The Fourth National Climate Assessment is a mandated product developed by the United States Global Change Research Program (USGCRP). The Global Change Research Act of 1990 requires the USGCRP to develop a national climate assessment every four years or less. These assessments are intended to evaluate the state of the science and the broad range of impacts of climate change in the United States. Since the Third National Climate Assessment (NCA3) released in 2014 (Melillo et al., 2014), the USGCRP has moved toward a sustained assessment process. This program evolution provides scientific updates and foundational knowledge that informs the third order draft of the assessment report, “Climate Change Impacts, Risks, and Adaptation in the United States” (hereafter “NCA4”), reviewed in this document. The draft NCA4 report reviewed here serves as Volume II of the assessment. The climate science discussed in the draft NCA4 is based largely on the Climate Science Special Report, or CSSR (USGCRP, 2017), which serves as Volume I of the fourth assessment. The CSSR is summarized in Chapter 2 of the draft NCA4.
The National Academies of Sciences, Engineering, and Medicine convened The Committee to Review the Draft Fourth National Climate Assessment (“The Committee”) in November 2017. The Committee is composed of experts able to evaluate the broad range of topics included in the draft NCA4, ranging from climate change science and impacts to responses and risk evaluation. The Committee was specifically charged with addressing the following Statement of Task questions (see also Appendix C for the Statement of Task):
- Does the report meet the requirements of Section 106 of the Global Change Research Act?
- Do the key messages reflect current understanding about observed and projected impacts to the United States, the challenges, opportunities and success stories for addressing risk, and identification of emerging issues related to climate change?
- Does the report accurately reflect the peer-reviewed scientific literature, with a particular focus on literature since the last National Climate Assessment (i.e., since approximately 2013)? Are there any critical content areas missing from the report?
- Are the findings documented in a consistent, transparent, and credible way?
- Is the report written at a technical level that is appropriate for the intended audience?
- Are the report’s key messages and graphics clear, internally consistent, and appropriate? Specifically, do they reflect supporting evidence, include an assessment of likelihood, and communicate effectively?
- Are the data and analyses handled in a consistent, transparent, and credible manner? Are statistical methods applied appropriately?
- What other significant improvements, if any, might be made in the document?
The Committee held an in-person meeting on November 29-30, 2017, in Washington, DC to discuss the draft NCA4 and begin developing their review report. This in-person meeting also included an open session where the Committee had the opportunity to learn more about the draft NCA4 report and development process from the Director of the National Climate Assessment and Chapter Lead Authors. Additional calls were held to discuss this review report and reach a consensus on the Statement of Task questions. Reviews of each chapter of the draft NCA4 were
conducted by small teams of committee members with the relevant expertise who then led discussion of their review with the full committee.
This review report provides a synthesis of the Committee’s overarching responses to the Statement of Task for the full draft NCA4 (Chapter 2) and specific comments for the report findings and each individual chapter of the draft report (Chapter 3). General advice and science-based recommendations are also provided for the draft NCA4 Frequently Asked Questions (Appendix A). Detailed line comments on draft NCA4 chapters are provided in Appendix B of this report. The Committee sought to provide constructive criticism that will enhance the draft NCA4, while recognizing that many decisions on report structure and length may constrain considerable expansion of new topics recommended for inclusion.
The National Academies has convened panels to review numerous USGCRP assessments in the past, including the draft Third National Climate Assessment (NRC, 2013; Melillo et al., 2014) and the draft assessment on the impacts of climate change on human health (NRC, 2015; USGCRP, 2016). Most relevant to the NCA4, the National Academies reviewed the draft CSSR (NASEM, 2017b), which was released in 2017 and is referenced throughout the draft NCA4.
Concurrent with the development of this review report, the National Academies directed an independent review of the draft Second State of the Carbon Cycle Report (SOCCR2). The SOCCR2 is a product of the USGCRP sustained assessment process and is intended to provide “a comprehensive assessment of the science and associated human dimensions of the carbon cycle of land, air, and water, with a focus on the United States and North America in a global context.” Given the relationship between the draft NCA4 and draft SOCCR2 content, some topics are discussed in both reports. The two committees appointed for these reviews only evaluated the content of the USGCRP draft report that they were appointed to review, addressing the questions in their respective charges. Therefore, some variation in the review of similar topics may be present in the two National Academies’ review reports.