Section 3 of the Fourth National Climates Assessment. Volume 2 by USGCRP. This LibreVox recording is in the public domain. Recording by Warren Caudi, Gurnee, Illinois. Chapter 1. Overview, Part 3. Reducing the Risks of Climate Change Climate change is projected to significantly affect human health, the economy and the environment in the United States, particularly in futures with high greenhouse gas emissions and limited or no adaptation. Recent findings reinforce the fact that without substantial and sustained reductions in greenhouse gas emissions and regional adaptation efforts, there will be substantial and far-reaching changes over the course of the 21st century with negative consequences for a large majority of sectors, particularly towards the end of the century. The impacts and costs of climate change are already being felt in the United States and changes in the likelihood or severity of some recent extreme weather events can now be attributed with increasingly higher confidence to human-caused warming. See Climate Science Special Report Chapter 3. Impacts associated with human health, such as premature deaths due to extreme temperatures and poor air quality, are some of the most substantial. Chapter 13 Air Quality, Key Message 1. Chapter 14 Human Health, Key Messages 1 and 4. Chapter 29 Mitigation, Key Message 2. While many sectors face large economic risks from climate change, other impacts can have significant implications for societal or cultural resources. Further, some impacts will very likely be irreversible for thousands of years, including those two species such as corals, Chapter 9 Oceans, Key Message 1, Chapter 27 Hawaiian Pacific Islands, Key Message 4, or that involve the crossing of thresholds, such as the effects of ice sheet disintegration on accelerated sea-level rise, leading to widespread effects on coastal development lasting thousands of years, Chapter 29 Mitigation, Key Message 2. Future impacts and risks from climate change are directly tied to decisions made in the present, both in terms of mitigation to reduce emissions of greenhouse gases, or remove carbon dioxide from the atmosphere, and adaptation to reduce risks from today's changed climate conditions and prepare for future impacts. Mitigation and adaptation activities can be considered complementary strategies. Mitigation efforts can reduce future risks, while adaptation actions can minimize the consequences of changes that are already happening as a result of past and present greenhouse gas emissions. Many climate change impacts and economic damages in the United States can be substantially reduced through global scale reductions in greenhouse gas emissions complemented by regional and local adaptation efforts. Chapter 29 Mitigation, Key Message 4. Our understanding of the magnitude and timing of risks that can be avoided varies by sector, region, and assumptions about how adaptation measures change the exposure and vulnerability of people, livelihoods, ecosystems, and infrastructure. Acting sooner rather than later generally results in lower costs overall for both adaptation and mitigation efforts and can offer other benefits in the near term. Chapter 29 Mitigation, Key Message 3. Since the third national climate assessment, NCA 3, in 2014, a growing number of states, cities, and businesses have pursued or expanded upon initiatives aimed at reducing greenhouse gas emissions and the scale of adaptation implementation across the country has increased. However, these efforts do not yet approach the scale needed to avoid substantial damages to the economy, environment, and human health expected over the coming decades. Chapter 28, Adaptation, Key Message 1. Chapter 29, Mitigation, Key Messages 1 and 2. Mitigation Many activities within the public and private sectors aim for or have the effect of reducing greenhouse gas emissions, such as the increasing use of natural gas in place of coal or the expansion of wind and solar energy to generate electricity. Fossil fuel combustion accounts for approximately 85% of total US greenhouse gas emissions with agriculture, land cover change, industrial processes, and methane from fossil fuel extraction and processing, as well as from waste, including landfills, wastewater treatment, and composting, accounting for most of the remainder. A number of efforts exist at the federal level to promote low-carbon energy technologies and to increase soil and forest carbon storage. State, local, and tribal government approaches to mitigating greenhouse gas emissions include comprehensive emissions reduction strategies, as well as sector and technology-specific policies. See Figure 1.19 Since NCA-3, private companies have increasingly reported their greenhouse gas emissions, announced emissions reductions targets, implemented actions to achieve those targets, and, in some cases, even put an internal price on carbon. Individuals and other organizations are also making choices every day to reduce their carbon footprints. Market forces and technological change, particularly within the electric power sector, have contributed to a decline in US greenhouse gas emissions over the past decade. In 2016, US emissions were at their lowest level since 1994. Power sector emissions were 25% below 2005 levels in 2016, the largest emissions reduction for a sector of the American economy over this time. This decline was in large part due to increases in natural gas and renewable energy generation, as well as enhanced energy efficiency standards and programs, Chapter 4, Energy, T-Message 2. Given these advances in electricity generation, transmission, and distribution, the largest annual sectoral emissions in the United States now come from transportation. As of the writing of this report, business as usual, as in no new policies, projections of US carbon dioxide and other greenhouse gas emissions show flat or declining trajectories over the next decade, with a central estimate of about 15% to 20% reduction below 2005 levels by 2025, Chapter 29, Mitigation, T-Message 1. Recent studies suggest that some of the indirect effects of mitigation actions could significantly reduce, or possibly even completely offset, the potential costs associated with cutting greenhouse gas emissions. Beyond reduction of climate pollutants, there are many benefits, often immediate, associated with greenhouse gas emissions reductions, such as improving air quality in public health, reducing crop damages from ozone, and increasing energy independence and security through increased reliance on domestic sources of energy. Chapter 13, Air Quality, T-Message 4. Chapter 29, Mitigation, T-Message 4. Adaptation Many types of adaptation actions exist, including changes to business operations, hardening infrastructure against extreme weather, and adjustments to natural resource management strategies. Achieving the benefits of adaptation can require upfront investments to achieve longer-term savings, engaging with different stakeholder interests and values, and planning under uncertainty. In many sectors, adaptation can reduce the cost of climate impacts by more than half. Chapter 28, Adaptation, T-Message 4. Chapter 29, Mitigation, T-Message 4. At the time of NCA-3's release in 2014, its authors found that risk assessment and planning were underway throughout the United States, but that on-the-ground implementation was limited. Since then, the scale and scope of adaptation implementation has increased, including by federal, state, tribal, and local agencies, as well as business, academic, and non-profit organizations, figure 1.20. While the level of implementation is now higher, it is not yet common nor uniform across the United States, and the scale of implementation for some effects and locations is often considered inadequate to deal with the projected scale of climate change risks. Communities have generally focused on actions that address risks from current climate variability and recent extreme events, such as making buildings and other assets incrementally less sensitive to climate impacts. Fewer communities have focused on actions to address the anticipated scale of future change and emergent threats, such as reducing exposure by preventing building in high-risk locations or retreating from at-risk coastal areas, Chapter 28, Adaptation, Key Message 1. Many adaptation initiatives can generate economic and social benefits in excess of their costs in both the near and long-term, Chapter 28, Adaptation, Key Message 4. Damages to infrastructure, such as road and rail networks, are particularly sensitive to adaptation assumptions with proactive measures that account for future climate risks estimated to be capable of reducing damages by large fractions. More than half of damages to coastal property are estimated to be avoidable through adaptation measures, such as shoreline protection and beach replenishment, Chapter 29, Mitigation, Key Message 4. Considerable guidance is available on actions whose benefits exceed their costs in some sectors, such as adaptation responses to storms and rising seas in coastal zones, to riverine and extreme precipitation flooding, and for agriculture at the farm level, but less so on other actions, such as those aimed at addressing risks to health, biodiversity and ecosystems services that may provide significant benefits but are not as well understood, Chapter 28, Adaptation, Key Message 4. Effective adaptation can also enhance social welfare in many ways that can be difficult to quantify, including improving economic opportunity, health, equity, national security, education, social connectivity and sense of place while safeguarding cultural resources and enhancing environmental quality. Aggregating these benefits into a single monetary value is not always the best approach and, more fundamentally, communities may value benefits differently. Considering various outcomes separately in risk management processes can facilitate participatory planning processes and allow for a specific focus on equity. Prioritizing adaptation actions for populations that face higher risks from climate change, including low income and marginalized communities, may prove more