1
Introduction
The Global Change Research Act of 1990 mandates the US Global Change Research Program (USGCRP) develop an assessment of global change every four years or less. The Fifth National Climate Assessment (NCA5) is the latest in a series of sustained assessments that evaluate the state of global change science and analyze the wide range of impacts of climate change in the United States. The assessments represent a consensus-based view of the state of the science and, although they are relevant for policy and decision making, they do not prescribe policy interventions (Crimmins, 2022). The first National Climate Assessment (NCA) was produced in 2001 (National Assessment Synthesis Team, 2001), the second in 2009 (Karl et al., 2009), the third in 2014 (Melillo et al., 2014), and the fourth in two volumes—volume I in 2017 (USGCRP, 2017) and volume II in 2018 (USGCRP, 2018a).
The National Academies of Sciences, Engineering, and Medicine (the National Academies) have a long history of providing advice to USGCRP by conducting formal reviews of the NCAs, USGCRP strategic plans, and other USGCRP products (NASEM, 2017a). Foundational National Academies reviews of USGCRP programs include National Research Council (2003) and (2004). Recent examples of National Academies reviews include the draft Fourth National Climate Assessment (NASEM, 2018a; USGCRP, 2018a), the draft Climate Science Special Report (NASEM, 2017b; USGCRP, 2017), the draft Second State of the Carbon Cycle Report (NASEM, 2018b; USGCRP, 2018b), the draft Third National Climate Assessment (Melillo et al., 2014; NRC, 2013), and the draft assessment on the impacts of climate change on human health (NASEM, 2015; USGCRP, 2016).
These reviews are authored by ad hoc committees or by the Committee to Advise the USGCRP. Established in July 2011, the Committee to Advise the USGCRP provides broad, ongoing advice from across the National Academies to the USGCRP. It also serves as a point of contact through which USGCRP can gain access to expertise throughout the National Academies for advice on specific aspects of the program. The National Academies convened an ad hoc Committee to Review the Draft Fifth National Climate Assessment (the “Committee”). The Committee is charged with providing a comprehensive, independent review of the draft NCA5 report, concurrent with the public comment period. The complete Statement of Task for the Committee’s review is provided in Box 1-1.
A number of elements are new to NCA5. Compared to the Fourth NCA, the draft NCA5 report added chapters on economics (Chapter 19) and social systems and justice (Chapter 20) and divided the physical science chapter into two chapters (Chapter 2 on Climate Trends and Chapter 3 on Earth System Processes). Also new to NCA5 are five “Focus On… Features” on topics that span multiple chapters. The NCA5 author team is larger and more diverse, with more than 500 authors and technical contributors. The NCA5 authors have also placed particular emphasis on figures, science communication, equity and justice, and the development of a web-first format for the report.
There were several opportunities for public engagement with the development of the draft NCA5 report, including engagement workshops, a call for technical input, calls for comment on the draft prospectus and the annotated outline for the draft NCA5 report, and two calls for artwork.
THE COMMITTEE’S APPROACH TO THIS REPORT
During fall 2022, the National Academies appointed the Committee, which is composed of 18 members who have expertise in climate change science, vulnerability, and adaptation in the regions and sectors covered in NCA5. Committee members were not authors of or technical contributors to the draft NCA5 report. The draft NCA5 report was released to both the Committee and the public on November 7, 2022. In addressing its tasks, the Committee met virtually three times from November to December 2022. The Committee held one open-session meeting to learn more about NCA5 and ask questions of the Director of the National Climate Assessment and other NCA5 authors. Individual chapters were reviewed by small teams of Committee members. In addition to chapter review teams, Committee members looked across the entire draft NCA5 report with particular attention to how well it addresses equity and justice and how clearly and accurately the report communicates the state of knowledge on climate change science. The Committee’s review was restricted to figures that had cleared copyright by January 27, 2023, and did not include other elements not available to the Committee, including the Glossary that is currently under development. Following the standard National Academies’ procedures, the Committee’s draft report then underwent a rigorous process of external peer review before publication.
REPORT ROADMAP
This report serves as the Committee’s comprehensive review of the draft NCA5 report. After this brief introduction (Chapter 1), Chapter 2 synthesizes the Committee’s overarching comments on the draft NCA5 report and makes recommendations for improvement. These comments cover both the structure across and within chapters as well as content across the entire draft NCA5 report. Chapter 3 provides detailed comments on each individual chapter as well as the five Focus On… Features, the Front Matter, and Appendixes 3 and 4; comments closely follow the questions in the Committee’s Statement of Task (Box 1-1). The individual chapter reviews use a common structure with a summary followed by comments on the introduction, key message and supporting text language, traceable accounts, graphics and boxes, equity and justice, data and analyses, literature cited, and other recommended changes, as applicable. Appendix A includes detailed line-by-line comments on each chapter in the draft NCA5 report. The Committee’s approach to this review was to provide constructive comments and specific suggestions to strengthen the accuracy, consistency, credibility, and accessibility of the key messages and supporting text in the draft NCA5 report. The Committee recognizes that NCA5 authors have limitations regarding structure and length and this review is careful to suggest places to eliminate writing where the Committee also suggests adding material. In its review, the Committee uses the term “climate change” to refer to anthropogenic climate change.
The primary audiences of NCA5 are “decision makers” including federal agencies, local and state governments, tribes, health care providers, educators, business owners, and the media (Allison Crimmins, personal communication). In its review, the Committee thought carefully about the audiences for NCA5 while developing recommendations related to effective communication. Tailoring communication to specific audiences is one of the fundamental principles of strategic science communication (Besley and Dudo, 2022) and contributes to desirable audience outcomes (Bostrom et al., 2013). Considering the breadth of potential audiences and users of NCA5 requires authors to communicate findings in a way that enhances accessibility while maintaining accuracy. When assessing whether the draft NCA5 report was written at an appropriate technical level, the Committee focused on two different target audiences—a broad audience base and a more technical audience base. Specifically, the Committee assessed chapter introductions, key messages and associated text, and figures from the perspective of targeting the broadest possible audiences, while the Committee expected the traceable accounts to target more technical audiences (e.g., the scientific research community). The Committee also considered how broad audiences might use some parts of the report, such as key messages, boxes, and figures.
