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Review of Individual Sections

This chapter provides detailed suggestions for revising the Executive Summary and six chapters of the draft Synthesis and Assessment Product (SAP) 2.4: Trends in Emissions of Ozone Depleting Substances, Ozone Layer Recovery, and Implications for Ultraviolet Radiation Exposure (draft dated August 20, 2007). The review of each section begins with the committee’s major comments, followed by a list of specific comments. The major comments for each SAP section highlight issues that need significant attention and may often relate to the issues raised in the “Overarching Comments” of this peer review report. In some cases, the specific comments that follow the major comments further relate to issues raised in the major or overarching comments; in other cases, these specific suggestions are relatively minor.

EXECUTIVE SUMMARY

The committee suggests many changes to the organization and content of the draft SAP and expects that many chapters of the draft SAP will be revised. Accordingly, the Executive Summary should be revised to reflect the major issues of chapters 1-6 in the final SAP. Regardless of which suggestions may be adopted by the SAP authoring team for the SAP chapters, the Executive Summary should be rewritten with consideration for the following comments.

Major Comments

The purpose of an Executive Summary is to highlight the major points of the document in a style that is organized and accessible for a variety of audiences. The Executive Summary in the draft SAP addresses specific and minor points while failing to highlight the major points. It is also not written for the intended audiences identified in the SAP prospectus:

“The audience for SAP 2.4 includes decisionmakers in the public (Federal, State, and local governments) and private realms (chemical industry, transportation and agriculture sectors, and climate policy and health-related interest groups), scientists, the international community, and the general public (CCSP 2007).”

The “Key Findings” section of the Executive Summary is organized as a partial outline of the chapters with a selection of bullets that have been taken—sometimes verbatim—from key findings throughout the chapters of the SAP. Within the context of the SAP chapters, these bullets are understandable; but, as presented in the Executive



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3 Review of Individual Sections This chapter provides detailed suggestions for revising the Executive Summary and six chapters of the draft Synthesis and Assessment Product (SAP) 2.4: Trends in Emissions of Ozone Depleting Substances, Ozone Layer Recovery, and Implications for Ultraviolet Radiation Exposure (draft dated August 20, 2007). The review of each section begins with the committee’s major comments, followed by a list of specific comments. The major comments for each SAP section highlight issues that need significant attention and may often relate to the issues raised in the “Overarching Comments” of this peer review report. In some cases, the specific comments that follow the major comments further relate to issues raised in the major or overarching comments; in other cases, these specific suggestions are relatively minor. EXECUTIVE SUMMARY The committee suggests many changes to the organization and content of the draft SAP and expects that many chapters of the draft SAP will be revised. Accordingly, the Executive Summary should be revised to reflect the major issues of chapters 1-6 in the final SAP. Regardless of which suggestions may be adopted by the SAP authoring team for the SAP chapters, the Executive Summary should be rewritten with consideration for the following comments. Major Comments The purpose of an Executive Summary is to highlight the major points of the document in a style that is organized and accessible for a variety of audiences. The Executive Summary in the draft SAP addresses specific and minor points while failing to highlight the major points. It is also not written for the intended audiences identified in the SAP prospectus: “The audience for SAP 2.4 includes decisionmakers in the public (Federal, State, and local governments) and private realms (chemical industry, transportation and agriculture sectors, and climate policy and health-related interest groups), scientists, the international community, and the general public (CCSP 2007).” The “Key Findings” section of the Executive Summary is organized as a partial outline of the chapters with a selection of bullets that have been taken—sometimes verbatim—from key findings throughout the chapters of the SAP. Within the context of the SAP chapters, these bullets are understandable; but, as presented in the Executive 13

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Review of CCSP SAP 2.4 14 Summary, they are not. Subheadings in this section are confusing. Fewer bullets should be presented in the Executive Summary (ES), and each bullet should be a synthesis of the separate but related key findings from the chapters. The key findings also include a lot of repetition; for example key findings on global and polar ozone based on observations are provided under ES.3.2 and repeated under ES.3.4. The authoring team should consider focusing on key statements of the future only in ES.3.4. The ordering of the key questions appears to be random. The Executive Summary should present the key questions in a logical order. For example, in Section ES.3.1 (beginning on SAP P. 6), the production bullet (L. 136-140) should come before the bullet on abundances (L. 123-135). In addition, the bullet on radiative forcing (L. 141- 146) would seem to belong in Section ES.3.4 (beginning on SAP P. 9). To fulfill its purpose, the Executive Summary should be restructured to accommodate its intended audiences. One restructuring option is to present each key question directly followed by an associated finding, as in the “Summary for Policymakers” in the Intergovernmental Panel on Climate Change/ Technology & Economic Assessment Panel (IPCC/TEAP) Special Report, Safeguarding the Ozone Layer and the Global Climate System: Issues Related to Hydrofluorocarbons and Perfluorocarbons (IPCC/TEAP 2005). With this option, each finding is more closely linked with the key question it addresses, as recommended in Chapter 2 of this review for all SAP sections. Another restructuring option is to organize the Executive Summary in three parts to address three audience categories: (1) “Recent Major Findings and Current Scientific Understanding” to inform the international community and the public in general, (2) “Additional Scientific Evidence and Related Information” to inform scientists, and (3) “Implications for Policy Formulation” to inform decision-makers. An example of this option is the Executive Summary in the World Meteorological Organization’s (WMO) report, Scientific Assessment of Ozone Depletion: 2006 (WMO 2007). In addition to restructuring, the Executive Summary of the draft SAP would benefit from an improved presentation of background information. The authoring team should consider defining key terms related to stratospheric ozone, as presented in SAP Chapter 1, for example. The Executive Summary does not define technical terms, making it confusing for a non-technical audience to read. Some specific examples of such terms are listed in the “Specific Comments” section below. An example of text to omit from the Executive Summary is the discussion in the first few pages about the organization of the report and the context of the report. This text could be moved into the preface when it is eventually written for the final SAP. Although the Executive Summary of the draft SAP is consistent with the findings of the SAP, it is not as effective as it could be. At a minimum, the Executive Summary should address the objectives and questions as presented in the SAP prospectus (specified in Sections 1.2 and 1.5 of the prospectus). Specific Comments • P. 7, L. 136-138, “Total global production and consumption of ozone-depleting substances (ODSs) and substitute chemicals have declined substantially since the late

