There is very high confidence that state, local, and private entities are increasingly taking, or are committed to taking, GHG mitigation action. Public statements and collated indices show an upward trend in the number of commitments, as well as the breadth and depth of commitments over the past five years.
' evidence: "Since NCA3, state, local, and tribal entities have announced new or enhanced efforts to reduce greenhouse gas (GHG) emissions. While some policies with emissions co-benefits have been eliminated, on net there has been an increase in initiatives aimed at reducing emissions. Figure 29.1 includes several types of state-level efforts and is sourced from Figure ES-3 of the America’s Pledge Phase 1 report, the most comprehensive listing of efforts across sectors currently available. The underlying state information is sourced from the U.S. Department of Energy, Appliance Standards Awareness Project, Open Energy Information, Rethink Food Waste Through Economics and Data, World Resources Institute, State of New York, California Air Resources Board, University of Minnesota, Land Trust Alliance, and the U.S. Forest Service.
U.S. state and local carbon pricing programs have increased in number since NCA3.{{< tbib '156' '7225530f-0579-4a4b-a1b3-bd1fa9ae55d2' >}} The Regional Greenhouse Gas Initiative has expanded the depth of emissions reductions activities and is considering adding transportation to their scope. California’s cap and trade program started in 2012 and expanded by linking to Quebec and Ontario in 2017. Emissions trading systems are scheduled in Massachusetts and under consideration in Virginia.{{< tbib '156' '7225530f-0579-4a4b-a1b3-bd1fa9ae55d2' >}}
U.S. states have both mandatory and voluntary programs that vary in stringency and impact. For example, 29 states, Washington, DC, and 3 territories have Renewable Portfolio Standards (RPS; https://energy.gov/eere/slsc/renewable-portfolio-standards-resources), which require some portion of electricity to be sourced from renewable energy; while 8 states and 1 territory have voluntary renewable portfolio goals.{{< tbib '42' '8ae1bf4d-4ea5-4c70-91bd-a1b7e3cc17fa' >}},{{
Federal budget levels for activities that have reduced GHG have remained steady over recent years. There is uncertainty around the implementation of federal initiatives, in part owing to the implementation of Executive Order 13783.{{< tbib '40' '12892612-06cb-4b04-86fa-b88ae37dc766' >}},{{
U.S. companies that report through the Carbon Disclosure Project increasingly (although not comprehensively) reported board-level oversight on climate issues, which rose from 50% in 2011 to 71% in 2017. Likewise, 59 U.S. companies recently committed to set science-based emissions reduction targets.{{< tbib '46' '47f855e2-eed7-4027-bedd-22313d13319e' >}} U.S. businesses are increasingly pricing carbon.{{< tbib '46' '47f855e2-eed7-4027-bedd-22313d13319e' >}},{{
As indicated in the Education Institutions Reporting Database, a growing number of universities have made emissions reduction commitments or deepened existing commitments{{< tbib '161' '46cee5f3-4325-4e5e-ac7f-012325111ba1' >}} as well as publicized the progress on their efforts.{{< tbib '162' 'ba372d89-ab64-4112-9d48-76f8f323c232' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/mitigation-avoiding-and-reducing-long-term-risks/finding/key-message-29-1.yaml identifier: key-message-29-1 ordinal: 1 process: "The scope for this chapter was determined by the federal Fourth National Climate Assessment (NCA4) Steering Committee, which is made up of representatives from the U.S. Global Change Research Program (USGCRP) member agencies (see App. 1: Process for more information regarding the Steering Committee). The scope was also informed by research needs identified in the Third National Climate Assessment (NCA3) and in subsequent gap analyses.{{< tbib '155' 'd6eb34ef-1bfb-4b90-a397-f6bb363086a0' >}} Prospective authors were nominated by their respective agency, university, organization, or peers. All prospective authors were interviewed with respect to their qualifications and expertise. Authors were selected to represent the diverse perspectives relevant to mitigation, with the final team providing perspectives from federal and state agencies, nonfederal climate research organizations, and the private sector. The author team sought public input on the chapter scope and outline through a webinar and during presentations at conferences and workshops.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors during extensive teleconferences, workshops, and email exchanges. These discussions were informed by the results of a comprehensive literature review, including the research focused on estimating the avoided or reduced risks of climate change. The authors considered inputs submitted by the public, stakeholders, and federal agencies and improved the chapter based on rounds of review by the public, National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors from other chapters of this assessment, as well as authors of the Climate Science Special Report (CSSR). For additional information on the overall report process, see Appendix 1: Process.
" report_identifier: nca4 statement: 'Mitigation-related activities are taking place across the United States at the federal, state, and local levels as well as in the private sector (very high confidence). Since the Third National Climate Assessment, a growing number of states, cities, and businesses have pursued or deepened initiatives aimed at reducing emissions (very high confidence).
' uncertainties: 'Figure 29.1 shows a count of each type of 30 measures across 6 categories, but it does not explore the relative stringency or emissions impact of the measures. The size, scope, time frame, and enforceability of the measures vary across states. Some state efforts and the majority of city efforts are voluntary, and therefore standards for reporting are heterogeneous. Efforts are underway to provide a rigorous accounting of the cumulative scale of these initiatives. Data collection through the America’s Pledge effort is an ongoing, iterative process and, by necessity, involves aggregating different measures into categories. Historically, state, local, and corporate policies change on different cycles.
' uri: /report/nca4/chapter/mitigation-avoiding-and-reducing-long-term-risks/finding/key-message-29-1 url: ~ - chapter_identifier: mitigation-avoiding-and-reducing-long-term-risks confidence: 'There is very high confidence that climate change is projected to substantially affect American livelihoods and well-being in the future compared to a future without climate change. The evidence supporting this conclusion is based on agreement across a large number of studies analyzing impacts across a multitude of sectors, scenarios, and regions. The literature clearly indicates that the adverse impacts of climate change are projected to substantially outweigh the positive effects. Although important uncertainties exist that affect our understanding of the timing and magnitude of some impacts, there is very high confidence that some effects will very likely lead to changes that are irreversible on human timescales.
' evidence: "Recent scientific and economic advances are improving the ability to understand and quantify the physical and economic impacts of climate change in the United States, including how those risks can be avoided or reduced through large-scale GHG mitigation. While the projected impacts of climate change across sectors and regions are well documented throughout this assessment, several multisector modeling projects are enabling the comparison of effects through the use of consistent scenarios and assumptions.{{< tbib '2' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}},{{
There is robust and consistent evidence that climate change is projected to adversely affect many components of the U.S. economy. Increasing temperatures, sea level rise, and changes in extreme events are projected to affect the built environment, including roads, bridges, railways, and coastal development. For example, coastal high tide flooding is projected to significantly increase the hours of delay for vehicles.{{< tbib '163' 'b4808700-a94a-44da-b2bb-d360a83146f1' >}} Annual damages to coastal property from sea level rise and storm surge, assuming no adaptation, are projected to range in the tens to hundreds of billions of dollars by the end of the century under RCP8.5 (Ch. 8: Coastal).{{< tbib '2' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}},{{
An increasing body of literature indicates that impacts to human health are likely to have some of the largest effects on the economy. Studies consistently indicate that climate-driven changes to morbidity and mortality can be substantial.{{< tbib '72' '81f96860-7931-48b6-9d57-32682728636f' >}},{{
Multiple lines of research have also shown that some climate change impacts will very likely be irreversible for thousands of years. For some species, the rate and magnitude of climate change projected for the 21st century is projected to increase the risk of extinction or extirpation (local-scale extinction) from the United States.{{< tbib '180' '25d5b793-3f5e-4c9f-9cb4-be71e84bf224' >}},{{
The scope for this chapter was determined by the federal Fourth National Climate Assessment (NCA4) Steering Committee, which is made up of representatives from the U.S. Global Change Research Program (USGCRP) member agencies (see App. 1: Process for more information regarding the Steering Committee). The scope was also informed by research needs identified in the Third National Climate Assessment (NCA3) and in subsequent gap analyses.{{< tbib '155' 'd6eb34ef-1bfb-4b90-a397-f6bb363086a0' >}} Prospective authors were nominated by their respective agency, university, organization, or peers. All prospective authors were interviewed with respect to their qualifications and expertise. Authors were selected to represent the diverse perspectives relevant to mitigation, with the final team providing perspectives from federal and state agencies, nonfederal climate research organizations, and the private sector. The author team sought public input on the chapter scope and outline through a webinar and during presentations at conferences and workshops.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors during extensive teleconferences, workshops, and email exchanges. These discussions were informed by the results of a comprehensive literature review, including the research focused on estimating the avoided or reduced risks of climate change. The authors considered inputs submitted by the public, stakeholders, and federal agencies and improved the chapter based on rounds of review by the public, National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors from other chapters of this assessment, as well as authors of the Climate Science Special Report (CSSR). For additional information on the overall report process, see Appendix 1: Process.
" report_identifier: nca4 statement: 'In the absence of more significant global mitigation efforts, climate change is projected to impose substantial damages on the U.S. economy, human health, and the environment (very high confidence). Under scenarios with high emissions and limited or no adaptation, annual losses in some sectors are estimated to grow to hundreds of billions of dollars by the end of the century (high confidence). It is very likely that some physical and ecological impacts will be irreversible for thousands of years, while others will be permanent (very high confidence).
' uncertainties: "This Key Message reflects consideration of the findings of several recent multisector modeling projects (e.g., Hsiang et al. 2017, O’Neill et al. 2017, EPA 2017, Houser et al. 2015){{< tbib '2' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}},{{
There is very high confidence that large-scale reductions in GHG emissions throughout the 21st century are projected to reduce the level of climate change projected to occur in the United States, along with the adverse impacts affecting human health and the environment. Across the literature, there are limited instances where mitigation, compared to a higher emissions scenario, does not provide a net beneficial outcome for the United States. While the content of this chapter is primarily focused on the 21st century, confidence in the ability of mitigation to avoid or reduce impacts improves when considering impacts beyond 2100.
' evidence: "There are multiple lines of research and literature available to characterize the effect of large-scale GHG mitigation in avoiding or reducing the long-term risks of climate change in the United States. Recent multisector impacts modeling projects, all of which feature consistent sets of scenarios and assumptions across analyses, provide improved capabilities to compare impacts across sectors and regions, including the effect of global GHG mitigation in avoiding or reducing risks.{{< tbib '2' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}},{{
Beyond these multisector modeling projects, an extensive literature of sector-specific studies compares impacts in the United States under alternative scenarios. A careful review of these studies, especially those published since the Third National Climate Assessment, finds strong and consistent support for the conclusion that global GHG mitigation can avoid or reduce the long-term risks of climate change in the United States. For example, mitigation is projected to reduce the risk of adverse impacts associated with extreme weather events,{{< tbib '29' '79a24453-16b4-4acf-9a83-cc902de94033' >}},{{
The finding that the magnitude and timing of avoided risks vary by sector and region, as well as due to changes in socioeconomics and adaptive capacity, is consistently supported by the broad literature base of multisector analyses (e.g., Hsiang et al. 2017, O’Neill et al. 2017, EPA 2017, Houser et al. 2015{{< tbib '2' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}},{{
The weight of evidence among studies in the literature indicates that the difference in climate impact outcomes between different scenarios is more modest through the first half of the century,{{< tbib '2' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}},{{
The scope for this chapter was determined by the federal Fourth National Climate Assessment (NCA4) Steering Committee, which is made up of representatives from the U.S. Global Change Research Program (USGCRP) member agencies (see App. 1: Process for more information regarding the Steering Committee). The scope was also informed by research needs identified in the Third National Climate Assessment (NCA3) and in subsequent gap analyses.{{< tbib '155' 'd6eb34ef-1bfb-4b90-a397-f6bb363086a0' >}} Prospective authors were nominated by their respective agency, university, organization, or peers. All prospective authors were interviewed with respect to their qualifications and expertise. Authors were selected to represent the diverse perspectives relevant to mitigation, with the final team providing perspectives from federal and state agencies, nonfederal climate research organizations, and the private sector. The author team sought public input on the chapter scope and outline through a webinar and during presentations at conferences and workshops.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors during extensive teleconferences, workshops, and email exchanges. These discussions were informed by the results of a comprehensive literature review, including the research focused on estimating the avoided or reduced risks of climate change. The authors considered inputs submitted by the public, stakeholders, and federal agencies and improved the chapter based on rounds of review by the public, National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors from other chapters of this assessment, as well as authors of the Climate Science Special Report (CSSR). For additional information on the overall report process, see Appendix 1: Process.
" report_identifier: nca4 statement: 'Many climate change impacts and associated economic damages in the United States can be substantially reduced over the course of the 21st century through global-scale reductions in greenhouse gas emissions, though the magnitude and timing of avoided risks vary by sector and region (very high confidence). The effect of near-term emissions mitigation on reducing risks is expected to become apparent by mid-century and grow substantially thereafter (very high confidence).
' uncertainties: "Quantifying the multisector impacts of climate change involves a number of analytic steps, each of which has its own potential sources of uncertainty. The timing and magnitude of projected future climate change are uncertain due to the ambiguity introduced by human choices, natural variability, and scientific uncertainty, which includes uncertainty in both scientific modeling and climate sensitivity. One of the most prominent sources involves the projection of climate change at a regional level, which can vary based on assumptions about climate sensitivity, natural variability, and the use of any one particular climate model. Advancements in the ability of climate models to resolve key aspects of atmospheric circulation, improved statistical and dynamic downscaling procedures, and the use of multiple ensemble members in impact analyses have all increased the robustness of potential climate changes that drive impact estimates described in the recent literature. However, key uncertainties and challenges remain, including the structural differences between sectoral impact models, the ability to simulate future impacts at fine spatial and temporal resolutions, and insufficient approaches to quantify the economic value of changes in nonmarket goods and services.{{< tbib '85' 'e311cbe3-cf61-445a-ae6f-130056df0558' >}} In addition, the literature on economic damages of climate change in the United States is incomplete in coverage, and additional research is needed to better reflect future socioeconomic change, including the ability of adaptation to reduce risk.
" uri: /report/nca4/chapter/mitigation-avoiding-and-reducing-long-term-risks/finding/key-message-29-3 url: ~ - chapter_identifier: mitigation-avoiding-and-reducing-long-term-risks confidence: 'There is very high confidence that the dual strategies of mitigation and adaptation being taken at national, regional, and local levels provide complementary opportunities to reduce the risks posed by climate change. Studies consistently find that adaptation would be particularly important for impacts occurring over the next several decades, a time period in which the effects of large-scale mitigation would not yet be easily recognizable. However, further analysis is needed to help resolve uncertainties regarding the timing and magnitude of adaptation, including the potential positive and negative co-effects with mitigation.
