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3 Comments on Each Chapter of the DraftFourth National Climate Assessment
Pages 17-112

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From page 17...
... Climate change increasingly threatens tribal and Indigenous communities' livelihoods, economies, health, and cultural identities through disruption of interconnected social, physical, and ecological systems. The Communities and Indigenous Peoples Report Findings (and supporting text)
From page 18...
... should be captured in the report findings. Placing this synthetic finding earlier in the report findings list could facilitate this and may provide additional context to readers as they read through the full report findings list.
From page 19...
... International Interests." Additional revisions to the report findings should also be made as appropriate, if changes to associated key messages occur as a result of other recommendations provided in this review report. CHAPTER 1: OVERVIEW Summary The Committee found the material contained in Chapter 1 to be accurate and well written, with attention given to many of the aspects of climate change that are dominant in the discussion of impacts including sea level rise, temperature, and precipitation.
From page 20...
... Chapter 1 would also be the appropriate place to clearly define the scope of uncertainty and risks evaluated in the draft NCA4, preview different types and sources of uncertainty and risk in climate assessment more generally, and discuss how to manage them. As described in Chapter 2 of this review report, it is important to differentiate between sources of uncertainty and risk because different types of risk call for different types of risk management solutions.
From page 21...
... See also "Highlighting New Developments in Climate Science, Impacts, and Responses" in Chapter 2 of this review report for recommendations on approaches to making this distinction. For the Call Out Box "Confidence and Uncertainty in Climate Science," it is suggested that "confidence" be defined so that it is not misinterpreted in this context.
From page 22...
... that distills key messages from the national topic and regional chapters. Chapter 1 is an appropriate location for such a graphic.
From page 23...
... The information is accurate, but careful attention should be given to which portions of the figure are necessary and effective in conveying the climate change impacts that are the central focus of the draft NCA4. Some impacts may not resonate or be readily understandable to a general audience without more detail (e.g., snowpack)
From page 24...
... and that the authors consider listing the legend information to the right of the figure so that the RCP/scenarios information is listed to the right of the y-axis showing temperature change projected for the end of the century. Figure 1.4 Figure 1.4 conveys too many messages for the intended audience to easily follow.
From page 25...
... Key messages are used to summarize the key findings of the fifteen chapters of the CSSR. These key messages are supplemented by discussions in seven boxes covering topics including natural variability, climate change indicators, greenhouse gas emissions targets, extreme events, the 2017 hurricane season, and climate models.
From page 26...
... The contents of the seven boxes is well chosen to supplement the key messages and address commonly raised questions about climate change. Key Message 6: Annual precipitation has increased across most of the northern and eastern United States and decreased across much of the southern and western United States; these regional trends are expected to continue over the coming century.
From page 27...
... (2016) provides a different conceptual view of sea level rise following warming events, which is a useful discussion to cite.
From page 28...
... This addition should highlight recent advances in understanding climate change impacts on hydrology, floods, and drought. In discussing human influence, there is a need to clarify the role of human activities (e.g., emissions of greenhouse gases)
From page 29...
... These include reduced snowpack and increased rain-to-snow ratio with warmer temperature; increased human water use due to warmer temperature and other factors; groundwater depletion (due to agriculture) ; warmer stream temperature; extreme precipitation mobilizing more transport of sediment and nutrients by rivers; sea level rise and salt water intrusion; and wildfires and other factors that affect water quality.
From page 30...
... As noted for Key Message 2, reference to the draft NCA4 Chapter 17 would be useful here, as water must be managed in the context of not only providing water resources but also considering energy, agricultural, and other sectors. Uncertainty should be included in Key Message 3 and not just in the supporting text that follows the message.
From page 31...
... This can have broader implications if the reduced detection is combined with aging infrastructure such that protection against flood and drought in the future is lessened, increasing risks. Other Recommended Changes The "Chapter Development" section provided in the traceable accounts indicates that Chapter 3 was developed to place more emphasis on vulnerability, risk, and management than in the NCA3 report, since the NCA3 focused largely on climate change impacts on hydrology, flood, and drought.
From page 32...
... Such concrete case examples tend to be very useful for illustrating climate change impacts to the reader (e.g., California Central Valley groundwater depletion, Floridian Aquifer salinization, Chesapeake Bay ecosystems)
From page 33...