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Review of Individual Sections 15 1980s…”, and P. 7, L. 141-143, “The combined radiative forcing (energy that can increase temperature) from ODSs and substitutes including hydrofluorocarbons (HFCs) is still increasing, but at a slower rate than in the 1980s”: In the Executive Summary, no distinction has been made among the original ODSs, the HCFC substitutes that have lower ODP, and the HFC substitutes that are not ODSs but have radiative forcing effects. The fact that ozone and ODSs and all substitutes have radiative forcing effects is not explained in the Executive Summary. Some examples of unexplained questions include: Which of these categories have declined since the late 1980s? All of them combined? A subset of combinations of these? Why do we care if the substitutes are declining? In the background information presented in the Executive Summary, these distinctions should be made clearly before presenting these findings. • P. 7, L. 153: There are significant ozone losses in the tropical stratosphere, as discussed in the WMO report (2007) (see also Randel and Wu 2007). • P. 7, L. 154: This statement refers to ozone depletion in the upper stratosphere, but P.3, L. 51 says the stratosphere is from 15-35 km (missing the upper stratosphere). These statements should be checked for consistency. • P. 8, L. 160: The term “stabilized” should not be used, as explained in the section on SAP Chapter 3 comments. • P. 8, L. 161-165: While “ozone hole area” may be in the realm of common knowledge, the phrases “ozone mass deficit” and “Equivalent Effective Stratospheric Chlorine” are not. “Below average” and “more intense meteorological conditions” are not defined, and the use of “higher minimum” may seem contradictory to the non- technical reader. The language should be simplified here, and any terms that are important but not common knowledge should be defined before use. • P. 8, L. 170: Either define the term “vortex” in the background information of the Executive Summary, or use more common language in place of this technical term. • P. 9, L. 180-181: This statement is repeated almost verbatim on P. 13 (L. 283- 284). It probably only needs to appear once, and P. 13 may be the best place for it. In addition, the authoring team should consider rephrasing the confusing wording in the phrase “increased by about 7% at the minimum ozone in 1993”. • P. 9, L. 184-185: In addition to ozone-depleting substances, ozone is also a greenhouse gas (see P. 10, L. 208-209). The authoring team should consider adding a bullet up front on the importance of ozone as a climate gas. • P. 9, L. 186: The statement that the ODS contribution to radiative forcing is 20% of that from carbon dioxide (CO2) is separated from the statement on P. 7, L. 145 that it is about 14% of the radiative forcing from CO2, methane (CH4), and nitrous oxide (N2O). This discussion should be merged to avoid confusion. Also, radiative forcing is expressed here as a percentage of CO2, differing from P. 10 (L. 208) where radiative forcing is expressed in units of watts per square meter (W/m2). Both units should be given or choose only one consistent expression of radiative forcing throughout the report, else these facts fail to give the larger picture to the reader. • P. 9, L. 187-189: This discussion should be merged with that on the radiative forcing from the substitutes because they are not really separable from a climate point-of- view (i.e., it makes no sense to talk about the radiative forcing of the ODSs in isolation). • P. 9, L. 188: Change “their” to “ODS”.

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Review of CCSP SAP 2.4 16 • P. 9, L. 197-198: This sentence is meaningless. What is meant by “region”— height, latitude, geography? What is meant by “extent of climate change”—the magnitude? The type of change? Where it occurs? The authoring team should consider deleting this sentence. • P. 9, L. 199: At all altitudes? • P. 9, L. 199-201: The combination of these two sentences read like increasing methane has contributed to decrease, instead of increase, in water vapor. The authoring team should revise this text. • P. 10, L. 208: Delete “of climate change”. • P. 10, L. 220 - P. 12, L. 260: Three sections of bullets describe model results for three latitude regions. There is no reason given for the importance and distinction of these three regions, and some bullets within each section are very similar except for small details. The authoring team should synthesize these bullets about recovery into one single section that explains the reason for the latitude distinctions. Also, why is there no discussion of the dynamical super-recovery in the midlatitudes (especially in the Northern Hemisphere), and the associated permanent sub-recovery in the tropics (as evident from the update to SAP figure 5.2 in Eyring et al. [2007])? This would seem to be an important result. • P. 10, L. 220: The term “model” has not been explained. Consider using a descriptive phrase, such as: “Three-dimensional chemistry-climate models designed to project future ozone changes…” • P. 11, L. 226: “up to 15 years earlier” is based on one model; it does not seem to be a representative assessment of the overall Community Climate Model (CCM) results, which seem to suggest recovery will largely follow effective equivalent stratospheric chlorine (EESC) over 60°S-60°N (see the update to SAP figure 5.2 in Eyring et al. [2007]). • P. 11, L. 227: “The assumed scenario for greenhouse gases” is meaningless without an explanation of this “scenario” and its source. • P. 11, L. 228: 5% only applies if you look at subregions; over 60°S-60°N, the value is more like 2%. Moreover, this is not super-recovery, as suggested by the text, as the CCMs were also about 2% higher than 1980 values in the 1960s (see the update to SAP figure 5.2 in Eyring et al. [2007]). • P. 11, L. 233-235: For the audience to whom this report is directed, the contrast between minimum ozone values not starting to increase until 2010 whereas the ozone mass deficit recovers earlier is hard to understand. The authoring team should explain this more clearly. • P. 11, L. 236-237: The statement is correct, but it needs context: for many of the models, Antarctic ozone follows EESC and so the point is that EESC recovers to 1980 values before 2060-2070. This may be partly realistic (decreasing age of air), and partly unrealistic (young age of air bias). • P. 11, L. 243: Change “at 2050” to “in 2050”. • P. 11, L. 243-244: This assertion depends on the scenario. The authoring team should be more specific here. • P. 11, L. 245-247: The text implies that one model predicts worsening Arctic ozone depletion. However, this model cannot be taken seriously, as its EESC is

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Review of Individual Sections 17 physically bizarre. (The WMO report did not take it seriously, so their expert judgment can be relied on in this respect.) In an assessment such as this SAP, good information should be sifted from the bad. To be fairly considered, this information should be presented with an assessment of its reliability. • P. 12, L. 248-260: These three bullets should either be expanded upon, moved, or eliminated. The first bullet uses the term “EESC” and mentions “different scenarios” again without explaining these concepts. In fact, the first sentence of the first bullet is incorrect because changes in CH4 and N2O and climate will dominate the future UV trend; furthermore, using the term “more dominated” is confusing and raises the question of more dominated in comparison to what? The second bullet talks about “the new method”, but it is not clear what this is or why it is important or different from a previously used method. The third bullet appears to be a partial restatement of information on P. 7 and 9. • P. 12, L. 260: “The (Special Report on Emissions Scenario) SRES A1B scenario” is not helpful without an explanation of this “scenario” and its source. Why not give a range of outcomes beyond just one scenario? • P. 12, L. 268 - P. 13, L. 278: How can ozone in midlatitudes increase if it is influenced by Arctic springtime total ozone values that have been lower than 1980 values? These two bullets seem to present a contradiction. • P. 13, L. 274-275: What is the basis for the statement that a significant part of the midlatitude ozone decreases over the U.S. have come from the Arctic? • P. 13, L. 280-284: This sentence is repeated almost verbatim from P. 9, L. 176 - P. 10, L. 181. • P. 13, L. 286: Are the effects “masked”, or is it just that the signal is too hard to discern from the noise and instrument uncertainties? • P. 13, L. 288-292: This bullet should include not just U.S. emissions but also production of ODSs by U.S. companies. • P. 13, L. 289-291: Perhaps the intended meaning of this sentence is better conveyed by rewriting it as follows: “The U.S. has also contributed to … attenuating surface UV changes, and mitigating the radiative forcing of the climate”. • P. 14, L. 293-295: The accuracy of this statement depends on how much of the bank gets released. • P. 14, L. 301-306: This bullet should also discuss radiative forcing. • P. 14, L. 304: Change “would have had” to “would have resulted in”. CHAPTER 1: INTRODUCTION In Chapter 1 of the draft SAP, the background information on ozone should be expanded and revised to accommodate readers who may not have technical knowledge in this area. The committee provides some suggestions below for improving the presentation of this background information.

