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Scientific Assessment of Ozone Depletion: 2006

  1. Scope of the 2006 Assessment

    The state of scientific understanding regarding the ozone-depletion issue has advanced in recent years as a result of the concerted efforts of hundreds of scientists worldwide. Acknowledging this progress, a number of governments informally have mentioned that the answer to the question "What's new regarding this issue?" is now of main interest.

    The most recent assessment (Scientific Assessment of Ozone Depletion: 2002; the "orange book") recognized this progression by taking a more focused (rather than encyclopedic) approach. Its five chapters built upon the knowledge of the broad-scoped 1998 assessment ("purple book"; 12 chapters) and focused on a few topics that were: (i) ones in which substantial advances had occurred (e.g., Arctic ozone; very short-lived gases) and (ii) updated/new information requested by the Parties to the Montreal Protocol.

    The 2006 assessment will continue in this tradition of updating the previous assessment by describing "what's new" and providing the Parties with information that they specifically request. The 2006 assessment updates the 2002 assessment and formally looks at the impact of climate change on stratospheric ozone.

  2. Approach of the 2006 Assessment

    The 2006 assessment aims to have focused, short chapters that build from the 2002 assessment and provide a cogent assessment of the current state of scientific understanding. A small steering committee (Attachment A) is engaged in helping the chapter teams achieve this objective. The 2006 assessment's chapter structure (sections III and IV, below) contains eight chapters. The structure is designed to make it straightforward to find information on key topics, especially regarding climate as well as the future scenarios (two topics that keenly interest the Parties).

    The Parties continue to be interested in understanding the impact of climate change on ozone depletion and explicitly asked that the 2006 assessment include the status of that understanding (Attachment B, "Terms of Reference"). The interactions between the ozone layer and the climate system are varied, e.g., cooling of the stratosphere and the consequent changes in the formation rate of polar stratospheric clouds. Further, changes in stratospheric climate will have significant impacts on the future levels of ozone and, hence, on distinguishing the changes in ozone levels due to climate change from those due to decreases in ozone-depleting substances. Consequently, the 2006 assessment will have two chapters dedicated to this topic of climate and the ozone layer. The 2006 ozone assessment draws from and builds upon the findings of the Intergovernmental Panel on Climate Change (IPCC) and Technology and Economic Assessment Panel (TEAP) 2005 special assessment report ("IPCC/TEAP Special Report on Safeguarding the Ozone Layer and the Global Climate System: Issues Related to Hydrofluorocarbons and Perfluorocarbons") and is being coordinated with the work of the IPCC's 2007 fourth major assessment (in preparation, to be published in 2007).

  3. 2006 Ozone-Layer Assessment Steering Committee

    Scientific Assessment Panel Cochairs:

    • Ayité-Lô Ajavon
    • Daniel L. Albritton
    • Robert T. Watson

    Scientific Community:

    • Marie-Lise Chanin (France)
    • Susana Diaz (Argentina)
    • John Pyle (United Kingdom)
    • A.R. Ravishankara (United States)
    • Ted Shepherd (Canada)