equitable and lead, for instance, to improved infrastructure in their communities and increase focus on efforts to promote community resilience that can improve their capacity to prepare for, respond to and recover from disasters. Chapter 28, Adaptation, Key Message 4. A significant portion of climate risk can be addressed by integrating climate adaptation into existing investments, policies and practices. Integration of climate adaptation into decision processes has begun in many areas, including financial risk reporting, capital investment planning, engineering standards, military planning and disaster risk management. A growing number of jurisdictions address climate risk in their land use, hazard mitigation, capital improvement and transportation plans and a small number of cities explicitly link their coastal and hazard mitigation plans using analysis of future climate risks. However, over the course of this century and especially under a higher scenario, RCP 8.5, reducing the risks of climate change may require more significant changes to policy and regulations at all scales, community planning, economic and financial systems, technology applications and ecosystems. Chapter 28, Adaptation, Key Message 5. Some sectors are already taking actions that go beyond integrating climate risk into current practices faced with substantial climate-induced changes in the future, including new invasive species and shifting ranges for native species, ecosystem managers have already begun to adopt new approaches, such as assisted migration and development of wildlife corridors. Chapter 7, Ecosystems, Key Message 2. Many millions of Americans live in coastal areas threatened by sea level rise. In all but the very lowest sea level rise projections, retreats will become an unavoidable option in some areas along the U.S. coastline. Chapter 8, Coastal, Key Message 1. The federal government has granted funds for the relocation of some communities, including the Biloxi Chitomaka Chakta tribe from Al Dijin Charles in Louisiana, figure 1.17. However, the potential need for millions of people and billions of dollars of coastal infrastructure to be relocated in the future creates challenging legal, financial, and equity issues that have not yet been addressed. Chapter 28, Adaptation, Key Message 5. In some areas, lack of historical or current data to inform policy decisions can be a limitation to assessments of vulnerabilities and or effective adaptation planning. For this national climate assessment, this was particularly the case for some aspects of the Alaska, U.S. Caribbean, and Hawaii and U.S. affiliated Pacific Islands regions. In many instances, relying on indigenous knowledges is among the only current means of reconstructing what has happened in the past. To help communities across the United States learn from one another in their efforts to build resilience to a changing climate, this report highlights common climate-related risks and possible response actions across all regions and sectors. What has happened since the last national climate assessment? Our understanding of and experience with climate science, impacts, risks, and adaptation in the United States have grown significantly since the third national climate assessment, NCA3, advancing our knowledge of key processes in the Earth's system, how human and natural forces are changing them, what the implications are for society, and how we can respond. Key Scientific Advances Detection and Attribution Significant advances have been made in the attribution of the human influence for individual climate and weather extreme events. See Climate Science Special Report, Chapters 3, 6, 7, and 8. Extreme Events and Atmospheric Circulation How climate change may affect specific types of extreme events in the United States and the extent to which atmospheric circulation in the mid-latitudes is changing or is projected to change, possibly in ways not captured by current climate models, are important areas of research where scientific understanding has advanced. See Climate Science Special Report, Chapters 5, 6, 7, and 9. Localized Information As computing resources have grown, projections of future climate from global models are now being conducted at finer scales, with resolution on the order of 15 miles, providing more realistic characterization of intense weather systems, including hurricanes. For the first time in the NCA process, See Level Rise projections incorporate geographic variation based on factors such as local land subsidence, ocean currents, and changes in Earth's gravitational field. See Climate Science Special Report, Chapters 9 and 12. Ocean and Coastal Waters Ocean acidification, warming, and oxygen loss are all increasing and scientific understanding of the severity of their impacts is growing. Both oxygen loss and acidification may be magnified in some U.S. coastal waters relative to the global average, raising the risk of serious ecological and economic consequences. See Climate Science Special Report, Chapters 2 and 13. Rapid Changes for Ice on Earth New observations from many different sources confirm that ice loss across the globe is continuing and, in many cases, accelerating. Since NCA-3, Antarctica and Greenland have continued to lose ice mass with mounting evidence that mass loss is accelerating. Observations continue to show declines in the volume of mountain glaciers around the world annual September minimum sea ice extent in the Arctic Ocean has decreased at a rate of 11% to 16% per decade since the early 1980s with accelerating ice loss since 2000. The annual sea ice extent minimum for 2016 was the second lowest on record. The sea ice minimums in 2014 and 2015 were also among the lowest on record. See Climate Science Special Report, Chapters 1, 11, and 12. Potential Surprises Both large-scale shifts in the climate system, sometimes called tipping points and compound extremes, have the potential to generate outcomes that are difficult to anticipate and may have high consequences. The more the climate changes, the greater the potential for these surprises. See Climate Science Special Report, Chapter 15. Extreme Events Climate change is altering the characteristics of many extreme weather and climate-related events. Some extreme events have already become more frequent, intense, widespread, or of longer duration and many are expected to continue to increase or worsen presenting substantial challenges for built, agricultural, and natural systems. Some storm types such as hurricanes, tornadoes, and winter storms are also exhibiting changes that have been linked to climate change although the current state of the science does not yet permit detailed understanding. See Climate Science Special Report, Executive Summary. Individual extreme weather and climate-related events, even those that have not been clearly attributed to climate change by scientific analyses reveal risks to society and vulnerabilities that mirror those we expect in a warmer world. Non-climate stressors, such as land use changes and shifting demographics, can also amplify the damages associated with extreme events. The National Oceanic and Atmospheric Administration estimates that the United States has experienced $44 billion weather and climate disasters since 2015 through April 6, 2018 incurring costs of nearly $400 billion. Hurricanes The 2017 Atlantic hurricane season alone is estimated to have caused more than $250 billion in damages and over 250 deaths throughout the U.S. Caribbean, Southeast, and Southern Great Plains. More than 30 inches of rain fell during Hurricane Harvey, affecting 6.9 million people. Hurricane Maria's high winds caused widespread devastation to Puerto Rico's transportation, agriculture, communication, and energy infrastructure. Extreme rainfall of up to 37 inches caused widespread flooding and mudslides across the island. The interruption to commerce and standard living conditions will be sustained for a long period while much of Puerto Rico's infrastructure is rebuilt. Hurricane Irma destroyed 25% of buildings in the Florida Keys. Floods In August 2016, a historic flood resulting from 20 to 30 inches of rainfall over several days devastated a large area of southern Louisiana, causing over $10 billion in damages and 13 deaths. More than 30,000 people were rescued from floodwaters that damaged or destroyed more than 50,000 homes, 100,000 vehicles, and 20,000 businesses. In June 2016, torrential rainfall caused destructive flooding throughout many West Virginia towns, damaging thousands of homes and businesses, and causing considerable loss of life. More than 1,500 roads and bridges were damaged or destroyed. The 2015-2016 El Nino poured 11 days of record-setting rainfall on Hawaii, causing severe urban flooding. Drought In 2015, drought conditions caused about $5 billion in damages across the Southwest and Northwest, as well as parts of the Northern Great Plains. California experienced the most severe drought conditions. Hundreds of thousands of acres of farmland remained fallow, and excess groundwater pumping was required to irrigate existing agricultural interests. Two years later in 2017, extreme drought caused $2.5 billion in agricultural damages across the Northern Great Plains. Field crops, including wheat, were severely damaged, and the lack of feed for cattle forced ranchers to sell off livestock. Wildfires During the summer of 2015, over 10.1 million acres, an area larger than the entire state of Maryland, burned across the United States, surpassing 2006 for the highest annual total U.S. acreage burned since record keeping began in 1960. These wildfire conditions were exacerbated by the preceding drought conditions in several states. The most extensive wildfires occurred in Alaska, where 5 million acres burned within the state. In Montana, wildfires burned in excess of 1 million acres. The costliest wildfires occurred in California, where more than 2,500 structures were destroyed by the Valley and Butte fires. Ensured losses alone exceeded $1 billion. In October 2017, a historic firestorm damaged or destroyed more than 15,000 homes, businesses, and other structures across California. See figure 