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Review of CCSP SAP 2.4 18 Major Comments The committee thinks the structure of SAP Chapter 1 would work better by first laying out the role of ozone in the climate system (including ultraviolet [UV]), discussing processes, and then move on to the scope of the report and the logic behind its structure. Since the general public is one of the audiences of this report, the authoring team should clarify some key issues that can be a source of confusion to the lay person. Otherwise, some people may just conclude that some issues are not well understood. Examples include: carbon dioxide warms the troposphere but cools the stratosphere; lower temperatures increase ozone in the upper stratosphere, but decrease ozone (for current halogen loading) in the polar lower stratosphere; ozone depletion and climate change are distinct issues, but they are related both in terms of physical processes and policy (e.g., trade-offs). Along the same lines, the authoring team should consider merging some of the important background given in the individual chapters into SAP Chapter 1. The authoring team should consider starting with chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), the transport of these species to the stratosphere, the differences between CFCs and HCFCs with respect to ozone depletion, their importance as greenhouse gases (GHGs), etc. Then move on to the chemistry and chemistry-climate interactions (as mentioned earlier). More than just gas-phase chemistry is important here. Therefore, the authoring team should consider moving the background information on polar chemistry to SAP Chapter 1, describing the difference between polar and mid- latitude chemistry up front. In any case, this background information comes far too late in Section 3.2.3.2.1 as polar ozone is already discussed in Section 3.2.1.2, for example. Section 1.2 of the prospectus states that the SAP 2.4 “will explore the interactions between climate change and stratospheric ozone changes”. The committee understands that a quantitative assessment of the impact of stratospheric ozone changes on climate is beyond the scope of the report, but nevertheless, some qualitative discussion is called for. Chapter 1 should provide a broad context for the climate issue to set the stage for a more detailed climate discussion in Chapter 4. Specific Comments • P. 15: Instead of stating that the ozone layer “contributes to changes in climate,” the authoring team should simply state that it “plays a significant role in the natural climate system”. L. 321-323: The wording “as well” makes it sound as if “the influence of stratospheric ozone changes on the temperature and its structure in the stratosphere” is different from Point Number 3 in L. 317-318, but they look the same. • P. 15, L. 315: Instead of the term “harsh”, the authoring team should choose a different, clearer, adjective—such as “damaging”. • The first figure appearing in SAP Chapter 1 is on P. 16; however, this figure is identified as “Figure 1.2” instead of “Figure 1.1.” Rename this figure as “Figure 1.1” and then renumber the rest of the figures in Chapter 1. • P. 16, L. 329: “Majority” could be anything over 50%—be up front and say the stratosphere has about 90% of the ozone and that most of the rest is in the troposphere.

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Review of Individual Sections 19 • P. 16, L. 339: Depending on the hemisphere, the contribution of tropospheric ozone to total ozone may be around 10% in the northern hemisphere and just a few percent in the southern hemisphere. • P. 17, L. 345-349: This text repeats what was stated on the previous page. The authoring team should consider rewriting this paragraph. • P. 18, Figure 1.3: This figure does not fully represent all of the ozone removal processes in the stratosphere. As a remedy, the title of this figure could begin with “A simplified representation of…”. In the line for ozone destruction in non-polar regions, there is an oxygen atom without a label, and the label should be added. In both of the lines for ozone destruction, “2 oxygen atoms” should be “2 oxygen molecules” instead. An alternative approach for the authoring team to consider is deleting Figures 1.3 and 1.4 altogether. Rather than focusing on the chemical mechanisms, a single figure could be inserted instead that is more useful for policymakers, simply illustrating that anthropogenic halogens cause stratospheric ozone depletion (perhaps in a top panel) and illustrating that anthropogenic nitrogen oxide (NOx) and hydrocarbons (not volatile organic compounds [VOCs], a lot of which come from trees) cause ozone formation (perhaps in a bottom panel). If the new figure could also indicate that shortwave UV light (which only penetrates the stratosphere) causes a breakdown of CFCs, and that visible light (which can penetrate to the surface) helps produce tropospheric ozone, then we would have a figure that conveyed the essential chemistry to policymakers. Figures 1.3 and 1.4 do not seem helpful for policymakers. • P. 18, L. 370: Mentioning fire extinguishants seems like far too much detail in this context. • P. 19, L. 374-376: This sentence repeats what was stated earlier. The authoring team should consider omitting or rewriting this sentence. • P. 19, L. 377: Transport is indeed very important! It’s a zeroth-order effect, in fact. Therefore, a 2D figure (latitude-height cross-section of ozone), such as the Figure in Box 1.2 of the IPCC/TEAP report (2005), would be very helpful to the reader. • P. 19, Figure 1.4: This figure and the corresponding text are misleading. Both methane and carbon monoxide are examples that are important but not included in this figure. Anything that can convert RO to RO2 or OH to HO2 will have the same effect, not just the VOCs that dominate this process in urban areas. In the reaction equation, ozone should be labeled as “ozone molecules”. In any event, everything in Figure 1.4 can be stated in less space in the text, calling the necessity of Figure 1.4 into question. • P. 19, L. 385: Should this statement read “near UV and visible radiation”? • P. 19, L. 386: After “UV”, add “(shorter wavelength)” to parallel the sentence structure in the previous line, and replace harsh with a clearer adjective as above.. • P. 19, L. 387: Add “stratospheric” before “ozone layer.” • P. 20, L. 393: Up to this point in the chapter, the description of stratospheric chemistry is incomplete. Before introducing CFCs in the next paragraph, this would be a good spot to expand the discussion of stratospheric chemistry, as highlighted above in the “Major Comments” for SAP Chapter 1. • P. 20, L. 410: Add “in” after “subsequently.” • P. 21, L. 420: Change “long lifetimes” to “lifetimes of many years.” • P. 22, L. 439: Replace “involvement” with “interactions.”

