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Introduction

The U.S. Climate Change Science Program (CCSP) was established in 2002 to coordinate climate and global change research conducted in the United States. Building upon and incorporating the U.S. Global Change Research Program of the previous decade, the program integrates federal research on climate and global change, as sponsored by 13 federal agencies and overseen by the Office of Science and Technology Policy, the Council on Environmental Quality, the National Economic Council, and the Office of Management and Budget. A primary objective of the CCSP is to provide the best possible scientific information to support public discussion and government and private sector decision making on key climate-related issues. To help meet this objective, the CCSP is producing a series of synthesis and assessment products that address its highest priority research, observation, and decision-support needs. The CCSP is conducting 21 such activities, covering topics such as the North American carbon budget and implications for the global carbon cycle, coastal elevation and sensitivity to sea-level rise, trends in emissions of ozone-depleting substances and ozone recovery and implications for ultraviolet radiation exposure, and use of observational and model data in decision support and decision making. Each of these documents has been / will be written by a team of authors selected on the basis of their past record of interest and accomplishment in the given topic. A list of the CCSP SAPs is provided in Appendix A.


The National Oceanic and Atmospheric Administration (NOAA) is the lead agency for CCSP Synthesis and Assessment Product (SAP) 3.2. NOAA’s stated purpose for SAP 3.2 is to provide information to those who use climate model outputs to assess the potential effects of human activities on climate, air quality and ecosystem behavior. (see Appendix B for full prospectus). SAP 3.2 is comprised of two components that assess the climate projections resulting from SAP 2.1a scenarios in the context of existing IPCC climate projections and isolate and assess the future climate impacts resulting from future emissions of short-lived species.


According to the guidance provided in the prospectus, SAP 3.2 is to be written in a style consistent with major international scientific assessments. To address these purposes and audiences, SAP 3.2 was given eight key questions to address (see Box 1).


In a review of the U.S. CCSP Strategic Plan, the National Research Council (NRC) recommended that synthesis and assessment products should be produced with



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Review of the U.S. Climate Change Science Program’s Synthesis and Assessment Product 3.2, “Climate Projections Based on Emission Scenarios for Long-lived and Short-lived Radiatively Active Gases and Aerosols” 1 Introduction The U.S. Climate Change Science Program (CCSP) was established in 2002 to coordinate climate and global change research conducted in the United States. Building upon and incorporating the U.S. Global Change Research Program of the previous decade, the program integrates federal research on climate and global change, as sponsored by 13 federal agencies and overseen by the Office of Science and Technology Policy, the Council on Environmental Quality, the National Economic Council, and the Office of Management and Budget. A primary objective of the CCSP is to provide the best possible scientific information to support public discussion and government and private sector decision making on key climate-related issues. To help meet this objective, the CCSP is producing a series of synthesis and assessment products that address its highest priority research, observation, and decision-support needs. The CCSP is conducting 21 such activities, covering topics such as the North American carbon budget and implications for the global carbon cycle, coastal elevation and sensitivity to sea-level rise, trends in emissions of ozone-depleting substances and ozone recovery and implications for ultraviolet radiation exposure, and use of observational and model data in decision support and decision making. Each of these documents has been / will be written by a team of authors selected on the basis of their past record of interest and accomplishment in the given topic. A list of the CCSP SAPs is provided in Appendix A. The National Oceanic and Atmospheric Administration (NOAA) is the lead agency for CCSP Synthesis and Assessment Product (SAP) 3.2. NOAA’s stated purpose for SAP 3.2 is to provide information to those who use climate model outputs to assess the potential effects of human activities on climate, air quality and ecosystem behavior. (see Appendix B for full prospectus). SAP 3.2 is comprised of two components that assess the climate projections resulting from SAP 2.1a scenarios in the context of existing IPCC climate projections and isolate and assess the future climate impacts resulting from future emissions of short-lived species. According to the guidance provided in the prospectus, SAP 3.2 is to be written in a style consistent with major international scientific assessments. To address these purposes and audiences, SAP 3.2 was given eight key questions to address (see Box 1). In a review of the U.S. CCSP Strategic Plan, the National Research Council (NRC) recommended that synthesis and assessment products should be produced with

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Review of the U.S. Climate Change Science Program’s Synthesis and Assessment Product 3.2, “Climate Projections Based on Emission Scenarios for Long-lived and Short-lived Radiatively Active Gases and Aerosols” independent oversight and review from the wider scientific and stakeholder communities (NRC, 2004). To meet this goal, NOAA has requested an independent review of SAP 3.2 by the NRC. The NRC appointed an ad hoc committee composed of eight members (Appendix C). The committee’s Statement of Task is included in Appendix D. The committee conducted its work by first carefully reading the draft SAP 3.2 report “Climate Projections Based on Emissions Scenarios for Long-Lived and Short-Lived Radiatively Active Gases and Aerosols” (draft dated May 9, 2007). The committee then met with the lead authors to ask questions about the authoring team’s research and formulation of the draft document. During this meeting, the committee also interacted with NOAA personnel, who outlined for the committee their expectations for SAP 3.2. This present document constitutes the committee’s review report, resulting from its careful study of the draft SAP 3.2 document and its interactions with those present at the aforementioned meeting. Herein the committee provides its review findings, and recommendations, suggestions, and options for the authors to consider in revising the draft SAP 3.2. In its review, the committee focused on substantive matters of content and did not proofread the document for grammatical or typographical errors.

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Review of the U.S. Climate Change Science Program’s Synthesis and Assessment Product 3.2, “Climate Projections Based on Emission Scenarios for Long-lived and Short-lived Radiatively Active Gases and Aerosols” BOX 1-1 Questions to be Addressed by CCSP Synthesis and Assessment Product 3.2 According to guidance in the CCSP prospectus outlining the purpose of SAP 3.2, the report will consist of two components. Climate projections for research and assessment based on the range of stabilization scenarios of long-lived greenhouse gas emissions and atmospheric concentrations developed by SAP 2.1a. These stabilization scenarios and their resulting long-lived greenhouse gas concentrations were generated by three unified assessment models. An assessment of the sign, magnitude, and duration of future climate impacts due to changing levels of short-lived gaseous and particulate species that may be subject to future mitigation actions to address air quality issues. SAP 3.2 is intended to provide information to those who use climate model outputs to assess the potential effects of human activities on climate, air quality, and ecosystem behavior. The key questions to be addressed by SAP 3.2 are: Do SAP 2.1a emissions scenarios differ significantly from IPCC emissions scenarios? If the SAP 2.1a emissions scenarios do fall within the envelope of emissions scenarios previously considered by the IPCC, can the existing IPCC climate simulations be used to estimate 50-to 100-year climate responses for the CCSP 2.1 CO2 emissions scenarios? What would be the changes to the climate system under the scenarios being put forward by SAP 2.1a? For the next 50 to 100 years, can the time-varying behavior of the climate projections using the emissions scenarios from SAP 2.1a be distinguished from one another or from the scenarios currently being studied by the IPCC? What are the impacts of the radiatively active short-lived species not being reported in SAP 2.1? How do the impacts of short-lived species compare with those of the well-mixed green house gases as a function of the time horizon examined? How do the regional impacts of short-lived species compare with those of long-lived gases in or near polluted areas? What might be the climate impacts of mitigation actions taken to reduce the atmospheric levels of short-lived species to address air quality issues?