2
Overarching Comments

In this chapter, the committee provides five overarching comments on the U.S. Climate Change Science Program’s (CCSP) 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). These overarching comments span more than one section of the SAP and address how responsive the authoring team was to their prospectus. Therefore, a number of important major comments that are technical and specific to a single chapter are not mentioned in the overarching comments below. In some cases, the comments on the separate sections of the draft SAP (see Chapter 3 of this report) offer detailed suggestions on how to address the overarching comments presented here.

RELATIONSHIP BETWEEN OZONE AND CLIMATE

Although the prospectus for SAP 2.4 (CCSP 2007) does not address the effects of ozone on climate, radiative forcing from ozone-depleting substances (ODSs) and their substitutes is covered in the SAP. The authoring team has indicated that changes in their approach to the SAP were made after the prospectus was finalized. Thus, the authoring team should explicitly acknowledge that this aspect of the SAP goes beyond the scope of the prospectus. The authoring team decided not to go further than radiative forcing in terms of climate effects, and they stated that the reason was that the 2006 climate change assessment (IPCC 2007) was not yet available when this SAP was developed. The committee appreciates this reasoning. However, the two-way coupling between ozone and climate is becoming increasingly important for attribution and, hence, for policy, and scientific research is evolving more and more in this direction. That was indeed a major rationale behind IPCC/TEAP (2005), a key reference document for this SAP. In Chapter 4 of the draft SAP, the authoring team brings up the issue of the effects of ozone on climate without fully pursuing this topic. The authoring team should include a more complete discussion that clearly states that ozone is part of the climate system and explains the ozone-climate connection at the process level. The authoring team should also clearly state that separating the treatment of the ozone depletion, ozone recovery, and climate change problems is scientifically artificial, and that from a scientific perspective, an integrated approach is called for in the future. The committee realizes that this SAP can make only a tentative first step in this respect, but it is nevertheless an important step.

As detailed in the committee’s major comments for Chapter 4 of the draft SAP (see Chapter 3 of this review), the authoring team should include additional discussion of climate change scenarios, rather than just sticking to the single baseline Special Report on



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2 Overarching Comments In this chapter, the committee provides five overarching comments on the U.S. Climate Change Science Program’s (CCSP) 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). These overarching comments span more than one section of the SAP and address how responsive the authoring team was to their prospectus. Therefore, a number of important major comments that are technical and specific to a single chapter are not mentioned in the overarching comments below. In some cases, the comments on the separate sections of the draft SAP (see Chapter 3 of this report) offer detailed suggestions on how to address the overarching comments presented here. RELATIONSHIP BETWEEN OZONE AND CLIMATE Although the prospectus for SAP 2.4 (CCSP 2007) does not address the effects of ozone on climate, radiative forcing from ozone-depleting substances (ODSs) and their substitutes is covered in the SAP. The authoring team has indicated that changes in their approach to the SAP were made after the prospectus was finalized. Thus, the authoring team should explicitly acknowledge that this aspect of the SAP goes beyond the scope of the prospectus. The authoring team decided not to go further than radiative forcing in terms of climate effects, and they stated that the reason was that the 2006 climate change assessment (IPCC 2007) was not yet available when this SAP was developed. The committee appreciates this reasoning. However, the two-way coupling between ozone and climate is becoming increasingly important for attribution and, hence, for policy, and scientific research is evolving more and more in this direction. That was indeed a major rationale behind IPCC/TEAP (2005), a key reference document for this SAP. In Chapter 4 of the draft SAP, the authoring team brings up the issue of the effects of ozone on climate without fully pursuing this topic. The authoring team should include a more complete discussion that clearly states that ozone is part of the climate system and explains the ozone-climate connection at the process level. The authoring team should also clearly state that separating the treatment of the ozone depletion, ozone recovery, and climate change problems is scientifically artificial, and that from a scientific perspective, an integrated approach is called for in the future. The committee realizes that this SAP can make only a tentative first step in this respect, but it is nevertheless an important step. As detailed in the committee’s major comments for Chapter 4 of the draft SAP (see Chapter 3 of this review), the authoring team should include additional discussion of climate change scenarios, rather than just sticking to the single baseline Special Report on 6