... Key Messages 1 and 2 affirm current understanding of: the critical nature of energy supply and delivery systems and their interconnectedness and interdependencies with other vital systems; the changing nature of energy supply and delivery systems and roles of energy technologies, markets, and policies in affecting the systems' vulnerabilities to climate change and extreme weather; critical systems that are becoming more interconnected. However, an examination of the subject matter as an energy process might be useful.
From page 34...
... The key messages accurately reflect supporting evidence and are communicated effectively. Other Recommended Changes Because energy supplies are typically privately owned and operated, private sector actions should be discussed in more detail and the importance of public-private partnerships should be highlighted.
From page 35...
... are not consistent. Comments Related to the Statement of Task Comments on Key Messages Key Message 1: Changes in land cover, which may be driven by societal choices concerning land use, continue to impact local- to global-scale weather and climate by altering the flow of energy and water between ecosystems and the atmosphere, with important feedback effects on the climate system.
From page 36...
... should be included. Key messages from this chapter are not specifically reflected in the draft NCA4's overarching report findings.
From page 37...
... note places in the draft chapter where more geographic or ecological specificity would be helpful, as well as parts of the text where technical terms should be replaced with nonspecialized language to improve readability for the intended audience. Comments Related to the Statement of Task Comments on Key Messages Generally, the key messages for Chapter 6 appropriately reflect the primary issues related to climate change for U.S.
From page 38...
... See Appendix B of this review report for additional suggested citations to support this key message. Key Message 2: It is highly likely that climate change will mostly decrease the ability of forest ecosystems to provide ecosystem services to society.
From page 39...
... are provided in Appendix B of this review report, in addition to some paleoecological studies. Comments on Traceable Accounts Overall, the findings are documented in a transparent and credible way and they reflect supporting evidence.
From page 40...
... The key messages in the draft chapter are overly generalized. The chapter would benefit considerably from expanded treatment of ecosystem services and discussion of climate mitigation strategies.
From page 41...
... It is also unclear why mitigation strategies are not mentioned in Key Message 2. Changes in biodiversity and ecosystem services can have a large impact on carbon sequestration and storage, as is cited in other chapter key messages.
From page 42...
... . Comments on Traceable Accounts In general, the traceable accounts need better documentation to support the key messages.
From page 43...
... Other areas with a need for increased resilience include disease, increased frequency of extreme events such as fire, drought, riverine and coastal flooding, sea level rise, and ocean acidification. • The interaction and fundamental underpinning of biodiversity and ecosystem services for topics covered in many other draft NCA4 chapters (Water, Energy, Land Cover and Land Use Change, Forests, Coastal Effects, Oceans and Marine Resources, etc.)
From page 44...
... • There is virtually no information provided on trends in ecosystem services, with the exception of those given on page 265 and a few other locations. Some of these topics should be brought forward as part of key messages.
From page 45...
... . This historical legacy exacerbates the impacts of climate change because Indigenous peoples are restricted to increasingly drier areas.
From page 46...
... The chapter includes strong statements on flooding that are justified by the science. The key messages are generally positive and are oriented toward informing response actions.
From page 47...
... Deleting the first sentence and the "However" start to the second sentence is suggested, with that information then conveyed solely in the supporting text. Key Message 3: As the pace of coastal flooding and erosion accelerates, climate impacts along our coasts are exacerbating preexisting social inequities as communities face difficult questions on determining who will pay for current impacts and future adaptation strategies and if, how, or when to relocate vulnerable communities.
From page 48...
... However, the key messages could be more effective if conveyed in a more positive tone to balance risk with adaptation and mitigation efforts. Other Recommended Changes The economic and social value of coastline properties is presented, but a further dive into real estate, insurance, and banking would be beneficial for the audience of this assessment report, 1 See http://www.southeastfloridaclimatecompact.org.
From page 49...
... CHAPTER 9: OCEAN AND MARINE RESOURCES Summary Chapter 9 is centered around three useful themes that underpin the key messages: projected impacts, opportunities for reducing risks, and emerging issues and research gaps. For the most part, these key messages are well selected and the discussion and findings are reported in a credible, transparent manner.
From page 50...