1.5. The tubs, atlas, nuns, and Redwood Valley fires caused a total of 44 deaths, and their combined destruction represents the costliest wildfire event on record. Tornadoes In March 2017, a severe tornado outbreak caused damage across much of the Midwest and into the Northeast. Nearly 1 million customers lost power in Michigan alone due to sustained high winds, which affected several states from Illinois to New York. Heat Waves Honolulu experienced 24 days of record-setting heat during the 2015-2016 El Nino event. As a result, the local energy utility issued emergency public service announcements to curtail escalating air conditioning use that threatened the electrical grid. New Aspects of this Report Hundreds of states, counties, cities, businesses, universities, and other entities are implementing actions that build resilience to climate-related impacts and risks, while also aiming to reduce greenhouse gas emissions. Many of these actions have been informed by new climate-related tools and products developed through the U.S. Global Change Research Program, USG-CRP, CENTS-NCA-3, Sea Appendix 3, Scenario Products and Data Tools. We briefly highlight a few of them here. In addition, several structural changes have been introduced to the report and new methods used in response to stakeholder needs for more localized information and to address key gaps identified in NCA-3. The third national climate assessment remains a valuable and relevant resource. This report expands upon our knowledge and experience as presented four years ago. Climate Science Special Report Early in the development of NCA-4, experts and administration officials recognized that conducting a comprehensive physical science assessment, Volume 1, in advance of an impacts assessment, Volume 2, would allow one to inform the other. The Climate Science Special Report, released in November 2017, is Volume 1 of NCA-4 and represents the most thorough and up-to-date assessment of climate science in the United States and underpins the findings of this report. Its findings are summarized in Chapter 2, Our Changing Climate. See the Key Scientific Advances section in this box and box 2.3 in Chapter 2 for more detail. Scenario Products As described in more detail in Appendix 3, Data Tools and Scenario Products, federal inter-agency groups developed a suite of high-resolution scenario products that span a range of plausible future changes in key environmental variables through at least 2100. These USG-CRP scenario products help ensure consistency across the report and improve the ability to synthesize across chapters. Where possible, authors have used these scenario products to frame uncertainty in future climate as it relates to the risks that are the focus of their chapters. In addition, the Indicators Inter-Agency Working Group has developed an Indicators Platform that uses observations or calculations to monitor conditions or trends in the Earth's system just as businesses might use the Unemployment Index as an indicator of economic conditions. See Figure 1.2 Localized Information With the increased focus on local and regional information in NCA4, USG-CRP agencies developed two additional products that not only inform this assessment but can serve as valuable decision support tools. The first are the State Climate Summaries, a peer-reviewed collection of climate change information covering all 10 NCA4 regions at the state level. In addition to standard data on observed and projected climate change, each state climate summary contains state-specific changes and their related impacts as well as a suite of complementary graphics. The second product is the US Climate Resilience Toolkit, which offers data-driven tools, information, and subject matter expertise from across the federal government in one easy-to-use location. So Americans are better able to understand the climate-related risks and opportunities impacting their communities and can make more informed decisions on how to respond. In particular, the case studies showcase examples of climate change impacts and accompanying response actions that complement those presented in Figure 1.1 and allow communities to learn how to build resilience from one another. New Chapters In response to public feedback on NCA3 and input solicited in the early stages of this assessment, a number of significant structural changes have been made. Most fundamentally, the balance of the report's focus has shifted from national-level chapters to regional chapters in response to a growing desire for more localized information on impacts. Building on this theme, the Great Plains Chapter has been split into Northern and Southern Chapters, Chapters 22 and 23, along the Kansas-Nebraska border. In addition, the US Caribbean is now featured as a separate region in this report, Chapter 20, focusing on the unique impacts, risks, and response capabilities in Puerto Rico and the US Virgin Islands. Public input also requested greater international context in the report, which has been addressed through two new additions. A new chapter focuses on topics, including the effects of climate change on US trade and businesses, national security, and US humanitarian assistance and disaster relief, Chapter 16. A new international appendix, Appendix 4, presents a number of illustrative examples of how other countries have conducted national climate assessments, putting our own effort into a global context. Given recent scientific advances, some emerging topics warranted a more visible platform in NCA4. A new chapter on air quality, Chapter 13, examines how traditional air pollutants are affected by climate change. A new chapter on sector interactions, multiple stressors, and complex systems, Chapter 17, evaluates climate-related risks to interconnected human and natural systems that are increasingly vulnerable to cascading impacts and highlights, advances in analyzing how these systems will interact with and respond to a changing environment. See box 1.3 Integrating Economics This report, to a much greater degree than previous national climate assessments, includes broader and more systematic quantification of climate change impacts in economic terms. While this is an emerging body of literature that is not yet reflected in each of the 10 NCA regions, it represents a valuable advancement in our understanding of the financial costs and benefits of climate change impacts. Figure 1.21 provides an illustration of the type of economic information that is integrated throughout this report. It shows the financial damages avoided under a lower scenario, RCP 4.5, versus a higher scenario, RCP 8.5. End of Section 3. Section 4 of the Fourth National Climate Assessment, Volume 2, by USG-CRP. This LibriVox recording is in the public domain. Recording by Warren Coddy, Gurnee, Illinois. Chapter 2. Our Changing Climate Key Message 1. Observed Changes in Global Climate Global climate is changing rapidly compared to the pace of natural variations in climate that have occurred throughout Earth's history. Global average temperature has increased by about 1.8 degrees Fahrenheit from 1901 to 2016, and observational evidence does not support any credible natural explanations for this amount of warming. Instead, the evidence consistently points to human activities, especially emissions of greenhouse or heat-trapping gases, as the dominant cause. Key Message 2. Future Changes in Global Climate Earth's climate will continue to change over the century and beyond. Past mid-century, how much the climate changes will depend primarily on global emissions of greenhouse gases and on the response of Earth's climate system to human-induced warming. With significant reductions in emissions, global temperature increase could be limited to 3.6 degrees Fahrenheit, 2 degrees Celsius, or less compared to pre-industrial temperatures. Without significant reductions, annual average global temperatures could increase by 9 degrees Fahrenheit, 5 degrees Celsius, or more by the end of this century compared to pre-industrial temperatures. Key Message 3. Warming and Acidifying Oceans The world's oceans have absorbed 93% of the excess heat from human-induced warming since the mid-20th century and are currently absorbing more than a quarter of the carbon dioxide emitted to the atmosphere annually from human activities, making the oceans warmer and more acidic. Increasing sea surface temperatures, rising sea levels, and changing patterns of precipitation, winds, nutrients, and ocean circulation are contributing to overall declining oxygen concentrations in many locations. Key Message 4. Rising Global Sea Levels Global average sea level has risen by about 7 to 8 inches, about 16 to 21 centimeters, since 1900, with almost half this rise occurring since 1993 as oceans have warmed and land-based ice has melted. Relative to the year 2000, sea level is very likely to rise 1 to 4 feet, 0.3 to 1.3 meters, by the end of the century. Emerging science regarding Antarctic ice sheet stability suggests that, for higher scenarios, a rise exceeding 8 feet, 2.4 meters, by 2100, is physically possible, although the probability of such an extreme outcome cannot currently be assessed. Key Message 5. Increasing U.S. Temperatures Annual average temperature over the contiguous United States has increased by 1.2 degrees Fahrenheit, 0.7 degrees Celsius, over the last few decades, and by 1.8 degrees Fahrenheit, 1 degrees Celsius, relative to the beginning of the last century. Additional increases in annual average temperature of about 2.5 degrees Fahrenheit, 1.4 degrees Celsius, are expected over the next few decades, regardless of future emissions, and increases ranging from 3 degrees Fahrenheit to 12 degrees Fahrenheit, 1.6 to 6.6 degrees Celsius, are expected by the end of century, depending on whether the world follows a higher or lower future scenario, with proportionally greater changes in high temperature extremes. Key Message 6. Changing U.S. Precipitation Annual precipitation since the beginning of the last century has increased across most of the northern and eastern United States and decreased across much of the southern and western United States. Over