' evidence: "Global-scale reductions in GHG emissions are projected to reduce many of the risks posed by climate change. However, Americans are already experiencing, and will continue to experience, impacts that have already been committed to because of past and present emissions.{{< tbib '5' '9f559c9b-c78e-4593-bcbe-f07661d29e16' >}},{{
Because of adaptation’s ability to reduce risk in ways that mitigation cannot, and vice versa, the weight of the evidence shows that the two strategies can act as complements. Several recent studies jointly model the effects of mitigation and adaptation in reducing overall risk to the impacts of climate change in the United States, focusing on infrastructure (e.g., Larsen et al. 2017, Melvin et al. 2016, Neumann et al. 2014){{< tbib '71' '5b27123a-8c6d-4e85-bd48-841436fdf9eb' >}},{{
The scope for this chapter was determined by the federal Fourth National Climate Assessment (NCA4) Steering Committee, which is made up of representatives from the U.S. Global Change Research Program (USGCRP) member agencies (see App. 1: Process for more information regarding the Steering Committee). The scope was also informed by research needs identified in the Third National Climate Assessment (NCA3) and in subsequent gap analyses.{{< tbib '155' 'd6eb34ef-1bfb-4b90-a397-f6bb363086a0' >}} Prospective authors were nominated by their respective agency, university, organization, or peers. All prospective authors were interviewed with respect to their qualifications and expertise. Authors were selected to represent the diverse perspectives relevant to mitigation, with the final team providing perspectives from federal and state agencies, nonfederal climate research organizations, and the private sector. The author team sought public input on the chapter scope and outline through a webinar and during presentations at conferences and workshops.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors during extensive teleconferences, workshops, and email exchanges. These discussions were informed by the results of a comprehensive literature review, including the research focused on estimating the avoided or reduced risks of climate change. The authors considered inputs submitted by the public, stakeholders, and federal agencies and improved the chapter based on rounds of review by the public, National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors from other chapters of this assessment, as well as authors of the Climate Science Special Report (CSSR). For additional information on the overall report process, see Appendix 1: Process.
" report_identifier: nca4 statement: 'Interactions between mitigation and adaptation are complex and can lead to benefits, but they also have the potential for adverse consequences (very high confidence). Adaptation can complement mitigation to substantially reduce exposure and vulnerability to climate change in some sectors (very high confidence). This complementarity is especially important given that a certain degree of climate change due to past and present emissions is unavoidable (very high confidence).
' uncertainties: 'It is well understood that adaptation will likely reduce climate risks and that adaptation and mitigation interact. However, there are uncertainties regarding the magnitude, timing, and regional/sectoral distribution of these effects. Developing a full understanding of the interaction between mitigation and adaptation, with detailed accounting of potential positive and negative co-effects, is an important research objective that is only beginning to be explored in the detail necessary to inform effective implementation of these policies. Quantifying the effectiveness of adaptation requires detailed analyses regarding the timing and magnitude of how climate is projected to affect people living in the United States and their natural and built environments. As such, the uncertainties described under Key Messages 1 and 2 are also relevant here. Further, uncertainty exists regarding the effectiveness of adaptation measures in improving resilience to climate impacts. For some sectors, such as coastal development, protection measures (for example, elevating structures) have been well studied and implemented to reduce risk. However, the effectiveness of adaptation in other sectors, such as the physiological response to more intense heat waves, is only beginning to be understood.
' uri: /report/nca4/chapter/mitigation-avoiding-and-reducing-long-term-risks/finding/key-message-29-4 url: ~ - chapter_identifier: water confidence: 'Increasing temperature is highly likely to result in early snowmelt and increased consumptive use. Uncertainty in precipitation and emission scenarios leads to low confidence in predicting water availability and the associated quality arising from changes in land-use scenarios. However, surface water and groundwater storage ensures medium confidence in water quantity and quality reliability, but spatial disparity in water efficiency could be better addressed through increased investment in water infrastructure for system maintenance.
' evidence: "Increasing air temperatures have substantially reduced the fraction of winter precipitation occurring as snow, particularly over the western United States,{{< tbib '37' 'd9661451-b35d-4e0c-9551-cbc60c45c5ef' >}},{{
As reported in the Climate Science Special Report and summarized in Chapter 2: Climate, average annual temperature over the contiguous United States has increased by 1.2°F (0.7°C) for the period 1986–2016 relative to 1901–1960, and by 1.8°F (1.0°C) based on a linear regression for the period 1895–2016. Surface and satellite data are consistent in their depiction of rapid warming since 1979. Paleo-temperature evidence shows that recent decades are the warmest of the past 1,500 years. Additionally, contiguous U.S. average annual temperature is projected to rise. Increases of about 2.5°F (1.4°C) are projected for the next few decades in all emission scenarios, implying that recent record-setting years may be common in the near future. Much larger rises are projected by late century: 2.8°–7.3°F (1.6°–4.1°C) in a lower scenario (RCP4.5) and 5.8°–11.9°F (3.2°–6.6°C) in a higher scenario (RCP8.5).
Annual precipitation has decreased in much of the West, Southwest, and Southeast and increased in most of the Northern and Southern Great Plains, Midwest, and Northeast. There are important regional differences in trends, with the largest increases occurring in the northeastern United States. In particular, mesoscale convective systems (organized clusters of thunderstorms)—the main mechanism for warm season precipitation in the central part of the United States—have increased in occurrence and precipitation amounts since 1979 (see Easterling et al. 2017, Key Finding 1{{< tbib '35' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}}).
Heavy precipitation events in most parts of the United States have increased in both intensity and frequency since 1901 (see Easterling et al. 2017, Key Finding 2{{< tbib '35' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}}) and are projected to continue to increase over this century. There are, however, important regional and seasonal differences in projected changes in total precipitation: the northern United States, including Alaska, is projected to receive more precipitation in the winter and spring, and parts of the southwestern United States are projected to receive less precipitation in the winter and spring (see Easterling et al. 2017, Key Finding 3{{< tbib '35' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}}).
Projections indicate large declines in snowpack in the western United States and shifts to more precipitation falling as rain rather than snow in the cold season in many parts of the central and eastern United States (see Easterling et al. 2017, Key Finding 4{{< tbib '35' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}}).
The human effect on recent major U.S. droughts is complicated. Little evidence is found for a human influence on observed precipitation deficits, but much evidence is found for a human influence on surface soil moisture deficits due to increased evapotranspiration caused by higher temperatures (see Wehner et al. 2017, Key Finding 2{{< tbib '36' 'a29b612b-8c28-4c93-9c18-19314babce89' >}}).
Future decreases in surface (top 10 cm) soil moisture from anthropogenic forcing over most of the United States are likely as the climate warms under higher scenarios (see Wehner et al. 2017, Key Finding 3{{< tbib '36' 'a29b612b-8c28-4c93-9c18-19314babce89' >}}). Substantial reductions in western U.S. winter and spring snowpack are projected as the climate warms. Earlier spring melt and reduced snow water equivalent have been formally attributed to human-induced warming and will very likely be exacerbated as the climate continues to warm. Under higher scenarios, and assuming no change to current water resources management, chronic, long-duration hydrological drought is increasingly possible by the end of this century (see Wehner et al. 2017, Key Finding 4{{< tbib '36' 'a29b612b-8c28-4c93-9c18-19314babce89' >}}).
Even though national water withdrawal has remained steady irrespective of population growth,{{< tbib '12' '81bd7c9e-d465-4eb4-a0d9-5b3f244c839e' >}} there is a significant spatiotemporal variability in water withdrawal (for example, a higher rate over the South) and water-use efficiency across the United States.{{< tbib '13' 'd68b9064-d5de-4eb8-8665-04427b77e030' >}} Siebert et al. 2010{{< tbib '54' 'c9641496-7c75-4570-adcb-ef3d77239fb6' >}} reported that irrigation use of groundwater has increased substantially over the past century and that groundwater use for irrigation in some areas has exceeded natural aquifer recharge rates.
Changes in air temperature and precipitation affect water quality in predictable ways. Attribution of water quality changes to climate change, however, is complicated by the multiple cascading, cumulative effects of climate change, land use, and other anthropogenic stressors on water quality. There has been a widespread increase in water temperatures across the United States.{{< tbib '74' 'af1c492e-fcd5-4491-bea3-45c80688e788' >}},{{
Figure 3.2 shows net, average volumetric rates of groundwater depletion (km3/year) in 40 assessed aquifer systems or subareas in the contiguous 48 states.{{< tbib '4' '35520257-6694-45bb-a0bf-bd14ba88a77c' >}} Variation in rates of depletion in time and space within aquifers occurs but is not shown. For example, in the Nebraska part of the northern High Plains, small water-table rises occurred in parts of this area, and the net depletion was negligible. In contrast, in the Texas part of the southern High Plains, development of groundwater resources was more extensive, and the depletion rate averaged 1.6 km3/year.{{< tbib '4' '35520257-6694-45bb-a0bf-bd14ba88a77c' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/water/finding/key-message-3-1.yaml identifier: key-message-3-1 ordinal: 1 process: "Chapter authors were selected based on criteria, agreed on by the chapter lead and coordinating lead authors, that included a primary expertise in water sciences and management, knowledge of climate science and assessment of climate change impacts on water resources, and knowledge of climate change adaptation theory and practice in the water sector.
The chapter was developed through technical discussions and expert deliberation among chapter authors, federal coordinating lead authors, and staff from the U.S. Global Change Research Program (USGCRP). Future climate change impacts on hydrology, floods, and drought for the United States have been discussed in the Third National Climate Assessment{{< tbib '6' '3ff0e30a-c5ee-4ed9-8034-288be428125b' >}} and in the USGCRP’s Climate Science Special Report.{{< tbib '35' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}},{{
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 (high confidence). Variable precipitation and rising temperature are intensifying droughts (high confidence), increasing heavy downpours (high confidence), and reducing snowpack (medium confidence). Reduced snow-to-rain ratios are leading to significant differences between the timing of water supply and demand (medium confidence). Groundwater depletion is exacerbating drought risk (high confidence). Surface water quality is declining as water temperature increases (high confidence) and more frequent high-intensity rainfall events mobilize pollutants such as sediments and nutrients (medium confidence).
' uncertainties: 'There is high uncertainty associated with projected scenarios, as they include many future decisions and actions that remain unknown. There also is high uncertainty with estimates of precipitation; this uncertainty is reflected in the wide range of climate model estimates of future precipitation. In contrast, because climate model simulations generally agree on the direction and general magnitude of future changes in temperature (given specific emission scenarios), there is a medium level of uncertainty associated with temperature projections. Overall, changes in land use are associated with a medium level of uncertainty. Even though there is low uncertainty regarding the expansion of urban areas, there is greater uncertainty regarding changes in agricultural land use. A medium level of uncertainty for water supply reflects a combination of high uncertainty in streamflow and low uncertainty in water demand. Uncertainty in water demand is low because of adaptation and increased water-use efficiency and because of water storage in reservoirs. Water storage capacity also reduces uncertainty in future groundwater conditions. Water temperature changes are relatively well understood, but other changes in water quality, particularly pollutant loads (such as nutrients, sediment, and pathogens), are associated with high uncertainty due to a combination of uncertain land-use changes and high uncertainty in streamflow and hydrologic processes.
' uri: /report/nca4/chapter/water/finding/key-message-3-1 url: ~ - chapter_identifier: water confidence: 'There is high confidence in the presence of a strong relationship between precipitation and temperature, indicating that changes in one will likely alter the statistics of the other and hence the likelihood of occurrence of extremes. The aging nature of the Nation’s water infrastructure is well documented. Not all aging infrastructure is deteriorating, however, and many aging projects are operating robustly under changing conditions. Unfortunately, no national assessment of deteriorating infrastructure or the fragility of infrastructure relative to aging exists. For example, the U.S. Army Corps of Engineers (USACE) has assessed how climate change projections with bias correction compare with the nominal design levels of USACE dams; however, this represents only a fraction of the Nation’s 88,000 dams. While age may be an imperfect proxy for deterioration, it is used here to call attention to the general concern that many elements of the Nation’s water infrastructure are likely not optimized to address changing climate conditions. There is high confidence that deteriorating water infrastructure (dams, levees, aqueducts, sewers, and water and wastewater treatment and distribution systems) compounds the climate risk faced by society.
Studies show that compound extreme events will likely have a multiplier effect on the risk to society, the environment, and built infrastructure. Sea level rise is expected to increase in a warming climate. Sea level rise adds to the height of future storm tides, reduces pressure gradients that are important for transporting fluvial water to the ocean, and enables greater upstream tide/wave propagation and coastal flooding.
There is high confidence in the existence of the interannual and decadal cycles but medium confidence in the ability to accurately simulate the joint effects of these cycles and anthropogenic climate change for water impacts.
Currently, coastal flood risk assessment is primarily based on univariate methods that consider changes in terrestrial flooding and ocean flooding separately, which may not reliably estimate the probability of interrelated compound extreme events. The expected changes in the frequency of extreme events and their compounding effects will likely have significant consequences for existing infrastructure systems. Because of the uncertainties in future precipitation and how extreme events compound each other, there is medium confidence in the effects of compound extremes (multiple extreme events) on infrastructure failure.
' evidence: "Heavy precipitation events in most parts of the United States have increased in both intensity and frequency since about 1900 and are projected to continue to increase over this century, with important regional differences (Ch. 2: Climate).{{< tbib '35' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}},{{
Infrastructure systems are typically sized to cope with extreme events expected to occur on average within a certain period of time in the future (for example, 25, 50, or 100 years), based on historical observations.{{< tbib '141' '112eb5c3-41b2-4a81-a07f-d467711c41eb' >}} There is substantial concern about the impacts of future changes in extremes on the existing infrastructure. However, the existing operational design and risk assessment frameworks (for example, rainfall intensity–duration–frequency, or IDF, curves and flood frequency curves) are based on the notion of time invariance (stationarity) in extremes.{{< tbib '109' '882957f7-f48f-4cd0-a294-acd47609938d' >}},{{
Variability in sea surface temperatures influences atmospheric circulation and subsequently affects the occurrence of regional wet and dry periods in the United States.{{< tbib '142' '78211ce6-158f-4caa-b7f8-0f80d32c895c' >}},{{
A number of models have been developed to incorporate the observed and/or projected changes in extremes in frequency analysis and risk assessment.{{< tbib '94' '8ed13492-803d-432e-a09f-1ec2e3b5c035' >}},{{
Previous studies show that compound extreme events can have a multiplier effect on the risks to society, the environment, and built infrastructure.{{< tbib '112' '2ec30e37-5594-44e2-acd4-a7a8b3964027' >}},{{
Chapter authors were selected based on criteria, agreed on by the chapter lead and coordinating lead authors, that included a primary expertise in water sciences and management, knowledge of climate science and assessment of climate change impacts on water resources, and knowledge of climate change adaptation theory and practice in the water sector.
The chapter was developed through technical discussions and expert deliberation among chapter authors, federal coordinating lead authors, and staff from the U.S. Global Change Research Program (USGCRP). Future climate change impacts on hydrology, floods, and drought for the United States have been discussed in the Third National Climate Assessment{{< tbib '6' '3ff0e30a-c5ee-4ed9-8034-288be428125b' >}} and in the USGCRP’s Climate Science Special Report.{{< tbib '35' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}},{{
Deteriorating water infrastructure compounds the climate risk faced by society (high confidence). Extreme precipitation events are projected to increase in a warming climate (high confidence) and may lead to more severe floods and greater risk of infrastructure failure in some regions (medium confidence). Infrastructure design, operation, financing principles, and regulatory standards typically do not account for a changing climate (high confidence). Current risk management does not typically consider the impact of compound extremes (co-occurrence of multiple events) and the risk of cascading infrastructure failure (high confidence).
' uncertainties: 'There are high uncertainties in future floods because of uncertainties in future long-term regional/local precipitation and uncertain changes in land use/land cover, water management, and other non-climatic factors that will interact with climate change to affect floods. There also are high uncertainties in future water supply estimates because of uncertainties in future precipitation. Drought increase due to combined precipitation and temperature change has a moderate uncertainty.
' uri: /report/nca4/chapter/water/finding/key-message-3-2 url: ~ - chapter_identifier: water confidence: 'The Key Message is stated with medium confidence due to the limited assessment that has been performed on water infrastructure systems and management regimes, and due to the nascent and limited assessment of proposed adaptive responses.