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Overarching Comments 7 Emissions Scenario (SRES) A1B. Use of a single scenario represents a major uncertainty for future ozone projections. Although the single baseline SRES A1B scenario is the only scenario that the Community Climate Model (CCM) modelers ran for the 2006 WMO/UNEP ozone assessment, the 2D models were run on a range of scenarios. Perhaps the authoring team could select one of the interactive 2D models from the assessment, benchmark it against the better CCMs, and then use the results from the full range of scenarios to include additional discussion of climate change scenarios. The authoring team should also explicitly state that they are not considering how drastic changes that might take place in the climate system might affect the ozone problem. ASSESSING U.S. CONTRIBUTIONS TO OZONE-DEPLETING SUBSTANCES AND RADIATIVE FORCING There are inconsistencies in the draft SAP in estimating U.S. contributions to production, consumption, and emissions of ozone-depleting substances (ODSs). There is also inconsistency in the draft SAP with regard to the confidence to be placed on these emission estimates: • Regarding production and consumption, there should not be inconsistencies in the numbers because they are obtainable from the World Meteorological Organization report, Scientific Assessment of Ozone Depletion: 2006 (WMO 2007). Lines 590-594 of the draft SAP state that “…during 1986- 1994 the U.S. accounted for 24-30% of total annual production and consumption of ODSs reported by the United Nations Environment Programme (UNEP) when weighted by the ozone depletion potentials (ODPs), since 2001 this fraction has been closer to 10%”. However, the numbers are given as 25-30% and “somewhat less since” on lines 1966 and 1967; lines 938-948 state 25-30% prior to 1993 and about 10% in 2001-2005. • Regarding emissions, the Executive Summary of the draft SAP does not provide any numbers (E.S.3.5, L. 288-292); lines 607-614 only state that U.S. emissions have declined by 81% since the 1980s. Lines 1978-1979 state that “…this analysis suggests that the U.S. accounted for 25% of global emissions, on average, during the 1990s, and somewhat less since”. Lines 1240-1254 give a consistent number of 18-35% for the 1990s (the committee’s interpretation of line 1252), but this text does not give a number for the more recent proportion of emissions from the United States. Lines 5214-5217 state that “Between 1985 and 2005, the fraction of ozone-depleting substances weighted by ODPs emitted by the U.S. relative to the total global emissions varied from about 20% in 1985 to a maximum of about 35% in the early 1990s, to a current level of roughly 20%”. • Regarding the U.S. contribution to global atmospheric mixing ratios, the authoring team should correct the following inconsistencies. The Key Findings section of Chapter 2 gives the U.S. emissions to total tropospheric chlorine (on L. 658) as approximately 20 (14-32)%, and 23 (19-29)% to bromine (line 680); however, line 1984 states 16-30% for chlorine and 21-26% for bromine. Line 1634 gives a number of 21 (16-30)% for chlorine for the past decade, and on line

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Review of CCSP SAP 2.4 8 1703, the proportion for bromine “has increased during the 2000s from 23 to 26%”. The committee is concerned with the inconsistency of the figures stated in the draft SAP and the use of “arbitrary uncertainties” applied to the development of scenarios and the quantification of future projections (e.g., P. 73, L. 1496). In estimating the U.S. contribution to past and future equivalent effective stratospheric chlorine (EESC) and radiative forcing, the method employed in the draft SAP is unjustified. Considering past contributions, the United States was a major consumer of fluorochemicals prior to 1985. Although the lack of available data presents significant uncertainty, it is reasonable to estimate that the U.S. contribution was roughly one-half of global emissions prior to 1975. To account for the uncertainty, assigning a range of error from a minimum of one- third of global emissions for each species up to a maximum of two-thirds will encompass the “rough estimate” of one-half of global emissions prior to 1975. After the publication of the ozone depletion theory in 1974 (Molina and Rowland 1974), there was a discontinuity in the use patterns of CFC-11 and CFC-12. In 1974, about 70% of global use of chlorofluorocarbons (CFCs) was as an aerosol propellant. Following the publication, there was almost a complete elimination of the use of CFCs in this application in the United States while many other countries continued use of the CFCs as propellants. Therefore, the U.S. fraction of global emissions of CFCs for 1985-1990 is not an accurate representation of the U.S. fraction of emissions prior to 1975, contrary to the approach presented in the draft SAP. Although pre-1975 information is indeed uncertain, as noted in the draft SAP, the committee judges that a more reasonable range of the U.S. fraction of emissions prior to 1975 is a lower bound of one third and an upper bound of two thirds of total global CFC-11 and CFC-12 emissions. Based on this information and the following points, the committee recommends a different approach to calculating the U.S. fractional contribution to global EESC and radiative forcing: • Of the anthropogenic ozone depleting substances, CFC-11 and CFC-12 are the major contributors to both EESC and radiative forcing through 1975. This is shown by the information in Table 2.2 and Figure 2.16 where these CFCs dominate contributions to chlorine, and hence, EESC and radiative forcing as well—even through 1985. To further support the point, Table 2.2 should be modified as follows: Add a column for 1975. o Show EESC for each of the compounds for each of the years. o HCFC-123 and any other hydrochlorofluorocarbon (HCFC) for o which data exist should be added for completeness. Table 2.2 and its footnotes do not explain why HCFC-123 is not included except that other contributions are likely to be small. Although Daniel and Velders (2007; on which Table 2.2 is based), did not include HCFC-123 in scenario A1, the numbers may be derived.

