Common Questions About Ozone (5)
Scientific Assessment of Ozone Depletion: 1994
Executive Summary
World Meteorological Organization Global Ozone Research and Monitoring Project - Report No. 37
United Nations Environment Programme
World Meteorological Organization
National Oceanic and Atmospheric Administration
National Aeronautics and Space Administration
When Did the Antarctic Ozone Hole First Appear?
The Antarctic ozone hole is a new phenomenon. The figure shows that observed ozone over the British Antarctic Survey station at Halley Bay, Antarctica first revealed obvious decreases in the early 1980s compared to data obtained since 1957. The ozone hole is formed each year when there is a sharp decline (currently up to 60%) in the total ozone over most of Antarctica for a period of about two months during Southern Hemisphere spring (September and October). Observations from three other stations in Antarctica, also covering several decades, reveal similar progressive, recent decreases in springtime ozone. The ozone hole has been shown to result from destruction of stratospheric ozone by gases containing chlorine and bromine, whose sources are mainly human-made halocarbon gases.
Before the stratosphere was affected by human-made chlorine and bromine, the naturally occurring springtime ozone levels over Antarctica were about 30-40% lower than springtime ozone levels over the Arctic. This natural difference between Antarctic and Arctic conditions was first observed in the late 1950s by Dobson. It stems from the exceptionally cold temperatures and different winter wind patterns within the Antarctic stratosphere as compared to the Arctic. This is not at all the same phenomenon as the marked downward trend in total ozone in recent years referred to as the ozone hole and shown in the figure below.
Changes in stratospheric meteorology cannot explain the ozone hole. Measurements show that wintertime Antarctic stratospheric temperatures of past decades have not changed prior to the development of the hole each September. Ground, aircraft, and satellite measurements have provided, in contrast, clear evidence of the importance of the chemistry of chlorine and bromine originating from human-made compounds in depleting Antarctic ozone in recent years.
A single report of extremely low Antarctic winter ozone in one location in 1958 by an unproven technique has been shown to be completely inconsistent with the measurements depicted here and with all credible measurements of total ozone.
Common Questions About Ozone
- [Introduction]
- How Can Chlorofluorocarbons (CFCs) Get to the Stratosphere If They're Heavier than Air?
- What is the Evidence that Stratospheric Ozone is Destroyed by Chlorine and Bromine?
- Does Most of the Chlorine in the Stratosphere Come from Human or Natural Sources?
- Can Changes in the Sun's Output Be Responsible for the Observed Changes in Ozone?
- When Did the Antarctic Ozone Hole First Appear?
- Why is the Ozone Hole Observed over Antarctica When CFCs Are Released Mainly in the Northern Hemisphere?
- Is the Depletion of the Ozone Layer Leading to an Increase in Ground-Level Ultraviolet Radiation?
- How Severe Is the Ozone Depletion Now, and Is It Expected to Get Worse?
Return to the WMO/UNEP Scientific Assessment of Ozone Depletion: 1994
- Executive Summary
- Common Questions About Ozone
- List of Authors, Contributors, and Reviewers of the Assessment
The World Wide Web version of the Executive Summary of the WMO/UNEP Scientific Assessment of Ozone Depletion: 1994 was prepared by Dr. Gregory P. Dubois-Felsmann of the National Center for Atmospheric Research, Boulder, Colorado, with support from NCAR's Advanced Study Program, in cooperation with Dr. Daniel L. Albritton and Dr. Christine A. Ennis of the NOAA Aeronomy Laboratory.
The Executive Summary may be reproduced or excerpted, without modification, provided the source is duly and conspicuously acknowledged in every instance as:
World Meteorological Organization, Scientific Assessment of Ozone Depletion: 1994, WMO Global Ozone Research and Monitoring Project - Report No. 37, Geneva, 1995.
Copies of the Executive Summary are available at no charge by writing to:
United Nations Environment Programme
Ozone Secretariat
P.O. Box 30552
Nairobi, Kenya
The Executive Summary was published in print in February 1995. The World Wide Web version was derived directly from the source of the printed edition and was made public in March 1996.