' evidence: "There is wide documentation in the scientific literature that water management practice and engineering design use the observed historical record as a guide to future expectations. This implies that significant departures from those expectations would pose greater-than-anticipated risks, and scenario analyses have demonstrated this to be the case, particularly in studies of large water supply systems. In particular, the Climate Science Special Report{{< tbib '5' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} notes the potential for increased clustering (for example, heat waves and drought) or sequences of extremes and rapid transitions in climate. There is a growing literature that documents the use of robustness-based planning approaches, especially for water supply planning but also for coastal planning. These approaches provide promising methodologies for addressing climate change in water planning, although their complexity and cost—and limited planning resources—may be impediments to wide-scale adoption.
The literature also provides examples of some more innovative approaches applied to managing risks in an adaptive manner, including updating reservoir operations,{{< tbib '116' '1cad6d5a-ed6a-4fa7-9f31-fcb196b570de' >}},{{
Chapter authors were selected based on criteria, agreed on by the chapter lead and coordinating lead authors, that included a primary expertise in water sciences and management, knowledge of climate science and assessment of climate change impacts on water resources, and knowledge of climate change adaptation theory and practice in the water sector.
The chapter was developed through technical discussions and expert deliberation among chapter authors, federal coordinating lead authors, and staff from the U.S. Global Change Research Program (USGCRP). Future climate change impacts on hydrology, floods, and drought for the United States have been discussed in the Third National Climate Assessment{{< tbib '6' '3ff0e30a-c5ee-4ed9-8034-288be428125b' >}} and in the USGCRP’s Climate Science Special Report.{{< tbib '35' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}},{{
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 (medium confidence). Current water management and planning principles typically do not address risk that changes over time, leaving society exposed to more risk than anticipated (medium confidence). 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.
' uncertainties: 'The key uncertainty in assessing the current state of preparation of the Nation’s water infrastructure and management for climate change is the lack of public data collected about key performance and risk parameters. This includes the state of water infrastructure, including dams, levees, distribution systems, storm water collection, and water and wastewater treatment systems. For some of these systems, current performance information may be available, but there is little knowledge of what future performance limitations may be. Furthermore, much of this information is not publicly available, although it may be collected by the many local and state agencies that operate these infrastructure systems. A large number of case studies have illustrated that observed and projected changes in climate could place systems at risk in ways that exceed current expectations.
' uri: /report/nca4/chapter/water/finding/key-message-3-3 url: ~ - chapter_identifier: energy-supply-delivery-and-demand confidence: 'Climate change is projected to affect the energy sector in many ways, but the overall effect of rising temperatures, changing precipitation patterns, and increases in the frequency and/or severity of extreme weather is to increase the risk of damage or disruption to energy sector assets and energy systems. The combined projection of increasing risk of damage or disruption is very likely, with high confidence.
' evidence: "The energy system’s vulnerability to climate change impacts is evidenced through two sources: 1) the historical experience of damage and disruption to energy assets and systems, using data and case studies from events such as Superstorm Sandy and Hurricanes Harvey, Irma, and Maria, as well as the 2011–2016 California drought, and 2) a growing base of scientific literature assessing and projecting the past and future role of climate change in driving damage and disruption to the energy sector. Federal government and international scientific efforts have documented the scope and scale of a changing climate’s effects on the U.S. energy system—factors that will need to be considered in long-term planning, design, engineering, operations, and maintenance of energy assets and supply chains if current standards of reliability are to be maintained or improved.{{< tbib '1' 'df09ee8d-ac10-4cd4-bcb1-a087c727d891' >}},{{
This Key Message claims that damage and/or disruption to energy systems is more likely in the future. This claim is based on the following specific climate change projections and their expected impacts on energy systems:
higher maximum air temperatures during heat waves and associated impacts on energy generation, delivery, and load (very likely, very high confidence){{< tbib '3' 'f9f08a1a-4e9f-462f-a96e-3342cc6b7813' >}},{{
higher average air temperatures and associated increases in energy demand for cooling (very likely, very high confidence){{< tbib '11' 'c4dacc8d-ffe6-4e2a-a083-c0c00db4264b' >}},{{
higher surface water temperatures and associated impacts on thermoelectric power generation (very likely, very high confidence){{< tbib '3' 'f9f08a1a-4e9f-462f-a96e-3342cc6b7813' >}},{{
shifts in streamflow timing in snow-dominated watersheds to earlier in the year{{< tbib '8' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and associated impacts on hydropower generation (very likely, very high confidence){{< tbib '86' '7f7ba1de-741c-4c22-a2d9-331c7a8a4134' >}},{{
increased frequency and intensity of drought (very likely, high confidence){{< tbib '54' 'a29b612b-8c28-4c93-9c18-19314babce89' >}} and associated impacts on biofuels production{{< tbib '3' 'f9f08a1a-4e9f-462f-a96e-3342cc6b7813' >}}
more frequent, intense, and longer-duration drought, particularly in snow-dominated watersheds in the western United States,{{< tbib '54' 'a29b612b-8c28-4c93-9c18-19314babce89' >}} and associated threat to hydropower production, oil and gas extraction and refining, and thermoelectric cooling{{< tbib '3' 'f9f08a1a-4e9f-462f-a96e-3342cc6b7813' >}},{{
increased wind intensity from Atlantic and eastern Pacific hurricanes (medium confidence){{< tbib '55' '52ce1b63-1b04-4728-9f1b-daee39af665e' >}} and associated impacts on coastal energy infrastructure{{< tbib '3' 'f9f08a1a-4e9f-462f-a96e-3342cc6b7813' >}}
increased rain intensity for hurricanes (high confidence) and increased frequency and intensity of heavy precipitation events (high confidence), including West Coast atmospheric river events (medium confidence),{{< tbib '89' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} and associated impacts on energy infrastructure{{< tbib '3' 'f9f08a1a-4e9f-462f-a96e-3342cc6b7813' >}}
increased relative sea level rise (very high confidence){{< tbib '47' '3bae2310-7572-47e2-99a4-9e4276764934' >}} and associated risk of enhanced flooding of coastal infrastructure as well as inland energy infrastructure along rivers{{< tbib '3' 'f9f08a1a-4e9f-462f-a96e-3342cc6b7813' >}}
increased frequency and intensity of heavy precipitation (very likely){{< tbib '89' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} and associated impacts to inland flooding of energy assets{{< tbib '3' 'f9f08a1a-4e9f-462f-a96e-3342cc6b7813' >}},{{
increased frequency of occurrence of conditions that support the formation of convective storms (thunderstorms, tornadoes, and high winds){{< tbib '55' '52ce1b63-1b04-4728-9f1b-daee39af665e' >}} and associated damage to electricity transmission and distribution lines (low confidence){{< tbib '1' 'df09ee8d-ac10-4cd4-bcb1-a087c727d891' >}},{{
The effects of extreme weather on energy system infrastructure have been well documented by researchers and synthesized into several assessment reports produced by federal agencies.{{< tbib '2' 'f0d12f1c-4eea-41ee-a818-58ad09513531' >}},{{
We sought an author team that could bring diverse experience, expertise, and perspectives to the chapter. Some members have participated in past assessment processes. The team’s diversity adequately represents the spectrum of current and projected impacts on the various components that compose the Nation’s complex energy system and its critical role to national security, economic well-being, and quality of life. The author team has demonstrated experience in the following areas:
characterizing climate risks to the energy sector—as well as mitigation and resilience opportunities—at national, regional, and state levels;
developing climate science tools and information for characterizing energy sector risks;
supporting local, state, and federal stakeholders with integrating climate change issues into long-range planning;
analyzing technological, economic, and business factors relevant to risk mitigation and resilience; and
analyzing energy system sensitivities to drivers such as policy, markets, and physical changes.
In order to develop Key Messages, the author team characterized current trends and projections based on wide-ranging input from federal, state, local, and tribal governments; the private sector, including investor-owned, state, municipal, and cooperative power companies; and state-of-the-art models developed by researchers in consultation with industry and stakeholders. Authors identified recent changes in the energy system (that is, a growing connectivity and electricity dependence that are pervasive throughout society) and focused on how these transitions could affect climate impacts, including whether the changes were likely to exacerbate or reduce vulnerabilities. Using updated assessments of climate forecasts, projections, and predictions, the team identified key vulnerabilities that require near-term attention and highlighted the actions being taken to enhance energy security, reliability, and resilience.
' report_identifier: nca4 statement: '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 (high confidence). The reliability, security, and resilience of the energy system underpin virtually every sector of the U.S. economy (high confidence). Cascading impacts on other critical sectors could affect economic and national security (high confidence).
' uncertainties: "The inability to predict future climate parameters with complete accuracy is one primary uncertainty that hinders energy asset owners, operators, and planners from anticipating, planning for, and acting on vulnerabilities to climate change and extreme weather. All climate change projections include a degree of uncertainty, owing to a variety of factors, including incomplete historical data, constraints on modeling methodologies, and uncertainty about future emissions. For some climate parameters, confidence in both the direction and magnitude of projected change is high, so expected impacts to the energy sector are well understood. For example, projected temperature changes across the United States uniformly indicate that the demand for cooling energy is projected to increase and the demand for heating energy is projected to decrease.{{< tbib '8' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}},{{
However, confidence is generally lower for other climate parameters projections, making it difficult to understand and prioritize the risks associated with climate hazards and lowering confidence levels in related energy sector impacts. There is uncertainty in projections regarding changes in the frequency and intensity of hurricanes and convective storms, the magnitude and timing of sea level rise, the connection between projected changes in precipitation and the likelihood of droughts and flooding, and the potential increased seasonal variability in wind and solar resources. Hurricanes and convective storms represent major threats to energy infrastructure in general and to electricity transmission and distribution grids in particular.{{< tbib '1' 'df09ee8d-ac10-4cd4-bcb1-a087c727d891' >}},{{
The reliable production and delivery of power enables modern electricity-dependent critical infrastructures to support American livelihoods and the national economy. There is very high confidence that a deepening dependence on electric power and increasing interdependencies within the energy system can increase the vulnerabilities and risks associated with extreme weather and climate hazards in some situations (very likely, very high confidence).
There is very high confidence that many trends in the changing energy system are very likely to continue and that changes will have potential effects on reliability and resilience. A primary factor affecting the increased use of natural gas and the deployment of renewable resources is the relative price of these generation sources. Existing proven resources of natural gas are sufficient to supply current demand for several decades.{{< tbib '91' '5808b554-dae9-4fb4-b457-96056c35ad7b' >}} Renewable technologies are very likely to continue falling in price, as manufacturers continue to improve their processes and take advantage of economies of scale.{{< tbib '92' '6b0561f4-931a-4001-862a-36c8650ffff6' >}} The degree of interconnection of critical systems is also very likely to increase. The continued deployment of smart grid devices, microgrids, and energy storage will likely provide multiple reliability and resilience benefits.{{< tbib '2' 'f0d12f1c-4eea-41ee-a818-58ad09513531' >}}
" evidence: "Large-scale changes in the energy sector are primarily evidenced through the U.S. Energy Information Administration’s (EIA) data collection and analysis. EIA collects monthly and annual surveys from every U.S. power plant; findings include the types of fuel each plant uses.{{< tbib '22' '60f5e1c1-679e-4df6-a559-72d815c5c728' >}} Several sources support claims that renewable technology deployment is growing while costs are falling: EIA data,{{< tbib '22' '60f5e1c1-679e-4df6-a559-72d815c5c728' >}},{{
We sought an author team that could bring diverse experience, expertise, and perspectives to the chapter. Some members have participated in past assessment processes. The team’s diversity adequately represents the spectrum of current and projected impacts on the various components that compose the Nation’s complex energy system and its critical role to national security, economic well-being, and quality of life. The author team has demonstrated experience in the following areas:
characterizing climate risks to the energy sector—as well as mitigation and resilience opportunities—at national, regional, and state levels;
developing climate science tools and information for characterizing energy sector risks;
supporting local, state, and federal stakeholders with integrating climate change issues into long-range planning;
analyzing technological, economic, and business factors relevant to risk mitigation and resilience; and
analyzing energy system sensitivities to drivers such as policy, markets, and physical changes.
In order to develop Key Messages, the author team characterized current trends and projections based on wide-ranging input from federal, state, local, and tribal governments; the private sector, including investor-owned, state, municipal, and cooperative power companies; and state-of-the-art models developed by researchers in consultation with industry and stakeholders. Authors identified recent changes in the energy system (that is, a growing connectivity and electricity dependence that are pervasive throughout society) and focused on how these transitions could affect climate impacts, including whether the changes were likely to exacerbate or reduce vulnerabilities. Using updated assessments of climate forecasts, projections, and predictions, the team identified key vulnerabilities that require near-term attention and highlighted the actions being taken to enhance energy security, reliability, and resilience.
' report_identifier: nca4 statement: '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 (very likely, very high confidence). 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.
' uncertainties: 'Future changes in the energy system, and the effect on energy system vulnerabilities to extreme weather and climate change, are uncertain and will depend on numerous factors that are difficult to predict, including macroeconomic and population growth; financial, economic, policy, and regulatory changes; and technological progress. Each of these factors can affect the cost of technologies, the growth in energy demand, the rate of deployment of new technologies, and the selection of sites for deployment.
' uri: /report/nca4/chapter/energy-supply-delivery-and-demand/finding/key-message-4-2 url: ~ - chapter_identifier: energy-supply-delivery-and-demand confidence: "There is very high confidence that many of the technologies and planning or operational measures necessary to respond to climate change exist and that their implementation is in progress.{{< tbib '29' '77e1b701-2408-407b-a507-2d47571297e0' >}} Although federal, state, local, and tribal governments and the private sector are already responding, there is very high confidence that the pace, scale, and scope of combined public and private efforts to improve preparedness and resilience of the energy sector are likely to be insufficient, given the nature of the challenge{{< tbib '1' 'df09ee8d-ac10-4cd4-bcb1-a087c727d891' >}},{{
Several entities have identified evidence for the planning and deployment of resilience solutions in the energy sector. Support comes from both industry and federal agencies, including the U.S. Department of Energy (DOE), the U.S. Environmental Protection Agency (EPA), and the Department of Homeland Security (DHS).{{< tbib '3' 'f9f08a1a-4e9f-462f-a96e-3342cc6b7813' >}},{{
We sought an author team that could bring diverse experience, expertise, and perspectives to the chapter. Some members have participated in past assessment processes. The team’s diversity adequately represents the spectrum of current and projected impacts on the various components that compose the Nation’s complex energy system and its critical role to national security, economic well-being, and quality of life. The author team has demonstrated experience in the following areas:
characterizing climate risks to the energy sector—as well as mitigation and resilience opportunities—at national, regional, and state levels;
developing climate science tools and information for characterizing energy sector risks;
supporting local, state, and federal stakeholders with integrating climate change issues into long-range planning;
analyzing technological, economic, and business factors relevant to risk mitigation and resilience; and
analyzing energy system sensitivities to drivers such as policy, markets, and physical changes.
In order to develop Key Messages, the author team characterized current trends and projections based on wide-ranging input from federal, state, local, and tribal governments; the private sector, including investor-owned, state, municipal, and cooperative power companies; and state-of-the-art models developed by researchers in consultation with industry and stakeholders. Authors identified recent changes in the energy system (that is, a growing connectivity and electricity dependence that are pervasive throughout society) and focused on how these transitions could affect climate impacts, including whether the changes were likely to exacerbate or reduce vulnerabilities. Using updated assessments of climate forecasts, projections, and predictions, the team identified key vulnerabilities that require near-term attention and highlighted the actions being taken to enhance energy security, reliability, and resilience.