the coming century, significant increases are projected in winter and spring over the northern Great Plains, the upper Midwest, and the northeast. Observed increases in the frequency and intensity of heavy precipitation events in most parts of the United States are projected to continue. Surface soil moisture over most of the United States is likely to decrease, accompanied by large declines in snowpack in the western United States and shifts to more winter precipitation falling as rain rather than snow. Key Message 7. Rapid Arctic Change In the Arctic, annual average temperatures have increased more than twice as fast as the global average, accompanied by thawing permafrost and loss of sea ice and glacier mass. Arctic-wide glacial and sea ice loss is expected to continue. By mid-century, it is very likely that the Arctic will be nearly free of sea ice in late summer. Permafrost is expected to continue to thaw over the coming century as well, and the carbon dioxide and methane released from thawing permafrost has the potential to amplify human-induced warming, possibly significantly. Key Message 8. Changes in Severe Storms Human-induced change is affecting atmospheric dynamics and contributing to the poleward expansion of the tropics and the northward shift in Northern Hemisphere winter storm tracks since 1950. Increases in greenhouse gases and decreases in air pollution have contributed to increases in Atlantic hurricane activity since 1970. In the future, Atlantic and eastern North Pacific hurricane rainfall and intensity are projected to increase, as are the frequency and severity of land-falling atmospheric rivers on the west coast. Key Message 9. Increases in Coastal Flooding Regional changes in sea-level rise and coastal flooding are not evenly distributed across the United States. Ocean circulation changes, sinking land, and Antarctic ice melt will result in greater than average sea-level rise for the northeast and western Gulf of Mexico under lower scenarios and most of the U.S. coastline other than Alaska under higher scenarios. Since the 1960s, sea-level rise has already increased the frequency of high tide flooding by a factor of 5 to 10 for several U.S. coastal communities. The frequency, depth, and extent of tidal flooding are expected to continue to increase in the future, as is the more severe flooding associated with coastal storms such as hurricanes and nor-easters. Key Message 10. Long-Term Changes The climate changes resulting from human-caused emissions of carbon dioxide will persist for decades to millennia. Self-reinforcing cycles within the climate system have the potential to accelerate human-induced change and even shift Earth's climate system into new states that are very different from those experienced in the recent past. Future changes outside the range projected by climate models cannot be ruled out and due to their systematic tendency to underestimate temperature change during past warm periods, models may be more likely to underestimate than to overestimate long-term future change. For a full chapter, including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash climate. End of Section 4. Section 5 of the Fourth National Climate Assessment, Volume 2 by USGCRP. This LibriVox recording is in the public domain. Recording by Warren Coddy, Gurnee, Illinois. Chapter 3. Water. Key Message 1. Changes in Water Quantity and Quality Significant changes in water quantity and quality are evident across the country. These changes, which are expected to persist, present an ongoing risk to coupled human and natural systems and related ecosystem services. Variable precipitation and rising temperature are intensifying droughts, increasing heavy downpours and reducing snowpack. Reduced snow-to-rain ratios are leading to significant differences between the timing of water supply and demand. Groundwater depletion is exacerbating drought risk. Surface water quality is declining as water temperature increases and more frequent high-intensity rainfall events mobilize pollutants such as sediments and nutrients. Key Message 2. Deteriorating Water Infrastructure at Risk Deteriorating water infrastructure compounds the climate risk faced by society. Extreme precipitation events are projected to increase in a warming climate and may lead to more severe floods and greater risk of infrastructure failure in some regions. Infrastructure design, operation, financing principles and regulatory standards typically do not account for a changing climate. Current risk management does not typically consider the impact of compound extremes, co-occurrence of multiple events, and the risk of cascading infrastructure failure. Key Message 3. Water Management in a Changing Future Water management strategies designed in view of an evolving future we can only partially anticipate will help prepare the nation for water and climate-related risks of the future. Current water management and planning principles typically do not address risk that changes over time, leaving society exposed to more risk than anticipated. While there are examples of promising approaches to manage climate risk, the gap between research and implementation, especially in view of regulatory and institutional constraints, remains a challenge. Ensuring a reliable supply of clean fresh water to individuals, communities and ecosystems together with effective management of floods and droughts is the foundation of human and ecological health. The water sector is also central to the economy and contributes significantly to the resilience of many other sectors, including agriculture, energy, urban environments and industry. Water systems face considerable risk, even without anticipated future climate changes. Limited surface water storage, as well as a limited ability to make use of long-term drought forecasts and to trade water across uses and basins, has led to a significant depletion of aquifers in many regions of the United States. Across the nation, much of the critical water and wastewater infrastructure is nearing the end of its useful life. To date, no comprehensive assessment exists of the climate-related vulnerability of U.S. water infrastructure, including dams, levees, aqueducts, sewers and water and wastewater distribution and treatment systems, the potential resulting damages, or the cost of reconstruction and recovery. Paleo-climate information, reconstructions of past climate derived from ice cores or tree rings, shows that over the last 500 years, North America has experienced pronounced wet, dry regime shifts that sometimes persisted for decades because such protracted exposures to extreme floods or droughts in different parts of the country are extraordinary compared to events experienced in the 20th century. They are not yet incorporated in water management principles and practice. Anticipated future climate change will exacerbate this risk in many regions. A central challenge to water planning and management is learning to plan for plausible future climate conditions that are wider in range than those experienced in the 20th century. Doing so requires approaches that evaluate plans over many possible futures instead of just one, incorporate real-time monitoring and forecast products to better manage extremes when they occur and update policies and engineering principles with the best available geoscience-based understanding of planetary change. While this represents a break from historical practice, recent examples of adaptation responses undertaken by large water management agencies, including major metropolitan water utilities and the U.S. Corps of Engineers, are promising. For full chapter, including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash water. End of Section 5. Section 6 of the Fourth National Climate Assessment, Volume 2 by USG-CRP. This LibriVox recording is in the public domain. Recording by Warren Cotty, Gurnee, Illinois. Chapter 4. Energy Supply Delivery and Demand. Key Message 1. Nationwide Impacts on Energy The nation's energy system is already affected by extreme weather events and due to climate change, it is projected to be increasingly threatened by more frequent and longer-lasting power outages affecting critical energy infrastructure and creating fuel availability and demand imbalances. The reliability, security, and resilience of the energy system underpin virtually every sector of the U.S. economy, cascading impacts on other critical sectors could affect economic and national security. Key Message 2. Changes in energy system affect vulnerabilities. Changes in energy technologies, markets, and policies are affecting the energy system's vulnerabilities to climate change and extreme weather. Some of these changes increase reliability and resilience while others create additional vulnerabilities. Changes include the following. Natural gas is increasingly used as fuel for power plants. Renewable resources are becoming increasingly cost competitive with an expanding market share and a resilient energy supply is increasingly important as telecommunications, transportation, and other critical systems are more interconnected than ever. Key Message 3. Improving energy system resilience. Actions are being taken to enhance energy security, reliability, and resilience with respect to the effects of climate change and extreme weather. This progress occurs through improved data collection, modeling, and analysis to support resilience planning, private and public-private partnerships supporting coordinated action, and both development and deployment of new innovative energy technologies for adapting energy assets to extreme weather hazards. Although barriers exist, opportunities remain to accelerate the pace, scale, and scope of investments in energy systems resilience. The nation's economic security is increasingly dependent on an affordable and reliable supply of energy. Every sector of the economy depends on energy from manufacturing to agriculture, banking, healthcare, telecommunications, and transportation. Increasingly, climate change and extreme weather events are affecting the energy system, threatening more frequent and longer-lasting power outages