Twenty Questions and Answers About the Ozone Layer: 2014 Update Scientific Assessment of Ozone Depletion: 2014

Twenty Questions and Answers About the Ozone Layer: 2014 Update Scientific Assessment of Ozone Depletion: 2014 World Meteorological Organization United Nations Environment Programme National Oceanic and Atmospheric Administration National Aeronautics and Space Administration European Commission This publication, Twenty Questions and Answers About the Ozone Layer: 2014 Update, is a component of the 2014 report of the Montreal Protocol Scientific Assessment Panel,Scientific Assessment of Ozone Depletion: 2014. This document is an update of Twenty Questions and Answers About the Ozone Layer: 2010 (Fahey, D.W., and M.I. Hegglin) and reflects the scientific information presented in the 2014 Assessment Report. It is a continuation of the updates of the first document with this title scope: Twenty Questions and Answers About the Ozone Layer: 2002 (Fahey, D.W.). Lead Author Stefan Reimann John P. Burrows Ronald G. Prinn Michaela I. Hegglin Swiss Federal Laboratories for University of Bremen, Germany Massachusetts Institute of University of Reading, UK Materials Science and Technology, Martyn P. Chipperfield Technology, USA Switzerland University of Leeds, UK John A. Pyle Coauthors Matthew Rigby Martin Dameris National Centre for Atmospheric David W. Fahey University of Bristol, UK DLR, Institut für Physik der Science, UK and University of NOAA ESRL Chemical Sciences Michelle L. Santee Atmosphäre, Germany Cambridge Division, USA Jet Propulsion Laboratory, California Christine A. Ennis A.R. Ravishankara Mack McFarland Institute of Technology, USA CIRES / NOAA ESRL Chemical Colorado State University / NOAA Dupont Chemicals & Guus J.M. Velders Sciences Division, USA ESRL Chemical Sciences Division, Fluoroproducts, USA USA RIVM (National Institute for Public Lucien Froidevaux Stephen A. Montzka Health and the Environment), The Jet Propulsion Laboratory, California Jose M. Rodriguez NOAA ESRL Global Monitoring Netherlands Institute of Technology, USA NASA Goddard Space Flight Division, USA Center, USA Darryn W. Waugh Nathan P. Gillett Eric R. Nash Johns Hopkins University, USA Environment Canada, Canada Megumi Seki NASA Goddard Space Flight Mark Weber UNEP Ozone Secretariat, Kenya Center, USA Sophie Godin-Beekmann University of Bremen, Germany Centre National de la Recherche Susan Solomon Contributors The authors would like to Scientifique, France Massachusetts Institute of Pablo O. Canziani Technology, USA acknowledge in addition the many Marco Gonzalez Pontificia Universidad Católica contributors to previous versions Sistemas de Energia, Costa Rica Wolfgang Steinbrecht – CONICET, Argentina of this document. Deutscher Wetterdienst Neil R.P. Harris Lucy J. Carpenter Hohenpeissenberg, Germany Reviewers University of Cambridge, UK University of York, UK William T. Sturges Special Recognition Kenneth W. Jucks John S. Daniel University of East Anglia, UK Malcolm K.W. Ko NASA Headquarters, USA NOAA ESRL Chemical Sciences David W.J. Thompson NASA Langley Research Center, David J. Karoly Division, USA Colorado State University, USA USA Melbourne University, Australia Nada Derek Timothy J. Wallington Michelle L. Santee Lambert J.M. Kuijpers Commonwealth Scientific and Ford Motor Company, USA Jet Propulsion Laboratory, California Industrial Research Organisation, Technical University Eindhoven, Institute of Technology, USA Ray F. Weiss Australia Netherlands University of California San Diego / Ross J. Salawitch Michael J. Kurylo Vitali E. Fioletov Scripps, USA University of Maryland, USA Universities Space Research Environment Canada, Canada Shigeo Yoden Rajendra Shende Association / Goddard Earth Peter von der Gathen Kyoto University, Japan TERRE Policy Centre, India Sciences, Technology, and Alfred Wegener Institute, Germany Research, USA Lingxi Zhou Theodore G. Shepherd Bradley D. Hall Chinese Meteorological University of Reading, UK Ulrike Langematz NOAA ESRL Global Monitoring Freie Universität Berlin, Germany Administration, China Division, USA Donald J. Wuebbles University of Illinois, USA Martin R. Manning Coordinating Editor Bryan Johnson New Zealand Climate Change Christine A. Ennis NOAA ESRL Global Monitoring In addition, this document was Research Institute, New Zealand CIRES / NOAA ESRL Chemical Division, USA discussed by other scientists who attended the Panel Review Meeting Amanda C. Maycock Sciences Division, USA Kathy Lantz for the 2014 Assessment report in University of Cambridge, UK NOAA ESRL Global Monitoring Technical Management Assistance Les Diablerets in June 2014: Division / CIRES, USA Pauline Midgley Debra A. Dailey-Fisher Ayité-Lô Ajavon University of Bern, Switzerland Zachary