Common Questions About Ozone (6)
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
Why is the Ozone Hole Observed over Antarctica When CFCs Are Released Mainly in the Northern Hemisphere?
Human emissions of CFCs do occur mainly in the Northern Hemisphere, with about 90% released in the latitudes corresponding to Europe, Russia, Japan, and North America. Gases such as CFCs that are insoluble in water and relatively unreactive are mixed within a year or two throughout the lower atmosphere (below about 10 km). The CFCs in this well-mixed air rise from the lower atmosphere into the stratosphere mainly in tropical latitudes. Winds then move this air poleward - both north and south - from the tropics, so that air throughout the stratosphere contains nearly the same amount of chlorine. However, the meteorologies of the two polar regions are very different from each other because of major differences at the Earth's surface. The South Pole is part of a very large land mass (Antarctica) that is completely surrounded by ocean. These conditions produce very low stratospheric temperatures which in turn lead to formation of clouds (polar stratospheric clouds). The clouds that form at low temperatures lead to chemical changes that promote rapid ozone loss during September and October of each year, resulting in the ozone hole.
In contrast, the Earth's surface in the northern polar region lacks the land/ocean symmetry characteristic of the southern polar area. As a consequence, Arctic stratospheric air is generally much warmer than in the Antarctic, and fewer clouds form there. Therefore, the ozone depletion in the Arctic is much less than in the Antarctic.
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.