and fuel shortages. Such events can have cascading impacts on other critical sectors, potentially affecting the nation's economic and national security. At the same time, the energy sector is undergoing substantial policy, market, and technology-driven changes that are projected to affect these vulnerabilities. The impacts of extreme weather and climate change on energy systems will differ across the United States. Low-lying energy facilities and systems located along inland waters or near the coasts are at elevated risk of flooding from more intense precipitation, rising sea levels, and more intense hurricanes. Increases in the severity and frequency of extreme precipitation are projected to affect inland energy infrastructure in every region. Rising temperatures in extreme heat events are projected to reduce the generation capacity of thermoelectric power plants and decrease the efficiency of the transmission grid. Rising temperatures are projected to also drive greater use of air conditioning and increase electricity demand, likely resulting in increases in electricity costs. The increase in annual electricity demand across the country for cooling is offset only marginally by the relatively small decline in electricity demand for heating. Extreme cold events, including ice and snow events, can damage power lines and impact fuel supplies. Severe drought, along with changes in evaporation, reductions in mountain snowpack, and shifting mountain snow melt timing is projected to reduce hydropower production and threatened oil and gas drilling and refining, as well as thermoelectric power plants that rely on surface water for cooling. Drier conditions are projected to increase the risk of wildfires and damage to energy production and generation assets and the power grid. At the same time, the nature of the energy system itself is changing. Low carbon-emitting natural gas generation has displaced coal generation due to the rising production of low-cost unconventional natural gas, in part supported by federal investment in research and development. In the last 10 years, the share of generation from natural gas increased from 20% to over 30% while coal has declined from nearly 50% to around 30%. Over the same time, generation from wind and solar has grown from less than 1% to over 5% due to a combination of technological progress, dramatic cost reductions, and federal and state policies. It is possible to address the challenges of a changing climate and energy system and both industry and governments at the local, state, regional, federal and tribal levels are taking actions to improve the resilience of the nation's energy system. These actions include planning and operational measures that seek to anticipate climate impacts and prevent or respond to damages more effectively as well as hardening measures to protect assets from damage during extreme events. Resilience actions can have co-benefits such as developing and deploying new innovative energy technologies that increase resilience and reduce emissions. While steps are being taken, an escalation of the pace, scale and scope of efforts is needed to ensure the safe and reliable provision of energy and to establish a climate-ready energy system to address present and future risks. For full chapter, including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash energy. End of section 6. Section 7 of the Fourth National Climate Assessment Volume 2 by USG-CRP This LibriVox recording is in the public domain. Recording by Warren Coddy, Gurnee, Illinois. Chapter 5 Land, Cover and Land Use, Change Key Message 1 Land, Cover, Changes, Influence, Weather and Climate Changes in land cover continue to impact local to global scale weather and climate by altering the flow of energy, water and greenhouse gases between the land and the atmosphere. Reforestation can foster localized cooling while in urban areas continued warming is expected to exacerbate urban heat island effects. Key Message 2 Climate impacts on land and ecosystems Climate change affects land use and ecosystems. Climate change is expected to directly and indirectly impact land use and cover by altering disturbance patterns, species distributions and the suitability of land for specific uses. The composition of the natural and human landscapes and how society uses the land affects the ability of the nation's ecosystems to provide essential goods and services. Climate can affect and be affected by changes in land cover, the physical features that cover the land such as trees or pavement and land use, human management and activities on land such as mining or recreation. A forest, for instance, would likely include tree cover but could also include areas of recent tree removals currently covered by open grass areas. Land cover and use are inherently coupled. Changes in land use practices can change land cover and land cover enables specific land uses. Understanding how land cover, use, condition and management vary in space and time is challenging. Changes in land cover can occur in response to both human and climate drivers. For example, demand for new settlements often results in the permanent loss of natural and working lands which can result in localized changes in weather patterns, temperature and precipitation. Aggregated over large areas, these changes have the potential to influence Earth's climate by altering regional and global circulation patterns, changing the albedo, reflectivity of Earth's surface and changing the amount of carbon dioxide, CO2, in the atmosphere. Conversely, climate change can also influence land cover resulting in a loss of forest cover from climate related increases in disturbances, the expansion of woody vegetation into grasslands and the loss of beaches due to coastal erosion amplified by rises in sea level. Land use is also changed by both human and climate drivers. Land use decisions are traditionally based on short-term economic factors. Land use changes are increasingly being influenced by distant forces due to the globalization of many markets. Land use can also change due to local, state and national policies such as programs designed to remove cultivation from highly erodible land to mitigate degradation, legislation to address sea level rise in local comprehensive plans or policies that reduce the rate of timber harvest on federal lands. Technological innovation has also influenced land use change with the expansion of cultivated lands from the development of irrigation technologies and more recently decreases in demand for agricultural land due to increases in crop productivity. The recent expansion of oil and gas extraction activities throughout large areas of the United States demonstrates how policy, economics, and technology can collectively influence and change land use and land cover. Decisions about land use, cover, and management can help determine society's ability to mitigate and adapt to climate change. For a full chapter, including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash land-changes. End of Section 7. Section 8 of the Fourth National Climate Assessment, Volume 2 by USGCRP. This LibriVox recording is in the public domain. Recording by Warren Coddy, Gurnee, Illinois. Chapter 6. Forests. Key Message 1. Ecological Disturbances and Forest Health. It is very likely that more frequent extreme weather events will increase the frequency and magnitude of severe ecological disturbances, driving rapid months to years and often persistent changes in forest structure and function across large landscapes. It is also likely that other changes, resulting from gradual climate change and less severe disturbances, will alter forest productivity and health and the distribution and abundance of species at longer time scales, decades to centuries. Key Message 2. Ecosystem Services. It is very likely that climate change will decrease the ability of many forest ecosystems to provide important ecosystem services to society. Tree growth and carbon storage are expected to decrease in most locations as a result of higher temperatures, more frequent drought, and increased disturbances. The onset and magnitude of climate change effects on water resources in forest ecosystems will vary, but are already occurring in some regions. Key Message 3. Adaptation. Forest management activities that increase the resilience of U.S. forests to climate change are being implemented with a broad range of adaptation options for different resources, including applications in planning. The future pace of adaptation will depend on how effectively social, organizational, and economic conditions support implementation. Forests on public and private lands provide benefits to the natural environment, as well as economic benefits and ecosystem services to people in the United States and globally. The ability of U.S. forests to continue to provide goods and services is threatened by climate change and associated increases in extreme events and disturbances. For example, severe drought and insect outbreaks have killed hundreds of millions of trees across the United States over the past 20 years, and wildfires have burned at least 3.7 million acres annually in all but three years from 2000 to 2016. Recent insect-caused mortality appears to be outside the historical context and is likely related to climate change. However, it is unclear if the apparent climate-related increase in fire-caused tree mortality is outside the range of what has been observed over centuries of wildfire occurrence. A warmer climate will decrease tree growth in most forests that are water-limited, for example, low-elevation ponderosa pine forests, but will likely increase growth in forests that are energy-limited, for example, sub-alpine forests where long-lasting snowpack and cold temperatures limit the growing season. Droughts and extreme high temperatures can cause heat-related stress in vegetation and, in turn, reduce forest productivity and increase mortality. The rate of climate warming is likely to influence forest health, that is, the extent to which ecosystem processes are functioning within their range of historic variation and competition between trees, which