prior to 1975, the U.S. contribution should be estimated as a minimum of one-third and a maximum of two-thirds of global emissions for each type of CFC; post-1975 estimates should also be adjusted accordingly. The justification for this approach begins with the fact that the United States was a major consumer of fluorochemicals before EPA estimates became available in 1985. After the publication of the ozone depletion theory in 1974, there was a discontinuity in the use patterns of CFCs (namely, CFC-11 and CFC-12)—of which 70% of global use was as an aerosol propellant. Although U.S. consumption data are not available prior to 1985 there is information on which to base a more realistic estimate. There was almost a complete elimination of the use of CFCs as a propellant in the United States after 1974, while many other countries continued use of the CFCs as propellants. Therefore, the U.S. fraction of global emissions of CFCs for 1985-1990, as represented in the SAP, is not an accurate representation of the U.S. fraction of emissions prior to 1975, contrary to the approach presented in the draft SAP. The committee’s recommended changes will provide a more realistic range of the U.S. contribution and will affect how U.S. contributions are estimated throughout the SAP.
To address the SAP goal to “describe how these findings relate to human activities, with a particular focus on the United States,” the authoring team should include a discussion of scientific issues that have policy implications. The draft SAP contains policy relevant information that should be stated more clearly as such in Chapter 6 and should be brought forward to the Executive Summary in a policy neutral manner. This proposed approach will make the SAP more useful for policymakers.
To address the SAP goal to “identify where research supported by CCSP agencies is critical for future assessments,” the authoring team should highlight research needs in each chapter where the research is discussed. Suggestions for accomplishing these goals appear in the committee’s specific comments for each SAP chapter.
The authoring team should specifically identify and accommodate the intended audiences of the SAP. The committee suggests some ways of reorganizing and editing the sections of the draft SAP in the following chapters of this report, including suggestions about the use of introductory material and the explanation of technical concepts.
The committee commends the SAP authoring team on developing a comprehensive document covering the scientific basis of this important climate issue. For the final SAP document, the authoring team would meet its goals and provide rigorous answers to its key questions by incorporating the committee’s suggestions detailed in this report.