Climate change continues to impact species and populations in significant and observable ways. Terrestrial, freshwater, and marine organisms are responding to climate change by altering individual characteristics, the timing of biological events, and their geographic ranges. Local and global extinctions may occur when climate change outpaces the capacity of species to adapt.
Climate change is altering ecosystem productivity, exacerbating the spread of invasive species, and changing how species interact with each other and with their environment. These changes are reconfiguring ecosystems in unprecedented ways.
The resources and services that people depend on for their livelihoods, sustenance, protection, and well-being are jeopardized by the impacts of climate change on ecosystems. Fundamental changes in agricultural and fisheries production, the supply of clean water, protection from extreme events, and culturally valuable resources are occurring.
Traditional natural resource management strategies are increasingly challenged by the impacts of climate change. Adaptation strategies that are flexible, consider interacting impacts of climate and other stressors, and are coordinated across landscape scales are progressing from theory to application. Significant challenges remain to comprehensively incorporate climate adaptation planning into mainstream natural resource management, as well as to evaluate the effectiveness of implemented actions.
Climate change continues to impact species and populations in significant and observable ways. Terrestrial, freshwater, and marine organisms are responding to climate change by altering individual characteristics, the timing of biological events, and their geographic ranges. Local and global extinctions may occur when climate change outpaces the capacity of species to adapt.
Climate change is altering ecosystem productivity, exacerbating the spread of invasive species, and changing how species interact with each other and with their environment. These changes are reconfiguring ecosystems in unprecedented ways.
The resources and services that people depend on for their livelihoods, sustenance, protection, and well-being are jeopardized by the impacts of climate change on ecosystems. Fundamental changes in agricultural and fisheries production, the supply of clean water, protection from extreme events, and culturally valuable resources are occurring.
Traditional natural resource management strategies are increasingly challenged by the impacts of climate change. Adaptation strategies that are flexible, consider interacting impacts of climate and other stressors, and are coordinated across landscape scales are progressing from theory to application. Significant challenges remain to comprehensively incorporate climate adaptation planning into mainstream natural resource management, as well as to evaluate the effectiveness of implemented actions.
Virtually Certain | Extremely Likely | Very Likely | Likely | About as Likely as Not | Unlikely | Very Unikely | Extremely Unlikely | Exceptionally Unlikely |
---|---|---|---|---|---|---|---|---|
99%–100% | 95%–100% | 90%–100% | 66%-100% | 33%-66% | 0%-33% | 0%-10% | 0%-5% | 0%-1% |
Very High | Hoch | Medium | Niedrig |
---|---|---|---|
Strong evidence (established theory, multiple sources, consistent results, well documented and accepted methods, etc.), high consensus | Moderate evidence (several sources, some consistency, methods vary and/or documentation limited, etc.), medium consensus | Suggestive evidence (a few sources, limited consistency, models incomplete, methods emerging, etc.), competing schools of thought | Inconclusive evidence (limited sources, extrapolations, inconsistent findings, poor documentation and/or methods not tested, etc.), disagreement or lack of opinions among experts |
Documenting Uncertainty: This assessment relies on two metrics to communicate the degree of certainty in Key Findings. See Guide to this Report for more on assessments of likelihood and confidence.
Biodiversity—the variety of life on Earth—provides vital services that support and improve human health and well-being. Ecosystems, which are composed of living things that interact with the physical environment, provide numerous essential benefits to people. These benefits, termed ecosystem services, encompass four primary functions: provisioning materials, such as food and fiber; regulating critical parts of the environment, such as water quality and erosion control; providing cultural services, such as recreational opportunities and aesthetic value; and providing supporting services, such as nutrient cycling.1 Climate change poses many threats and potential disruptions to ecosystems and biodiversity, as well as to the ecosystem services on which people depend.