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Review of CCSP SAP 2.4 20 • P. 22, Figure 1.1: Discussion of this figure could be expanded to include much more about the role of ozone in the climate system and vice versa. Figure 1.1 lacks methane and N2O components. • P. 24, L. 483: Not all CFC substitutes are “climate friendly.” • P. 24, L. 491: After “Perfluorocarbons”, add “and referenced therein.” CHAPTER 2: OZONE-DEPLETING SUBSTANCES Chapter 2 of the draft SAP is comprehensive in its discussion of the production, consumption, emissions, and atmospheric abundances of ODSs and total equivalent chlorine. Although the committee was impressed with the completeness of this review of ODSs, which includes all the information required, it is not presented in an understandable way. Chapter 2 is a long chapter, and its organization was difficult to follow. To aid other readers, the authoring team should consider including an introduction to the chapter and a brief discussion about the organization of the chapter. Chapter 2 should include more thorough explanations throughout, should synthesize information on production, consumption, emissions, and banks, and should explain the various measures of ozone before presenting the key findings. Making the detailed suggestions in the following comments will improve the readability and the accuracy of the synthesis presented in Chapter 2. Chapter 2 of the draft is written at level only understood by halocarbon experts rather than a level accessible for professionals who work at the interface between science and policy. Major Comments Background information should be presented at the beginning of the draft SAP Chapter 2, perhaps defining concepts and incorporating parts of the key issues section, before presenting the key findings. As part of this background information, the authoring team should add a box in either SAP Chapter 1 or the introduction to SAP Chapter 2 to explain the life cycle of fluorochemicals, define consumption, and explain the relationship between production, consumption, emission, atmospheric concentrations, and EESC or radiative forcing. Elements of that box should include the following: • A cartoon similar to Figure SPM-1 of the IPCC/TEAP Special Report on Ozone and Climate (IPCC/TEAP 2005). • A definition of consumption, in agreement with the Clean Air Act and the Montreal Protocol: Consumption = Production + Imports – Exports. Include a statement that consumption equals production at the global level. Under the Montreal Protocol, the primary control is on consumption and not emissions. This means that there is no control of “banks under the Protocol.” Probably not to be stated in the SAP, an issue of note is the growing movement in the United States to control HFCs through control of consumption. The justification and implication of this definition are the basis for focusing on consumption in Chapter

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Review of Individual Sections 21 2. Because of the focus on consumption, all SAP figures showing production should show consumption instead. • A simple explanation of how a vintaging model works to calculate emissions from consumption. This might be done with a link to Box 2.1, with information in that box being generalized to how a vintaging model works with a focus on the Environmental Protection Agency (EPA) model for estimating U.S. contributions. As already recommended in Chapter 2 (Major Comments) of this review, Box 2.1 should be extended to 2020. • A simple explanation of how atmospheric concentrations are calculated from emissions. • A simple explanation of how radiative forcing is calculated from concentrations. • A link to Box 2.2 for EESC. • A simple explanation of the “bottom-up” method of estimating concentrations vs. the “top-down” method of estimating emissions. It would be important to demonstrate, for one or a few compounds, that the two approaches to estimating atmospheric abundances (i.e., bottom-up/top-down) converge. This could be accomplished with material reported in Chapter 2 or with references to previous work. Perhaps a figure could be used as well. This can then be used to emphasize in the text, and perhaps in the key points, the importance of continued atmospheric concentration measurements (top-down) because they will be needed in the future if the reporting of global emissions of some compounds becomes incomplete. In addition to the explanation of these concepts, the authoring team should synthesize information on production, consumption, emissions, and banks—perhaps all together in one chart. The authoring team should add a plot showing the consistency between the measured and expected mixing ratios for compounds where the production numbers are well established. The graphical display of this agreement could be used to indicate that continued measurements are needed in order to have good emissions estimates (in particular, for species where reporting is poor). The issue on methyl bromide is not brought forward. This issue is the one example where the U.S. is not doing well. Methyl bromide is unique in that it not only has substantial natural contributions, but also has significant unregulated emissions. The committee recommends that Chapter 2 include a “box” focusing on methyl bromide. A figure in the box (perhaps a pie chart) could indicate the sources of methyl bromide (critical use exemption, quarantine and preshipment [QPS], natural, etc.), and how those sources have changed over time. The importance of critical use exemptions and QPS should be highlighted in a concise key finding bullet. The rising contributions (from the United States and other countries) due to these uses have policy implications. The key findings section should be reworded so that each one is short and concise (a few sentences maximum) with fewer numbers. To summarize the numbers supporting the findings, perhaps a table or figure could be inserted instead. As part of the synthesis of the draft SAP, the authoring team should include a simplified summary statement for the whole chapter.

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Review of CCSP SAP 2.4 22 Specific Comments • P. 26-28: the Key Issues section should reflect the policy issues described above; P. 29-34: Key Findings Section should address the key issues. • P. 27, L. 526: As written, the text suggests that HFCs are ODSs. To correct this, add “and their substitutes” after “substances”. • P. 28, L 554-555: Rewrite this question to read, “What were, what are, and what will be the contributions of the United States to production and emissions of ODSs and substitute chemicals in the past, in the present, and in the future?”. • P. 29-31, “Key Findings” section: In the first four “Key Findings” bullets, the authoring team should consider removing the portions related to global warming potential (GWP) to the last bullet of this section, where these ideas can be presented with some context and then synthesized. • P. 29, L. 574 & 577: “ODP-Tons” and “CO2-equivalents” have not yet been defined at these points in this chapter. • P. 29, L. 576: Replace “to applications” with “regarding applications” instead. • P. 30, L. 600-614: In this key findings section, L. 601-602 give proportions of global production in the form of CFCs, HCFCs, and HFCs. The authoring team should also state the values in ODP-Tons and supply the corresponding numbers for the United States. • P. 33, L. 663-681: This paragraph (and associated text, P. 44 to 47) provides a particularly good explanation of U.S. emissions of methyl bromide, but it is only mentioned in passing in Chapter 6. The authoring team should consider highlighting the importance of this text. • P. 34, L. 688-689: Replace “EESC calculated” with “calculated EESC” instead. • P. 36, L. 736: Since fluorine is also a halogen, change “halogen” to “Cl and Br”. • P. 37, L. 753-757: The differences between the two data sets almost certainly are dominated, according to the supporting information supplied here and subsequently, by the increasingly limited coverage of reporting to Alternative Fluorocarbons Environmental Acceptability Study (AFEAS). This point should be made more clearly in the first sentence. • P. 37, L. 755-756: Define “Article 5” countries where this is first mentioned. • P. 38, L. 781-782: A clear distinction should be made here between where the figure caption ends and the chapter text resumes. • P. 38, Figure 2.2: The U.S.-global ratio going negative, and the underlying information in the chapter, is very difficult to understand. Given the definition of consumption = production + import – export, the only way U.S. consumption can go negative is if inventories are decreased so that export is the dominant factor. This seems very unlikely. Also, what are the baselines used? Changes made to Figure 2.2 should also be reflected on P. 46, L. 939 & 942. • P. 39, L. 782: Clarify which “substitutes” these are (i.e., whether HFCs are included). • P. 39, Table 2.1: Here and elsewhere in the chapter, the focus appears to be more on production than consumption. Consumption is the more relevant measure of U.S. contribution to emissions reductions and should be the focus, and the weighted GWP