... The information and literature citations in the traceable accounts are linked to the key messages, but the Chapter 9 authors should be consistent in how the reported confidence and likelihoods are ordered within the key messages. Other Recommended Changes Risk and adaptation measures are generally addressed in the discussion of the key messages, but examples of approaches that could lead to resilience are not apparent.
From page 51...
... It could be made more effective through substantial improvements to message clarity. The most beneficial improvements would include: reorganizing key messages around impacts rather than forcings in order to avoid oversimplification of impact pathways and unnecessary redundancy in the text; strengthening discussion of recent trends and knowledge advancements since the NCA3; organizing the progression of paragraphs and sections into a tighter logical flow; and explicating baselines in
From page 52...
... Related to this, figures and case studies should be more tightly coupled to key messages. Comments Related to the Statement of Task Comments on Key Messages The key messages generally include references to the most important pathways associated with climate change impacts on the agricultural sector and rural communities.
From page 53...
... It is suggested that the Chapter 10 authors consider rebalancing this set of materials to reflect projected impacts emphasized in the key messages. There may be some missed opportunities for reinforcing key messages with tables, figures and case study boxes.
From page 54...
... Then, when measuring projected changes from baselines, there is some unevenness in how economic estimates are provided, and in general it is not clear from the current text what the authors think are the most important/risk-prone/expensive impact pathways among the many that are listed in the chapter. Is it possible to compare projected risks or impacts across the different key messages on economic or other quantitative terms?
From page 55...
... Some additional specific areas of improvement that are addressed in line-by-line comments (see Appendix B of this review report) include: • Further development of discussion of land use change as an adaptation mechanism, which is acknowledged in the text but not addressed with much detail or any examples • Impacts of climate change and carbon dioxide accumulation on nutritional quality of crops, which may be an emerging research area to note • Impacts on pathways of off-farm environmental impacts beyond runoff and erosion • Some synthesis comments of major modeling and experimental efforts since the NCA3, either in the body text or traceable accounts section References to consider including in this chapter, along with other detailed comments, are provided in Appendix B
From page 56...
... Comments Related to the Statement of Task Comments on Key Messages The selected key messages are appropriate, generally clear, consistent, and communicated appropriately for the intended audience. Key Message 2: Damages from extreme weather events demonstrate current urban infrastructure vulnerabilities.
From page 57...
... . These efforts are being expanded further by the American Society of Civil Engineers Committee in the ongoing development of a manual of practice on adaptive design and risk management on the adaptation to a changing climate, with a report titled, "Climate Resilient Infrastructure." Increases in salinity, temperature, and humidity due to a changing climate could result in an increase in corrosion and degradation rates, reducing life expectancy of the built environment and jeopardizing integrity, efficiency, and safety.
From page 58...
... • Expanded attention to urban transportation systems and underground structures, as they are vulnerable to local flooding, sea level rise, and storm surges. • Inclusion of impacts of localized flooding due to extreme precipitation.
From page 59...
... These interdependencies are discussed in the draft NCA4 Chapter 17 and crossreferencing might be appropriate, as these systems are also subject to other stressors, such as population growth, economic demands, and technological changes and their potential compounding effects. Comments on Key Messages Key Message 1: A reliable, safe, and efficient U.S.
From page 60...
... Other areas of recommended expansion of discussion include vulnerabilities of metrorail transit systems to local flooding, sea level rise, and storm surges. Additionally, increases in
From page 61...
... This is acknowledged in the traceable accounts section for Key Message 3, but most references in traceable accounts for all key messages in this chapter are to news reports or gray literature. This may reflect the state of the science on transportation impacts; if peer-reviewed literature on the topic is limited, it could be noted explicitly.
From page 62...
... This is mentioned later in the chapter, but, if included in Key Message 1, would provide important context and links to non-climate stressor interaction with climate impacts. Key Message 2: More frequent and severe wildfires due to climate change pose an increasing risk to human health through impacts on air quality.
From page 63...
... CHAPTER 14: HUMAN HEALTH Summary Chapter 14 appropriately evaluates scientific evidence on the human health consequences of climate change and is written at a technical level that is appropriate for the intended audience. The key messages are generally effective and highlight major impacts of climate change on human health.