  4. Overview: Chapters and Lead Authors
    Chapter 1:Long-Lived Compounds
    Cathy Clerbaux (France)
    Derek Cunnold (USA)
    Chapter 2:Halogenated Very Short-Lived Substances
    Kathy Law (France)
    Bill Sturges (UK)
    Chapter 3:Global Ozone: Past and Present
    Martyn Chipperfield (UK)
    Vitali Fioletov (Canada)
    Chapter 4:Polar Ozone: Past and Present
    Paul Newman (USA)
    Markus Rex (Germany)
    Chapter 5:Climate-Ozone Connections
    Mark Baldwin (USA)
    Martin Dameris (Germany)
    Chapter 6:The Ozone Layer in the 21st Century
    Greg Bodeker (New Zealand)
    Darryn Waugh (USA)
    Chapter 7:Surface Ultraviolet Radiation: Past, Present, and Future
    Alkiviadis Bais (Greece)
    Dan Lubin (USA)
    Chapter 8:Projections and Impacts
    John Daniel (USA)
    Guus Velders (Netherlands)
    Questions and Answers About the Ozone Layer
    David W. Fahey (USA)
  5. Detail: Chapter Topics and Authors
    Chapter 1:Long-Lived Compounds
    Lead Authors: Cathy Clerbaux (France) and Derek Cunnold (USA)
    Coauthors: J. Anderson (USA), P. Bernath (Canada), A. Engel (Germany), P. Fraser (Australia), E. Mahieu (Belgium), A. Manning (UK), J. Miller (USA), S. Montzka (USA), R. Prinn (USA), S. Reimann (Switzerland), C. Rinsland (USA), P. Simmonds (UK), D. Verdonik (USA), D. Wuebbles (USA), Y. Yokouchi (Japan)
    Focus: Controlled substances with which the Protocol has dealt (CFCs, HCFCs, etc., with HFCs and methyl bromide included) and ozone/climate-related constituents (e.g., methane, N2O, PFCs). Major sections address trends and budgets, based on observations and models. Shorter sections include carbon dioxide, methane, N2O. The information takes into account, and draws from, the data and analyses in the 2005 special assessment report by the IPCC/TEAP. The chapter provides basic information necessary for the 2006 ozone assessment to describe, in following chapters, the interactions of climate change and ozone depletion (estimates of the radiative cooling of the stratosphere) caused by greenhouse gases and other source gases. The chapter assesses the feasibility of attribution of emissions of halogenated compounds to specific regions via inverse modeling. It covers the status of understanding on ODS degradation products in the stratosphere, e.g., HCl, HF, CF2O, examines how the degradation products change with time in the stratosphere, and discusses whether these changes are consistent with the Montreal Protocol.
    Chapter 2:Halogenated Very Short-Lived Substances
    Lead Authors:Kathy Law (France) and William Sturges (UK)
    Coauthors: D. Blake (USA), N. Blake (USA), J. Burkholder (USA), J. Butler (USA), R.A. Cox (UK), P. Haynes (UK), M. Ko (USA), K. Kreher (New Zealand), M. Céline (France), K. Pfeilsticker (Germany), J. Plane (UK), R. Salawitch (USA), C. Schiller (Germany), B.-M. Sinnhuber (Germany), R. von Glasow (Germany), N. Warwick (UK), D. Wuebbles (USA), S. Yvon-Lewis (USA)
    Focus: Short-lived compounds (atmospheric lifetimes of less than about 0.5 year) that are current or potential future compounds of relevance to the ozone layer. Major emphases of the chapter are: (i) discussion of sources, chemistry, transport, and importance to the stratospheric halogen budget of the short-lived gases in the Protocol, or of current discussion, for which papers exist (e.g., n-propyl bromide); (ii) updates to the thinking developed in the 2002 assessment regarding the "very" short-lived substances and their possible impact on stratospheric ozone. The transport of "degraded" products into the stratosphere is discussed, as is the connection to bromine loading in the stratosphere (source gases versus Bry measurements in the stratosphere). The level of bromine in the stratosphere due to short-lived natural emissions is also examined.
    Chapter 3:Global Ozone: Past and Present
    Lead Authors: Martyn Chipperfield (UK) and Vitali Fioletov (Canada)
    Coauthors: B. Bregman (Netherlands), J. Burrows (Germany), B. Connor (New Zealand), J. Haigh (UK), N. Harris (UK), A. Hauchecorne (France), L. Hood (USA), S.R. Kawa (USA), J. Krzyscin (Poland), J. Logan (USA), N.J. Muthama (Kenya), L. Polvani (USA), W. Randel (USA), T. Sasaki (Japan), J. Stähelin (Switzerland), R. Stolarski (USA), L. Thomason (USA), J. Zawodny (USA)