Building on the findings of the Third National Climate Assessment (NCA3),2 this chapter provides additional evidence that climate change is significantly impacting ecosystems and biodiversity in the United States. Mounting evidence also demonstrates that climate change is increasingly compromising the ecosystem services that sustain human communities, economies, and well-being. Both human and natural systems respond to change, but their ability to respond and thrive under new conditions is determined by their adaptive capacity, which may be inadequate to keep pace with rapid change. Our understanding of climate change impacts and the responses of biodiversity and ecosystems has improved since NCA3. The expected consequences of climate change will vary by region, species, and ecosystem type. Management responses are evolving as new tools and approaches are developed and implemented; however, they may not be able to overcome the negative impacts of climate change. Although efforts have been made since NCA3 to incorporate climate adaptation strategies into natural resource management, significant work remains to comprehensively implement climate-informed planning. This chapter presents additional evidence for climate change impacts to biodiversity, ecosystems, and ecosystem services, reflecting increased confidence in the findings reported in NCA3. The chapter also illustrates the complex and interrelated nature of climate change impacts to biodiversity, ecosystems, and the services they provide.
<b>Lipton</b>, D., M. A. Rubenstein, S.R. Weiskopf, S. Carter, J. Peterson, L. Crozier, M. Fogarty, S. Gaichas, K.J.W. Hyde, T.L. Morelli, J. Morisette, H. Moustahfid, R. Muñoz, R. Poudel, M.D. Staudinger, C. Stock, L. Thompson, R. Waples, and J.F. Weltzin, 2018: Ecosystems, Ecosystem Services, and Biodiversity. In <i>Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II</i> [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 268–321. doi: 10.7930/NCA4.2018.CH7
All life on Earth, including humans, depends on the services that ecosystems provide, including food and materials, protection from extreme events, improved quality of water and air, and a wide range of cultural and aesthetic values. Such services are lost or compromised when the ecosystems that provide them cease to function effectively. Healthy ecosystems have two primary components: the species that live within them, and the interactions among species and between species and their environment. Biodiversity and ecosystem services are intrinsically linked: biodiversity contributes to the processes that underpin ecosystem services; biodiversity can serve as an ecosystem service in and of itself (for example, genetic resources for drug development); and biodiversity constitutes an ecosystem good that is directly valued by humans (for example, appreciation for variety in its own right).3 Significant environmental change, such as climate change, poses risks to species, ecosystems, and the services that humans rely on. Consequently, identifying measures to minimize, cope with, or respond to the negative impacts of climate change is necessary to reduce biodiversity loss and to sustain ecosystem services.4
This chapter focuses on the impacts of climate change at multiple scales: the populations and species of living things that form ecosystems; the properties and processes that support ecosystems; and the ecosystem services that underpin human communities, economies, and well-being. The key messages from NCA3 (Table 7.1) have been strengthened over the last four years by new research and monitoring networks. This chapter builds on the NCA3 findings and specifically emphasizes how climate impacts interact with non-climate stressors to affect ecosystem services. Furthermore, it describes new advances in climate adaptation efforts, as well as the challenges natural resource managers face when seeking to sustain ecosystems or to mitigate climate change (Figure 7.1).
