Scientific Assessment of Ozone Depletion: 2006
Twenty Questions and Answers About the Ozone Layer: 2006 Update
Ozone is a very small part of our atmosphere, but its presence is nevertheless vital to human well-being.
Most ozone resides in the upper part of the atmosphere. This region, called the stratosphere, is more than 10 kilometers (6 miles) above Earth's surface. There, about 90% of atmospheric ozone is contained in the "ozone layer," which shields us from harmful ultraviolet light from the Sun.
However, it was discovered in the mid-1970s that some human-produced chemicals could destroy ozone and deplete the ozone layer. The resulting increase in ultraviolet radiation at Earth's surface may increase the incidences of skin cancer and eye cataracts.
Following the discovery of this environmental issue, researchers focused on a better understanding of this threat to the ozone layer. Monitoring stations showed that the abundances of the ozone-depleting chemicals were steadily increasing in the atmosphere. These trends were linked to growing production and use of chemicals like chlorofluorocarbons (CFCs) for refrigeration and air conditioning, foam blowing, and industrial cleaning. Measurements in the laboratory and the atmosphere characterized the chemical reactions that were involved in ozone destruction. Computer models employing this information could then predict how much ozone depletion was occurring and how much more could occur in the future.
Observations of the ozone layer showed that depletion was indeed occurring. The most severe and most surprising ozone loss was discovered to be recurring in springtime over Antarctica. The loss in this region is commonly called the "ozone hole" because the ozone depletion is so large and localized. A thinning of the ozone layer also has been observed over other regions of the globe, such as the Arctic and northern middle latitudes.
The work of many scientists throughout the world has provided a basis for building a broad and solid scientific understanding of the ozone depletion process. With this understanding, we know that ozone depletion is occurring and why. And, most important, we know that if ozone-depleting gases were to continue to accumulate in the atmosphere, the result would be more depletion of the ozone layer.
In response to the prospect of increasing ozone depletion, the governments of the world crafted the 1987 United Nations Montreal Protocol as a global means to address this global issue. As a result of the broad compliance with the Protocol and its Amendments and Adjustments and, of great significance, industry's development of "ozonefriendly" substitutes for the now-controlled chemicals, the total global accumulation of ozone-depleting gases has slowed and begun to decrease. This has reduced the risk of further ozone depletion. Now, with continued compliance, we expect recovery of the ozone layer by the late 21st century. The International Day for the Preservation of the Ozone Layer, 16 September, is now celebrated on the day the Montreal Protocol was agreed upon.
This is a story of notable achievements: discovery, understanding, decisions, actions, and verification. It is a story written by many: scientists, technologists, economists, legal experts, and policymakers. And, dialogue has been a key ingredient.
To help foster a continued interaction, this component of the Scientific Assessment of Ozone Depletion: 2006 presents 20 questions and answers about the often-complex science of ozone depletion. The answers are updates of those first presented in the previous ozone Assessment, Scientific Assessment of Ozone Depletion: 2002. The questions address the nature of atmospheric ozone, the chemicals that cause ozone depletion, how global and polar ozone depletion occur, and what could lie ahead for the ozone layer. A brief answer to each question is first given in italics; an expanded answer then follows. The answers are based on the information presented in the 2006 and earlier Assessment reports. These reports and the answers provided here were all prepared and reviewed by a large international group of scientists1.
1. The update of this component of the Assessment was discussed by the 77 scientists who attended the Panel Review Meeting for the 2006 Ozone Assessment (Les Diablerets, Switzerland, 19-23 June 2006). In addition, subsequent contributions, reviews, or comments were provided by the following individuals: S.A. Montzka (special recognition), R.J. Salawitch (special recognition), D.L. Albritton, S.O. Andersen, P.J. Aucamp, M.P. Baldwin, A.F. Bias, G. Bodeker, J.F. Bornman, G.O. Braathen, J.P. Burrows, M.-L. Chanin, C. Clerbaux, M. Dameris, J.S. Daniel, S.B. Diaz, E.G. Dutton, C.A. Ennis, V. Eyring, V.E. Fioletov, N.P. Gillet, N.R.P. Harris, M.K.W. Ko, L. Kuijpers, G.L. Manney, R.L. McKenzie, R. Müller, E.R. Nash, P.A. Newman, T. Peter, A.R. Ravishankara, A. Robock, M.L. Santee, U. Schmidt, G. Seckmeyer, T.G. Shepherd, R.S. Stolarski, W.T. Sturges, J.C. van der Leun, G.J.M. Velders, D.W.Waugh, C.S. Zerefos.