' report_identifier: nca4 statement: 'Actions are being taken to enhance energy security, reliability, and resilience with respect to the effects of climate change and extreme weather (very high confidence). 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 (very high confidence).
' uncertainties: "The most significant uncertainties affecting future investments in climate resilience are related to evaluating the costs, benefits, and performance of resilience investments—and the costs of inaction. To make informed investments, decision-makers need standardized cost–benefit frameworks and methodologies, as well as reliable, high-resolution (temporal and spatial) climate change projections of critical weather and climate parameters.{{< tbib '1' 'df09ee8d-ac10-4cd4-bcb1-a087c727d891' >}},{{
The high complexity of the energy system introduces uncertainty in whether particular actions could yield unintended consequences. Using the examples above, energy storage, distributed generation, microgrids, and other technologies and practices can contribute to resilience. However, unless evaluated in a systematic manner, the adoption of technologies and practices will likely lead to unintended consequences, including environmental (such as air quality), economic, and policy impacts.
Significant uncertainty is also found in the future pace of mitigation efforts that will, in turn, influence the need for resilience investments. Some level of climate change will continue, given past and current emissions of heat-trapping greenhouse gases. However, without an effective mitigation strategy, the need for additional adaptation and resilience investments becomes greater. Uncertainty about the rate of stabilizing and reducing greenhouse gas emission levels (mitigation) compounds the challenge of characterizing the magnitude and timing of additional resilience investments.
The pace of development and deployment of resilient cost-effective energy technologies are also uncertain and will likely be critical to implementing resilience strategies at scale. These technologies will likely include improvements in areas such as energy storage, distributed generation, microgrids, and cooling for thermoelectric power plants.{{< tbib '1' 'df09ee8d-ac10-4cd4-bcb1-a087c727d891' >}},{{
There is medium confidence that deforestation throughout much of the continental United States promotes climate warming through a decrease in carbon sequestration and reduced transpiration. There is low confidence that wildland fires will impact climate, because many of the associated processes and characteristics produce counteracting effects. There is high confidence that urbanization produces local-scale climate change, but there is low confidence in its influence on precipitation patterns. There is high confidence that surface air temperature is reduced near areas of irrigated agriculture and medium confidence that downwind precipitation is increased.
' evidence: "The Land-Use and Climate, IDentification of robust impacts (LUCID) project{{< tbib '88' '9724e954-e516-40f1-9d0c-12396f63bd12' >}},{{
The study of the influence of wildland fire on climate is at its advent and lacks a significant knowledge base.{{< tbib '98' 'b541b2e9-ffac-447b-9098-6516f9a7bd8d' >}},{{
The urban heat island (UHI) is perhaps the most unambiguous documentation of anthropogenic modification of climate.{{< tbib '159' '71fd8e9a-5d84-4d79-bff0-35da4ee4e999' >}} Two studies have found that the stunning rate of urbanization in China has led to regional warming,{{< tbib '105' '994fde97-75e2-462d-8d41-f70b096c01c0' >}},{{
Chapter authors developed the chapter through technical discussions, literature review, and expert deliberation via email and phone discussions. The authors considered feedback from the general public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information about the overall process for developing the report, see Appendix 1: Process.
The topic of land-use and land-cover change (LULCC) overlaps with numerous other national sectoral chapters (for example, Ch. 6: Forests; Ch. 10: Ag & Rural; Ch. 11: Urban) and is a fundamental characteristic of all regional chapters in this National Climate Assessment. This national sectoral chapter thus focuses on the dynamic interactions between land change and the climate system. The primary focus is to review our current understanding of land change and climate interactions by examining how land change drives changes in local- to global-scale weather and climate and how, in turn, the climate drives changes in land cover and land use through both biophysical and socioeconomic responses. Where possible, the literature cited in this chapter is specific to changes in the United States.
" report_identifier: nca4 statement: '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 (high confidence). Reforestation can foster localized cooling (medium confidence), while in urban areas, continued warming is expected to exacerbate urban heat island effects (high confidence).
' uncertainties: "Land use and land cover are dynamic; therefore, climate is influenced by a constantly changing land surface. Considerable uncertainties are associated with land-cover and land-use monitoring and projection.{{< tbib '161' '06e194ef-b57f-4a5e-b633-7e58386dcfd8' >}},{{
There is high confidence that climate change will contribute to changes in agricultural land use; however, there is low confidence in the direction and magnitude of change due to uncertainties in the capacity to adapt to climate change. There is high confidence that climate change will impact urbanization in coastal areas, where sea level rise will continue to have direct effects. There is medium confidence that climate change will alter natural disturbance regimes; however, land management activities, such as fire suppression strategies, are likely to be of equal or greater importance. There is low confidence that climate change will result in changes to land cover resulting from changes in species distribution environmental suitability.
' evidence: "Much of the research assessing the impact of climate change on agriculture has been undertaken as part of the Agricultural Model Intercomparison and Improvement Project (AgMIP),{{< tbib '128' 'b84b193b-ca98-479c-b5ef-fe94e5ffd39c' >}} which has been understandably focused on productivity and food security.{{< tbib '128' 'b84b193b-ca98-479c-b5ef-fe94e5ffd39c' >}},{{
Chapter authors developed the chapter through technical discussions, literature review, and expert deliberation via email and phone discussions. The authors considered feedback from the general public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information about the overall process for developing the report, see Appendix 1: Process.
The topic of land-use and land-cover change (LULCC) overlaps with numerous other national sectoral chapters (for example, Ch. 6: Forests; Ch. 10: Ag & Rural; Ch. 11: Urban) and is a fundamental characteristic of all regional chapters in this National Climate Assessment. This national sectoral chapter thus focuses on the dynamic interactions between land change and the climate system. The primary focus is to review our current understanding of land change and climate interactions by examining how land change drives changes in local- to global-scale weather and climate and how, in turn, the climate drives changes in land cover and land use through both biophysical and socioeconomic responses. Where possible, the literature cited in this chapter is specific to changes in the United States.
" report_identifier: nca4 statement: 'Climate change affects land use and ecosystems. Climate change is expected to directly and indirectly impact land use and cover by altering disturbance patterns (medium confidence), species distributions (medium confidence), and the suitability of land for specific uses (low confidence). 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 (high confidence).
' uncertainties: "Determining the impact of climate change on agriculture requires the integration of climate, crop, and economic models,{{< tbib '176' 'e929c4c4-1ded-4644-9814-ab19f1a8b4eb' >}} each with its own sources of uncertainty that can propagate through the three models. Sources of uncertainty include the response of crops to the intermingled factors of CO2 fertilization, temperature, water, and nitrogen availability; species-specific responses; model parameterization; spatial location of irrigated areas; and other factors.{{< tbib '129' '21eb6d9e-0c16-47cd-81b4-95c61584731f' >}},{{
Published literature and model projections imply high confidence that more frequent extreme weather events will increase the frequency and extent of large ecological disturbances, driving rapid (months to years) and often persistent changes in forest structure and function across large landscapes. Forests are long-lived and inherently resilient to climatic variability, so long-term monitoring (of, for example, growth and productivity, structure, regeneration, and species distribution and abundance) will be needed to confirm the direct effects of incremental changes in temperature. As a result, there is medium confidence that changes resulting from direct (but gradual) climate change and less severe disturbances will occur in the context of altered forest productivity, health, and species distribution and abundance that occur at longer timescales (decades to centuries).
' evidence: "Many ecological responses to climate change in U.S. forests are mediated though disturbance, because the occurrence and magnitude of most major forest disturbances are sensitive to subtle changes in climate.{{< tbib '1' '212b019e-f046-40a4-bc19-5e752527fb1c' >}} Published literature since the Third National Climate Assessment (NCA3) continues to show an increase in the frequency of large (thousands to hundreds of thousands of acres) ecological disturbances in forests across the United States. There is strong evidence that these changes, in combination with accumulated fuels, have resulted in larger wildfires in recent years (the past 10 to 20 years),{{< tbib '2' 'df19cf82-b4eb-4281-a379-2f1863e7142f' >}},{{
Although the increasing size and costs of fighting wildfires are known with high certainty,{{< tbib '158' '75a9f6ad-7530-4f06-83ba-9db2cfb2e7c2' >}} short- and long-term effects on forests vary according to the ability of tree species to survive or regenerate after wildfire.{{< tbib '159' '1192f0ee-6948-433f-91e5-166267541d52' >}} Future fire regimes and their impacts on U.S. forests will be governed by climate as well as topography, ecosystem productivity, and vegetation adaptations to fire. For example, altered distribution and abundance of dominant plant species may affect the frequency and extent of future wildfires (Ch. 29: Mitigation). The potential of an area to reburn (that is, burn again after experiencing a previous fire) will depend on how the previous fire was suppressed, the severity of that fire, how rapidly fuel accumulated after the fire, and postfire management activities.{{< tbib '53' 'f82cbbbd-e33b-418a-8f5b-9a39e06f3fa8' >}} These variables create uncertainty in predicting the spatial distribution, number, and sizes of wildfires in future decades.
The published literature contains strong evidence that insects are causing rapid changes in forest structure and function across large landscapes. Causal factors are primarily elevated temperatures, droughts, and water stress, which exert indirect effects mediated through host tree species and direct effects on insects. For example, in western North America, several species of bark beetles have had notable outbreaks over the past 30 years, and some have exceeded the spatial extent of what has been previously documented, affecting ecosystem services at broad spatial scales.{{< tbib '3' '74435108-c954-43b3-a05c-5717d9a53620' >}} The spatial extent of recent outbreaks of mountain pine beetles represents an area larger than the 11 smallest U.S. states combined, and insect outbreak models project increased probabilities of mountain pine beetle population success in the future.{{< tbib '23' '703f4c0b-a9f3-4393-ad55-e26a62fa5a95' >}} In addition, evidence suggests that climate change is expanding the range of bark beetles in both the western and eastern United States,{{< tbib '66' '98e8338c-3c49-49f7-9334-d4c28a901ad0' >}},{{
The magnitude and direction of defoliator responses to climate change vary, limiting our ability to project the effects of climate change{{< tbib '69' '68d16e4e-dc4a-4bb6-8592-c8ff6cea4937' >}} and preventing generalizations about climate-related effects on defoliators, despite their importance throughout the United States. Fungal pathogens that depend on stressed plant hosts for colonization are expected to perform better and have greater impacts on forests.{{< tbib '63' '29ccd0a0-9e94-4f1d-9f91-bca006e3a975' >}},{{
Mounting evidence suggests that some bird and insect populations show changes in distribution that align with temperature increases in recent decades (Ch. 7: Ecosystems).{{< tbib '160' 'ab72ca84-1290-4fcc-9167-7e98600795c3' >}},{{
Understanding and predicting the effects of climate change on forests are obscured by the slow response times of long-lived trees.{{< tbib '87' '79707634-1d52-4c53-ac9e-2ec3a4856854' >}} Increasing evidence suggests that climate-related stresses weaken trees, predisposing them to additional stresses that take many years to be observed,{{< tbib '88' '401a75ed-2a6e-492e-8088-0fe197e50676' >}} and that growth reductions following drought can persist for years.{{< tbib '7' 'abe49f4d-90c4-40e2-a4b9-a58158c00560' >}},{{
Lead authors, chapter authors, and technical contributors engaged in multiple technical discussions via teleconference between September 2016 and March 2018, which included a review of technical inputs provided by the public and a broad range of published literature as well as professional judgment. Discussions were followed by expert deliberation on draft Key Messages by the authors and targeted consultation with additional experts by the authors and technical contributors. A public engagement webinar on May 11, 2017, solicited additional feedback on the report outline. Webinar attendees provided comments and suggestions online and through follow-up emails. Strong emphasis was placed on recent findings reported in the scientific literature and relevance to specific applications in the management of forest resources.
' report_identifier: nca4 statement: '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 (high confidence). 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 timescales (decades to centuries; medium confidence).
' uncertainties: 'Although wildfire frequency and extent are very likely to increase in a warmer climate, spatial and temporal patterns of fire are difficult to project, especially at smaller than regional scales. The effects of a warmer climate are well known for some insect species (such as bark beetles), but the effects of long-term thermal changes on most insect species and their community associates are uncertain. Scientific information on the effects of climate change on fungal pathogens is sparse, making projections of forest diseases uncertain. It is possible to project that some tree species will have decreased growth and others increased growth, but the magnitude of growth changes is uncertain. Finally, species distribution and abundance are likely to change in a warmer climate, but the magnitude, geographic specificity, and rate of future changes are uncertain.
' uri: /report/nca4/chapter/forests/finding/key-message-6-1 url: ~ - chapter_identifier: forests confidence: 'Because of variability in forest structure and function and species-level variation in adaptive capacity to climate change, it is difficult to project future changes in forest conditions at smaller than regional scales. Hence, there is medium confidence about how ecosystem services will be affected in different forest ecosystems, including effects on tree growth and carbon storage, as a function of higher temperature, more frequent drought, and increased disturbance. Observations from recent droughts and changing snowfall/snowmelt dynamics provide high confidence that climate change effects on water are already occurring in some regions, although the onset and magnitude of future effects will vary regionally.
' evidence: "Altered forest conditions caused by a changing climate are likely to influence the quantity and quality of many of the ecosystem services that humans derive from forests, and climate change is expected to increase the frequency and severity of natural disturbances in the coming decades and to reduce forest growth in most places.{{< tbib '18' '71c75d19-f2ad-4bf1-9cb8-b9a08f8c3ef0' >}} Extreme high temperatures can also cause heat-related stress in vegetation and exacerbate drought conditions, potentially increasing tree mortality and reducing forest productivity.{{< tbib '7' 'abe49f4d-90c4-40e2-a4b9-a58158c00560' >}},{{
Most evidence suggests that increased carbon sinks (caused by higher growth rates and more forest area in some regions) will not be sufficient to offset higher emissions from increased disturbances and enhanced release of carbon from decomposition in the future.{{< tbib '114' '6bd92a32-feef-4b92-a124-49555ada8b5d' >}},{{
Land-use change that increases forest cover (such as cropland converted to forestland) is a major contributor to reductions in atmospheric CO2,{{< tbib '116' '1c5cb83e-eb5f-4e99-8d1a-3f044b57381a' >}} but this conversion is expected to slow in the near future.{{< tbib '118' '44fcdc28-381a-41b6-b267-c4fd63ebc0d5' >}} The estimated net carbon flux in the United States associated with forestland conversion is approximately zero, with gains in forestland constituting +23 teragrams (Tg) of carbon per year and losses resulting in emissions of −23 Tg carbon per year over the last decade. The estimated emissions constitute decades, and in some cases centuries, of accumulated carbon within forest ecosystems, which is abruptly or gradually released to the atmosphere during conversion from forest to nonforest land. In contrast, gains in forestland represent carbon sequestration only from new growth of live biomass and the accumulation of newly dead organic matter over the 20 or so years since the renewal of forest cover.