From page 64...
... Review Comments Related to the Statement of Task Comments on Key Messages Key messages are generally clear and consistent, but some small changes would strengthen their impact. The chapter authors should also review the Health Report Finding provided in the draft NCA4, which the Committee found to be particularly effective in conveying a strong, succinct message about health impacts.
From page 65...
... However, the chapter neglects to mention that these effects are not felt equally in the present day either. Comments on Traceable Accounts The text discussing confidence and uncertainty would be more helpful if it specified which aspect of the key message has uncertainty (e.g., is the magnitude uncertain but the direction of change certain?
From page 66...
... Review Comments Related to the Statement of Task Comments on Key Messages The key messages reflect current understanding, but some specific changes are suggested. Key Message 1: Climate change threatens Indigenous peoples' livelihoods and economies, including agriculture, fishing, forestry, recreation, and tourism.
From page 67...
... Boxes for Key Messages 1 and 3 or cross-references to case studies described in other chapters are two possible ways of increasing these details. "Key Message 4" is mentioned repeatedly in the chapter but is not included among the key messages, text, or traceable accounts.
From page 68...
... that document insights and information from Indigenous Peoples and give examples. Comments on Traceable Accounts The traceable accounts address all of the issues of the key messages, with appropriate citations, but as noted in the "Comments on Literature Cited" section, they are often without specific examples.
From page 69...
... CHAPTER 16: CLIMATE EFFECTS ON U.S. INTERNATIONAL INTERESTS Summary Chapter 16 explores climate change in the context of international interests in a standalone chapter, which is a new and welcome addition to the national climate assessment.
From page 70...
... Comments on Literature Cited To the extent it is available, the chapter reflects the peer-reviewed literature. There have been climate assessments for other nations and a selection of these (including Canada)
From page 71...
... Throughout the draft NCA4, the significance of these connections, and interdependencies are evident and this chapter explains and makes more prominent these complexities. It is an important and appreciated addition to this draft fourth assessment.
From page 72...
... . Comments Related to the Statement of Task Comments on Key Messages The chapter's key messages are generally clear, consistent and communicated appropriately for the intended audiences.
From page 73...
... Flagging key messages in Box 17.1 is also effective. However, all boxes should relate to the chapter topic.
From page 74...
... . Comments on Traceable Accounts The findings are documented in the report in a consistent, transparent and credible manner.
From page 75...
... Comments Related to the Statement of Task Comments on Key Messages In all cases, including diversity across the region (north to south; large urban areas to rural areas, etc.) , the key messages reflect current understanding about observed and projected impacts.
From page 76...
... Comments on Traceable Accounts The traceable accounts are strong and could be used as a model for other chapters where improvements to the traceable accounts are suggested. They are clearly articulated and indicate confidence clause by clause in some cases, which is appropriate.
From page 77...
... This is a major investment in infrastructure that makes these cities more vulnerable to sea level rise and discussion of this could fit in the Charleston case study that is already included in the draft chapter. Comments Related to the Statement of Task Comments on Key Messages Overall, the selected materials and treatment of key messages is appropriate.
From page 78...
... This is a major investment to port facilities and with this infrastructure expansion comes more vulnerability to sea level rise; discussion of this could fit in the Charleston case study. The Southeast Florida Regional Climate Change Compact7 is only mentioned in passing on page 754 and it is recommended that this example be expanded.
From page 79...
... Caribbean Chapter of the draft NCA4 represents a welcome addition to the national climate assessment. Previously, this region was incorporated into the Southeast regional chapter, which made it more challenging to emphasize unique climate impacts and responses occurring in the Caribbean Region.
From page 80...
... Virgin Islands, the approach taken paints a complex, but reasonably accurate picture of climate impacts through a multidimensional lens and concludes with a section on the value of adaptive capacity and building resilience. The key messages are in line with the current understanding about observed and projected impacts to the United States from the perspective and position of small islands in the Caribbean Sea and Atlantic Ocean.
From page 81...
... Comments on Traceable Accounts Generally, the key messages are presented and documented in a consistent manner and make understandable links between the literature and the likelihood and confidence provided in Key Messages 2-5, although likelihood and confidence statements are not provided in the key messages, as they are in other chapters. The challenge of presenting information for the two sets of islands with very different information bases and conditions makes transparency difficult.