will affect the distributions of some species. Large-scale disturbances over thousands, two-hundreds of thousands of acres that cause rapid change over days to years and more gradual climate change effects over decades will alter the ability of forests to provide ecosystem services, although alterations will vary greatly depending on the tree species and local biophysical conditions. For example, whereas crown fires, forest fires that spread from tree-top to tree-top, will cause extensive areas of tree mortality in dense, dry forests in the western United States that have not experienced wildfire for several decades. Increased fire frequency is expected to facilitate the persistence of sprouting hardwood species, such as quaking aspen in western mountains and fire-tolerant pine and hardwood species in the eastern United States. See regional chapters for more detail on variation across the United States. Drought, heavy rainfall, altered snowpack and changing forest conditions are increasing the frequency of low summer streamflow, winter and spring flooding and low water quality in some locations with potential negative impacts on aquatic resources and on water supplies for human communities. From 1990 to 2015, U.S. forests sequestered 742 teragrams, T.G. of carbon dioxide, CO2, per year, offsetting approximately 11% of the nation's CO2 emissions. U.S. forests are projected to continue to store carbon, but at declining rates as affected by both land use and lower CO2 uptake as forests get older. However, carbon accumulation in surface soils at depths of 0 to 4 inches can mitigate the declining carbon sink of U.S. forests if reforestation is routinely implemented at large spatial scales. Implementation of climate-informed resource planning and management on forest lands has progressed significantly over the past decade. The ability of society and resource management to continue to adapt to climate change will be determined primarily by socioeconomic factors and organizational capacity. A viable forest-based workforce can facilitate timely actions that minimize negative effects of climate change. Ensuring the continuing health of forest ecosystems and where desired and feasible, keeping forest land in forest cover are key challenges for society. For full chapter, including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash forests. Section 9 of the Fourth National Climate Assessment Volume 2 by USGCRP This LibriVox recording is in the public domain. Recording by Warren Cotty, Gurnee, Illinois. Chapter 7 Ecosystems, Ecosystem Services, and Biodiversity. Key Message 1 Impacts on Species and Populations Climate change continues to impact species and populations in significant and observable ways. Terrestrial, freshwater, and marine organisms are responding to climate change by altering individual characteristics, the timing of biological events, and their geographic ranges. Local and global extinctions may occur when climate change outpaces the capacity of species to adapt. Key Message 2 Impacts on Ecosystems Climate change is altering ecosystem productivity, exacerbating the spread of invasive species and changing how species interact with each other and with their environment. These changes are reconfiguring ecosystems in unprecedented ways. Key Message 3 Ecosystem Services at Risk The resources and services that people depend on for their livelihoods, sustenance, protection, and well-being are jeopardized by the impacts of climate change on ecosystems. Fundamental changes in agricultural and fisheries production, the supply of clean water, protection from extreme events, and culturally valuable resources are occurring. Key Message 4 Challenges for Natural Resource Management Traditional natural resource management strategies are increasingly challenged by the impacts of climate change. Adaptation strategies that are flexible consider interacting impacts of climate and other stressors and are coordinated across landscape scales are progressing from theory to application. Significant challenges remain to comprehensively incorporate climate adaptation planning into mainstream natural resource management as well as to evaluate the effectiveness of implemented actions. Biodiversity, the variety of life on Earth, provides vital services that support and improve human health and well-being. Ecosystems, which are composed of living things that interact with the physical environment, provide numerous essential benefits to people. These benefits, termed ecosystem services, encompass four primary functions. Provisioning materials such as food and fiber, regulating critical parts of the environment, such as water quality and erosion control, providing cultural services, such as recreational opportunities and aesthetic value, and providing supporting services, such as nutrient cycling. Climate change poses many threats and potential disruptions to ecosystems and biodiversity, as well as to the ecosystem services on which people depend. Building on the findings of the Third National Climate Assessment, NCA-3, this chapter provides additional evidence that climate change is significantly impacting ecosystems and biodiversity in the United States. Mounting evidence also demonstrates that climate change is increasingly compromising the ecosystem services that sustain human communities, economies, and well-being. Both human and natural systems respond to change, but their ability to respond and thrive under new conditions is determined by their adaptive capacity, which may be inadequate to keep pace with rapid change. Our understanding of climate change impacts and the responses of biodiversity and ecosystems has improved since NCA-3. The expected consequences of climate change will vary by region, species, and ecosystem type. Management responses are evolving as new tools and approaches are developed and implemented. However, they may not be able to overcome the negative impacts of climate change, although efforts have been made since NCA-3 to incorporate climate adaptation strategies into natural resource management. Significant work remains to comprehensively implement climate-informed planning. This chapter presents additional evidence for climate change impacts to biodiversity, ecosystems, and ecosystem services, reflecting increased confidence in the findings reported in NCA-3. The chapter also illustrates the complex and interrelated nature of climate change impacts to biodiversity, ecosystems, and the services they provide. For full chapter, including references and traceable accounts, see HTTPS colon double backslash NCA 2018 dot globalchange.gov backslash chapter backslash ecosystems. End of section 9. Section 10 of the Fourth National Climate Assessment, Volume 2 by USG-CRP. This LibriVox recording is in the public domain. Recording by Warren Caudy, Gurnee, Illinois. Chapter 8. Coastal Effects. Key Message 1. Coastal economies and property are already at risk. America's trillion-dollar coastal property market and public infrastructure are threatened by the ongoing increase in the frequency, depth, and extent of tidal flooding due to sea level rise with cascading impacts to the larger economy. Higher storm surges due to sea level rise and the increased probability of heavy precipitation events exacerbate the risk. Under a higher scenario, RCP 8.5, many coastal communities will be transformed by the lighter part of the century. And even under lower scenarios, RCP 4.5 or RCP 2.6, many individuals and communities will suffer financial impacts as chronic high tide flooding leads to higher costs and lower property values. Actions to plan for and adapt to more frequent, widespread, and severe coastal flooding would decrease direct losses and cascading economic impacts. Key Message 2. Coastal environments are already at risk. Fisheries, tourism, human health, and public safety depend on healthy coastal ecosystems that are being transformed, degraded, or lost due in part to climate change impacts, particularly sea level rise and higher numbers of extreme weather events. Restoring and conserving coastal ecosystems and adopting natural and nature-based infrastructure solutions can enhance community and ecosystem resilience to climate change, help to ensure their health and vitality, and decrease both direct and indirect impacts of climate change. Key Message 3. Social challenges intensified. As the pace and extent of coastal flooding and erosion accelerate, climate change impacts along our coasts are exacerbating pre-existing social inequities as communities face difficult questions about determining who will pay for current impacts and future adaptation and mitigation strategies, and if, how, or when to relocate. In response to actual or projected climate change losses and damages, coastal communities will be among the first in the nation to test existing climate-relevant legal frameworks and policies against these impacts and, thus, will establish precedents that will affect both coastal and non-coastal regions. The Coast's Chapter of the Third National Climate Assessment, published in 2014, focused on coastal lifelines at risk, economic disruption, uneven social vulnerability, and vulnerable ecosystems. This Coastal Effects Chapter of the Fourth National Climate Assessment updates those themes with a focus on integrating the socio-economic and environmental impacts and consequences of a changing climate. Specifically, the Chapter builds on the threat of rising sea levels, exacerbating tidal and storm surge flooding, the state of coastal ecosystems, and the treatment of social vulnerability by introducing the implications for social equity. U.S. Coasts are dynamic environments and economically vibrant places to live and work. As of 2013, coastal shoreline counties were home to 133.2 million people or 42% of the population. The Coasts are economic engines that support jobs in defense, fishing, transportation, and tourism industries, contribute substantially to the U.S. gross domestic product, and serve as hubs of commerce, with seaports connecting the country with global trading partners. Coasts are home to diverse ecosystems, such as beaches, intertidal