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Review of Individual Sections 23 values should be available. CFC and HCFC data are reported to EPA, and the EPA vintaging model should be able to provide estimates of HFC consumption. Also, here and elsewhere in the chapter, the GWPs used must be specified; those listed in the appendix or those from the IPCC Second Assessment Report (SAR), the values the U.S. uses for purposes of reporting under the United Nations Framework Convention on Climate Change (UNFCCC). • P. 39, L. 798: Is it correct to state that HCFC production is decreasing instead of increasing? The authoring team should consider including a graph of compound class vs. year, similar to Figure 2.16 (P. 94), except showing production instead of GWP. • P. 40, Figure 2.3: Explain how carbon tetrachloride (CCl4) makes ozone (negative ODP). Also, what is the source of the HFC data? It is not the United Nations (UN), as production of HFCs is not reported under either the Montreal or Kyoto Protocol. • P. 42, Figure 2.4 and elsewhere in the chapter where HFC-23 is discussed, consider the following points: The assumption that production = emissions is wrong for HFC-23. In the o U.S., Europe, and Japan, significant amounts of HFC-23 are destroyed. Additionally, some HFC-23 is captured for use as a specialty low temperature refrigerant and as a fire extinguishant. In the U.S., HFC-23 emissions and total HCFC-22 production are reported o annually to the EPA in aggregate. The EPA vintaging model should capture the refrigerant and fire o extinguishant HFC-23 emissions. Information from the two sources listed above should be used to show o trends in U.S. HFC-23 emissions both on an absolute basis and as a percentage of total. Can HFCs other than 23 and 134a be estimated? On P. 43, an estimate is o provided. The authoring team should consider carrying this estimate through and including it on Figures 2.3b and 2.4. These comments about HFC-23 also apply to: P. 45 (L. 918-919), P. 58 o (L. 1171-1173), and P. 59 (L. 1200-1207). • P. 42, Figure 2.4 caption: In L. 851, change “Global trends in production” to “Global production”; in L. 852, delete “to these trends”. The figure does not plot trends (although, trends can be inferred from the time series). • P. 44, L. 897: This is the first use of the term “feedstock” in this chapter, so this should be defined. • P. 44, L. 903: Is 0.5% a proportion of production for ODSs? • P. 44, L. 904: HCFC-22 should be added to the list of ODSs used as feedstock. • P. 44, L. 909: Does an increase of only 9% mean that methyl bromide (MeBr) is a small contributor to ODS? • P. 46, L. 942: It seems possible that negative consumption for carbon tetrachloride could occur in a single year (errors in the individual contributions or short term lags), but the committee doesn’t see how it can occur for several years. • P. 46: Should the U.S. contribution be compared to the population? • P. 46, L. 949: where did the 62% come from? No supporting information could be found for a figure this large.

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Review of CCSP SAP 2.4 48 Southern Hemisphere). Two-dimensional, non-interactive models should not be considered projections, as they are physically unrealizable. Furthermore, the circulation changes predicted by 2D interactive models could be of dubious value. Two-dimensional models are probably best used to look at the differences between scenarios. Chapter 5 is uncritical of CCM results that are deemed unreliable by WMO. For example, in many places, recovery dates or depletions are quoted from models explicitly designated “unreliable” by WMO (2007) (those with the dashed lines in the plots), yet they seem to be given full weight in this report. The two models in question (AMTRAC and MRI) had Cly that was clearly physically wrong (and stated as such in the WMO report). So, why even consider them? In general, Chapter 5 of the draft SAP lacks an adequate “assessment” concerning the models: results are presented without enough context or discussion of what the authors believe. Where there are discrepancies between different models, the authoring team should provide at least some value-added expert opinion. (Much of this can actually rely on the WMO report.) The authoring team should include some update from the WMO report, since 18 months have passed from when it was coming into final form. At the very least, the CCM discussion should have been based on Eyring et al. (2007), not the WMO report, given that the WMO report had none of the “reliable” models going past 2050, whereas Eyring et al. (2007) show two of them out to 2100 (one of which is a U.S. model). The results published in the Eyring et al. paper represent a straightforward update of the results in the WMO report, but some of the simulations were not completed in time to be included in the WMO report. Nevertheless, the Eyring et al. paper represents the current consensus of the CCM community, and so the relevant figures should be taken from it. In fact, the authoring team would be justified in including additional model simulations beyond those shown in the Eyring et al. paper, especially from the U.S. models, for the most complete picture. The authoring team should include more discussion of the differences between midlatitude and tropical changes, since much of the discussion in Chapter 5 is for the 60°S-60°N aggregate. This point is especially pertinent in light of the recent paper by Randel and Wu (2007)—the results of which were highlighted in the WMO report— noting significant decreases in the stratospheric column in the tropics (in agreement with the CCMs). In particular, the models are pointing to a strong dynamical (transport- induced) super-recovery in the Northern Hemisphere midlatitudes, which could see total ozone returning to 1980 levels before 2020 (evident from the update to SAP figure 5.2 in the Eyring et al. paper). This should be discussed in SAP Chapter 3, and the implications of this certainly have relevance for the United States and pertinence for modeling and attribution of climate change (i.e., observed ozone changes cannot be imposed and reversed in line with EESC as a scenario to force climate models in the 21st century). For P. 238, 239, and 240, Figure 5.7 and Table 5.2, two additional scenarios should be added here and in supporting information: (1) a scenario that shows zero emissions of EPA estimates of CFCs and halons that could be economically recovered within the United States (and globally, if available from IPCC or EPA estimates) and destroyed, and (2) a scenario that reduces HCFC production consistent with U.S. proposals to the Montreal Protocol (as on the ozone secretariat web site) for acceleration of the HCFC phaseout in developed and developing countries; information in the U.S.

