1. Atmosphere & Climate Change
Section #2:
The Ozone Shield

2. Ozone Layer
an area in the stratosphere where ozone is highly concentrated
ozone is a molecule made of three oxygen atoms
this layer absorbs most of the UV light from the sun
UV light is harmful to organisms & damages the genetic material in living cells

3. Chemicals that Deplete the Ozone
CFCs (chlorofluorocarbons)
man made “miracle” chemical
nonpoisonous & nonflammable
they do not corrode metals
popular as coolants in refrigerators & air conditioners
used in making plastic foams
used as a propellant in spray cans

4. CFCs
chemically stable at Earth’s surface because they do not combine with other chemicals or break down substances
but up in the stratosphere, CFC molecules break apart & begin to destroy the protective ozone

5. Problems with CFCs
scientists began to worry about the impact of CFCs in the atmosphere in the 1970s
each CFC molecule that breaks up releases one to four chlorine atoms that remain in in the stratosphere for many years
a single chlorine atom can destroy 100,000 ozone molecules

6. CFCs Destroying the Ozone

7. CFCs Destroying the Ozone

8. CFCs Destroying the Ozone

9. The Ozone Hole
first news of a hole in the ozone layer came out in 1985 from scientists studying the ozone layer over the South Pole
data revealed that the ozone layer over the poles had thinned by 50 to 98 percent during the spring

10. Satellite Images of the Ozone Hole Growing Over 2 Decades

11. How Does the Ozone Hole Form?
clouds do not normally form in the stratosphere because it is so dry there
however, during the polar winter, when temperatures drop below -80°C, high altitude clouds called POLAR STRATOSPHERIC CLOUDS begin to form because condensation can occur
outside of the polar region, it is too warm in the stratosphere for clouds to form

12. How Does the Ozone Hole Form?
on the surface of these polar stratospheric clouds, the products of CFCs are converted to molecular chlorine
when sunlight returns in the spring, these chlorine molecules split into two chlorine atoms by UV radiation where they rapidly begin destroying ozone
thin spots & holes can last for several months

14. Effects on Humans
as the amount of ozone in the stratosphere decreases, more UV light is able to pass through the atmosphere where it reaches Earth’s surface
UV light damages DNA & makes the body more susceptible to skin cancer

15. More UV radiation can penetrate at the poles where the ozone holes is located.

16. Effects on Plants
UV light can kill phytoplankton at the ocean’s surface
loss of phytoplankton disrupts the ocean’s food chains & reduces fish harvests
reduction of phytoplankton also means more CO2 is left in the atmosphere which is a greenhouse gas

17. Effects on Plants
UV light can also damage land plants by interfering with photosynthesis
this damage could impact crops & create a lower yield during harvesting
this will disrupt the food chains of many organisms, & humans too

18. Effects on Animals
UV light can damage amphibians like toads & salamanders
normal UV levels kill many eggs of amphibians that lack shells & are laid in the shallow water of ponds & streams
at higher levels, UV light can kill more eggs putting the amphibian population at risk

20. Protecting the Ozone Layer
in 1987, soon after the first news of the holes in the ozone layer, a group of nations met in Canada to take action against ozone depletion
called the Montreal Protocol, these nations agreed to sharply limit their production of CFCs

21. Protecting the Ozone Layer
in 1992, developed countries met again & agreed to eliminate most CFCs by 1995
the U.S. pledged to ban all substances that pose a significant danger to the ozone layer by 2000

22. Protecting the Ozone Layer
chemical companies have developed CFC replacements that can be used in aerosol cans & in air conditioners
decline in developed countries is profound due to the overwhelming collaborative efforts from so many involved countries

23. World CFCs Production

24. Why are Holes in the Ozone Layer Still a Problem?
CFC molecules remain active in the stratosphere for 60 to 120 years
even though production has stopped, CFCs that were released 30 years ago are still actively destroying ozone today
it will be many years until the ozone layer completely recovers