Economic conditions and population growth will affect national and global production and consumption of wood products, which can temporarily sequester carbon (currently 189 Tg carbon per year, or 8% of the global forest sink).{{< tbib '120' 'ffa77675-22b0-499b-a6d5-5108b3595472' >}} Increases in wood products carbon are contingent on a sustained or increasing rate of harvest removals of forest carbon or on a shift toward forest products that exist for long periods of time before they are no longer suitable for reuse or recycling. In the United States, 76% of the annual domestic harvest input to the wood products pool in 2015 (110 Tg carbon) was offset by release processes (84 Tg carbon), yielding a corresponding net increase in wood products of 26 Tg carbon.{{< tbib '14' '81430bfc-5d67-4109-982a-4cfd344f057c' >}} However, if harvest rates decline (as they did in 2007–2009, during the last economic recession), net additions to wood products will likely be lower than emissions from wood harvested in prior years.{{< tbib '14' '81430bfc-5d67-4109-982a-4cfd344f057c' >}} Looking ahead, carbon storage in wood products is expected to increase by 7–8 Tg carbon per year over the next 25 years.{{< tbib '171' '70bc9ca3-4303-4dca-af68-4fc733395664' >}}
Snowfall amount, timing, and melt dynamics are affecting water availability and stream water quality in the western United States, where less precipitation is falling as snow and more as rain in winter months, leading to longer and drier summer seasons.{{< tbib '121' 'e450ba2c-db69-43c8-8af4-e0c8ce7c8f2f' >}} Furthermore, rapid opening of forests in the western United States by wildfire has caused faster spring snowmelt through increased solar radiation and decreased reflectivity of radiation from charcoal,{{< tbib '128' '4d98fcfd-e95f-4060-923d-40e8453ce930' >}} leading to drier summer conditions that offset increased water yield following a disturbance.{{< tbib '127' 'b86c02d3-167a-4c9e-a17c-be4cba9283db' >}} The persistence of winter snowpack in the northeastern United States has declined over the last few decades; mid-winter thaws have become more common, and snowmelt flushing of mobilized soil nutrients into streams has become less common, although increased variability in climate–hydrology interactions can alter flushing.{{< tbib '172' '8c6e713b-c943-4d9f-a3a9-2333218d6587' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/forests/finding/key-message-6-2.yaml identifier: key-message-6-2 ordinal: 2 process: 'Lead authors, chapter authors, and technical contributors engaged in multiple technical discussions via teleconference between September 2016 and March 2018, which included a review of technical inputs provided by the public and a broad range of published literature as well as professional judgment. Discussions were followed by expert deliberation on draft Key Messages by the authors and targeted consultation with additional experts by the authors and technical contributors. A public engagement webinar on May 11, 2017, solicited additional feedback on the report outline. Webinar attendees provided comments and suggestions online and through follow-up emails. Strong emphasis was placed on recent findings reported in the scientific literature and relevance to specific applications in the management of forest resources.
' report_identifier: nca4 statement: '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 (medium confidence). The onset and magnitude of climate change effects on water resources in forest ecosystems will vary but are already occurring in some regions (high confidence).
' uncertainties: "It is difficult to identify geographically specific changes in forest conditions at fine scales because of high spatial variability in forest structure and function and variability in projections of climate change and how it will affect large disturbances (drought, wildfire, insect outbreaks). Uncertainties about the rate and magnitude of climate change effects on carbon sequestration are moderately high, because it is difficult to project future trends in forest cover and socioeconomic influences on forest management (for example, demand for wood products, bioenergy). Although empirical evidence for young trees indicates that atmospheric enrichment of CO2 can enhance tree growth, few long-term data on mature trees are available on which to base inferences about long-term forest productivity.{{< tbib '173' 'bac5e675-3edc-4fe0-8981-7379e1597b39' >}} Temporal patterns and magnitude of carbon sequestration, especially after 2050, will be affected by uncertainties related to future land-use conversions (from forests to other uses and vice versa) and the production of wood products.
" uri: /report/nca4/chapter/forests/finding/key-message-6-2 url: ~ - chapter_identifier: forests confidence: "There is high confidence that climate change adaptation planning in forest management is occurring, particularly in U.S. federal agencies (especially national forests in the western and northeastern United States) (Ch. 28: Adaptation){{< tbib '19' '0a09b8e3-ab3b-43fc-8aa2-836e74c38dc6' >}},{{
Climate change vulnerability assessments and adaptation planning efforts for forest ecosystems have been conducted at many locations (for example, forests in the western United States and upper Midwest) over the last decade.{{< tbib '19' '0a09b8e3-ab3b-43fc-8aa2-836e74c38dc6' >}},{{
In general, practices that mitigate stressors in forest and aquatic systems increase resistance (the ability of a system to withstand a perturbation) and resilience (the ability of a system to return to a previous state after a perturbation) to climate change.{{< tbib '127' 'b86c02d3-167a-4c9e-a17c-be4cba9283db' >}},{{
There is strong evidence that stand density management can increase forest resistance and resilience to disturbances, including wildfire and bark beetle infestations in dry forest types. A growing body of evidence suggests that reducing stand density in most forest types can increase forest resilience to drought by increasing soil water availability and decreasing competition.{{< tbib '146' 'e945cd6d-9213-49b2-8633-4dd1e81dcce6' >}},{{
Wildfire has been an important disturbance in aquatic ecosystems for millennia,{{< tbib '180' '4de79d1a-c0f9-4897-93cf-d4cd27ff3fcb' >}} and its frequency will increase in the future. Management responses to changing climate and fire regimes will need to be developed in the context of how past land use impaired aquatic function. Coordinating restoration in adjacent riparian and forest habitats can help ensure that beneficial effects of fire are retained across the aquatic–terrestrial interface.{{< tbib '181' '69e62c01-f7fc-4959-b674-dffbf3056025' >}}
Examples of on-the-ground implementation of adaptation options to increase ecosystem resistance and resilience to climate change are emerging in the scientific literature.{{< tbib '138' '7242780c-93ee-4a39-9505-d0bd2f67c62b' >}},{{
Lead authors, chapter authors, and technical contributors engaged in multiple technical discussions via teleconference between September 2016 and March 2018, which included a review of technical inputs provided by the public and a broad range of published literature as well as professional judgment. Discussions were followed by expert deliberation on draft Key Messages by the authors and targeted consultation with additional experts by the authors and technical contributors. A public engagement webinar on May 11, 2017, solicited additional feedback on the report outline. Webinar attendees provided comments and suggestions online and through follow-up emails. Strong emphasis was placed on recent findings reported in the scientific literature and relevance to specific applications in the management of forest resources.
' report_identifier: nca4 statement: 'Forest management activities that increase the resilience of U.S. forests to climate change are being implemented (high confidence), with a broad range of adaptation options for different resources, including applications in planning (medium confidence). The future pace of adaptation will depend on how effectively social, organizational, and economic conditions support implementation (high confidence).
' uncertainties: "Evidence for the long-term effectiveness of climate change adaptation is derived primarily from our current understanding of how specific actions (for example, forest thinning, restoration of riparian systems, conservation of biodiversity) sustain the functionality of terrestrial and aquatic systems.{{< tbib '127' 'b86c02d3-167a-4c9e-a17c-be4cba9283db' >}} Physical and biological conditions of ecosystems are constantly changing, and interactions among multiple ecosystem stressors could have unforeseen outcomes on ecosystem composition, structure, and function. Thus, the long-term effectiveness of adaptation actions for increasing forest resistance and resilience to climate change is uncertain until a sufficient time series of monitoring data is available, requiring decades of observations.
The future pace of adaptation and barriers to its implementation are also uncertain, and it is expected that many forest management challenges will persist in the future. However, new challenges and barriers may emerge,{{< tbib '182' 'ac1e037e-f276-44c5-a884-4f5447709308' >}} and it is difficult to predict how society and organizations will respond.
" uri: /report/nca4/chapter/forests/finding/key-message-6-3 url: ~ - chapter_identifier: ecosystems-ecosystem-services-and-biodiversity confidence: 'There is high confidence that species and populations continue to be impacted by climate change in significant and observable ways.
There is high confidence that terrestrial, freshwater, and marine organisms are likely responding to climate change by altering individual characteristics, the timing of biological events, and their geographic ranges.
There is high confidence that local and global extinctions are likely to occur when climate change outpaces the capacity of species to adapt.
' evidence: "Changes in individual characteristics: Beneficial effects of adaptive capacity depend on adequate genetic diversity within the existing population and sufficient population sizes. In addition, successful adaptive responses require relatively slow or gradual environmental change in relation to the speed of individual or population-level responses.{{< tbib '13' '7406884d-2302-4644-aa50-12ed8baf4fd7' >}} Empirical evidence continues to suggest that plastic changes and evolution have occurred in response to recent climate change{{< tbib '10' '33aaaa4b-92cf-4bf7-9a3d-a38098c0025d' >}},{{
Changes in range: Shifts in species’ ranges have been documented in both terrestrial and aquatic ecosystems as species respond to climate change.{{< tbib '35' '5f4fd70c-6663-44b9-8dba-8c2a4913bf16' >}},{{
These shifts have been linked to climate velocity—the rate and direction of change in temperature patterns.{{< tbib '30' '03aea694-50fe-4d1e-b29e-091adfb0353b' >}},{{
Changes in phenology: In marine and freshwater systems, the transition from winter to spring temperatures is occurring earlier in the year, as evidenced by satellite measures of sea surface temperature dating back to 1981.{{< tbib '23' '55f15317-d7a2-4ae3-99f1-5e77129d2dfe' >}} In addition, the timing of sea ice melt is occurring earlier in the spring at a rate of about 2 days per decade and has advanced by 25–30 days since 1979 in some regions.{{< tbib '24' 'bf21b6fb-c6f8-431a-82a5-09c4e12fe5f5' >}} Shifts in phenology have been well documented in terrestrial, marine, and freshwater systems.{{< tbib '113' '912dbad9-8981-4cb5-8044-eabf0e563dbf' >}} As with range shifts, changes to phenology are expected to continue as the climate warms.{{< tbib '114' 'd0c3b72c-3080-42de-a8e4-dc0edf9d8c56' >}}
Extinction risks: The rate and magnitude of climate impacts can exceed the abilities of even the most adaptable species, potentially leading to tipping points and abrupt system changes. In the face of rapid environmental change, species with limited adaptive capacity may experience local extinctions or even global extinctions.{{< tbib '126' '3def47b9-0e32-440b-bef1-f9bc176a7dd0' >}},{{
Topics for the chapter were selected to improve the consistency of coverage of the report and to standardize the assessment process for ecosystems and biodiversity. Chapter leads went through the detailed technical input for the Third National Climate Assessment and pulled out key issues that they felt should be updated in the Fourth National Climate Assessment. The chapter leads then came up with an author team with expertise in these selected topics. To ensure that both terrestrial and marine issues were adequately covered, most sections have at least one author with expertise in terrestrial ecosystems and one with expertise in marine ecosystems.
Monthly author calls were held beginning in December 2016, with frequency increasing to every other week as the initial chapter draft deadline approached. During these calls, the team came up with a work plan and fleshed out the scope and content of the chapter. After the outline for the chapter was created, authors reviewed the scientific literature, as well as the technical input that was submitted through the public call. After writing the State of the Sector section, authors pulled out the main findings to craft the Key Messages.
' report_identifier: nca4 statement: 'Climate change continues to impact species and populations in significant and observable ways (high confidence). Terrestrial, freshwater, and marine organisms are responding to climate change by altering individual characteristics, the timing of biological events, and their geographic ranges (likely, high confidence). Local and global extinctions may occur when climate change outpaces the capacity of species to adapt (likely, high confidence).
' uncertainties: "Changes in individual characteristics: Species and populations everywhere have evolved in response to reigning climate conditions, demonstrating that evolution will be necessary to survive climate change. Nonetheless, there is very limited evidence for evolutionary responses to recent climate change. As reviewed by Crozier and Hutchings 2014,{{< tbib '10' '33aaaa4b-92cf-4bf7-9a3d-a38098c0025d' >}} only two case studies document evolutionary responses to contemporary climate change in fish, as opposed to plasticity without evolution or preexisting adaptation to local conditions, and both cases involved the timing of annual migration.{{< tbib '241' '5ff1aba6-775c-4a18-8b90-055d5119b3c0' >}},{{
Changes in range: Although the evidence for shifting ranges of many terrestrial and aquatic species is compelling, individual species are responding differently to the magnitude and direction of change they are experiencing related to their life history, complex mosaics of microclimate patterns, and climate velocity.{{< tbib '243' '6776454b-6265-4ff0-8c4d-9f0463e3c710' >}},{{
There is high confidence that climate-induced changes are occurring within and across ecosystems in ways that alter ecosystem productivity and how species interact with each other and their environment.
There is high confidence that such changes can likely create mismatches in resources, facilitate the spread of invasive species, and reconfigure ecosystems in unprecedented ways.
' evidence: "Primary productivity: Diverse observations suggest that global terrestrial primary production has increased over the latter 20th and early 21st centuries,{{< tbib '48' '10bc8ec0-deed-40ff-9d4e-1b202da596bf' >}},{{
Projections also suggest that changes in productivity will not be equal across trophic levels: changes in primary productivity are likely to be amplified at higher levels of the food web;{{< tbib '149' '0f046395-da6c-4d4c-adcf-846b68586180' >}},{{
Changes in phenology: Synchronized timing of seasonal events across trophic levels ensures access to key seasonal food sources,{{< tbib '25' 'b3ed2c28-4717-4cdc-9e8e-5b79a8be84b1' >}},{{
Invasive species: Changes in habitat and environmental conditions can increase the viability of introduced species and their ability to establish.{{< tbib '69' 'a4c21da1-a84d-4e9f-bf8d-f6c4f81939a2' >}},{{
Invasive species’ impacts on ecosystems are likely to have a greater negative impact on human communities that are more dependent on the landscape/natural resources for their livelihood and cultural well-being.{{< tbib '251' '99e9a2aa-b071-47fd-906d-81fd55914789' >}},{{
Species interactions and emergent properties: Human-caused stressors such as land-use change and development can also lead to novel environmental conditions and ecological communities that are further degraded by climate impacts (Ch. 11: Urban, KM 1) .{{< tbib '13' '7406884d-2302-4644-aa50-12ed8baf4fd7' >}},{{
Changes in community composition vary relative to invasion rates of new species, local extinction, and recruitment and growth rates of resident species, as well as other unknown factors.{{< tbib '260' '00b388e8-5db4-4aa7-acbb-c1c8237aa4bd' >}} In some cases, such as Pacific Northwest forests, community turnover has been slow to date, likely due to low exposure or sensitivity to the direct and indirect impacts of climate change,{{< tbib '259' '6e6cd811-f193-4b44-8bb7-f65b8c43f5fe' >}} while in other places, like high-latitude systems, dramatic shifts in community composition have been observed.{{< tbib '261' '23eba59a-13f9-4881-8bb7-f07677d5e8db' >}} Differential responses within and across communities are expected due to individual sensitivities of community members. For example, as a result of the uncertainties associated with range shifts, the impact of individual species’ range shifts on ecosystem structure and function and the potential for the creation of novel community assemblages have medium certainty. The interplay of physical drivers resulting in range shifts and the ways in which interactions of species in new assemblages shape final outcomes affecting ecosystem dynamics is uncertain, although there is more certainty in how ecosystem services will change locally. There is still high uncertainty in the rate and magnitude at which community turnover will occur in many systems; still, there is widespread agreement of high turnover and major changes in age and size structure with future climate impacts and interactions with other disturbance regimes.{{< tbib '259' '6e6cd811-f193-4b44-8bb7-f65b8c43f5fe' >}},{{
Climate-induced warming is predicted to increase overlaps between some species that would normally be separated in time. For example, tree host species could experience earlier bud burst, thus overlapping with the larval stage of insect pests; this increase in synchrony between normally disparate species can lead to major pest outbreaks that alter community composition, productivity, ecological functioning, and ecosystem services.{{< tbib '262' 'eb499fee-65b6-4fb6-80cf-a09dd60561c4' >}} Direct climate impacts, such as warmer winters and drought-induced stress on forests, can interact with dynamics of pest populations to render systems more susceptible to damage in indirect ways. In the case of the bark beetle, for example, forests that have experienced drought are more vulnerable to damage from beetle attacks.{{< tbib '138' '678c7f6b-c6d0-4634-b4e0-c46db5544fa0' >}},{{
Topics for the chapter were selected to improve the consistency of coverage of the report and to standardize the assessment process for ecosystems and biodiversity. Chapter leads went through the detailed technical input for the Third National Climate Assessment and pulled out key issues that they felt should be updated in the Fourth National Climate Assessment. The chapter leads then came up with an author team with expertise in these selected topics. To ensure that both terrestrial and marine issues were adequately covered, most sections have at least one author with expertise in terrestrial ecosystems and one with expertise in marine ecosystems.