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Review of Individual Sections 49 submission to the ozone secretariat can be generalized to develop a representative scenario. Both of these scenarios are required for decision support of policy issues being considered by the United States. The reference list in Chapter 5 includes almost no journal papers. The authoring team should consider expanding their literature review for this chapter, including original studies rather than just citing the assessment, where appropriate. Specific Comments • P. 204, L. 4262: Why only consider column ozone? This seems overly narrow. • P. 204, L. 4266-4270: The wording needs to be tightened up. What non-halogen emissions are discussed here? And how is this different from climate change (it says “also” on L. 4268)? Does the text intend to mean changes in solar cycle and volcanic eruptions, or just those phenomena themselves? • P. 204, L. 4275: All ODSs will not be gone by mid-century. ODSs in 1980 were well above zero. More generally, the authoring team should discuss the selection of 1980 as the baseline year. • P. 205, L. 4284: “Will show” is strange wording. • P. 205, L. 4284-4292: It is really the combination between climate change and halogens that matters, so this should be discussed more generally. These lines read as if ozone is determined by halogens until 2050, and afterwards ozone is determined by climate change. That is too simplistic. Why is there no discussion of the dynamical super-recovery in the midlatitudes (especially in the Northern Hemisphere), and the associated permanent sub-recovery in the tropics? This would seem to be a big story! • P. 205, L. 4286-4287: In fact, the CCMs suggest that circulation changes will be of comparable importance in many regions (tropics, Northern Hemisphere midlatitudes, possibly even the Arctic). In fact, the tropical changes in the stratospheric column observed today may well be mainly due to climate change (though this has yet to be demonstrated). • P. 205, L. 4289-4291: Not just then, but already. • P. 206, L. 4317: “Up to 15 years earlier” is based on one model; it does not seem to be a representative assessment of the overall CCM results, which (the committee would say) rather seem to suggest recovery will largely follow EESC over 60°S-60°N (see the update to SAP figure 5.2 in the Eyring et al. paper). • P. 206, L. 4320: Five percent only applies if you look at subregions; over 60°S- 60°N, it is probably more like 2%. And this is not super-recovery, as suggested by the text, as the CCMs were also 2% higher than 1980 values in the 1960s. • P. 207, L. 4329: The statement is correct, but it needs context: for many of the models, Antarctic ozone follows EESC, and so the point is that EESC recovers to 1980 values before 2060-2070. This may be partly realistic (decreasing age of air), and partly unrealistic (young age of air bias). • P. 207, L. 4338: The text implies that one model predicts worsening Arctic ozone depletion. However, this model cannot be taken seriously, as its EESC is physically bizarre. (The WMO report did not take it seriously, so their expert judgment can be

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Review of CCSP SAP 2.4 50 relied on in this respect.) In an assessment such as this SAP, good information should be sifted from the bad. To be fairly considered, this information should be presented with an assessment of its reliability. • P. 207, L. 4343: Isn’t it virtually tautological to say that halogens will have a negligible effect on ozone when there are no halogens left? Is the text actually saying anything more than this? • P. 210-211, L. 4412-4414: That the indirect radiative forcing due to ozone loss falls to zero before the direct RF does is merely a point of definition; that is how the indirect RF is defined (rather arbitrarily). In fact, the ozone loss attributable to ODSs began before 1980 (see Figure 3.2, P.118). • P. 212-213, Section 5.1: This is almost a verbatim repetition of the key findings. A proper introduction should be included. • P. 213, L. 4454-4456: What is the reference for this statement? Halogen effects are changing slowly, and there is increasing evidence for circulation changes (and, in the upper stratosphere, effects of stratospheric cooling). • P. 213, L. 4461: Replace “should be” with “are”. • P. 214, L. 4473-74: The uncertainty in these scenarios should be discussed. • P. 215, L. 4508-4509: Check the consistency of these numbers with Figure 4.9. • P. 215, L. 4509: Change “0.5%” to “1.0%”. • P. 215, L. 4510: Change “1.0%” to “0.5%”. • P. 217, Section 5.2.2: If 2D models are to be shown, then the authoring team should include a more critical discussion of why, and what aspects can be trusted of the projections. For example, if non-interactive results are included, they cannot be considered part of the projections, but only to look at the difference between interactive and non-interactive as representing the effects of climate change. So, it is for attribution rather than projection purposes. (This is how the non-interactive 2D models were used in WMO [2007], apart from Figure 1(c) of the Executive Summary, which seems to have included the non-interactive 2D models from Figure 6-9 of WMO [2007] [displayed in SAP 2.4 as Figure 5.1] in constructing its range of model projections.) • And along the same lines, are the interactive 2D models trustworthy? To include CO2 cooling is fine, but circulation changes from a 2D model surely cannot be trusted as they are not physically based (e.g., they can be induced by Rayleigh drag or strong diffusion). The committee is not sure what is meant by “calculating the residual circulation from heating rates”—this makes no sense. What is the role of circulation changes in these models? • In the WMO report (2007), the 2D models were included to be able to consider different scenarios, which the CCMs were not able to consider because of computational limitations. Arguably, the differences between scenarios from the 2D models would be of value. But for the baseline projections, the 2D models need to be discounted. Do we really believe a projection of 60°S-60°N ozone being 5% above 1980 values in 2100 (Figure 5.1), when it is not seen in the CCMs (Eyring et al. 2007)? • P. 217, L. 4542: CCMs are now better able (than 2D models) to represent global ozone, too. • P. 219, Figure 5.1: Why is the super-recovery different in the two hemispheres?