Climate change impacts on ecosystems reduce their ability to improve water quality and regulate water flows. |
Climate change, combined with other stressors, is overwhelming the capacity of ecosystems to buffer the impacts from extreme events like fires, floods, and storms. |
Landscapes and seascapes are changing rapidly, and species, including many iconic species, may disappear from regions where they have been prevalent or become extinct, altering some regions so much that their mix of plant and animal life will become almost unrecognizable. |
Timing of critical biological events, such as spring bud burst, emergence from overwintering, and the start of migrations, has shifted, leading to important impacts on species and habitats. |
Whole system management is often more effective than focusing on one species at a time, and can help reduce the harm to wildlife, natural assets, and human well-being that climate disruption might cause. |
There is increasing evidence that climate change is impacting biodiversity, and species and populations are responding in a variety of ways. Individuals may acclimate to new conditions by altering behavioral, physical, or physiological characteristics, or populations may evolve new or altered characteristics that are better suited to their current environment. Additionally, populations may track environmental conditions by moving to new locations. The impacts of climate change on biodiversity have been observed across a range of scales, including at the level of individuals (such as changes in genetics, behavior, physical characteristics, and physiology), populations (such as changes in the timing of life cycle events), and species (such as changes in geographic range).5
Changes in individual characteristics: At an individual level, organisms can adapt to climate change through shifts in behavior, physiology, or physical characteristics.5,6,7,8 These changes have been observed across a range of species in terrestrial, freshwater, and marine systems.5,6,7,8 Some individuals have the ability to immediately alter characteristics in response to new environmental conditions. Behavioral changes, such as changes in foraging, habitat use, or predator avoidance, can provide an early indication of climate change impacts because they are often observable before other impacts are apparent.6
However, some immediate responses to environmental conditions are not transmitted to the next generation. Ultimately, at least some evolutionary response is generally required to accommodate long-term, directional change.9 Although relatively fast evolutionary changes have been documented in the wild,10,11,12 rapid environmental changes can exceed the ability of species to track them.13 Thus, evidence to date suggests that evolution will not fully counteract negative effects of climate change for most species. Importantly, many human-caused stressors, such as habitat loss or fragmentation (Figure 7.2) (see also Ch. 5: Land Changes, “State of the Sector” and KM 2), reduce the abundance as well as the genetic diversity of populations. This in turn compromises the ability of species and populations to cope with additional disturbances.14
Changes in phenology: The timing of important biological events is known as phenology and is a key indicator of the effects of climate change on ecological communities.16,17,18,19 Many plants and animals use the seasonal cycle of environmental events (such as seasonal temperature transitions, melting ice, and seasonal precipitation patterns) as cues for blooming, reproduction, migration, or hibernation. Across much of the United States, spring is starting earlier in the year relative to 20th-century averages, although in some regions spring onset has been delayed (Figure 7.3) (see also Ch. 1: Overview, Figure 1.2j).20,21,22 In marine and freshwater systems, the transition from winter to spring temperatures23 and the melting of ice24 are occurring earlier in the spring, with significant impacts on the broader ecosystem. Phytoplankton can respond rapidly to such changes, resulting in significant shifts in the timing of phytoplankton blooms and causing cascading food web effects (Ch. 9: Oceans, KM 2).19,24
One emerging trend is that the rate of phenological change varies across trophic levels (position in a food chain, such as producers and consumers),25,26 resulting in resource mismatches and changes to species interactions. Migratory species are particularly vulnerable to phenological mismatch if their primary food source is not available when they arrive at their feeding grounds or if they lack the flexibility to shift to other food sources.27,28,29
Changes in range: Climate change is resulting in large-scale shifts in the range and abundance of species, which are altering terrestrial, freshwater, and marine ecosystems.2,30,31,32,33 Range shifts reflect changes in the distribution of a population in response to changing environmental conditions and can occur as a result of directional movement or different rates of survival (Ch. 1: Overview, Figure 1.2h). The ability of a species to disperse affects the rate at which species can shift their geographic range in response to climate change and hence is an indicator of adaptive capacity.34 Climate change has led to range contractions in nearly half of studied terrestrial animals and plants in North America; this has generally involved shifts northward or upward in elevation.35 High-elevation species may be more exposed to climate change than previously expected36 and seem particularly affected by range shifts.37 In marine environments, many larval and adult fish have also shown distribution shifts—primarily northward, but also along coastal shelves and to deeper water—that correspond with changing conditions.38
Species vary in the extent to which they track different aspects of climate change (such as temperature and precipitation),39,40,41 which has the potential to cause restructuring of communities across many ecosystems. This variation is increasingly being considered in research efforts in order to improve predictions of species range shifts.42,43,44 Finally, habitat fragmentation and loss of connectivity (due to urbanization, roads, dams, etc.) can prevent species from tracking shifts in their required climate; efforts to retain, restore, or establish climate corridors can, therefore, facilitate movements and range shifts.18,45,46,47
Climate-driven changes in ecosystems derive from the interacting effects of species- and population-level responses, as well as the direct impacts of environmental drivers. Since NCA3, there have been advances in our understanding of several fundamental ecosystem properties and characteristics, including: primary production, which defines the overall capacity of an ecosystem to support life; invasive species; and emergent properties and species interactions. Particular ecosystems that are experiencing specific climate change impacts, such as ocean acidification (Ch. 9: Oceans), sea level rise (Ch. 8: Coastal, KM 2), and wildfire (Ch. 6: Forests, KM 1), can be explored in more detail in sectoral and regional chapters (see also Ch. 1: Overview, Figures 1.2i, 1.2g, and 1.2k).
