1. Chapter 18 section 4 How might human activities be affecting the temperature of Earth’s atmosphere? How have human activities affected the Ozone layer?

2. A. Global Warming 1. Most changes in world climates are caused by natural factors 2. Global warming is the gradual increase in the temperature of Earth’s atmosphere.

3. 3. The Greenhouse Hypothesis: -The process by which gases in Earth’s atmosphere trap this energy is called the greenhouse effect.

4. 4. greenhouse gases: -carbon dioxide, water vapor and methane

5. 5. Changing levels of carbon dioxide: -since the late 1800s, the level of carbon dioxide has increased -burning of wood and fossil fuels increase C02 in air

6. 6. Climate Variation Hypothesis: -some scientist think the increase in global warming is due to natural variations in climate -the amount of sun energy increases or decreases from year to year

7. 7. Possible Effects: a. Farmers could plant two crops a year b. some fertile fields might become “dust bowls” c. warmer ocean water could increase strength of hurricanes d. sea levels would rise

8. B. Ozone Depletion 1.Ozone filters out much of the harmful ultraviolet radiation from the sun

11. 2. Chlorofluorocarbons: -major cause of ozone depletion -were used in air conditioners, refrigerators, cleaners aerosol sprays -the chlorine in the molecule break down ozone into oxygen atoms

14. 3. Results of Ozone Depletion: -a decrease in ozone means an increase in the amount of ultraviolet radiation that reaches Earth’s surface.

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