Atmosphere& Climate Change

Section #2:The Ozone Shield

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

Chemicals that Depletethe 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

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

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

CFCs Destroying the Ozone

CFCs Destroying the Ozone

CFCs Destroying the Ozone

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

Satellite Images of the Ozone Hole Growing Over

2 Decades

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

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

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

More UV radiation

can penetrate

at the poles

where the ozone

holes is located.

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

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

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

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

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

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

World CFCs Production

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