Changing primary productivity: Almost all life on Earth relies on photosynthetic organisms. These primary producers, such as plants and phytoplankton, are responsible for producing Earth’s oxygen, are the base of most food webs, and are important components of carbon cycling and sequestration. Diverse observations suggest that global terrestrial primary production has increased over the latter 20th and early 21st centuries.48,49,50,51 This change has been attributed to a combination of the fertilizing effect of increasing atmospheric CO2, nutrient additions from human activities, longer growing seasons, and forest regrowth, although the precise contribution of each factor remains unresolved (Ch. 6: Forests, KM 2; Ch. 5: Land Changes, KM 1).50,51,52 Regional trends, however, may differ significantly from global averages. For example, heat waves, drought, insect outbreaks, and forest fires in some U.S. regions have killed millions of trees in recent years (Ch. 6: Forests, KM 1 and 2).
Marine primary production depends on a combination of light, which is prevalent at the ocean’s surface, and nutrients, which are available at greater depths. The separation between surface and deeper ocean layers has grown more pronounced over the past century as surface waters have warmed.53 This has likely increased nutrient limitation in low- and midlatitude oceans. Direct evidence for declines in primary productivity, however, remains mixed.54,55,56,57,58,59,60
Invasive species: Climate change is aiding the spread of invasive species (nonnative organisms whose introduction to a particular ecosystem causes or is likely to cause economic or environmental harm). Invasive species have been recognized as a major driver of biodiversity loss.61,62,63 The worldwide movement of goods and services over the last 200 years has resulted in an increasing rate of introduction of nonnative species globally,64,65 with no sign of slowing.66 Global ecological and economic costs associated with damages caused by nonnative species and their control are substantial (more than $1.4 trillion annually).61 The introduction of invasive species, along with climate-driven range shifts, is creating new species interactions and novel ecological communities, or combinations of species with no historical analog.67,68 Climate change can favor nonnative invading species over native ones.69,70 Extreme weather events aid species invasions by decreasing native communities’ resistance to their establishment and by occasionally putting native species at a competitive disadvantage, although these relationships are complex and warrant further study.71,72,73,74 Climate change can also facilitate species invasions through physiological impacts, such as by increasing per capita reproduction and growth rates.69,75,76
Changing species interactions and emergent properties: Emergent properties of ecosystems refer to changes in the characteristics, function, or composition of natural communities. This includes changes in the strength and intensity of interactions among species, altered combinations of community members (known as assemblages), novel species interactions, and hybrid or novel ecosystems.78 There is mounting evidence that in some systems (such as plant–insect food webs), higher trophic levels are more sensitive than lower trophic levels to climate-induced changes in temperature, water availability,79,80,81 and extreme events.82 Predator responses to these stressors can lead to higher energetic needs and increased consumption,83 shifts or expansion in seasonal demand on prey resources, or resource mismatches.84,85 Some predators may be able to adapt to changing conditions by switching to alternative or novel food sources86 or adjusting their behavior to forage in cooler habitats to alleviate heat stress.87 Such changes at higher trophic levels directly affect the energetic demands and mortality rates of prey88 and have important impacts on ecosystem functioning, such as biological activity and productivity (as indicated by community respiration rates),89 and on the flow of energy and nutrients within communities and across habitats. For example, in Alaska, brown bears have recently altered their preference for salmon to earlier-ripening berries, changing both salmon mortality rates and the transfer of oceanic nutrients to terrestrial habitats.90 Warming is changing community composition, as species with lower tolerances to disturbance91 and nonoptimal conditions92 are outcompeted. Declining diversity in life histories as a result of climate change is also expected to result in more uniform, less varied population structures, in turn resulting in increased competition and potentially contributing to local extinctions and reduced community resilience.29,93
