Climate change poses many challenges that affect society and the natural world. With these challenges, however, come opportunities to respond. By taking steps to adapt to and mitigate climate change, the risks to society and the impacts of continued climate change can be lessened. The National Climate Assessment, coordinated by the U.S. Global Change Research Program (USGCRP), is a mandated report intended to inform response decisions. These reports are required to be developed every four years and provide the most comprehensive and up-to-date evaluation of climate change impacts available for the United States, making them a unique and important climate change document.
The draft Fourth National Climate Assessment (NCA4) report reviewed here addresses a wide range of topics of high importance to the United States and society more broadly, extending from human health and community well-being to the built environment, to businesses and economies, and to ecosystems and natural resources. The report is being developed by hundreds of experts representing federal, state, and local governments, academia, non-government organizations, and the private sector, with further input from community engagement events and public comment. The scale of this collaboration is rare and impressive and the rich array of perspectives introduced through this process provides an opportunity to develop a foundational climate change report that informs and highlights adaptation and mitigation efforts and serves as a valuable resource for broad audiences.
As part of the NCA4 development process, the National Academies of Sciences, Engineering, and Medicine was tasked with convening a panel of experts to provide an external peer review of the draft report. The Committee to Review the Draft Fourth National Climate Assessment (“The Committee”) evaluated the draft NCA4 to determine if it meets the requirements of the federal mandate, whether it provides accurate information grounded in the scientific literature, and whether it effectively communicates climate science, impacts, and responses for general audiences including the public, decision makers, and other stakeholders (see Chapter 1 and Appendix C for the full Statement of Task). The Committee approached this charge by developing overarching feedback on the full draft report (Chapter 2) and providing specific comments for individual chapters (Chapter 3 and Appendix B) and the Frequently Asked Questions appendix (Appendix A of this review report).
The Committee was impressed by the accuracy of information and thorough discussion of the predominant aspects of climate change and impacts presented in the draft NCA4. The 1,506-page draft report provides a strong foundation of climate science and a solid discussion of climate change impacts occurring or likely to occur in the United States. The topics are well-selected and logically organized around key messages. The introduction of new national topic and regional chapters since the Third National Climate Assessment (NCA3) is a welcome addition and improves the comprehensiveness of the assessment. The new national topic chapter, “Sectoral Interdependencies, Multiple Stressors, and Complex Systems” is an excellent addition because it facilitates discussion of the inherent challenges introduced by climate change in interlinked systems. Discussion of this critical topic should also be integrated more broadly across draft report chapters. The expanded discussion provided in regional chapters in the draft NCA4 relative to the NCA3 was found to be one of the draft report’s greatest strengths. These regional chapters provide a relatively holistic treatment of relevant climate change impacts and
are effective in conveying the complex nature of climate change and the linkage among impacts that extend across sectors and topic areas. Regional chapters where specific examples of adaptation and mitigation responses are given are especially strong. The Committee thinks these chapters will resonate well with readers and draw them more fully into the broader report as they learn about climate change impacts “in their backyard.”
The draft report represents an expansive and diverse range of information that will be most accessible to readers when the key messages are conveyed clearly and consistently, when linkages across chapters and topics are provided, and when examples of response actions can be drawn on to support the key messages. By improving the communication of key aspects of the draft NCA4, this document could be further strengthened.
Specific overarching recommendations for improving the draft NCA4 include:
Linking Impacts with Response Examples: Incorporate more examples in the draft NCA4 that highlight new and ongoing adaptation and mitigation activities. These should include actions in the private sector, public-private partnerships, and government at multiple scales.
The Committee found the examples of adaptation and mitigation response actions to be very impactful in the draft NCA4, when they are used. Many new actions have been taken in recent years. Examples of these actions could be provided more widely throughout the draft report to illustrate advancements and provide information on how the impacts of climate change are being addressed.
Communicating Report Findings: Reframe the Overview Chapter of the draft NCA4 to center around the twelve report findings that reflect the impacts and responses that are discussed throughout the draft report.
The Overview Chapter (Chapter 1 in the draft NCA4) is expected to be a go-to for readers who are interested in a short synthesis of the NCA4 contents and should complement the “Report in Brief” that will be developed by the NCA4 authors. The chapter is well written and scientifically accurate, but it places strong emphasis on climate science that is already well covered in Chapter 2 of the draft report. The Overview would be more effective if greater focus were given to the impacts and responses discussed across the draft NCA4 report.
Communicating Key Messages: Key messages should be presented using more explicit and concise language. Examples that align with key messages should be included wherever possible in the supporting text and figures. More of the key messages should be supported by examples of response actions to facilitate solution-oriented communication and information sharing.
The draft NCA4 key messages tend to be long and are sometimes hard to follow. This reduces their impact because readers cannot readily identify the take-home points. Tightening language and further prioritizing which information should be included in the key messages versus the supporting text would improve their effectiveness. Many figures in the draft report are not well connected to the key messages. Because the draft report is shaped around the key messages, figures that are closely aligned with the messages would be most useful. Key messages are also an appropriate place to highlight examples of ongoing and planned response actions.
Communicating Uncertainty and Risk: The various types of risk included in the draft NCA4 should be defined more explicitly. Improved consistency in the types of risk discussed and inclusion across chapters is also recommended.
The draft NCA4 report deals with a broad range of uncertainties and risks inherent to the content of a national climate assessment. While some types of uncertainty and risk are discussed (e.g., likelihood and confidence), improved differentiation and more standardized treatment is needed across the draft report.
Bridging Topics and Scales: Linkages to interrelated topics among chapters should be increased throughout the draft NCA4 to ensure consistent treatment of similar topics and to provide readers with a clearer understanding of how impacts and responses at national to regional scales are connected.
The draft NCA4 covers a wide range of topics that are inherently connected. Because of the structuring of the report into national topic, regional, and response chapters, these connections are often missing from the report, leading to coverage of some topics in only one chapter, or in multiple chapters but in different ways. Improved cross-referencing across chapters would better highlight the interconnected nature of the material, guide readers through the information in a manner that will allow them to explore their topics of interest, and make the report more broadly useful.
Highlighting New Developments in Climate Science, Impacts, and Responses: Authors of the draft NCA4 should explicitly identify significant advancements made since the Third National Climate Assessment, with emphasis on emerging science, impacts, and examples of new response actions.
Since the NCA3 was published, scientific research has continued to advance understanding of climate change impacts and the number of response activities has increased. Distinguishing what is new demonstrates measurable progress that is important for informing the NCA4 audience and may also facilitate more solution-oriented messaging of impacts and responses across the report.
The Committee appreciates the opportunity to provide suggestions during the development of this important climate assessment. Attention to the recommendations provided throughout this review report will strengthen the draft NCA4 and improve its ability to reach broad audiences and inform new and continuing adaptation and mitigation responses to climate change.