From page 82...
... The key messages address main impacts, vulnerabilities, and adaptations in major sectors of concern within the region. Key message structure and language is clear and internally consistent.
From page 83...
... makes significant mention of the importance of and impacts on the Great Lakes in the region, but this is not mentioned in the key messages. The Chapter 21 authors should consider adding a key message on the Great Lakes, or incorporating Great Lakes impacts into Key Messages 3 and 5 (at least)
From page 84...
... Comments on Literature Cited The discussion of impacts of increased moisture in agricultural systems might benefit from further contextualization and discussion of the potential for future drying. The traceable accounts section cites the CSSR: "future higher temperatures will likely lead to greater frequencies and magnitudes of agricultural droughts throughout the continental United States as the resulting increases in evapotranspiration outpace projected precipitation increases." Additional literature supports this possible impact based on the Coupled Model Intercomparison Project, including Douville and Piazotta (2017)
From page 85...
... , and the largely extra-regional authorship could raise concerns for some stakeholders in these states. Comments Related to the Statement of Task Comments on Key Messages For the most part, the topics included in the key messages reflect current understanding about observed and projected impacts in the region, and they identify widely recognized issues with respect to climate change.
From page 86...
... See also the "Comments on Traceable Accounts" section of this chapter review. Key Message 2: Agricultural production in the Northern Great Plains, with gross revenue of $52.3B per year, has benefited from longer growing seasons and other recent climatic changes.
From page 87...
... . Also, the supporting text for Key Message 2 describes some important trends, especially more land being broken out for row crops, but does not explain how much attribution belongs with climate change.
From page 88...
... Headwaters Economics offers several important studies that could be considered by the chapter authors.9 Key Message 4: Fossil fuel and renewable energy production and distribution infrastructure is expanding within the Northern Great Plains. Climate change and extreme weather events put this infrastructure at risk, as well as the supply of energy it contributes to support individuals, communities, and the U.S.
From page 89...
... It is noted that each chapter in the draft NCA4 handles traceable accounts differently, with some, like this chapter, providing new information not previously discussed in the chapter and being relatively short. The Committee suggests better alignment of key message text and the traceable accounts to avoid seeming like afterthoughts, and where possible, more inclusion of specific examples of adaptation with the key messages.
From page 90...
... More specific line comments for this chapter are provided in Appendix B CHAPTER 23: SOUTHERN GREAT PLAINS Summary Chapter 23 surveys the diverse set of anticipated climate change impacts on the industries, communities and ecosystems of the Southern Great Plains region.
From page 91...
... For example, better descriptions are needed of baselines and how climate changes are expected to affect deviations from those baselines. Tables, figures and case study boxes should be better used to reinforce key messages.
From page 92...
... The "Description of evidence base" explains only the general source of information for a particular key message, whereas most chapters provide specific evidence. The Chapter 23 authors should make better use of the traceable accounts section for strengthening supporting evidence for key messages, increasing transparency, and providing resources for readers wishing to explore any particular topic in the chapter in more detail.
From page 93...
... More balanced discussion of species distribution changes and expanded discussion of demonstrated benefits of climate adaptation and mitigation actions in the region would improve this chapter. Comments Related to the Statement of Task Comments on Key Messages Organization and content of the key messages is clear, consistent, and makes the findings accessible.
From page 94...
... Key Message 5: Communities on the front lines of climate change experience the first, and often the worst, effects. Frontline communities in the Northwest include Tribal and Indigenous peoples, the economically disadvantaged, and those most dependent on natural resources for their livelihoods.
From page 95...
... The Committee recommends this language be used elsewhere in the NCA4, as it helps greatly in orientating readers to the direct relevance of the key messages to them, or to communities they know. See also "Other Recommended Changes" section of this chapter review for additional suggestions related to Key Message 3.
From page 96...
... Traceable accounts effectively describe the evidence base and uncertainty of the key messages. The chapter gives excellent treatment to a full range of biophysical, socioeconomic and cultural impacts and provides strong examples of adaptation and mitigation strategies that give the reader tangible cases to increase understanding.
From page 97...