Lawrence NOAA ESRL Chemical Sciences North-South Environment, Togo New Mexico Institute of Mining Rolf Müller Division, USA Forschungszentrum Jülich, and Technology, USA Stephen O. Andersen Graphic Art Design Institute for Governance & Germany Gloria L. Manney Dennis Dickerson Sustainable Development, USA Hiroaki Naoe NWRA / New Mexico Institute Respond Grafiks, USA of Mining and Technology, USA Julie M. Arblaster Japan Meteorological Agency, Australian Bureau of Meteorology, Japan Publication Layout and Design Olaf Morgenstern Australia Nayna Morjaria National Institute of Water Steven Pawson Design & Print Studio, and Atmospheric Research, Pieter Aucamp NASA Goddard Space Flight University of Reading, UK New Zealand Ptersa, South Africa Center, USA Paul A. Newman Gufran Beig Thomas Peter NASA Goddard Space Flight Indian Institute of Tropical ETH Zurich, Switzerland Center, USA Meteorology, India David Plummer Geir O. Braathen Environment Canada, Canada World Meteorological Organization, Lorenzo Polvani Switzerland Columbia University, USA 2 Section II: The ozone depletion process Twenty Questions and Answers About the Ozone Layer: 2014 Update Scientific Assessment of Ozone Depletion: 2014 This document answers some of the most commonly asked questions about the ozone layer. Lead Author Michaela I. Hegglin Coauthors David W. Fahey Mack McFarland Stephen A. Montzka Eric R. Nash Contributors Pablo O. Canziani, Lucy J. Carpenter, John S. Daniel, Nada Derek, Vitali E. Fioletov, Peter von der Gathen, Bradley D. Hall, Bryan Johnson, Kathy Lantz, Zachary Lawrence, Gloria L. Manney, Olaf Morgenstern, Paul A. Newman, Stefan Reimann, Matthew Rigby, Michelle L. Santee, Guus J.M. Velders, Darryn W. Waugh, Mark Weber World Meteorological Organization United Nations Environment Programme National Oceanic and Atmospheric Administration National Aeronautics and Space Administration European Commission Michaela I. Hegglin (Lead Author), David W. Fahey, Mack McFarland, Stephen A. Montzka, and Eric R. Nash, Twenty Questions and Answers About the Ozone Layer: 2014 Update, Scientific Assessment of Ozone Depletion: 2014, 84 pp., World Meteorological Organization, Geneva, Switzerland, 2015. Published in January 2015 ISBN: 978-9966-076-02-1 2 Section I: Ozone in our atmosphere Contents Introduction 5 Section I: Ozone in our atmosphere Q1: What is ozone and where is it in the atmosphere? 8 Q2: How is ozone formed in the atmosphere? 10 Q3: Why do we care about atmospheric ozone? 12 Q4: How is total ozone distributed over the globe? 14 Q5: How is ozone measured in the atmosphere? 17 Section II: The ozone depletion process Q6: How do emissions of halogen source gases lead to stratospheric ozone depletion? 19 Q7: What emissions from human activities lead to ozone depletion? 22 Q8: What are the reactive halogen gases that destroy stratospheric ozone? 27 Q9: What are the chlorine and bromine reactions that destroy stratospheric ozone? 31 Q10: Why has an “ozone hole” appeared over Antarctica when ozone-depleting substances are present throughout the stratosphere? 33 Section III: Stratospheric ozone depletion Q11: How severe is the depletion of the Antarctic ozone layer? 37 Q12: Is there depletion of the Arctic ozone layer? 42 Q13: How large is the depletion of the global ozone layer? 46 Q14: Do changes in the Sun and volcanic eruptions affect the ozone layer? 49 Section IV: Controlling ozone-depleting substances Q15: Are there controls on the production of ozone-depleting substances? 52 Q16: Has the Montreal Protocol been successful in reducing ozone-depleting substances in the atmosphere? 55 Section V: Implications of ozone depletion and the Montreal Protocol Q17: Does depletion of the ozone layer increase ground-level ultraviolet radiation? 59 Q18: Is depletion of the ozone layer the principal cause of global climate change? 62 Q19: Have Montreal Protocol controls of ozone-depleting substances also protected Earth’s climate? 68 Section VI: Stratospheric ozone in the future Q20: How is ozone expected to change in the coming decades? 74 Additional Topics Global Ozone Network 18 Understanding Stratospheric Ozone Depletion 21 The Discovery of the Antarctic Ozone Hole 36 The 2002 Antarctic Ozone Hole 41 Initial Signs of Ozone Recovery 48 The Antarctic Ozone Hole and Southern Hemisphere Surface Climate 67 3 Introduction Ozone is present only in small amounts in Earth’s atmosphere. Nevertheless, it is vital to human well-being and ecosystem health. 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 radiation from the Sun. In the mid-1970s, it was discovered that some human-produced chemicals could lead to depletion of the ozone layer. The resulting increase in ultraviolet

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