Global Climate Change Removal of greenhouse gases would decrease downward flow of energy; now energy away from surface is greater than energy toward surface. Sudden Removal of all Greenhouse Gases

39. 39 MET 112 Global Climate Change Removal of greenhouse gases would decrease downward flow of energy; now energy away from surface is greater than energy toward surface. Thus, average surface temperature starts to decrease. Sudden Removal of all Greenhouse Gases

40. 40 MET 112 Global Climate Change As surface cools, emission of radiation decreases until balance is restored. At this point, cooling stops Sudden Removal of all Greenhouse Gases

41. 41 MET 112 Global Climate Change As surface cools, emission of radiation decreases until balance is restored. At this point, cooling stops and equilibrium is restored. Average surface temperature = -18°C Result: A Very Cold Planet!

42. 42 MET 112 Global Climate Change Question  Start with the following diagram and assume the earth’s surface temperature is 15C and that the atmosphere has greenhouse gases.  Imagine that the concentrations of greenhouse gases were to increase by 50%. 1. Draw two more diagrams illustrating (with arrows) how the energy balance would change with the increase in greenhouse gases and explain why. 2. How would the average surface temperature change? Surface Average surface temperature = 15°C

43. 43 MET 112 Global Climate Change Earth’s Greenhouse Effect  Without the greenhouse effect, the surface temperature of Earth would be –  Greenhouse gases play an important role in shaping climate. – –

44. 44 MET 112 Global Climate Change Earth’s Greenhouse Effect  Without the greenhouse effect, the surface temperature of Earth would be –Way Cold (-18°C)  Greenhouse gases play an important role in shaping climate. –More GHGs – warmer climate –Less GHGs – cooler climate

45. 45 MET 112 Global Climate Change

46. 46 MET 112 Global Climate Change Activity 2 Greenhouse Effect Draw a diagram showing how the earth is heated by the Sun. Include arrows and/or lines to indicate the ‘Energy Balance” of the earth. Energy Balance – Energy coming in and energy going out. Clouds, and reflected energy