Ozone Scenario

Stratospheric ozone is a very important gas because it absorbs most of the sun's harmful ultraviolet radiation and prevents it from reaching Earth's surface. However, the ozone layer has been depleting as the result of a complex set of circumstances and chemistry. 

Ozone depletion is the term commonly used to describe the thinning of the earth’s protective stratospheric ozone layer. Ozone depletion occurs when the natural balance between the production and destruction of stratospheric ozone is tipped in favour of destruction. Natural phenomena, such as volcanoes, and human-generated ozone depleting substances (ODS) can upset that balance, removing ozone faster than nature can produce it.

One of the negative effects of ozone depletion is an increase in the number of people suffering from skin cancer. The relationship between skin cancer and uv radiation is well established. People of fair skin are generally more prone to skin cancer. For example, Queensland, Australia, which has high natural rates of uv radiation and a population largely of Northern European descent, has the highest rate of skin cancer in the world. 

Ozone depletion is monitored with a Total Ozone Mapping Spectrometer (TOMS), which is a satellite instrument that measures total vertical ozone column concentrations. TOMS measures the total solar radiance incident on the satellite and, by comparing it to the uv radiation scattered back from the atmosphere, is able to compute total ozone amounts. Because it depends upon scattered solar radiation, TOMS does not work at night. As a result, between the first day of fall and the first day of spring, there will be parts of the high latitudes that will have no data. This area begins at the South Pole on the first day of fall, reaches its maximum on the first day of winter, and then shrinks back to zero on the first day of spring. Ozone measurements given by TOMS are in Dobson units--a measure of total ozone in a vertical column. One Dobson unit is equal to a depth of 0.001 mm at standard temperature and pressure.

A TOMS instrument was carried aboard Nimbus-7. From November 1, 1978 to May 6, 1993, this satellite provided the only source of high-resolution global information about ozone. Meteor-3, a Russian satellite, also carried a TOMS. It stopped operating on December 27, 1994. From that date until September 12, 1996, no TOMS data were available. Since then, however, the Earth Probe TOMS and ADEOS TOMS have provided data.  For more information about TOMS, visit the TOMS Home Page.

Situation 
In the 1970s, researchers began to think that human activity could affect the ozone.  At the time, they were focusing on the exhaust from supersonic airplanes and the space shuttle. However, after studying other possible causes for ozone depletion, the international community came to a consensus that certain synthetic chemical compounds called chlorofluorocarbons (CFCs) were largely responsible for the ozone loss. As a result, the Montreal Protocol was adopted in 1987, calling for the worldwide elimination of CFCs and other ozone-destroying substances. So far, the Montreal Protocol has been signed by more than 160 nations.  

The Protocol has been updated several times, most recently in 1995. Since knowledge of the ozone depletion problem continues to increase rapidly, the director of the United Nations Environment Programme (UNEP) plans another update.  The next meeting to update the Protocol will occur in the year 2000 and once again be held in Montreal. 

There are still many (including some vocal scientists) who would like to abandon the Montreal Protocol. Some think a causal relationship has not been proved, while others contend that enforcement of the Montreal Protocol is too costly. In fact, in 1996, legislation was introduced in the US Senate that would have ended United States compliance. There is also concern about developing countries and countries that have not yet signed the protocol.  

The government of Queensland, Australia, is concerned that the Montreal Protocol is too lax on its control of some substances. The Queensland government has called upon your Earth Systems Science team to act as consultants to review the many issues that surround ozone depletion.  Your role is to evaluate the current understanding of the cause-and-effect interrelationships of Earth's systems related to ozone depletion. The Queensland officials who will attend the 2000 Montreal Protocal meeting will use your information to prepare for the meeting. 

Assignments
Over the next two weeks (Week A and Week B) you will work individually and in teams to address the ozone depletion situation. Use the links below to access your assignments.

Week A: Teacher as Problem Solver
Private Theory Activity and Rubric
Individually, identify what you believe to be true and the reasons for why you have those beliefs regarding ozone depletion.

Week A: Teacher as Problem Solver
Knowledge-Building Activity and Rubric
As a team, build ESS knowledge about the ozone depletion event described in the scenario, and develop a problem statement.

Week B: Teacher as Model Builder
Model-Building Activity and Rubric
Using your team's original or revised problem statement, build an ESS model that includes the ESS relationship statements and evidence that support your conclusions (recommendations or solutions).

Privacy Statement and Copyright^© 1997-2000 by Wheeling Jesuit University/NASA Classroom of the Future™. All rights reserved.