Monthly author calls were held beginning in December 2016, with frequency increasing to every other week as the initial chapter draft deadline approached. During these calls, the team came up with a work plan and fleshed out the scope and content of the chapter. After the outline for the chapter was created, authors reviewed the scientific literature, as well as the technical input that was submitted through the public call. After writing the State of the Sector section, authors pulled out the main findings to craft the Key Messages.
' report_identifier: nca4 statement: 'Climate change is altering ecosystem productivity, exacerbating the spread of invasive species, and changing how species interact with each other and with their environment (high confidence). These changes are reconfiguring ecosystems in unprecedented ways (likely, high confidence).
' uncertainties: "Primary productivity: There is still high uncertainty in how climate change will impact primary productivity for both terrestrial and marine ecosystems. For terrestrial systems, this uncertainty arises from an incomplete understanding of the impacts of continued carbon dioxide increases on plant growth;{{< tbib '132' '388e7305-fea3-40ad-a42f-55fccb5fa0df' >}},{{
Phenology: Models of phenology, particularly those leveraging advanced statistical modeling techniques that account for multiple drivers in phenological forecasts,{{< tbib '265' '416437c8-7830-491a-9903-c1054cff913a' >}} enable extrapolation across space and time, given the availability of gridded climatological and satellite data.{{< tbib '21' '3307a62c-ed45-4399-bcb9-f77e71b1e626' >}},{{
The majority of terrestrial plant phenological research to date has focused on patterns and variability in the onset of spring, with far fewer studies focused on autumn.{{< tbib '270' 'f773b2e9-428c-455b-82f9-a4dbf065d44b' >}} However, autumn models have large biases in describing interannual variation.{{< tbib '271' 'f707c003-8d84-4a07-9136-17693ece0969' >}},{{
Invasive species: There is some uncertainty in knowing how much a nonnative species will impact an environment, if and when it is introduced, although there are methods available for estimating this risk.{{< tbib '278' '1e9b900d-0a4c-428e-9e76-8b97858a3800' >}},{{
Species interactions and emergent properties: Climate change impacts to ecosystem properties are difficult to assess and predict, because they arise from interactions among multiple components of each system, and each system is likely to respond differently. One generalization that can be made arises from fossil records, which show climate-driven mass extinctions of specialists followed by novel communities dominated by generalists.{{< tbib '67' '7843f759-b2e4-4298-a2cb-eda2a2d35a9e' >}} Although there is widespread consensus among experts that novel interactions and ecosystem transitions will result from ecological responses to climate change,{{< tbib '85' 'e3cd2dc9-3bb4-422a-a2d4-a55ca8651758' >}} these are still largely predicted consequences, and direct evidence remains scarce; thus, estimates of how ecosystem services will change remain uncertain in many cases.{{< tbib '13' '7406884d-2302-4644-aa50-12ed8baf4fd7' >}},{{
High uncertainty remains for many species and ecosystems due to a general lack of basic research on baseline conditions of biotic interactions; community composition, structure, and function; and adaptive capacity; as well as the interactive, synergistic, and antagonistic effects of multiple climate and non-climate stressors.{{< tbib '67' '7843f759-b2e4-4298-a2cb-eda2a2d35a9e' >}},{{
There is high confidence that the resources and services that people depend on for livelihoods, sustenance, protection, and well-being are likely jeopardized by the impacts of climate change on ecosystems.
There is high confidence that fundamental changes in agricultural and fisheries production, the supply of clean water, protection from extreme events, and culturally valuable resources are likely occurring.
' evidence: "Similar to the Third National Climate Assessment, results of this review conclude that climate change continues to affect the availability and delivery of ecosystem services to society through altered agricultural and fisheries production, protection from storms and flooding in coastal zones, a sustainable harvest, pollination services, the spread of invasive species, carbon storage, clean water supplies, the timing and intensity of wildfire, the spread of vector-borne diseases, and recreation.{{< tbib '1' 'eae18d2c-125c-45d5-bd2d-36b4c87f9cce' >}},{{
Provisioning services: Regional changes in critical provisioning services (food, fiber, and shelter) have been observed as range shifts occur. These result in spatial patterns of winners and losers for human communities dependent on these resources. For example, as the distribution of harvestable tree species changes over time in response to climate change, timber production will shift in ways that create disconnects between resource availability and ownership rights.{{< tbib '286' '50c190f6-01ab-41be-8a09-9e2978884b98' >}}Although fisheries are more often treated as common property resources (with attendant problems related to the overuse and mismanagement of common resources),{{< tbib '287' 'e529b0dd-5c4d-4320-83ef-b3a61e054420' >}} disconnects emerge with respect to the definitions of management units and jurisdictional conflict and uncertainty.{{< tbib '97' 'f147452b-e846-4fdd-aad9-3110322e071c' >}} Shifting distribution patterns can potentially affect access to both harvested and protected natural resources, cultural services related to the rights of Indigenous peoples and to recreation, and the aesthetic appreciation of nature in general (Ch. 15: Tribes, KM 1).{{< tbib '288' '18b0c713-a454-42dc-9cbe-a810ae153c75' >}}
Additionally, changes in physical characteristics in response to climate change can impact ecosystem services. In the ocean, the combination of warmer water and less dissolved oxygen can be expected to promote earlier maturation, smaller adult body size, shorter generation times, and more boom–bust population cycles for large numbers of fish species.{{< tbib '289' '7badc287-a489-4f16-b031-edce65965a43' >}} These changes would have profound ecosystem effects, which in turn would affect the value of ecosystem services and increase risk and volatility in certain industries.
Altered phenology can also impact ecosystem services. Based on standardized indices of the timing of spring onset,{{< tbib '21' '3307a62c-ed45-4399-bcb9-f77e71b1e626' >}} 2012 saw the earliest spring recorded since 1900 across the United States.{{< tbib '21' '3307a62c-ed45-4399-bcb9-f77e71b1e626' >}},{{
Potential asynchronies may impact some pollination services, although other pollinator–plant relationships are expected to be robust in the face of shifting phenology.{{< tbib '291' 'd05ab8a0-f695-4af5-8a33-3426ab4b8eb8' >}},{{
Regulating services: Average carbon storage in the contiguous United States is projected to increase by 0.36 billion metric tons under RCP4.5 and 3.0 billion metric tons under RCP8.5.{{< tbib '104' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} However, carbon storage is projected to decrease for U.S. forests (Ch. 6: Forests, KM 2). Increases in overall carbon storage are projected for the Northwest, and decreases are projected for the Northeast and Midwest.{{< tbib '104' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} Furthermore, shorter winters and changing phenology may affect the incidence and geographic extent of vector-borne diseases (Ch. 14: Human Health, KM 1).{{< tbib '284' '514a2503-fc83-4e60-81d1-04421ff8ebc2' >}},{{
Cultural services: Climate change is expected to impact recreation and tourism in the United States, as well as cultural resources for Indigenous peoples (Ch. 15: Tribes, KM 1).{{< tbib '95' '0aa04555-0142-4697-a5cc-00c7cab4e9e8' >}},{{
Supporting services: Climate change is impacting supporting services, which are the services that make all other ecosystem services possible. Climate change impacts include alterations in primary production and nutrient cycling.{{< tbib '48' '10bc8ec0-deed-40ff-9d4e-1b202da596bf' >}},{{
Topics for the chapter were selected to improve the consistency of coverage of the report and to standardize the assessment process for ecosystems and biodiversity. Chapter leads went through the detailed technical input for the Third National Climate Assessment and pulled out key issues that they felt should be updated in the Fourth National Climate Assessment. The chapter leads then came up with an author team with expertise in these selected topics. To ensure that both terrestrial and marine issues were adequately covered, most sections have at least one author with expertise in terrestrial ecosystems and one with expertise in marine ecosystems.
Monthly author calls were held beginning in December 2016, with frequency increasing to every other week as the initial chapter draft deadline approached. During these calls, the team came up with a work plan and fleshed out the scope and content of the chapter. After the outline for the chapter was created, authors reviewed the scientific literature, as well as the technical input that was submitted through the public call. After writing the State of the Sector section, authors pulled out the main findings to craft the Key Messages.
' report_identifier: nca4 statement: '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 (likely, high confidence). Fundamental changes in agricultural and fisheries production, the supply of clean water, protection from extreme events, and culturally valuable resources are occurring (likely, high confidence).
' uncertainties: 'One of the major challenges to understanding changes in ecosystem services due to climate change arises from matching the scale of the ecosystem change to the scale at which humans are impacted. Local conditions may vary greatly from changes expected at larger geographic scales. This uncertainty can work in both directions: local estimates of changes in ecosystems services can be overestimated when local impacts of climate change are less than regional-scale impacts. However, estimates of local impacts on ecosystem services can be underestimated when local impacts of climate change exceed regional projections. Another major source of uncertainty is related to the emergent properties of ecosystems related to climate change. Since observation of human impacts of these emergent ecosystem properties is lacking, it is difficult to predict how humans will be impacted and how they might adapt.
' uri: /report/nca4/chapter/ecosystems-ecosystem-services-and-biodiversity/finding/key-message-7-3 url: ~ - chapter_identifier: ecosystems-ecosystem-services-and-biodiversity confidence: 'There is high confidence that traditional natural resource management strategies are increasingly challenged by the impacts of climate change.
There is high confidence that adaptation strategies that are flexible, consider the emerging and interactive impacts of climate and other stressors, and are coordinated across local and landscape scales are progressing from theory to application.
There is high confidence that significant challenges remain to comprehensively incorporate climate adaptation planning into mainstream natural resource management, as well as to evaluate the effectiveness of implemented actions.
' evidence: "Climate change is increasingly being recognized as a threat to biodiversity and ecosystems. For example, a recently developed threat classification system for biodiversity{{< tbib '300' '49aa5b13-50c3-4212-b964-de5fc77d00df' >}} has been adopted by the International Union for Conservation of Nature, which stands in contrast to previous frameworks that did not include climate change as a threat.{{< tbib '301' '30466af4-916e-49c7-ad6c-86494541a17f' >}} Moving away from traditional management strategies that aim to retain existing species and ecosystems and implementing climate-smart management approaches are likely to be the most effective way to conserve species, ecosystems, and ecosystem services in the future.{{< tbib '194' '14abc4e6-e419-4686-880f-cd2f3e28e11c' >}}
Ecosystem-based management strategies, where decisions are made at the ecosystem level,{{< tbib '217' 'd9702d65-fced-4531-85ff-3009aec0c6cb' >}} and programs that consider climate change impacts along with other human-caused stressors are becoming more established and seek to optimize benefits among diverse societal goals.{{< tbib '302' '22ac15b9-740c-4180-8262-ba830f22a050' >}} A number of regional to national networks have been implemented, including the Department of the Interior’s (DOI) Climate Adaptation Science Centers{{< tbib '303' 'bbf30f16-931f-4669-8da6-58096cd94679' >}} and the NOAA Regional Integrated Sciences and Assessment Programs,{{< tbib '304' 'e01214c9-2895-465f-80fe-cfe4d771057a' >}} that bring together multiple stakeholders to develop approaches for dealing with climate change. Landscape Conservation Cooperatives (LCCs) were established by DOI Secretarial Order 3289 in 2009 to provide transboundary support and science capacity for adaptive resource management. The U.S. Fish and Wildlife Service (Service) is no longer providing dedicated staff and funding to support the governance and operations of the 22 LCCs, consistent with its FY2018 and FY2019 budget requests. The Service will continue to support cooperative landscape conservation efforts as an equal partner, working with states and other partners on priority conservation and management issues. Federal and state agencies with responsibilities for natural resources have begun to implement proactive and climate-smart management approaches. Recent examples (within the last 10 years) include the development of the National Marine Fisheries Service’s Climate Science Strategy{{< tbib '215' '372d0974-9c5c-4501-be26-0a787ba59ec3' >}},{{
In addition, federal agencies are developing policies and approaches that consider ecosystem services and related climate impacts within existing planning and decision frameworks.{{< tbib '225' '65b928dc-e404-4d88-b0ff-15618c3c784a' >}} For example, NOAA’s Fisheries Ecosystem-Based Fisheries Management Policy specifically considers climate change and ecosystem services. By framing management strategies and actions within an ecosystem services context, communication about the range of benefits derived from biodiversity and natural ecosystems can be improved, and managers, policymakers, and the public can better envision decisions that support climate adaptation. Restoration efforts can also help conserve important ecosystem services (Ch. 21: Midwest, Figure 21.7).
An example of an effective, collaborative effort to manage climate impacts took place in Puerto Rico during a recent drought. In order to better manage the impacts of the drought on the environment, people, and water resources, Puerto Rico developed a special task force composed of government officials, federal partners, and members of academia to evaluate the progression, trends, and effects of drought in the territory. Weekly reports from the task force provided recommended actions for government officials and updated the public about the drought (Ch. 20: U.S. Caribbean, Box 20.3).
Changes in Individual characteristics: Maintaining habitat connectivity is important to ensure gene flow among populations and maintain genetic diversity, which provides the platform for evolutionary change. Additionally, assisted migration can be used to increase genetic diversity for less mobile species, which is important to facilitate evolutionary changes.{{< tbib '213' 'dcbe9b79-4d34-4564-8bff-a1679897d9f3' >}}
Changes in range: Climate-induced shifts in plant and animal populations can be most effectively addressed through landscape-scale and ecosystem-based conservation and management approaches. Increasing habitat connectivity for terrestrial, freshwater, and marine systems is a key climate adaptation action that will enable species to disperse and follow physiological niches as environmental conditions and habitats shift.{{< tbib '206' 'a3076178-f049-4380-9bc8-a601baae8ebb' >}} More active approaches like seed sourcing and assisted migration may be considered for planted species or those with limited natural dispersal ability.{{< tbib '308' 'dac4918b-3fe4-48e6-927f-7e67346d62e1' >}} However, for any assisted migration, there could be unforeseen and unwanted consequences. Although a provision to analyze and manage the potential consequences of assisted migration would not guarantee successful outcomes, developing such policies is warranted toward minimizing unintended consequences.{{< tbib '213' 'dcbe9b79-4d34-4564-8bff-a1679897d9f3' >}},{{
Changes in phenology: Direct management of climate-induced phenological shifts or mismatches is challenging, as managers have few if any direct measures of control on phenology.{{< tbib '248' '1abd1782-8c41-462c-bd73-e61111765d30' >}} However, research into how species’ phenologies are changing has the potential to support improved conservation outcomes by identifying high-priority phenological periods and informing changes in management actions accordingly. In Vermont grassland systems, for example, research on grassland bird nesting phenology identified the timing of haying as a critical stressor. In response, the timing of haying has been modified to accommodate the nesting phenology of several declining species, including the bobolink, demonstrating the potential for phenological data to support a successful conservation program.{{< tbib '309' '05ac76f1-7f9a-400e-b190-ddfc2a265d41' >}},{{
Invasive species: Focusing efforts on the prevention, eradication, and control of invasive species and the implementation of early detection and rapid response (EDRR) can be considered an adaptation strategy to help maintain healthy ecosystems and preserve biodiversity such that natural systems are more resistant and resilient to climate change and extreme weather events.{{< tbib '202' 'be0239b6-6114-431d-9fe1-a3ce7216a07a' >}},{{
Topics for the chapter were selected to improve the consistency of coverage of the report and to standardize the assessment process for ecosystems and biodiversity. Chapter leads went through the detailed technical input for the Third National Climate Assessment and pulled out key issues that they felt should be updated in the Fourth National Climate Assessment. The chapter leads then came up with an author team with expertise in these selected topics. To ensure that both terrestrial and marine issues were adequately covered, most sections have at least one author with expertise in terrestrial ecosystems and one with expertise in marine ecosystems.
