NAME: ___________________________________
DATE: ___________________
Ozone depletion
Molecules of ozone, a form of oxygen, formed a thin layer in the earth's outer atmosphere hundreds
of millions of years ago. This layer has protected all forms of life from the potentially fatal effects of
ultra-violet radiation from the sun.
Ozone depletion timeline
In the early 1970s scientists began to be concerned about damage to this protective layer caused
by atmospheric pollution.
In 1974 two United States chemists predicted that a class of chemicals called chlorofluorocarbons
(CFCs), widely used in aerosol spray cans, would seriously damage the ozone layer.
In May 1985 British scientists produced the first direct evidence that this was actually happening.
Antarctic atmospheric data going back to 1957 showed an alarming decline in ozone values over
Antarctica each spring - effectively a hole in the ozone layer.
In September 1987 an international meeting in Montreal created the world's first environmental
convention. The Montreal Protocol set limits on the use of CFCs and related chemicals, including
halons (widely used in fire extinguishers). Nations agreed to freeze production at 1986 levels and
gradually cut it back, eventually eliminating use of the chemicals.
In September 1987 an international team returned from the Antarctic to reveal that the cause of the
ozone hole was human-produced chlorine and bromine molecules escaping to the stratosphere and,
under ultraviolet radiation, breaking down into 'free' atoms which can break ozone molecules apart.
The team found that in the very cold Antarctic stratosphere, ice crystals provide a surface on which
ozone-destroying reactions can proceed apace. They found that in springtime, the combination of
continuing cold conditions with sunlight brought the greatest rate of ozone depletion.
In June 1990 an international meeting in London voted for a strengthened Montreal Protocol under
which CFCs, halons and other ozone-destroying chlorine compounds would be phased out by 2005
(most would be phased out by 2000). This target has essentially been met, but the longer-term
results of the Montreal and London protocols will take many years to assess, as the chemicals
already released will remain in the atmosphere for years to come.
In spring 2006 the ozone hole over Antarctica was arguably the largest on record, with average
ozone levels over Antarctica the thinnest ever observed. Polar stratospheric clouds (PSCs), which
form during periods of very low temperatures, chemically alter normally-inert CFCs and related
chemicals to destroy ozone in the presence of sunlight, effectively putting a hole in earth's protective
ozone blanket.
In about 2018 a decrease in the size of the ozone hole is expected and decreasing levels of ozonedestroying CFCs have already been observed. Temperature trends in the stratosphere are
responsible for the delayed effect.
Work in the Ice, Ocean, Atmosphere and Climate (IOAC) program at the Australian Antarctic
Division is aimed at helping to assess trends in temperatures and ozone concentrations in the
stratosphere, as well as understanding the chemical processes related to PSCs. Climate modelling
and observations indicate that lower atmosphere is warming as a direct consequence of enhanced
greenhouse gas emission. While increased CO2 warms the lower atmosphere, it cools the
stratosphere. A long-term cooling trend has been observed in the stratosphere (with short-lived
warmings due to large volcanic events), and this is likely influencing the size of the polar vortex,
which in turn influences the formation of polar stratospheric clouds and the size of the ozone hole.
SOURCE: http://classroom.antarctica.gov.au/climate/ozone-depletion
NAME: ___________________________________
DATE: ___________________
QUESTIONS
Instructions:
Answer each question in detail using complete sentences. Cite your evidence.
1. What are the consequences of ozone depletion?
2. How does human activity add to the problem?
3. What is being done to prevent it?
4. What do you think should be done? What can you do?