Increasing evidence since NCA3 demonstrates that climate change continues to affect the availability and delivery of ecosystem services, including changes to provisioning, regulating, cultural, and supporting services. Humans, biodiversity, and ecosystem processes interact with each other dynamically at different temporal and spatial scales.94 Thus, the climate-related changes to ecosystems and biodiversity discussed in this and other chapters of this report all have consequences for numerous ecosystem services. In addition, these climate-related impacts interact with other non-climate stressors, such as pollution, overharvesting, and habitat loss, to produce compounding impacts on ecosystem services.95,96
The adaptive capacity of human communities to deal with these changes will partly determine the magnitude of the resulting impacts to ecosystem services. For example, the shifting range of fish stocks (Ch. 9: Oceans, KM 2), an example of a provisioning ecosystem service, may require vessels to travel further from port, invest in new fishing equipment, or stop fishing altogether; each of these responses implies increasing levels of costs to society.97 A reduction in biodiversity that impacts the abundance of charismatic and aesthetically valuable organisms, such as coral reefs, can lead to a reduction in wildlife-related ecotourism and may result in negative economic consequences for the human communities that rely on them for income.3 Climate change can also impact ecosystem services such as the regulation of climate and air, water, and soil quality.98 Although climate change impacts on ecosystem services will not be uniformly negative, even apparently positive impacts of climate change can result in costly changes. For example, in areas experiencing longer growing seasons (Ch. 10: Ag & Rural, KM 3), farmers would need to shift practices and invest in new infrastructure (Ch. 12: Transportation, KM 1 and 2) in order to fully realize the benefits of these climate-driven changes. Moreover, different human communities and segments of society will be more vulnerable than others based on their ability to adapt; jurisdictional borders, for instance, may limit human migration in response to climate change.99
Oyster reefs exemplify the myriad ways in which ecosystem components support ecosystem services, including water quality regulation, nutrient and carbon sequestration, habitat formation, and shoreline protection. These services are reduced when oyster reefs are impacted by climate change through, for example, sea level rise100,101 and ocean acidification.102 A recent study estimated that the economic value of the non-harvest ecosystem services provided by oyster reefs ranges from around $5,500 to $99,400 (in 2011 dollars) per year per hectare. The value of shoreline protection varied depending on the location but had the highest possible value of up to $86,000 per hectare per year (in 2011 dollars).103 Coral reefs, which provide shoreline protection and support fisheries and recreation, are also threatened by ocean warming and acidification. The loss of recreational benefits associated with coral reefs in the United States is projected to be $140 billion by 2100 (in 2015 dollars) under a higher scenario (RCP8.5) (Ch. 9: Oceans, KM 1).104
All regions and ecosystems of the United States are experiencing the impacts of climate change. However, impacts will vary by region and ecosystem: not all areas will experience the same types of impacts, nor will they experience them to the same degree (Ch. 2: Climate, KM 5 and 6). Regional variation in climate impacts are covered in detail in other sectoral and regional chapters of the Fourth National Climate Assessment. However, in Figure 7.5, a wide range of regional examples are provided at multiple scales to demonstrate the varied ways in which biodiversity, ecosystems, and ecosystem services are being impacted around the United States.
Click on a region for examples of impacts to biodiversity, ecosystems, and ecosystem services.
Climate change continues to alter species’ characteristics, phenologies, abundances, and geographical ranges, but not all species are affected equally. Generalists (species that use a wide range of resources) are better able to adapt to or withstand climate-driven changes,90 while specialists (species that depend on just a few resources), small or isolated populations, and species at the edge of their ranges have limited abilities to adjust to unfavorable or new environmental conditions.27,105,106
Species’ survival depends on the presence and flexibility of traits to adapt to climate change; traits may occur within the existing genetic structure of a population (that is, plasticity) or arise through evolution. Changes in individual characteristics are one of the most immediate mechanisms an organism has to cope with environmental change, and species have demonstrated both plastic and evolutionary responses to recent climate change.9,10,11,12 For example, snowshoe hares rely on coat color to camouflage them from predators, but earlier spring snowmelts have increased the number of white animals on snowless backgrounds. While individual animals have exhibited some ability to adjust the rate of molting, they have limited capacity to adjust the timing of color change.9 Consequently, evolution in the timing of molting may be needed to ensure persistence under future climate conditions.