    Focus: Updated status of the observations of global ozone and rationalization of the variance (all scales) of the observations, including the potential roles of climate change and other non-halogen effects. This chapter assesses the insights that are possible by analyzing a combination of different satellite and ground-based data sets and sondes, as well as the role of large-scale, longer-term dynamics in the ozone changes of the lower stratosphere. Observations of aerosols, and the possible influences of changes in aerosols as well as the solar cycle, are core information for this chapter. The chapter applies rigorous statistical methods in defining ozone changes. Discussion of causes of past ozone changes is also included in the chapter by the analysis of a range of model simulations (2D and 3D).
    Chapter 4:Polar Ozone: Past and Present
    Lead Authors: Paul Newman (USA) and Markus Rex (Germany)
    Coauthors: P. Canziani (Argentina), K. Carslaw (UK), K. Drdla (USA), S. Godin-Beekmann (France), D. Golden (USA), C. Jackman (USA), K. Kreher (New Zealand), U. Langematz (Germany), R. Müller (Germany), H. Nakane (Japan), R. Salawitch (USA), M. Santee (USA), M. van Hobe (Germany), S. Yoden (Japan)
    Focus: Polar ozone/temperature changes and processes. The chapter includes a thorough update on the understanding of ozone trends and variance in the Arctic and Antarctic winter/spring season, building upon recent extensive field studies and theory. The Antarctic section additionally assesses recent changes and near-term expectations. Past assessments have underscored the fact that small year-to-year variability is expected (e.g., changes in vortex patterns and early formation and/or breakup) and, here, the overall picture for the persistence of the ozone hole for decades is explored. The unusual Antarctic ozone hole of 2002 is a major point of discussion in this context. The climatology of polar stratospheric clouds (PSCs) would be discussed in the context of both polar regions. Our understanding of the observed ozone changes due to halogen loading, temperature changes, and dynamical processes is highlighted.
    Chapter 5:Climate-Ozone Connections
    Lead Authors: Mark Baldwin (USA) and Martin Dameris (Germany)
    Coauthors: J. Austin (USA), S. Bekki (France), B. Bregman (Netherlands), N. Butchart (UK), E. Cordero (USA), N. Gillett (UK), H.-F. Graf (UK), C. Granier (France/USA), D. Kinnison (USA), S. Lal (India), T. Peter (Switzerland), W. Randel (USA), J. Scinocca (Canada), D. Shindell (USA), H. Struthers (New Zealand), M. Takahaski (Japan), D. Thompson (USA)
    Focus: The interactions of climate change and ozone-layer depletion, with a special emphasis on the effects of climate on the ozone layer. The effect of stratospheric ozone depletion on climate is an emphasis of the 2005 IPCC/TEAP special report and the 2007 IPCC assessment, and hence is not a primary focus here. This chapter specifically addresses the question of how climate change will affect the evolution of the ozone layer and ozone recovery, with emphasis on the mechanisms and key processes involved. Coupled chemistry-climate models are included to elucidate and examine the mechanisms and processes. This chapter discusses water vapor (including observations of its changes), aerosol sulfur, changes in source gases, temperature trends, and their feedbacks to both chemistry and dynamics. Progress since 2002 on the topic of stratosphere-troposphere/surface climate linkages is assessed. There is a separate look at the impact of climate change on polar springtime ozone depletion.
    Chapter 6:The Ozone Layer in the 21st Century
    Lead Authors: Greg Bodeker (New Zealand) and Darryn Waugh (USA)
    Coauthors: H. Akiyoski (Japan), P. Braesicke (UK), V. Eyring (Germany), D. Fahey (USA), E. Manzini (Italy), M. Newchurch (USA), R. Portmann (USA), A. Robock (USA), K. Shine (UK), W. Steinbrecht (Germany), E. Weatherhead (USA)
    Focus: Stabilization of ozone depletion and the onset of recovery. Given that stratospheric chlorine loading has stabilized and may have already started to decline, it is natural to ask whether ozone recovery has also started. This is a key "closure" issue for the Montreal Protocol. This chapter describes a framework for describing the evolution of the ozone layer, including the polar regions, and evaluating future ozone abundances. Its two primary issues are (i) the detection and attribution of ozone recovery, and (ii) the projections of future ozone through the 21st Century. A focus of this chapter is on variability of ozone abundances and the challenge of making statistically reliable statements. Factors affecting the attribution of ozone behavior are discussed. Model predictions include a discussion of uncertainties and the potential for future surprises.