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Overarching Comments 9 • The use and emissions of other ODSs did not undergo the discontinuity as in the case for CFC-11 and CFC-12. Thus, the U.S. fraction of global emissions of these other ODSs for 1985-1990 is a reasonable representation of the U.S. fraction of emissions prior to 1985. The committee recommends modifying the approach to estimating the U.S. contributions to atmospheric concentrations (as shown in Figure 2.11) as described below. U.S. fractional contributions to EESC and radiative forcing can then be calculated as ranges by taking the ratios of the values calculated for EESC and radiative forcing from those concentrations to the global values. • For CFC-11 and CFC-12: Proposed approach Approach in draft SAP pre-1975 Lower and upper bounds Lower and upper bounds representing representing U.S. emissions as one- U.S. emissions as half and twice the third and two-thirds of global 1985-1990 average U.S. fraction of emissions for each species global emissions for each species 1975-1985 Assume two scenarios: U.S. emissions as half and two times the 1985-1990 average U.S. fraction (from Environmental Protection From the lower bound, continued to Agency [EPA] vintaging model) of 1985 and beyond using EPA vintaging global emissions for each species model minus 20%; from the upper bound, continued to 1985 and beyond 1985 and beyond Assume EPA vintaging model using EPA vintaging model plus 20% estimates of U.S. emissions with 20% error bars starting from each of the two points defined by the scenarios described above • For all other ODSs: Proposed approach Approach in draft SAP Pre-1985 Assume two scenarios: U.S. Lower and upper bounds representing emissions as 1/1.5 times and 1.5 U.S. emissions as half and twice the times the 1985-1990 average U.S. 1985-1990 average U.S. fraction of fraction (from EPA vintaging global emissions for each species model) of global emissions for each species 1985 and beyond Assume EPA vintaging model From the lower bound, continued to estimates of U.S. emissions with 1985 and beyond using EPA vintaging 20% error bars starting from each of model minus 20%; from the upper the two points defined by the bound, continued to 1985 and beyond scenarios described above using EPA vintaging model plus 20% The text should clearly describe the rationale outlined above, stating that this approach is used because no data currently exists to better define U.S. contributions and commenting that this is only a rough estimate based on plausible scenarios.

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Review of CCSP SAP 2.4 10 The upper and lower bounds of the combined scenarios can then be used to calculate ranges for use in Figures 2.12, 2.13, 2.14 and 2.15. The range should be shown as a band without showing a mean since a mean has no real meaning given the uncertainties. To the extent possible, all figures showing consumption (consumption to be shown instead of production) should be extended to 2020 to be consistent with Chapter 5 of the draft SAP. As the draft SAP points out (L. 1300), there are substantial differences (factor of two) between the model estimates and estimates made from measurements over the United States during regional pollution events. Admittedly, these differences could be caused by non-representative observational sampling for the entire United States. Nevertheless, the problem is that the accuracy of the vintaging model estimates is not established and an “arbitrary uncertainty of 20% is assumed” (line 1275). The draft SAP should emphasize the uncertainty in U.S. emission estimates in the summary sections. (Also, see Chapter 3 in this report.) Overall, the draft SAP does not provide enough discussion of uncertainties in current understanding and projections. For this document, a thorough discussion would be appropriate, as the committee has outlined above. RESEARCH NEEDS Regarding the overall goals of the report, the report did not “identify where research supported by CCSP agencies is critical for future assessments,” as required in Section 1.2 of the prospectus for SAP 2.4 (CCSP 2007). Because the focus of the SAP is on the United States, the authoring team should begin addressing this goal by outlining the significant contributions that U.S.-funded research (e.g., satellite programs, aircraft missions, laboratory studies, modeling efforts) have made to the world’s understanding of the ozone layer. To identify research needs that are evident from our current understanding, some suggestions are as follows: • Continued observations to monitor ozone recovery and to allow an attribution of the separate effects of decreasing halogens and of climate change. The latter, for example, stresses the importance of measuring changes in the vertical profile of ozone. • An improved ability to quantify the impact of short-lived compounds on lower stratospheric ozone. • The development of comprehensive, self-consistent chemistry-climate models (coupled to oceans, tropospheric chemistry, etc.). • Process-based observational studies for model validation • Maintaining a capability to address specific uncertainties in chemical processes or atmospheric concentrations, such as chlorine peroxide (ClOOCl) photolysis rates, the abundance of atmospheric bromine, and fugitive gas emissions from new technologies. Recently, the U.S. Climate Change Science Program hosted a workshop in Washington, DC, on the topic of future research needs for stratospheric ozone. Because