OZONE IN OUR ATMOSPHERE
- What is ozone and where is it in the atmosphere?
Figure Q1-1 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q1-2 [eps] [small jpeg] [large jpeg] [ppt] - How is ozone formed in the atmosphere?
Figure Q2-1 [eps] [small jpeg] [large jpeg] [ppt] - Why do we care about atmospheric ozone?
Figure Q3-1 [eps] [small jpeg] [large jpeg] [ppt] - Is total ozone uniform over the globe?
Figure Q4-1 [eps] [small jpeg] [large jpeg] [ppt] - How is ozone measured in the atmosphere?
Figure Q5-1 [eps] [small jpeg] [large jpeg] [ppt] THE OZONE DEPLETION PROCESS
- What are the principal steps in stratospheric ozone depletion caused by human activities?
Figure Q6-1 [eps] [small jpeg] [large jpeg] [ppt] - What emissions from human activities lead to ozone depletion?
Figure Q7-1 [eps] [small jpeg] [large jpeg] [ppt] - What are the reactive halogen gases that destroy stratospheric ozone?
Figure Q8-1 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q8-2 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q8-3 [eps] [small jpeg] [large jpeg] [ppt] - What are the chlorine and bromine reactions that destroy stratospheric ozone?
Figure Q9-1 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q9-2 [eps] [small jpeg] [large jpeg] [ppt] - Why has an "ozone hole" appeared over Antarctica when ozone-depleting gases are present throughout the stratosphere?
Figure Q10-1 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q10-2 [eps] [small jpeg] [large jpeg] [ppt] STRATOSPHERIC OZONE DEPLETION
- How severe is the depletion of the Antarctic ozone layer?
Figure Q11-1 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q11-2 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q11-3 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q11-Box [eps] [small jpeg] [large jpeg] [ppt] - Is there depletion of the Arctic ozone layer?
Figure Q12-1 [eps] [small jpeg] [large jpeg] [ppt] - How large is the depletion of the global ozone layer?
Figure Q13-1 [eps] [small jpeg] [large jpeg] [ppt] - Do changes in the Sun and volcanic eruptions affect the ozone layer?
Figure Q14-1 [eps] [small jpeg] [large jpeg] [ppt] CONTROLLING OZONE-DEPLETING GASES
- Are there regulations on the production of ozone-depleting gases?
Figure Q15-1 [eps] [small jpeg] [large jpeg] [ppt] - Has the Montreal Protocol been successful in reducing ozone-depleting gases in the atmosphere?
Figure Q16-1 [eps] [small jpeg] [large jpeg] [ppt] IMPLICATIONS OF OZONE DEPLETION
- Does depletion of the ozone layer increase ground-level ultraviolet radiation?
Figure Q17-1 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q17-2 [eps] [small jpeg] [large jpeg] [ppt] - Is depletion of the ozone layer the principal cause of climate change?
Figure Q18-1 [eps] [small jpeg] [large jpeg] [ppt]
Figure Q18-2 [eps] [small jpeg] [large jpeg] [ppt] STRATOSPHERIC OZONE IN THE FUTURE
- How will recovery of the ozone layer be identified?
Figure Q19-1 [eps] [small jpeg] [large jpeg] [ppt] - When is the ozone layer expected to recover?
Figure Q20-1 [eps] [small jpeg] [large jpeg] [ppt]
ADDITIONAL TOPICS
- Global Ozone Dobson Network - end of Question 5
- Understanding Stratospheric Ozone Depletion - end of Question 6
- Heavier-Than-Air CFCs - end of Question 7
- Replacing the Loss of "Good" Ozone in the Stratosphere - end of Question 8
- The Discovery of the Antarctic Ozone Hole - end of Question 10
- The Anomalous 2002 Antarctic Ozone Hole - end of Question 11
Technical Note: The graphics and powerpoint files included on the distributed CD contained errors.
For all users, some problems were discovered with the Twenty Questions and Answers PowerPoint files on the CD, located in the folder titled "Q&A Figures." New PowerPoint files are available here on the Twenty Questions and Answers About Ozone: 2006 Update webpage. Alternatively, Windows users may successfully insert the jpeg files on the CD into PowerPoint files.
Additionally for Mac users, some problems were discovered with many of the jpeg files for both the Twenty Questions and Answers and Chapters, especially when importing into PowerPoint. If experiencing any problems with a jpeg file, select one of two ways to obtain a useable jpeg. 1) Download the figure from the collection of chapter figures webpage. 2) Correct the jpeg with the following procedure... Open the jpeg file into Preview and save it as a PDF file. The resulting pdf file may be inserted into PowerPoint, or used like any other pdf file.