1. Catalyst 5/4 Should developed countries bear the brunt of the responsibility for reducing CO 2 emissions because they produce more? Developed countries can more easily adapt to global warming. Should they be responsible for offering assistance to developing countries?

3. Structure of the Atmosphere Made up of several vertical layers Troposphere - bottom layer Where weather occurs Temperature decrease with elevation At the top is tropopause - acts as a lid Stratosphere - above the troposphere Stratospheric ozone layer just above the tropopause Protects again UV radiation

5. Ultraviolet Radiation and Ozone Ozone layer in the stratosphere called the ozone shield Absorbs most of the potentially hazardous ultraviolet radiation from the sun Ultraviolet radiation consists of wavelengths between 0.1 and 0.4 μm Ultraviolet A (UVA) Ultraviolet B (UVB) Ultraviolet C (UVC).

6. Ultraviolet Radiation and Ozone Ozone layer in the stratosphere called the ozone shield Absorbs most of the potentially hazardous ultraviolet radiation from the sun Ultraviolet radiation consists of wavelengths between 0.1 and 0.4 μm Ultraviolet A (UVA) Ultraviolet B (UVB) Ultraviolet C (UVC).

8. Ultraviolet Radiation and Ozone Ultraviolet C (UVC) Shortest wavelength and most energetic of the types of ultraviolet radiation Sufficient energy to break apart diatomic oxygen (O 2 ) Each of these oxygen atoms may combine with an O 2 molecule to create ozone UVC strongly absorbed in the stratosphere, and negligible amounts reach the Earth’s surface

9. Ultraviolet Radiation and Ozone Ultraviolet A (UVA) Longest wavelength Least energy of the three types of ultraviolet radiation UVA can cause some damage to living cells Not affected by stratospheric ozone, and is transmitted to the Earth’s surface

10. Ultraviolet Radiation and Ozone Ultraviolet B (UVB) Energetic and strongly absorbed by stratospheric ozone Ozone is the only known gas that absorbs UVB Depletion of ozone in the stratosphere results in an increase in the UVB that reaches the surface of the Earth

11. Ultraviolet Radiation and Ozone Approximately 99% of all ultraviolet solar radiation (all UVC and most UVB) is absorbed by the ozone layer Natural service function Protects us from the potentially harmful effects of ultraviolet radiation

12. Measurement of Stratospheric Ozone First measured in 1920s using Dobson ultraviolet spectrometer. Dobson unit (DU) - 1DU = 1 ppb O 3 Now have measurements from all over the world for 30 years Ground based measurements first identified ozone depletion over the Antarctic Concentrations have been decreasing since the mid- 1970s “Ozone hole”

13. Ozone Depletion: Causes Chloroflurocarbons (CFCs): Family of organic compounds made up of carbon, chlorine, and fluorine Example: Freon-12 (CCl 2 F 2 ) Gaseous CFCs deplete the ozone Discovered through research done by Rowland and Molina

14. Ozone Depletion: Effects Human Health Sunburns More eye cataracts and skin cancer Immune system suppression Food and Forests Reduced yields for some crops Reduced seafood supplies from reduced phytoplankton Decreased forest productivity for UV-sensitive tree species Climate Change CFCs act as a greenhouse gases

15. Ozone Depletion: Effects Wildlife Increased eye cataracts in some species Decreased populations of aquatic species sensitive to UV radiation Reduced populations of surface phytoplankton Disrupted aquatic food webs from reduced phytoplankton Air Pollution and Materials Increased acid deposition Increased photochemical smog Degradation of outdoor paints and plastics

16. Think Box Which of these effects do you think are most threatening? Why?

17. Ozone Depletion: Solutions Montreal Protocol (1987) 36 nations Goal: Cut CFC emissions by about 35% between 1989 and 2000. Copenhagen Protocol (1992) An amendment that accelerated the phase-out of key ozone-depleting chemicals These agreements have been signed by all 196 of the world’s countries Ozone levels should return to 1980 levels by 2036 (18 years earlier than projected)

18. Ozone Depletion: Solutions Prevention to solve an environmental issue First time nations and governments worked together to solve a global issue Convincing and dramatic scientific evidence CFCs produced by a small number of international companies Private sector forced to find more profitable substitute chemicals

19. Ozone Depletion: Solutions CFC substitutes Hydroflourocarbons (HFCs) Acts as a greenhouse gas U.S. government asked the UN to enact mandatory reductions in HFC emissions through the Montreal Protocol Would like to do the same for N2O

20. Think Box What lessons do you think we can learn from ozone depletion in trying to solve the problem with global warming?

21. Objectives for practice 1. Describe the evidence for ozone depletion 2. Discuss the process that leads to ozone depletion 3. Identify and describe the effects of ozone depletion 4. Construct strategies to deal with ozone depletion