Monthly author calls were held beginning in December 2016, with frequency increasing to every other week as the initial chapter draft deadline approached. During these calls, the team came up with a work plan and fleshed out the scope and content of the chapter. After the outline for the chapter was created, authors reviewed the scientific literature, as well as the technical input that was submitted through the public call. After writing the State of the Sector section, authors pulled out the main findings to craft the Key Messages.
' report_identifier: nca4 statement: 'Traditional natural resource management strategies are increasingly challenged by the impacts of climate change (high confidence). 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 (high confidence).
' uncertainties: "Better predictive models are necessary to create effective adaptation strategies, but they can be hampered by a lack of sufficient data to adequately incorporate important biological mechanisms and feedback loops that influence climate change responses.{{< tbib '232' '92530347-b16b-4ada-a59e-af0c7cbe2426' >}} This can be most effectively addressed if resource management approaches and monitoring efforts increasingly expand programs, especially at the community or ecosystem level, to detect and track changes in species composition, interactions, functioning, and tipping points, as well as to improve model inputs.{{< tbib '312' '3f4eb2c9-be96-4c86-b7a8-c8ae52e2445f' >}},{{
Changes in individual characteristics: Although genetic diversity is important for evolution and potentially for increasing the fitness of individuals, it does not guarantee that a species will adapt to future environmental conditions. Failure to adapt may occur when a species or population lacks genetic variability in a particular trait that is under selection (such as heat tolerance) as a result of climate change,{{< tbib '7' '161a6359-6e48-4cd4-bbb0-1def2934c83f' >}} despite having high overall genetic diversity.
Changes in Range: Although potential strategies for adaptation to range shifts can be readily identified, the lack of experience implementing these approaches to meet this issue results in uncertainty in the efficacy of different approaches. Another big uncertainty is the incomplete information on the ecology and responses of species and ecosystems to climate change.
Changes in phenology: Phenological sensitivity may also be an important component of organismal adaptive capacity{{< tbib '315' 'f0930c90-8717-4075-8d10-aa8beda3d0fd' >}} and thus species' vulnerability to climate change, although additional research is required before resource managers can utilize known relative vulnerabilities to prioritize management activities.
Invasive species: There is some uncertainty in the optimal management approach for a given species and location. Best practices for management actions are often context specific; one approach will not fit all scenarios. Management of climate change and invasive species needs to explore such variables as the biology of the target species, the time of year or day for maximizing effectiveness, the ecological and sociocultural context, legal and institutional frameworks, and budget constraints and timeliness.{{< tbib '281' 'bb0bd25d-6d90-4336-95d4-6dde685079ce' >}}
" uri: /report/nca4/chapter/ecosystems-ecosystem-services-and-biodiversity/finding/key-message-7-4 url: ~ - chapter_identifier: coastal-effects confidence: 'There is very high confidence that the frequency and extent of tidal flooding is already increasing and will continue to increase with SLR and that this flooding threatens the trillion-dollar coastal property market and public infrastructure. There is limited research using varied methods to quantify the direct and indirect economic impacts that will be experienced under different amounts of SLR. Nevertheless, there is a high level of confidence that these losses will be dramatic under SLR associated with the higher emission scenario (RCP8.5) and significant even under lower scenarios (RCP4.5 or RCP2.6), based on property values and geographic exposure to inundation. U.S. economic history provides strong evidence that extensive property market losses have the potential to impact businesses, personal wealth, and mortgage-related securities. Similarly, historic disaster events such as hurricanes and earthquakes provide a very high level of confidence that impacts to critical transportation and energy networks will harm the economy. Considering the uncertainty inherent in future human behavior and policy responses, including flood insurance policy, it is possible that individuals and institutions will act to reduce future flooding, to lessen the exposure and sensitivity of critical assets, and to create policies that assist individuals and businesses most impacted; hence, there is medium confidence that many coastal communities will be transformed by 2100 under any scenario and that many individuals will be financially devastated under lower emission scenarios (RCP4.5 or RCP2.6). Considering current exposure of assets and the latest SLR science, large economic losses in coastal regions that will generate cascading impacts to the overall economy of the United States are considered to be likely. The overall high confidence is the net result of considering the evidence base, the well-established accumulation of economic assets and activities in coastal areas, and the directional trend of sea level rise.
' evidence: "Significant impacts to coastal communities, properties, infrastructure, and services are already occurring in low-lying areas of the country such as Miami Beach and Fort Lauderdale in Florida; Norfolk, Virginia; and Charleston, South Carolina.{{< tbib '61' '66ea5840-4fdb-457c-a206-5c09d331445c' >}},{{
Satellite and tide gauge data show that sea level rise (SLR) rates are increasing,{{< tbib '36' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}} and research has shown that this increase is driven by emissions that are warming the planet.{{< tbib '129' '94a8514e-063e-45ef-b893-11c82b49a597' >}},{{
Applying digital elevation models to determine the extent and number of communities and the amount of property and infrastructure that would be impacted by different amounts of SLR illustrates the magnitude of investments that are at risk.{{< tbib '56' '2db2b107-2e02-4f3a-b1e7-98301e28395d' >}},{{
The importance of coastal economies and infrastructure to the overall national economy is well documented (for example, the National Oceanic and Atmospheric Administration’s [NOAA] Economics: National Ocean Watch; NOAA port data), as are the economic ripple effects of impacts to property markets.{{< tbib '57' '6e83fde3-5f98-4fd1-ae2c-d11aced414ac' >}},{{
The selection of the author team for the Coastal Effects chapter took into consideration the wide scope and relative sufficiency of the Third National Climate Assessment (NCA3) Coastal chapter. With input and guidance from the NCA4 Federal Steering Committee, the coordinating lead authors made the decision to convene an all-federal employee team with representation from key federal agencies with science, management, and policy expertise in climate-related coastal effects, and to focus the content of the chapter on Key Messages and themes that would both update the work conducted under NCA3 and introduce new themes. For additional information on the author team process and structure, refer to Appendix 1: Process.
A central component of the assessment process was a chapter lead authors’ meeting held in Washington, DC, in May 2017. The Key Messages were initially developed at this meeting. Key vulnerabilities were operationally defined as those challenges that can fundamentally undermine the functioning of human and natural coastal systems. They arise when these systems are highly exposed and sensitive to climate change and (given present or potential future adaptive capacities) insufficiently prepared or able to respond. The vulnerabilities that the team decided to focus on were informed by a review of the existing literature and by ongoing interactions of the author team with coastal managers, planners, and stakeholders. In addition, the author team conducted a thorough review of the technical inputs and associated literature. Chapter development was supported by numerous chapter author technical discussions via teleconference from April to September 2017.
' report_identifier: nca4 statement: '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 (RCP8.5), many coastal communities will be transformed by the latter part of this century, and even under lower scenarios (RCP4.5 or RCP2.6), 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. (Likely, High Confidence)
' uncertainties: "The main source of uncertainty is in the magnitude of SLR that will occur and how it will vary across different regions, which depend in part on the amount and speed with which global society will reduce emissions. While global climate models and SLR models have improved since NCA3,{{< tbib '142' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} uncertainty remains about exactly how much SLR will occur where and by when with different emissions levels. Even though there is uncertainty about the magnitude, the probabilistic approach to the SLR technical report to the Fourth National Climate Assessment,{{< tbib '36' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}} together with impacts already documented around the country from high tide flooding,{{< tbib '143' '33a582e6-f606-4e31-bb1f-6c3da8cfd45d' >}} gives us high confidence of the threat to coastal property and infrastructure. Adaptive responses to SLR risk and impacts, including individual action and public policy development, are also significant sources of uncertainty. For example, there is uncertainty about future development patterns in coastal regions, including both new development and migration inland, which has the potential to change the magnitude of coastal property and infrastructure at risk. The U.S.-specific research on potential migration away from the coast due to SLR and other climate impacts is very limited.{{< tbib '102' '2ddba35f-6036-4428-b4c7-800dd57b3313' >}}
Future flood insurance policy is another specific source of uncertainty. Under the latest legislation (the Federal Emergency Management Agency’s Homeowner Flood Insurance Affordability Act{{< tbib '140' '32404d0b-928c-4338-9c1a-b14282cb9491' >}}), flood insurance rates are gradually rising; development of new policies related to affordability or to the requirement to carry flood insurance in order to have a federally backed mortgage could change behaviors.
While figures for the economic value of certain sectors dependent on the ocean and Great Lakes are available through NOAA’s “Economics: National Ocean Watch,”{{< tbib '144' '2aa0aa30-d41d-4c09-8557-2cb1e40c3f7f' >}} similar information for the economic and social value of other sectors, such as real estate and insurance/reinsurance, would be beneficial for the audience of this assessment report, especially decision-makers.
" uri: /report/nca4/chapter/coastal-effects/finding/key-message-8-1 url: ~ - chapter_identifier: coastal-effects confidence: 'There is high confidence that coastal ecosystems are particularly vulnerable to climate change. They have already been dramatically altered by human stressors, as documented in extensive and conclusive evidence; additional stresses from climate change point to a growing likelihood of coastal ecosystems being pushed past tipping points from which they will not be able to recover. The overall high confidence is the net result of considering the evidence base, the dramatically altered ecosystems from human stresses, and the directional trend of sea level rise.
' evidence: "Multiple lines of evidence have determined that coastal environments are critical to support coastal fisheries, tourism, and human health and safety.{{< tbib '74' '8be5daa4-2526-49b8-9b71-c9434e436a87' >}},{{
There is growing evidence that one part of the solution to help coastal ecosystems and human communities be more resilient to climate change, including SLR and increasingly intense or frequent storms, is to conserve or restore coastal habitats such as wetlands, beaches and dunes, oyster and coral reefs, and mangroves{{< tbib '74' '8be5daa4-2526-49b8-9b71-c9434e436a87' >}},{{
The selection of the author team for the Coastal Effects chapter took into consideration the wide scope and relative sufficiency of the Third National Climate Assessment (NCA3) Coastal chapter. With input and guidance from the NCA4 Federal Steering Committee, the coordinating lead authors made the decision to convene an all-federal employee team with representation from key federal agencies with science, management, and policy expertise in climate-related coastal effects, and to focus the content of the chapter on Key Messages and themes that would both update the work conducted under NCA3 and introduce new themes. For additional information on the author team process and structure, refer to Appendix 1: Process.
A central component of the assessment process was a chapter lead authors’ meeting held in Washington, DC, in May 2017. The Key Messages were initially developed at this meeting. Key vulnerabilities were operationally defined as those challenges that can fundamentally undermine the functioning of human and natural coastal systems. They arise when these systems are highly exposed and sensitive to climate change and (given present or potential future adaptive capacities) insufficiently prepared or able to respond. The vulnerabilities that the team decided to focus on were informed by a review of the existing literature and by ongoing interactions of the author team with coastal managers, planners, and stakeholders. In addition, the author team conducted a thorough review of the technical inputs and associated literature. Chapter development was supported by numerous chapter author technical discussions via teleconference from April to September 2017.
' report_identifier: nca4 statement: '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 (highly likely, high confidence). 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 (likely, high confidence).
' uncertainties: "The exact amount of coastal habitat loss that is due to climate change versus other human stressors or multiple stressors can be hard to ascertain, because these stressors are all acting simultaneously on coastal habitats. Nevertheless, it is clear that climate change is one of the important stressors impacting coastal habitats and leading to the degradation or loss of these ecosystems, such as the loss of coral habitats to bleaching events due to rising ocean temperatures and the loss of coastal wetlands due to more intense storm events.
The use of natural and nature-based infrastructure (NNBI) to improve coastal resilience is being implemented in many different states (for example, the use of living shorelines is expanding in Maryland, North Carolina, New Jersey, Louisiana, and other states, and the Rebuild by Design competition is implementing a variety of coastal resilience projects in New York and New Jersey), although there remain some uncertainties about how much storm and erosion risk reduction is provided by different techniques or projects and in different settings. The efficacy of NNBI remains uncertain in many instances; comprehensive monitoring, particularly during and after storms, would be required to ascertain how well these features are functioning for protection services. This monitoring could inform future coastal resilience planning and decisions, including the benefits, costs, and/or tradeoffs involved in considering NNBI options.{{< tbib '157' '8197f2a0-796a-47b1-869b-5f3492855db4' >}}
" uri: /report/nca4/chapter/coastal-effects/finding/key-message-8-2 url: ~ - chapter_identifier: coastal-effects confidence: 'There is very high confidence that structural inequalities in coastal communities will be exacerbated by climate change and its attendant effects (for example, storms, erosion). In the absence of clear policies and legal precedent, questions about land ownership and home ownership will persist.
' evidence: "Reports and peer-reviewed articles are clear that socioeconomic challenges are being both driven and intensified by climate change.{{< tbib '33' '5d78768d-4392-494e-90c1-466cd61644c7' >}} Particularly on the coasts, where there are multiple risks to contend with, including hurricanes, SLR, shoreline erosion, and flooding, the high cost of adaptation is proving to be beyond the means of some communities and groups.{{< tbib '97' '17dfdc09-42c6-48e9-8756-88f04887a960' >}},{{
The selection of the author team for the Coastal Effects chapter took into consideration the wide scope and relative sufficiency of the Third National Climate Assessment (NCA3) Coastal chapter. With input and guidance from the NCA4 Federal Steering Committee, the coordinating lead authors made the decision to convene an all-federal employee team with representation from key federal agencies with science, management, and policy expertise in climate-related coastal effects, and to focus the content of the chapter on Key Messages and themes that would both update the work conducted under NCA3 and introduce new themes. For additional information on the author team process and structure, refer to Appendix 1: Process.
A central component of the assessment process was a chapter lead authors’ meeting held in Washington, DC, in May 2017. The Key Messages were initially developed at this meeting. Key vulnerabilities were operationally defined as those challenges that can fundamentally undermine the functioning of human and natural coastal systems. They arise when these systems are highly exposed and sensitive to climate change and (given present or potential future adaptive capacities) insufficiently prepared or able to respond. The vulnerabilities that the team decided to focus on were informed by a review of the existing literature and by ongoing interactions of the author team with coastal managers, planners, and stakeholders. In addition, the author team conducted a thorough review of the technical inputs and associated literature. Chapter development was supported by numerous chapter author technical discussions via teleconference from April to September 2017.
