1. Section 2 The Ozone Shield

2. Ozone Layer Ozone is the chemical compound O3
Large concentration is found in the stratosphere
Ozone Layer absorbs most UV radiation coming from the sun
UV radiation can damage organisms cells
UV-B- most absorbed by ozone

3. Ozone Depletion and CFC’s
CFC’s (chloroflourocarbons)uses:
coolants in refrigerators and air
conditioners
making plastic foam
propellant in spray cans
CFC’s are stable near Earth but break down in the stratosphere due to UV radiation. Once they are broken apart, they destroy the protective ozone.

4. Chemicals That Cause Ozone Depletion
Each CFC molecule contains from one to four chlorine atoms, and scientists have estimated that a single chlorine atom in the CFC structure can destroy 100,000 ozone molecule.

5. Ozone Hole over Antarctica
It takes years for CFCs to reach the stratosphere from the Earth's surface

7. Ozone Layer
First noticed in 1970 from satellite photos over the South Pole
What Causes it?
During the cold polar winters, dry stratospheric air over the pole is isolated.
Air becomes so cold that it condenses and forms clouds
(Polar Stratospheric clouds: high-altitude clouds made of water and nitric acid at - 80° C)
Chlorine from CFCs builds up on the surface of the clouds
When the pole begins to warm the chlorine goes back to depleting ozone.

8. Effects of Ozone Thinning
Damages DNA in humans and other animals, such as amphibians.
Increases in cases of skin cancer.
Interferes with photosynthesis in plants and algae. This may lower crop yields and disrupt the food chain.

9. Protecting the Ozone Layer
1987- Montreal Protocol: Group of nations met and agreed to sharply limit production of CFC’s.

10. Protecting the Ozone Layer
Many nations banned the use of CFCs in 1992 (US stopped production by 2000)
Why are CFCs still a problem?
CFCs molecules remain in the stratosphere for 60 – 120 years

11. Section 3 Global Warming

12. What is climate change?
Global climate change = describes trends and variations in Earth’s climate
Temperature, precipitation, storm frequency
Global warming = an increase in Earth’s average temperature
Earth’s climate has varied naturally through time
The rapid climatic changes taking place now are due to human activity: fossil fuels, combustion, and deforestation

13. Greenhouse Effect The earth is like a greenhouse
The atmosphere acts like the glass – which lets the sun’s rays pass through.
The earth absorbs this as heat energy and keeps it in, only letting a little heat out
The gases in the atmosphere absorb the radiation keeping it from escaping out to space
This absorption of radiation by gases is called the greenhouse effect

14. The Greenhouse Effect

15. The Greenhouse Effect Greenhouse gases (absorb and radiate heat)
water vapor
carbon dioxide
CFC’s
methane
nitrous oxide
Trap heat near the Earth’s surface.

16. General increase because of burning fossil fuels(not just in winter)
Greenhouse gases
Since 1958 (in Hawaii) CO2 levels have been measured – reflective of the entire earth (the gases have traveled across the entire Pacific Ocean)
Levels are higher in the winter: fewer leaves on the trees (dying grasses and leaves release carbon)
General increase because of burning fossil fuels(not just in winter)

17. Methane Greenhouse gases
Methane (CH4) is the second most prevalent greenhouse gas emitted in the United States from human activities.
Accounted for about 9% of all U.S. greenhouse gas emissions from human activities.
Over 60% of total CH4 emissions come from human activities.
Methane is emitted by natural sources such as wetlands, as well as human activities such as leakage from natural gas systems and the raising of livestock.
U.S. Methane Emissions, By Source

18. Global Warming Where does all the CO2 come from?
Power plants and cars that burn fossil fuels and deforestation
Why be concerned?
CO2 is a greenhouse gas
Scientists believe the increase will warm earth more than normal
Direct correlation between CO2 levels and global warming

19. CO2 in the Atmosphere
Amounts of carbon dioxide in the air vary with the seasons. Levels fall in the summer when more photosynthesis is occurring. They increase in winter with plant decay.
Levels have increased 20% in <50 years.
Increased levels are due to burning of fossil fuels.

21. Global Warming
Because temperatures are rising at a similar rate to the increase in greenhouse gases, scientists have hypothesized that that the temperature increases are caused by the gases

22. Consequences of Warmer Earth
Plants flowering earlier.
Birds nesting earlier.
Melting of polar ice caps causing sea levels to rise.
Coastal Areas flooded (Nearly 3 billion people live within 100 km of a coast)
Excess sea water can change freshwater aquifers near coasts
Warming the oceans could change currents that influence weather today
As oceans heat up, typhoons and hurricanes will become more common.

23. Consequences of Warmer Earth
World weather patterns may be affected.
Heat related deaths may increase as well as other health problems increase.
Warmer temperatures may cause increase in disease causing insects.
Longer growing seasons, more pollen, more asthma
Warmer weather allow mosquitoes and other disease carrying organisms to live longer

24. Consequences con’t
Weather changes may cause droughts, changes in crop yields, and other problems for agriculture.
Climate changes could cause changes in the ranges where plants species and animal species may be found.

25. Reducing Greenhouse Emissions
Kyoto Protocol: requires developed nations to lower emission of greenhouse gases average of 5% below level by the year US did not ratify.

26. 1997 Kyoto Protocol US is largest emitter of CO2
The Kyoto Protocol to the United Nations Framework Convention on Climate Change is an international treaty that sets binding obligations on industrialized countries to reduce emissions of greenhouse gases.
US is largest emitter of CO2