zones, reefs, sea grasses, salt marshes, estuaries, and deltas that support a range of important services, including fisheries, recreation, and coastal storm protection. U.S. Coasts span three oceans, as well as the Gulf of Mexico, the Great Lakes, and Pacific and Caribbean islands. The social, economic, and environmental systems along the Coasts are being affected by climate change. Threats from sea level rise, SLR, are exacerbated by dynamic processes such as high tide and storm surge flooding. Chapter 19 Southeast, Key Message 2 Erosion, Chapter 26 Alaska, Key Message 2 Waves and their effects Saltwater intrusion into coastal aquifers and elevated groundwater tables. Chapter 27 Hawaii and Pacific Islands, Key Message 1 Chapter 3 Water, Key Message 1 Local rainfall, Chapter 3 Water, Key Message 1 River runoff, Chapter 3 Water, Key Message 1 Increasing water and surface air temperatures, Chapter 9 Oceans, Key Message 3 and Ocean acidification. Sea Chapter 2 Climate, Key Message 3 and Chapter 9 Oceans, Key Messages 1, 2, and 3 for more information on ocean acidification, hypoxia, and ocean warming. Although storms, floods, and erosion have always been hazards, in combination with rising sea levels, they now threaten approximately 1 trillion dollars in national wealth held in coastal real estate and the continued viability of coastal communities that depend on coastal water, land, and other resources for economic health and cultural integrity. Chapter 15 Tribes, Key Messages 1 and 2 For a full chapter, including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash coastal. End of Section 10 Section 11 of the Fourth National Climate Assessment Volume 2 by USG-CRP This LibriVox recording is in the public domain. Recording by Warren Caudy, Gurney, Illinois. Chapter 9 Oceans and Marine Resources Key Message 1 Ocean Ecosystems The nation's valuable ocean ecosystems are being disrupted by increasing global temperatures through the loss of iconic and highly valued habitats and changes in species composition and food web structure. Ecosystem disruption will intensify as ocean warming, acidification, deoxygenation, and other aspects of climate change increase. In the absence of significant reductions in carbon emissions, transformative impacts on ocean ecosystems cannot be avoided. Key Message 2 Marine Fisheries Marine fisheries and fishing communities are at high risk from climate-driven changes in the distribution, timing, and productivity of fishery-related species. Ocean warming, acidification, and deoxygenation are projected to increase these changes in fishery-related species, reduce catches in some areas, and challenge effective management of marine fisheries and protected species. Fisheries management that incorporates climate knowledge can help reduce impacts, promote resilience, and increase the value of marine resources in the face of changing ocean conditions. Key Message 3 Extreme Events Marine ecosystems and the coastal communities that depend on them are at risk of significant impacts from extreme events with combinations of very high temperatures, very low oxygen levels, or very acidified conditions. These unusual events are projected to become more common and more severe in the future, and they expose vulnerabilities that can motivate change, including technological innovations to detect, forecast, and mitigate adverse conditions. Americans rely on ocean ecosystems for food, jobs, recreation, energy, and other vital services. Increased atmospheric carbon dioxide levels change ocean conditions through three main factors, warming seas, ocean acidification, and deoxygenation. These factors are transforming ocean ecosystems, and these transformations are already impacting the U.S. economy and coastal communities, cultures, and businesses. While climate-driven ecosystem changes are pervasive in the ocean, the most apparent impacts are occurring in tropical and polar ecosystems, where ocean warming is causing the loss of two vulnerable habitats, coral reef and sea ice ecosystems. The extent of sea ice in the Arctic is decreasing, which represents a direct loss of important habitat for animals like polar bears and ringed seals that use it for hunting, shelter, migration, and reproduction, causing their abundances to decline. Chapter 26 Alaska Key Message 1 Warming has led to mass bleaching and or outbreaks of coral diseases off the coastlines of Puerto Rico, the U.S. Virgin Islands, Florida, Hawaii, and the U.S. Affiliated Pacific Islands. Chapter 20 U.S. Caribbean Key Message 2 Chapter 27 Hawaii and Pacific Islands Key Message 4 That threatened reef ecosystems and the people who depend on them. The loss of recreational benefits alone from coral reefs in the United States is expected to reach $140 billion, discounted at 3% in 2015 dollars, by 2100. Reducing greenhouse gas emissions, for example under RCP 4.5, see the scenario product section of Appendix 3 for more on scenarios, could reduce these cumulative losses by as much as $5.4 billion, but will not avoid many ecological and economic impacts. Ocean warming, acidification, and deoxygenation are leading to changes in productivity, recruitment, survivorship, and in some cases, active movements of species to track their preferred temperature conditions with most moving northward or into deeper water with warming oceans. These changes are impacting the distribution and availability of many commercially and recreationally valuable fish and invertebrates. The effects of ocean warming, acidification, and deoxygenation on marine species will interact with fishery management decisions from seasonal and spatial closures to annual quota setting, allocations, and fish stock rebuilding plans. Accounting for these factors is the cornerstone of climate-ready fishery management. Even without directly accounting for climate effects, precautionary fishery management and better incentives can increase economic benefits and improve resilience. Short-term changes in weather or ocean circulation can combine with long-term climate trends to produce periods of very unusual ocean conditions that can have significant impacts on coastal communities. Two such events have been particularly well documented, the 2012 Marine Heat Wave in the northwestern Atlantic Ocean and the sequence of warm ocean events between 2014 and 2016 in the northeastern Pacific Ocean, including a large, persistent area of very warm water referred to as the blob. Ecosystems within these regions experienced very warm conditions, more than 3.6 degrees Fahrenheit, 2 degrees Celsius, above the normal range, that persisted for several months or more. Extreme events in the oceans other than those related to temperature, including ocean acidification and low-oxygen events, can lead to significant disruptions to ecosystems and people, but they can also motivate preparedness and adaptation. For a full chapter, including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash oceans. End of section 11 Section 12 of the Fourth National Climate Assessment Volume 2 by USG-CRP This LibriVox recording is in the public domain. Recording by Warren Coddy, Gurney, Illinois. Chapter 10. Agriculture and Rural Communities Key Message 1. Reduced Agricultural Productivity Food and forage production will decline in regions experiencing increased frequency and duration of drought. Shifting precipitation patterns, when associated with high temperatures, will intensify wildfires that reduce forage on rangelands, accelerate the depletion of water supplies for irrigation, and expand the distribution and incidence of pests and diseases for crops and livestock. Modern breeding approaches and the use of novel genes from crop-wild relatives are being employed to develop higher-yielding, stress-tolerant crops. Key Message 2. Degredation of Soil and Water Resources The degradation of critical soil and water resources will expand as extreme precipitation events increase across our agricultural landscape. Sustainable crop production is threatened by excessive runoff, leaching and flooding, which results in soil erosion, degraded water quality in lakes and streams, and damage to rural community infrastructure. Management practices to restore soil structure and the hydrologic function of landscapes are essential for improving resilience to these challenges. Key Message 3. Health Challenges to Rural Populations and Livestock Challenges to human and livestock health are growing due to the increased frequency and intensity of high-temperature extremes. Extreme heat conditions contribute to heat exhaustion, heat stroke, and heart attacks in humans. Heat stress in livestock results in large economic losses for producers. Expanded health services in rural areas, heat-tolerant livestock, and improved design of confined animal housing are all important advances to minimize these challenges. Key Message 4. Vulnerability and Adaptive Capacity of Rural Communities Residents in rural communities often have limited capacity to respond to climate change impacts due to poverty and limitations in community resources. Communication, transportation, water, and sanitary infrastructure are vulnerable to disruption from climate stressors. Achieving social resilience to these challenges would require increases in local capacity to make adaptive improvements in shared community resources. In 2015, U.S. agricultural producers contributed $136.7 billion to the economy and accounted for 2.6 million jobs. About half of the revenue comes from livestock production. Other agriculture-related sectors in the food supply chain contributed an additional $855 billion of gross domestic product and accounted for 21 million jobs. In 2013, about 46 million people or 15% of the U.S. population lived in rural counties covering 72% of the nation's land area. From 2010 to 2015, a historic number of rural counties experienced population declines and recent demographic trends point to relatively slow employment and population growth in rural areas as well as high rates of poverty. Rural communities where livelihoods are more tightly interconnected with agriculture are particularly vulnerable to the agricultural volatility related to