' report_identifier: nca4 statement: 'As the pace and extent of coastal flooding and erosion accelerate, climate change impacts along our coasts are exacerbating preexisting 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. (Likely, Very High Confidence)
' uncertainties: 'The main uncertainty for this Key Message is predicated on how different types of coastal effects (chronic flooding versus storms) will impact areas and communities along the coast. The degree of variation between communities means that it will be challenging to predict exactly which communities will be affected and to what extent, but the evidence thus far is clear: when it comes to climate-driven challenges and adaptation strategies, areas that have traditionally been underrepresented will continue to suffer more than wealthier or more prominent areas. Large-scale infrastructure investments are made in some areas and not others, and some local governments will not be able to afford what they need to do.
The variability in state laws and the pace at which those laws are evolving (such as shoreline management plans and setback policies for structures in the coastal zone) create major uncertainty.
' uri: /report/nca4/chapter/coastal-effects/finding/key-message-8-3 url: ~ - chapter_identifier: oceans-and-marine-resources confidence: 'The amount of research and agreement among laboratory results, field observations, and model projections demonstrate very high confidence that ecosystem disruption has occurred due to climate change, particularly in tropical coral reef and sea ice-associated ecosystems due to the global increase of ocean temperatures. It is very likely that ecosystem disruption will intensify later this century under continued carbon emissions, as there is very high confidence that warming, acidification, deoxygenation, and other aspects of climate change will accelerate. While conservation and management practices can build resilience in some ecosystems, there is very high confidence that only reductions in carbon emissions can avoid significant ecosystem disruption, especially in coral reef and sea ice ecosystems.
' evidence: "Ocean warming has already impacted biogenically built habitats. Declines in mussel beds, kelp forests, mangroves, and seagrass beds, which provide habitat for many other species, have been linked to ocean warming and interactions of warming with changes in oxygen levels or other stressors (see Ch. 27: Hawaiʻi & Pacific Islands, Key Message 4 for impacts on mangrove systems in the Pacific Islands).{{< tbib '155' 'ca6665ed-2cb2-4a8c-959b-47a6a7dbbc29' >}},{{
Some of the most apparent ecosystem changes are occurring in the warmest and coldest ocean environments, in coral reef and sea ice ecosystems. Live coral cover in coral reef ecosystems around the world has declined from a baseline of about 50%–75% to only 15%–20% (the current average for most regions; see Bruno & Valdivia 2016; Eddy et al. 2018),{{< tbib '69' '907c63d3-2172-4d33-a185-620258ec628d' >}},{{
Species differ in their response to warming, acidification, and deoxygenation. This imbalance in sensitivity will lead to ecosystem reorganization, as confirmed by a number of recent ecosystem models focused on phytoplankton{{< tbib '17' '6f235775-bc4f-4dc8-ab04-5bb4e45761d7' >}},{{
Global-scale coral bleaching events in 1987, 1998, 2005, and 2015–2016 have caused a rapid and dramatic reduction of living coral cover; as the regularity of these events increases, their effects on ecosystem integrity may also increase.{{< tbib '7' '1f10cc44-9e2f-491c-a0ac-5ab533130318' >}},{{
Conservation measures, such as ecosystem-based fisheries management (Key Message 2) and marine-protected areas that reduce or respond to these other stressors, can increase resilience;{{< tbib '66' '3febdda6-8289-4929-a0f6-2184ff560ff8' >}},{{
The goal when building the writing team for the Oceans and Marine Resources chapter was to assemble a group of scientists who have experience across the range of marine ecosystems (such as coral reefs and temperate fisheries) that are important to the United States and with expertise on the main drivers of ocean ecosystem change (temperature, deoxygenation, and acidification). We also sought geographic balance and wanted a team that included early-career and senior scientists.
We provided two main opportunities for stakeholders to provide guidance for our chapter. This included a town hall meeting at the annual meeting of the Association for the Sciences of Limnology and Oceanography and a broadly advertised webinar hosted by the National Oceanic and Atmospheric Administration. Participants included academic and government scientists, as well as members of the fisheries and coastal resource management communities. We also set up a website to collect feedback from people who were not able to participate in the town hall or the webinar.
An important consideration in our chapter was what topics we would cover and at what depth. We also worked closely with the authors of Chapter 8: Coastal Effects to decide which processes and ecosystems to include in which chapter. This led to their decision to focus on the climate-related physical changes coming from the ocean, especially sea level rise, while our chapter focused on marine resources, including intertidal ecosystems such as salt marshes. We also decided that an important goal of our chapter was to make the case that changing ocean conditions have a broad impact on the people of the United States. This led to an emphasis on ecosystem services, notably fisheries and tourism, which are easier to quantify in terms of economic impacts.
' report_identifier: nca4 statement: '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 (very high confidence). Ecosystem disruption will intensify as ocean warming, acidification, deoxygenation, and other aspects of climate change increase (very likely, very high confidence). In the absence of significant reductions in carbon emissions, transformative impacts on ocean ecosystems cannot be avoided (very high confidence).
' uncertainties: "Further research is necessary to fully understand how multiple stressors, such as temperature, ocean acidification, and deoxygenation, will concurrently alter marine ecosystems in U.S. waters. More research on the interaction of multiple stressors and in scaling results from individual to population or community levels is needed.{{< tbib '27' 'd3f2fc9b-6acf-48b0-b5d1-0f8c620e7f35' >}},{{
Most species have some capacity to acclimate to changes in thermal and chemical conditions, depending on the rate and magnitude at which conditions change, and there may be enough genetic variation in some populations to allow for evolution.{{< tbib '73' 'b003220c-7fb3-44b3-b329-d6581d727dd4' >}},{{
There is high confidence that climate change-driven alterations in the distribution, timing, and productivity of fishery-related species will likely lead to increased risk to the Nation’s valuable marine fisheries and fishing communities. There is very high confidence that future ocean warming will very likely increase these changes in fishery-related species, reduce catches in some areas, and challenge effective management of marine resources. There is high confidence that ocean acidification and deoxygenation will likely reduce catches in some areas, which will challenge effective management of marine fisheries and protected species.
' evidence: "Most evidence of the impacts of climate variability on U.S. living marine resources comes from numerous studies examining the response of these species to variability in ocean temperature. There is strong evidence that fluctuations in ocean temperature, either directly or indirectly via impacts to food web structure, are associated with changes in the distribution,{{< tbib '31' '4c1d952b-234b-4f64-8757-d94e3565b067' >}},{{
These observational and experimental studies have provided the foundation for the development of models projecting future impacts of changing climate and ocean conditions on fisheries. Global and regional applications of such models provide strong evidence that changes in future ocean warming will alter fisheries catches in U.S. waters.{{< tbib '64' 'fda5d878-d7b2-48d9-a2c4-bb0721262ce5' >}},{{
Fisheries management in the United States has become increasingly effective at setting sustainable harvest levels, and the number of U.S. fisheries that are overfished or subjected to overfishing has declined in most regions.{{< tbib '212' 'fe404309-3247-4e64-a401-c4916db3fd2a' >}} Science-informed management in general has been shown to be effective in improving ecosystem status{{< tbib '107' '901dd046-6f95-42d3-932a-7bb1071c02ac' >}} and has been projected to greatly improve the benefits from marine resources.{{< tbib '65' '1ca5d69a-758a-4d01-bdd9-fbb8537a8ae1' >}} Climate change presents new challenges to management systems, as some species move across management boundaries and away from traditional fishing grounds and as productivity patterns shift. Management approaches that do not consider climate-driven ecosystem changes can lead to overfishing when the environment shifts rapidly.{{< tbib '76' 'fb1f46cd-8b70-4a44-923a-66df61ffa0be' >}},{{
The goal when building the writing team for the Oceans and Marine Resources chapter was to assemble a group of scientists who have experience across the range of marine ecosystems (such as coral reefs and temperate fisheries) that are important to the United States and with expertise on the main drivers of ocean ecosystem change (temperature, deoxygenation, and acidification). We also sought geographic balance and wanted a team that included early-career and senior scientists.
We provided two main opportunities for stakeholders to provide guidance for our chapter. This included a town hall meeting at the annual meeting of the Association for the Sciences of Limnology and Oceanography and a broadly advertised webinar hosted by the National Oceanic and Atmospheric Administration. Participants included academic and government scientists, as well as members of the fisheries and coastal resource management communities. We also set up a website to collect feedback from people who were not able to participate in the town hall or the webinar.
An important consideration in our chapter was what topics we would cover and at what depth. We also worked closely with the authors of Chapter 8: Coastal Effects to decide which processes and ecosystems to include in which chapter. This led to their decision to focus on the climate-related physical changes coming from the ocean, especially sea level rise, while our chapter focused on marine resources, including intertidal ecosystems such as salt marshes. We also decided that an important goal of our chapter was to make the case that changing ocean conditions have a broad impact on the people of the United States. This led to an emphasis on ecosystem services, notably fisheries and tourism, which are easier to quantify in terms of economic impacts.
' report_identifier: nca4 statement: 'Marine fisheries and fishing communities are at high risk from climate-driven changes in the distribution, timing, and productivity of fishery-related species (likely, high confidence). 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 (warming: very likely, very high confidence; acidification and deoxygenation: likely, high confidence). 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.
' uncertainties: "While shifts in the productivity and distribution of living marine resources and ecosystem structure are expected to change catch potential and catch composition in U.S. regions, many uncertainties exist. Projections of catch potential have largely been performed using dynamical bioclimatic envelope models (e.g., Cheung et al.).{{< tbib '103' 'a354ff5e-743d-4588-a0a8-411d21820076' >}} In these models, the spatial population dynamics of fish stocks are forced by temperature (with additional net primary productivity effects on carrying capacity and pH and oxygen effects on growth) and do not include the potential for major changes in species interactions, as has previously occurred with warming events (e.g., Vergés et al.){{< tbib '32' 'e4313895-fb80-4d31-906c-2fadb9da71de' >}} and food web structure (e.g., Fay et al.).{{< tbib '179' 'f12c40d3-4265-4e90-b852-026deec041fd' >}} Furthermore, recent studies indicate that zooplankton and export production may serve as better indicators of carrying capacity for fisheries than net primary productivity.{{< tbib '210' '41f0be78-707a-4169-8838-2446d6587a79' >}},{{
In addition, climate change is only one of many stressors affecting fish dynamics. Future fish distribution, abundance, and productivity will depend on the interaction between these stressors, including fishing and climate-related stressors. Conceptually and empirically, it is clear that fishers are responding to a wide diversity of factors and may not narrowly follow shifting fish populations.{{< tbib '83' '2331d02c-7dc2-4a6f-8244-4806c2360f53' >}},{{
Because there is very high confidence and very high likelihood that oceans will get warmer, more acidified, and have lower oxygen content in response to elevated atmospheric carbon dioxide levels,{{< tbib '15' '5d047224-4e72-46d1-87f5-042c9617472d' >}} it is very likely and there is very high confidence that extreme events will occur with increased intensity and frequency in the future.{{< tbib '6' '1d63deea-30f3-4fa1-ba08-3a969b23aa16' >}},{{
Marine heat waves have been described as regions of large-scale and persistent positive sea surface temperature anomalies that can vary in size, distribution, timing, and intensity akin to their terrestrial counterparts.{{< tbib '137' '963c8f97-8680-43df-8b28-59a376735f17' >}},{{
Each of these events resulted in documented impacts to ecosystems and, in many cases, to the human communities to which they were connected. The recent major events in the U.S. northwest Atlantic and North Pacific led to economic challenges in the American lobster, Dungeness crab, and Gulf of Alaska Pacific cod fisheries.{{< tbib '1' '1dfd2171-2be3-40b2-a8e2-c0df84ec462a' >}},{{
Abrupt warming can induce other ecosystem-level impacts. The North Pacific event featured an extensive bloom of the harmful algae Pseudo-nitzschia{{< tbib '4' '5300d778-0b4e-44bb-9449-c6a36ead3636' >}},{{
Extreme events with corrosive (Ω < 1) and/or low oxygen conditions can occur when deep waters, which are generally corrosive and have low oxygen levels, are brought into the coastal area during upwelling. They can also occur in response to the delivery of corrosive freshwater from the landscape, ice melting, and storms. These conditions now occur more frequently in coastal waters of the Pacific coast of the United States.{{< tbib '39' 'a080ee24-4ede-4f85-b205-79175e0dc77f' >}},{{
Heat wave, high-acidity, and low-oxygen events are all produced by variability in the system occurring on timescales ranging from days to years. For example, recent marine heat waves have been linked to natural climate modes such as the North Atlantic Oscillation, Atlantic Multidecadal Oscillation, Pacific Decadal Oscillation, or North Pacific Gyre Oscillation, which change over several years.{{< tbib '3' '257c4627-9b78-41ce-a824-ebfe008a4c88' >}},{{
The intensity of corrosive events along the upwelling margin of the Pacific coast of the United States is increasing due to more intense winds over the past decade and ocean acidification.{{< tbib '15' '5d047224-4e72-46d1-87f5-042c9617472d' >}},{{
There is ample evidence that extreme events motivate adaptive change in human systems. For example, Hurricane Katrina and Superstorm Sandy motivated communities near the affected areas to expand planning against future storms.{{< tbib '234' '8f522585-8c4d-4c72-ab01-76c071942cbc' >}},{{
The goal when building the writing team for the Oceans and Marine Resources chapter was to assemble a group of scientists who have experience across the range of marine ecosystems (such as coral reefs and temperate fisheries) that are important to the United States and with expertise on the main drivers of ocean ecosystem change (temperature, deoxygenation, and acidification). We also sought geographic balance and wanted a team that included early-career and senior scientists.
We provided two main opportunities for stakeholders to provide guidance for our chapter. This included a town hall meeting at the annual meeting of the Association for the Sciences of Limnology and Oceanography and a broadly advertised webinar hosted by the National Oceanic and Atmospheric Administration. Participants included academic and government scientists, as well as members of the fisheries and coastal resource management communities. We also set up a website to collect feedback from people who were not able to participate in the town hall or the webinar.
An important consideration in our chapter was what topics we would cover and at what depth. We also worked closely with the authors of Chapter 8: Coastal Effects to decide which processes and ecosystems to include in which chapter. This led to their decision to focus on the climate-related physical changes coming from the ocean, especially sea level rise, while our chapter focused on marine resources, including intertidal ecosystems such as salt marshes. We also decided that an important goal of our chapter was to make the case that changing ocean conditions have a broad impact on the people of the United States. This led to an emphasis on ecosystem services, notably fisheries and tourism, which are easier to quantify in terms of economic impacts.
' report_identifier: nca4 statement: '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 (very likely, very high confidence), and they expose vulnerabilities that can motivate change, including technological innovations to detect, forecast, and mitigate adverse conditions.
' uncertainties: "The description above assumes that natural modes of climate variability remain the same and can be simply added to baseline conditions set by the global climate. There is evidence that some natural climate modes may change in the future. As mentioned in the narrative, the climate oscillations linked to the 2014–2016 event in the North Pacific increase in amplitude in climate model projections.{{< tbib '3' '257c4627-9b78-41ce-a824-ebfe008a4c88' >}},{{
For biogeochemistry, other factors may amplify the global changes at the regional level as well, especially in the coastal environment. These factors include local nutrient runoff, freshwater input, glacial runoff, spatial variability in retentive mechanisms, variability in upwelling strength, cloud cover, and stability of sedimentary deposits (for example, methane).{{< tbib '15' '5d047224-4e72-46d1-87f5-042c9617472d' >}},{{