... . Key Message 3: Homes, beaches, fish, and other coastal resources in the Southwest have experienced sea level rise, ocean heating, ocean acidification, and reduced oxygen, all manifestations of human-caused climate change.
From page 98...
... Also, in the traceable accounts "Major uncertainties" it is unclear why there is no mention of variation in ocean acidification levels and vulnerability of species, similar to what is provided for sea level rise, especially since it is mentioned in the main body of the chapter. Key Message 4: Traditional foods, livelihoods, cultural resources, and spiritual well being of Indigenous peoples in the Southwest are affected by drought, wildfire, and ocean warming.
From page 99...
... Comments on Traceable Accounts Overall, the key messages are documented in a consistent, transparent, and credible way. However, some information is missing or inconsistently treated among main chapter text and traceable accounts sections.
From page 100...
... • Readers could also benefit from reference to available state and local climate assessments and climate plans resources. Reference to other relevant draft NCA4 chapters should also be added, including those focused on water, oceans, and ecosystem services.
From page 101...
... Comments Related to the Statement of Task Comments on Key Messages The key messages accurately reflect the understanding described in the text of the chapter with respect to past and projected changes and the associated risks for ecosystems and society. The key messages convey the main topics of the chapter, but are vaguer than the main text and traceable accounts.
From page 102...
... , whereas the key messages emphasize effects on ecosystems and communities. Graphics should be selected to more clearly illustrate the key messages.
From page 103...
... Traceable accounts effectively describe the process and evidence base of the key messages. Comments Related to the Statement of Task Comments on Key Messages Key Message 1: Dependable and safe water supplies for Pacific Island communities and ecosystems are threatened by rising temperatures, sea level rise, and increased risk of
From page 104...
... . Granted, the rates have changed dramatically, but the overall amount of anomalous sea level rise in 1993-2011 is large and that in 2012-2015 is relatively small.
From page 105...
... Comments on Traceable Accounts Overall, the key messages are documented in a consistent, transparent and credible way. In the "Description of confidence and likelihood" section for Key Message 3, it is stated that: "There is very high confidence that a continued rise in global temperature will lead to increases in the rate of sea level rise." The Committee agrees with this, but it is suggested that the authors add that while there is high confidence that sea level will rise, there is not much confidence in the actual amount of sea level rise -- the increased rate could fall within a wide range of possible outcomes.
From page 106...
... The key messages are effective and accurate, but could be improved by incorporating stronger language that ties in concrete examples. Comments Related to the Statement of Task Comments on Key Messages The key messages reflect current understanding and current and emerging conversations, especially in terms of risk management and risk reduction.
From page 107...
... Comments on Traceable Accounts Chapter findings are documented in a consistent, transparent and credible manner with high to medium levels of confidence. The findings are communicated effectively and rather easily for intended audiences.
From page 108...
... The Committee sees the value in including economic risks and impacts in the draft NCA4, which are primarily only included in this chapter. As noted in the comments in the "Front Matter: Report Findings" section earlier in Chapter 3 of this review, the revised NCA4 should address economic impacts more broadly in the national topic and regional chapters to complement the discussion of impacts.
From page 109...
... Key Message 2: Substantial global-scale greenhouse gas emissions reductions are shown to significantly reduce climate change impacts and economic damages across the United States, though the magnitude and timing of avoided risks varies by sector and region. Key Message 2 would be improved by revising to "the magnitude and timing of avoided risks varies by sector, region and population adaptive capacity (or socioeconomics)
From page 110...
... More broadly, considerable research has been published recently for inclusion in the forthcoming IPCC Special Report on 1.5oC and should be cited in this chapter, which could support and inform Key Messages 2 and 3. Comments on Graphics and Tables Figure 29.1 is effective and a welcome addition to the draft NCA4.
From page 111...
... However, there is a larger body of available literature that could be draw on to support the chapter text, which the Committee recommends the Chapter 29 authors consider including to bolster the traceable accounts. Comments on Data and Analyses The data and analyses included in this chapter are consistent, transparent, and credible, to a point.
From page 112...
... Reference to other national topic chapters where mitigation is possible is also suggested (e.g., Chapter 7, "Ecosystems, Ecosystem Services, and Biodiversity," Chapter 10, "Agriculture and Rural Communities," etc.)


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