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Review of Individual Sections 51 • P. 220, L. 4584: “Most” CCMs (at least for the future projections) do not include a QBO. • P. 220, L. 4585: How can the QBO make it difficult to “define recovery”? • P. 220, L. 4586: This one model projection is actually two, and they are both not to be trusted for this purpose. The WMO authors explicitly said so (WMO 2007). So, the results should not be highlighted. • P. 220, L. 4588: Need to update! • P. 220, L. 4590: Climate change is evident much earlier, in certain regions. • P. 220, L. 4591: This value is from AMTRAC, which is also 2-5% above the 1980 values in the 1960s. So this wording is very misleading. • P. 221, Figure 5.2 (and associated discussion): There is no discussion at all of possible circulation changes, yet they are quite evident from this figure. The authoring team should at least replace this figure with the one in Eyring et al. (2007). The authoring team should include some critique of AMTRAC and MRI, if the results are to be shown. And note that there is a lot of uncertainty associated with the 1980 baseline. (This does not refer to the fact that ozone loss begins earlier, but rather that the use of the 1980 baseline requires statistical acrobatics which lead to unreliable estimates of the ozone depletion.) • P. 221, L. 4621: Yes, but for many of the models the EESC recovery date is earlier, too. This might be partly true (faster Brewer-Dobson [BD] circulation, so decreasing age of air), but also partly wrong (young age of air bias in models). There needs to be an assessment here. • P. 222, L. 4625: Why even mention this one model (thus giving credence to it), if the authoring team does not believe its projection? • P. 224, Section 5.2.3: This section needs more quantification (and some references). • P. 224, L. 4658: It seems tautological to say that climate change will dominate over the effects of ODSs when there are no ODSs left. • P. 225, L. 4665: “Preoccupied” is an inappropriate word to use here. • P. 225, L. 4666-4667: This long-term, world-wide decrease contradicts what is said in the middle paragraph on P.145. • P. 225, L. 4682: Sure, but these AMTRAC results are not trusted. The midlatitude Cly is unphysically high, for numerical reasons that are understood. • P. 239, L. 4921: This point needs some explanation. • P. 241, L. 4956: To avoid confusion, the reference should be to section 5.5.1.2, not just section 5.5.1, to make clear that the differences that are being talked about are between Newman et al. (2006) and the WMO report, in each region (polar and midlatitudes), and not between polar and midlatitudes. • P. 242, Figure 5.8: Why duplicate a figure that is already in Chapter 2? (In Chapter 2, the figure is even referred to!) • P. 243, L. 4995-4996: For a discussion of life cycle analysis, a reference to the IPCC/TEAP report (2005) would be good. • P. 244, L. 5003: Change “5.7%” to “5.6%”. • P. 245 & 246, L. 5032-5041 & 5047-5056: Information in these sections is repetitive.

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Review of CCSP SAP 2.4 52 • P. 245, Section 5.5.3.2: This paragraph is repeated verbatim immediately below. • P. 246, L. 5060: Is ozone depletion really so nonlinear (apart from the ozone hole)? Changes of less than 10% should be reasonably linear. • So far, the report is assuming, in coming up with its estimates, that all observed ozone changes are attributable to ODSs. But, there are many studies indicating that a substantial fraction of the observed changes (~30% in NH midlatitudes) are due to changes in transport, rather than ODSs. So, the U.S. ODS-related contribution to ozone changes would be reduced accordingly. CHAPTER 6: IMPLICATIONS FOR THE UNITED STATES This chapter starts with a discussion of why the changes in ozone over the United States are not directly connected with the U.S. emissions of ODSs. Such a discussion is likely necessary to the purpose of this report, but the chapter largely does not capture the content it should have to be useful to policymakers. Several major comments are made below, as well as a number of more specific comments. Major Comments “Implications for the United States” can be viewed in three ways: in terms of accountability, impacts, and management. To address accountability, Chapter 6 of the draft SAP should assess the past contribution of the U.S. to ozone depletion (EESC) and climate change (radiative forcing) due to consumption of ODSs, and how U.S. actions have contributed to reducing past, current, and future contributions to those issues. To address impacts, the authoring team should assess potential impacts in the United States due to global consumption of ODSs. This can only be addressed in terms of the atmospheric sciences since the report was not designed to be an effects report. And finally, the authoring team should discuss the remaining management issues related to ODSs and what information can be provided from a scientific perspective to inform these management decisions. Each of these three implications should be addressed in Chapter 6 with summary points being carried forward to the Executive Summary. A main problem with Chapter 6 is the lack of discussion of ODS management issues that are currently being discussed heavily by policymakers, both in the United States and internationally through the Montreal Protocol. Although the committee does not suggest that the specific bills before Congress or specific measures before the Montreal Protocol should be included, the authoring team should include a generic discussion of these issues. Several examples of the key issues to examine are provided below: • Representative Henry Waxman of California has sponsored a bill (H.R. 3448) that would accelerate the phase-out of HCFCs, but this bill includes an exemption to allow the continued use of HCFC-123 in specific applications. The United States and the other parties to the Montreal Protocol are implementing an

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Review of Individual Sections 53 accelerated phase-out of HCFCs. The SAP should discuss the science potentially affecting policy issues associated with HCFCs. • Phasing out ODSs has potential implications to climate change due both to energy efficiency issues and the potential direct climate impacts of replacement compounds. The authoring team should include a discussion about the tradeoffs between ozone and climate policy as ODSs are eliminated. (There is much material on this in the IPCC/TEAP report [2005], which could be drawn upon.) • While there is a very general discussion about the importance of banked quantities of ODSs, there is no discussion about the size of the banks, especially the banks that could be economically recovered and destroyed, in the United States or elsewhere in the world, nor any discussion about possible policy considerations to reduce or eliminate the banks so that effects on ozone could be reduced. • There are some additional issues associated with the Montreal Protocol that should be discussed. For example, there are ongoing considerations for the effects of emissions of short-lived ODSs such as CF3I, n-propyl bromide, and other compounds (WMO 2007). There is a need for three-dimensional modeling studies and an assessment of such short-lived compounds to meet the needs of policymakers. Another example is the ongoing considerations about methyl bromide. There is also no discussion of the potential role of indirect GWPs (a direct connection between stratospheric ozone and climate) in policymaking. Chapter 1 of the IPCC/TEAP report included a detailed discussion of indirect GWPs, including their uncertainties and potential pitfalls, and this material could be drawn upon. Chapter 4 discusses the effects of carbon dioxide and human-impacted greenhouse gases on ozone. The authoring team should consider including a discussion of the role that the United States plays in the production and emission of such gases, and the resulting implications on ozone policy. The SAP would also benefit by including a discussion about the interrelationships between ozone policy and climate policy, both for the United States and internationally. More specifically, the SAP does not address the fact that limiting future emissions of methane is a “win-win” situation, in that methane affects ozone depletion and climate change. A concerted effort to reduce natural gas leaks and/or trap and burn (for fuel) methane emitted by landfills would help the ozone layer (less methane means less water, which means less HOx and more mid-latitude ozone and less PSCs and more polar ozone). There is ample scientific literature that points to the beneficial effects to the ozone layer from less methane, and other scientific literature that points to beneficial effects to global climate of less methane. A similar argument could be made regarding the win-win situation if N2O emissions could be reduced (by, for example, more use of treated livestock manure as a beneficial product, rather than waste). Charts such as Figure 1.1 that simply indicate “the intricate coupling of the issues” are not too useful for policymakers; however, a figure showing the ODP and GWP of methane and N2O, and demonstrating the positive effect for both ozone and climate of reductions in methane and N2O, would certainly be useful to policymakers. The authoring team should also consider highlighting these options in the SAP Executive Summary.

