Stratospheric Ozone Depletion

 

   

Introduction

The issue of stratospheric ozone depletion burst on to the scene in the 1970s and was a dominant environmental concern throughout the 1980s. Fear of a thinning ozone layer (or "ozone hole") and increased levels of UV-B radiation reaching earth and causing skin cancer prompted an unprecedented level of global cooperation to address the problem. An international political process that came to be known as The Montreal Protocol resulted in a worldwide phase-out of the main class of compounds believed responsible for causing the problem (chlorofluorocarbons or CFCs - see above). Recent research and measurements of ozone levels using the space-based Total Ozone Mapping Spectrometer (TOMS - see image above) suggests that these efforts have slowed rates of ozone depletion and that the ozone layer is likely to return to more "normal" conditions over the next 50-100 years.

We start with the stratospheric ozone depletion story because it is an excellent case study to illustrate how environmental scientists approach their work, how science and politics become intertwined, and how economics and public perception of an issue often become determining factors in whether an issue is addressed or ignored. We will first learn about the formation of the ozone layer and its importance to life on earth, followed by a review of the science behind ozone depletion and the formation of the ozone hole. We will then examine the political and social response to this issue, the Montreal Protocol process, and the current status of the ozone layer and its recovery.

Readings

Begin by reading the on-line publication entitled "Reports to the Nation on Our Changing Planet:
Our Ozone Shield," prepared by the National Oceanographic and Atmospheric Administration (NOAA). This report was written in 1992 but it provides an excellent overview of the early formation of the ozone layer, the first discovery of an ozone hole, and the global response to the problem. You can find this report here:

http://www.ogp.noaa.gov/library/rtnf92.htm

You should then read the report "Ozone is Essential to Life on Earth," prepared by the National Aeronautics and Space Administration (NASA). This report gives a little more information on how ozone-depleting substances (ODS) actually destroy stratospheric ozone. You can find this report here:

http://earthobservatory.nasa.gov/Library/Ozone/printall.php

Lastly, you should review portions of a document titled "Twenty Questions and Answers About the Ozone Layer," prepared by the Environmental Protection Agency (EPA). In particular, you should read the introduction and then focus on questions 1, 2, 3, 6, 7, 9, 10, 11, 12, 13, 15, 16, 17 and 20. This report may be a little harder to read than the others; don't get too caught up in the details, just review the questions and try and get a basic understanding of the answers. You will need Adobe Acrobat Reader to view this report (http://help.allegheny.edu/tutorials/downloads.php). The actual report can be found here:

http://www.epa.gov/ozone/science/unepSciQandA.pdf

Questions to Consider

In addition to reviewing and answering the questions for homework assignment #1 (due on Friday, Jan 25), consider these questions as you do the readings.

  1. Why was the formation of the stratospheric ozone layer essential to the evolution of life on earth?
  2. What is meant by the "natural" creation and destruction of ozone in the stratosphere, and how is that different from ozone depletion caused by human activities?
  3. How does the release of CFCs and other ozone-depleting substances actually result in the destruction of stratospheric ozone?
  4. How were scientists able to learn about stratospheric ozone depletion, and what are some of the challenges associated with studying an issue like this?
  5. How has the Montreal Protocol process helped to address the stratospheric ozone depletion issue and what is the current condition of the ozone layer?

Additional Cool Websites

http://ozonewatch.gsfc.nasa.gov/

Prepared by Eric Pallant and Terry Bensel 1/06; updated by Caryl Waggett 7/06.