climate. Climate change has the potential to adversely impact agricultural productivity at local, regional, and continental scales through alterations in rainfall patterns, more frequent occurrences of climate extremes including high temperatures or drought, and altered patterns of pest pressure. Risks associated with climate change depend on the rate and severity of the change and the ability of producers to adapt to changes. These adaptations include altering what is produced, modifying the inputs used for production, adopting new technologies, and adjusting management strategies. U.S. agricultural production relies heavily on the nation's land, water, and other natural resources and these resources are affected directly by agricultural practices and by climate. Climate change is expected to increase the frequency of extreme precipitation events in many regions of the United States. Because increased precipitation extremes elevate the risk of surface runoff, soil erosion, and the loss of soil carbon, additional protective measures are needed to safeguard the progress that has been made in reducing soil erosion and water quality degradation through the implementation of grassed waterways, cover crops, conservation tillage, and waterway protection strips. Climate change impacts such as changes in extreme weather conditions have a complex influence on human and livestock health. The consequences of climate change on the incidence of drought also impact the frequency and intensity of wildfires and this holds implications for agriculture and rural communities. Rural populations are the stewards of most of the nation's forests, watersheds, rangelands, agricultural land, and fisheries. Much of the rural economy is closely tied to the natural environment. Rural residents and the lands they manage have the potential to make important economic and conservation contributions to climate change mitigation and adaptation, but their capacity to adapt is impacted by a host of demographic and economic concerns. For full chapter, including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash agriculture-rural. End of section 12 section 13 of the Fourth National Climate Assessment volume 2 by USGCRP. This LibriVox recording is in the public domain. Recording by Warren Coddy, Gurnee, Illinois. Chapter 11 Built Environment, Urban Systems, and Cities. Key Message 1 Impacts on Urban Quality of Life The opportunities and resources in urban areas are critically important to the health and well-being of people who work, live, and visit there. Climate change can exacerbate existing challenges to urban quality of life, including social inequality, aging, and deteriorating infrastructure and stressed ecosystems. Many cities are engaging in creative problem-solving to improve quality of life while simultaneously addressing climate change impacts. Key Message 2 Forward-looking design for urban infrastructure Damages from extreme weather events demonstrate current urban infrastructure vulnerabilities. With its long service life, urban infrastructure must be able to endure a future climate that is different from the past. Forward-looking design informs investments in reliable infrastructure that can withstand ongoing and future climate risks. Key Message 3 Impacts on Urban Goods and Services Interdependent networks of infrastructure, ecosystems, and social systems provide essential urban goods and services. Damage to such networks from current weather extremes and future climate will adversely affect urban life. Coordinated local, state, and federal efforts can address these interconnected vulnerabilities. Key Message 4 Urban Response to Climate Change Cities across the United States are leading efforts to respond to climate change. Urban adaptation and mitigation actions can affect current and projected impacts of climate change and provide near-term benefits. Challenges to implementing these plans remain. Cities can build on local knowledge and risk management approaches, integrate social equity concerns, and join multi-city networks to begin to address these challenges. Urban areas where the vast majority of Americans live are engines of economic growth and contain land valued at trillions of dollars. Cities around the United States face a number of challenges to prosperity, such as social inequality, aging and deteriorating infrastructure, and stressed ecosystems. These social infrastructure and environmental challenges affect urban exposure and susceptibility to climate change effects. Urban areas are already experiencing the effects of climate change. Cities differ across regions in the acute and chronic climate stressors they are exposed to and how these stressors interact with local geographic characteristics. Cities are already subject to higher surface temperatures because of the urban heat island effect, which is projected to get stronger. Recent extreme weather events reveal the vulnerability of the built environment, infrastructures such as residential and commercial buildings, transportation, communications, energy, water systems, parks, streets, and landscaping, and its importance to how people live, study, recreate, and work. Heat waves and heavy rainfalls are expected to increase in frequency and intensity. The way city residents respond to such incidents depends on their understanding of risk, their way of life, access to resources, and the communities to which they belong. Infrastructure designed for historical climate trends is vulnerable to future weather extremes and climate change. Investing in forward-looking design can help ensure that infrastructure performs acceptably under changing climate conditions. Urban areas are linked to local, regional, and global systems. Situations where multiple climate stressors simultaneously affect multiple city sectors, either directly or through system connections, are expected to become more common. When climate stressors affect one sector, cascading effects on other sectors increase risks to residents' health and well-being. Cities across the nation are taking action in response to climate change. U.S. cities are at the forefront of reducing greenhouse gas emissions and many have begun adaptation planning. These actions build urban resilience to climate change. For full chapter including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash built-environment. End of section 13. Section 14 of the Fourth National Climate Assessment, Volume 2 by USG-CRP. This Slibervox recording is in the public domain. Recording by Warren Coddy, Gurney, Illinois. Chapter 12. Transportation. Key Message 1. Transportation at Risk. A reliable, safe, and efficient U.S. transportation system is at risk from increases in heavy precipitation, coastal flooding, heat, wildfires, and other extreme events as well as changes to average temperature. Throughout this century, climate change will continue to pose a risk to U.S. transportation infrastructure with regional differences. Key Message 2. Impacts to Urban and Rural Transportation. Extreme events that increasingly impact the transportation network are inducing societal and economic consequences, some of which disproportionately affect vulnerable populations. In the absence of intervention, future changes in climate will lead to increasing transportation challenges, particularly because of system complexity, aging infrastructure, and dependency across sectors. Key Message 3. Vulnerability Assessments. Engineers, planners, and researchers in the transportation field are showing increasing interest and sophistication in understanding the risks that climate hazards pose to transportation assets and services. Transportation practitioner efforts demonstrate the connection between advanced assessment and the implementation of adaptive measures, though many communities still face challenges and barriers to action. Transportation is the backbone of economic activity, connecting manufacturers with supply chains, consumers with products and tourism, and people with their workplaces, homes, and communities across both urban and rural landscapes. However, the ability of the transportation sector to perform reliably, safely, and efficiently is undermined by a changing climate. Heavy precipitation, coastal flooding, heat, wildfires, free slough cycles, and changes in average precipitation and temperature impact individual assets across all modes. These impacts threaten the performance of the entire network with critical ramifications for economic vitality and mobility, particularly for vulnerable populations and urban infrastructure. Sea level rise is progressively making coastal roads and bridges more vulnerable and less functional. Many coastal cities across the United States have already experienced an increase in high tide flooding that reduces the functionality of low elevation roadways, rail, and bridges, often causing costly congestion and damage to infrastructure. Inland transportation infrastructure is highly vulnerable to intense rainfall and flooding. In some regions, the increasing frequency and intensity of heavy precipitation events reduce transportation system efficiency and increase accident risk. High temperatures can stress bridge integrity and have caused more frequent and extended delays to passenger and freight rail systems and air traffic. Transportation is not only vulnerable to impacts of climate change, but also contributes significantly to the causes of climate change. In 2016, the transportation sector became the top contributor to U.S. greenhouse gas emissions. The transportation system is rapidly growing and evolving in response to market demand and innovation. This growth could make climate mitigation and adaptation progressively more challenging to implement and more important to achieve. However, transportation practitioners are increasingly invested in addressing climate risks as evidenced in more numerous and diverse assessments of transportation sector vulnerabilities across the United States. For a full chapter, including references and traceable accounts, see HTTPS colon double backslash nca2018.globalchange.gov backslash chapter backslash transportation. End of section 14.