    Chapter 7:Surface Ultraviolet Radiation: Past, Present, and Future
    Lead Authors: Alkiviadis Bais (Greece) and Daniel Lubin (USA)
    Coauthors: A. Arola (Finland), G. Bernhard (USA), M. Blumthaler (Austria), N. Chubarova (Russia), C. Erlick (Israel), H.P. Gies (Australia), N. Krotkov (USA), K. Lantz (USA), B. Mayer (Germany), R. McKenzie (New Zealand), R. Piacentini (Argentina), G. Seckmeyer (Germany), J. Slusser (USA), C.S. Zerefos (Greece)
    Focus: Updated status of the changes and variance in observations of surface ultraviolet radiation, and expectations for the future. Estimation of long-term changes from ground-based measurements and advances in understanding satellite versus ground-based observations are areas of particular interest for this update. The chapter updates work since 2002 on the analysis of UV variability, as well as any relevant advances in instrumental approaches to the measurement of surface UV and/or advances in analyzing and modeling data. The influences of tropospheric gases (including ozone), aerosols, clouds, and other factors on UV are discussed. Predictions of future UV based on ozone predictions from Climate Chemistry Models, links with the recovery of the ozone layer, and factors related to climate change are topics of the chapter.
    Chapter 8:Projections and Impacts
    Lead Authors: John Daniel (USA) and Guus Velders (Netherlands)
    Coauthors: A. Douglass (USA), P. Forster (UK), D. Hauglustaine (France), I. Isaksen (Norway), L. Kuijpers (Netherlands), A. McCulloch (UK), T. Wallington (USA)
    Focus: Projected future behavior/scenarios of equivalent effective stratospheric chlorine (EESC). Future scenarios are developed (via interaction with the Technology and Economic Assessment Panel) for emissions of controlled substances expected under the Protocol and other assumptions. The major characteristics of the future abundances are explored, and the differences among the scenarios are quantified with respect to the estimated anthropogenic impact of ODSs on stratospheric ozone depletion. Updated ODPs and GWPs are also presented in the chapter.
    Questions and Answers About the Ozone Layer
    Lead Author:David W. Fahey (USA)
    This popular section will be updated, for example expanding discussion of ozone layer-climate change connections. Revisions will address new topics since the 2002 ozone assessment, e.g., "Why was the 2002 ozone hole so unusual?"
  6. Timetable
    Draft outline completed, circulated for commentFebruary 2005
    Lead Authors and Coauthors of the chapters establishedJune
    Chapter outlines drafted, early preparation steps begin30 June
    Meeting: Lead Authors (Paris); text preparation continues26-27 July
    First drafts of chapters completed, distribution to Lead Authorslate October
    Lead Authors Review Meeting (Washington, DC)30 November-2 December
    Second draft of chapters completed and mail peer review starts14 February 2006
    Mail peer-review comments due13 March
    Panel Review Meeting (Les Diablerets, Switzerland)19-23 June
    Final chapter text completedlate July
    Preprint volume to UNEP for distribution to governments30 December 2006
    Final printed copies availableMarch 2007
  7. Request from the Governments

    The following are the Terms of Reference for the Scientific Assessment Panel, from Decision XV/53 of the Parties to the Montreal Protocol:

    "...for the 2006 report, the Scientific Assessment Panel should consider issues including:

    1. Assessment of the state of the ozone layer and its expected recovery;
    2. Evaluation of specific aspects of recent annual Antarctic ozone holes, in particular the hole that occurred in 2002;
    3. Evaluation of the trends in the concentration of ozone-depleting substances in the atmosphere and their consistency with reported production and consumption of ozone-depleting substances;
    4. Assessment of the impacts of climate change on ozone-layer recovery;
    5. Analysis of atmospheric concentrations of bromine and the likely quantitative implications of the results on the state of the ozone layer;
    6. Description and interpretation of the observed changes in global and polar ozone and in ultraviolet radiation, as well as set future projections and scenarios for those variables, taking also into account the expected impacts of climate change... "