Slide 1

Atmosphere
& Climate Change
Section #2:
The Ozone Shield


Slide 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


Slide 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


Slide 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


Slide 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


Slide 6

CFCs Destroying the Ozone


Slide 7

CFCs Destroying the Ozone


Slide 8

CFCs Destroying the Ozone


Slide 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


Slide 10

Satellite Images of the Ozone
Hole Growing Over 2 Decades


Slide 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


Slide 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


Slide 13


Slide 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


Slide 15

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


Slide 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


Slide 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


Slide 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


Slide 19


Slide 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


Slide 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


Slide 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


Slide 23

World CFCs Production


Slide 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