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Overarching Comments 11 this committee has not seen the workshop proceedings, it is not possible to assess the extent to which they might help meet the requirement of this prospectus. The SAP authoring team might consider ultimately attaching those proceedings as an appendix to this SAP. However, the committee regards it as important that the prospectus be addressed in a seamless manner, tying the research needs to the scientific analysis in the SAP. POLICY IMPLICATIONS Although the point of this product is to provide information for policymakers, the draft SAP lacks a discussion of scientific issues that have policy implications. The draft SAP presents policy-relevant information that should be stated more clearly as such and should be brought forward to the Executive Summary in a policy-neutral manner. Additional policy relevant information should be added that should also be brought forward to the Executive Summary. Objectives of the assessment include (from the prospectus): “(ii) to provide the scientific basis for decision support to guide management and policy decisions that affect the ozone layer and emissions of ozone-depleting substances;…” “The primary users of SAP 2.4 are intended to include, but are not limited to, officials involved in formulating climate and environmental policy….” Furthermore, the questions to be addressed include, “What are the various possible emissions scenarios that can be considered for any future policy actions on emissions of ozone-depleting gases?” Thus, it is appropriate to look at current policy issues involving ODSs. These issues include: • HCFCs: allocation of production and consumption allowances domestically and acceleration of the phaseout schedules for developed and developing countries internationally. • Banks of ODSs: the potential for destruction of quantities of ODSs contained in equipment and products to enhance ozone protection and decrease contributions to climate change. • Expanding uses of methyl bromide as in quarantine and pre-shipment, and continued controversy over critical use exemptions of methyl bromide. Relevant information in the sections should be made clearer relative to these issues, this information should be expanded, and it should be carried forward to the Executive Summary, all in a policy neutral manner. The information should include the U.S. fraction of past and projected future consumption and emissions of ODSs, as well as related by-product emissions and substitutes for ODSs. These numbers should be expressed in absolute amounts, ODP weighted amounts, and GWP weighted amounts. This information will show how U.S. actions have contributed to the success of the Montreal Protocol in achieving its goals to protect stratospheric ozone and the unintended consequence of climate protection. The information will also provide a partial scientific basis for decisions on the issues listed above. Information from other chapters will provide additional basis for those decisions.

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Review of CCSP SAP 2.4 12 PRESENTATION AND ORGANIZATION One of the committee’s tasks is to determine whether SAP 2.4 is effectively presented to its intended audiences. Keeping in mind the intended audiences described in the prospectus, the draft SAP does not provide enough introductory information in each chapter for the key points to be understood by a non-technical audience. One suggestion is to include WMO’s 20 questions document (Fahey 2007) as an appendix in the SAP, since it is written for a broad audience. The authoring team should include pedagogical introductory information and contextual language for the key issues and key findings. Chapter 3 (Review of Individual Sections) of this review provides additional suggestions for introducing essential concepts in each chapter of the draft SAP. As a matter of organization, it is difficult for the reader to correlate the key issues and key findings at the beginning of each SAP chapter to the associated discussions within the chapters. The authoring team should establish a clearer relationship among the key issues, key findings, and associated discussion for each topic. REFERENCES 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. Fahey, D.W. 2007. Twenty Questions and Answers about the Ozone Layer: 2006 Update. Geneva: World Meteorological Organization. Available online: http://ozone.unep.org/Assessment_Panels/SAP/Scientific_Assessment_2006/Twe nty_Questions.pdf. IPCC/TEAP (Intergovernmental Panel on Climate Change/Montreal Protocol’s Technology and Economic Assessment Panel). 2005. Safeguarding the Ozone Layer and the Global Climate System: Issues Related to Hydrofluorocarbons and Perfluorocarbons. IPCC/TEAP Special Report. Geneva: IPCC. Available online: http://arch.rivm.nl/env/int/ipcc/pages_media/SROC- final/SpecialReportSROC.html. IPCC (Intergovernmental Panel on Climate Change). 2007. Climate Change 2007 - The Physical Science Basis: Working Group I Contribution to the Fourth Assessment Report of the IPCC. Cambridge: Cambridge University Press. Molina, M.J., and F.S. Rowland. 1974. Stratospheric sink for chlorofluoromethanes: chlorine atomc-atalysed destruction of ozone. Nature 249:810−812. WMO (World Meteorological Organization). 2007. Scientific Assessment of Ozone Depletion: 2006. Available online: http://ozone.unep.org/Assessment_Panels/SAP/Scientific_Assessment_2006/inde x.shtml.