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Review of CCSP SAP 2.4 54 The discussion of surface UV measurements has problems as in Chapter 3 of the draft SAP. It is not clear how section 6.5 fits into “Implications for the U.S.” Perhaps the title of the Chapter 6 could be changed. For the section describing “a world avoided”, the committee commends the authoring team’s attempt to make the point that we would be facing an even more delayed recovery if the participating nations had not taken action when they did. Specific Comments • P. 250, L. 5171: Emissions of what? • P. 251, L. 5197-5207: Suggest the following rewrite, or something similar: The UV changes over the U.S. have has been measured from ground stations. Unfortunately, as discussed earlier, surface UV measurements are strongly affected by clouds, aerosol, and air pollution, thus they are not a good reference for estimating changes in UV from long term changes in ozone. Such changes in UV, however, can be estimated from the satellite record of column ozone and backscattered UV as described in Ch. 3. and calculated from satellite observations of column ozone. Trends derived from observations from the surface have large uncertainties because of high variability and influence of clouds and aerosols. • Calculations Estimates of UV based on satellite observations of column ozone and reflectivity of the surface suggest that the averaged erythemal irradiance (which is a weighted combination of UVA and UVB based on skin sensitivity) over the United States increased roughly by about 7% when the ozone minimum was reached in 1993 and is now about 4% higher than in 1979. Direct surface-based observations do not show significant trends over the U.S. in UV levels over the past three decades because effects of clouds and aerosol have likely masked the increase in UV due to ozone depletion over this region. For “ground stations,” the authoring team should consider provide more detail, such as the number and location of these stations. • P. 251, L. 5210: Why is it difficult to accurately quantify the U.S. fraction? Is this statement in conflict with the statement on the previous page?: “The contribution of emissions from the U.S. to the global burden of ozone-depleting substances can also be quantified” (L. 5176-5177). • P. 252, L. 5214-5217: After updating the percentages as discussed in this review, also discuss the implications of these percentages. For example, since it accounts for xx% of the global emissions currently, it is clear that the U.S. needs to carefully consider its role in additional policy considerations. It would be nice to see a table that discusses the effects from individual gases to get to the percentages provided, either here or in an earlier chapter. • P. 252, L. 5223: Should the CUEs be specified? • P. 252, L. 5224-5227: Similarly, discuss policy implications of the banked amounts, but also try to be more quantitative in the discussion. If possible, provide information on the individual contributions to the banked amount for the U.S. and the rest of the world.

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Review of Individual Sections 55 P. 253, L. 5240-5243: Why are two different units used, one absolute (W/m2) the • other % weighted by100 year GWP? Do the %GWP apply only to U.S. or global? • P. 253, L. 5245: Reduced the climate forcing by how much? Recall the claim earlier that this can be quantified. • P. 255, L. 5285-5286: This sentence needs rewording so that its meaning is clarified. REFERENCES Bodeker, G.E., H. Shiona, and H. Eskes. 2005. Indicators of Antarctic ozone depletion. Atmospheric Chemistry and Physics 5:2603-2615. Bodeker, G.E., H. Struthers, and B.J. Connor. 2002. Dynamical containment of Antarctic ozone depletion. Geophysical Research Letters 29(7). Bodeker, G.E., and D.W. Waugh. 2007. The Ozone Layer in the 21st Century. Chapter 6 In Scientific Assessment of Ozone Depletion: 2006. Global Ozone Research and Monitoring Project - Report No. 50. Geneva: World Meteorological Organization. Available online: http://ozone.unep.org/Assessment_Panels/SAP/Scientific_Assessment_2006/inde x.shtml. CCSP (U.S. Climate Change Science Program). 2007. CCSP Synthesis and Assessment Product 2.4: Prospectus for Trends in Emissions of Ozone-Depleting Substances, Ozone Layer Recovery, and Implications for Ultraviolet Radiation Exposure. Washington, DC: U.S. Climate Change Science Program. Available online: http://www.climatescience.gov/Library/sap/sap2-4/sap2-4prospectus-final.pdf. Dessler, A.E. 2000. The Chemistry and Physics of Stratospheric Ozone. International Geophysics Series: Academic Press. Eyring, V., N. Butchart, D.W. Waugh, H. Akiyoshi, J. Austin, S. Bekki, G.E. Bodeker, B.A. Boville, C. Brühl, M.P. Chipperfield, E. Cordero, M. Dameris, M. Deushi, V.E. Fioletov, S.M. Frith, R.R. Garcia, A. Gettelman, M.A. Giorgetta, V. Grewe, L. Jourdain, D.E. Kinnison, E. Mancini, E. Manzini, M. Marchand, D.R. Marsh, T. Nagashima, P.A. Newman, J.E. Nielsen, S. Pawson, G. Pitari, D.A. Plummer, E. Rozanov, M. Schraner, T.G. Shepherd, K. Shibata, R.S. Stolarski, H. Struthers, W. Tian, and M. Yoshiki. 2006. Assessment of temperature, trace species and ozone in chemistry-climate model simulations of the recent past. Journal of Geophysical Research 111:D22308. Eyring, V., D.W. Waugh, G. E. Bodeker, E. Cordero, H. Akiyoshi, J. Austin, S.R. Beagley, B.A. Boville, P. Braesicke, C. Brühl, N. Butchart, M.P. Chipperfield, M. Dameris, R. Deckert, M. Deushi, S.M. Frith, R.R. Garcia, A. Gettelman, M.A. Giorgetta, D.E. Kinnison, E. Mancini, E. Manzini, D.R. Marsh, S. Matthes, T. Nagashima, P.A. Newman, J.E. Nielsen, S. Pawson, G. Pitari, D.A. Plummer, E. Rozanov, M. Schraner, J.F. Scinocca, K. Semeniuk, T.G. Shepherd, K. Shibata, B. Steil, R.S. Stolarski, W. Tian, and M. Yoshiki. 2007. Multimodel projections of stratospheric ozone in the 21st century. Journal of Geophysical Research 112:D16303.

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Review of Individual Sections 57 von Hobe, M., Salawitch, R. J., Canty, T., Keller-Rudek, H., Moortgat, G. K., Grooß, J.- U., Muller, R., and Stroh, F. 2007. Understanding the kinetics of the ClO dimer cycle. Atmospheric Chemistry and Physics 7:3055-3069. WMO (World Meteorological Organization). 2003. Scientific Assessment of Ozone Depletion: 2002. Global Ozone Research and Monitoring Project - Report No. 47. Geneva. ———. 2007. Scientific Assessment of Ozone Depletion: 2006. Global Ozone Research and Monitoring Project - Report No. 50. Geneva. Available online: http://ozone.unep.org/Assessment_Panels/SAP/Scientific_Assessment_2006/inde x.shtml. Yang, E.-S., D. M. Cunnold, M. J. Newchurch, R. J. Salawitch. 2005. Change in ozone trends at southern high latitudes. Geophysical Research Letters 32:L12812.

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