Shifts in range and phenology also indicate species’ ability to cope with climate change through the presence and flexibility of particular traits (for example, behavior and dispersal abilities). In studies spanning observational periods of up to 140 years, terrestrial animal communities have shifted ranges an average of 3.8 miles per decade.107 Larger shifts of up to 17.4 miles per decade have been recorded for marine communities17,38,108 in observations spanning up to a century. Birds in North America have shifted their ranges in the last 60 years, primarily northward.109 Pollinators have been affected, too, with decreases in abundance and shifts upslope seen over the past 35 years.110 Models suggest that shifts in species’ ranges will continue, with freshwater and marine organisms generally moving northward to higher latitudes and to greater depths and terrestrial species moving northward and to higher elevations.111,112 However, this capacity to adapt to climate change through range shifts is not infinite: many organisms have limited dispersal ability and newly suitable habitat in which to colonize, and all organisms are limited in the range of environments to which they can adapt.
Shifts in phenology have been well documented in terrestrial, marine, and freshwater systems.113 As with range shifts, changes to phenology are expected to continue as the climate warms.114 Changes in phenology can have significant impacts on ecosystems and the services they provide, as evidenced by shifts in the production and phenology of commercially important marine groundfish,38,115 inland fish species,116 migratory fish such as salmon,10,117,118 and invertebrates such as northern shrimp and lobster (Ch. 18: Northeast, KM 2 and Box 18.1).119,120
The many components of climate change (for example, rising temperatures, altered precipitation, ocean acidification, and sea level rise) can have interacting and potentially opposing effects on species and populations, which further complicates their responses to climate change.41,121,122 In addition, species are responding to many other factors in addition to climate change, such as altered species interactions and non-climate stressors such as land-use change (Ch. 5: Land Changes, “State of the Sector” and KM 2) and resource extraction (for example, logging and commercial fishing).
Compounding stressors can result in species lagging behind temperature change and occupying nonoptimal conditions.123 For example, iconic species of salmon have lost access to much of their historical habitat due to barriers or degradation caused by pollution and land-use change, leading to significant losses in spawning and cold water habitats that could have supported adaptation and provided refuge against increasing climate impacts.124,125
The rate and magnitude of climate impacts can exceed the abilities of even the most adaptable species and potentially lead to tipping points, which result in abrupt system changes and local extinctions.126,127 For example, climate change appears to have contributed to the local extinction of populations of the Federally Endangered Karner blue butterfly in Indiana (Ch. 21: Midwest, KM 3). Compounded climate stress arises when populations with limited capacity to adapt also experience high exposure to climate change, posing substantial risks to certain ecosystems and the services they provide to society. Bull trout in the Northwest, for example, show the least genetic diversity in the same regions where summer temperature and winter streamflows are projected to be the highest due to climate change (Figure 7.2).15 Further decline of salmon and trout will impact a cherished cultural resource, as well as popular sport and commercial fisheries. Identifying the most vulnerable species and understanding what makes them relatively more at risk than other species are, therefore, important considerations for prioritizing and implementing effective management actions.35,127,128,129
Climate change impacts also occur at the ecosystem scale, changing fundamental ecosystem characteristics, properties, and related ecosystem services; altering important trophic relationships; and affecting how species and populations interact with each other.
Because primary producers are the base of the food web, climate impacts to primary production can have significant effects that radiate throughout the entire ecosystem. While climate models project continued increases in global terrestrial primary production over the next century,130,131 these projections are uncertain due to a limited understanding of the impacts of continued CO2 increases on terrestrial ecosystem dynamics;132,133,134 the potential effects of nutrient limitation;135 the impacts of fire136 and insect outbreaks;137 and an incomplete understanding of the impacts of changing climate extremes.138,139 Furthermore, even without these factors, projections suggest decreasing primary production in many arid regions due to worsening droughts, similar to responses observed in the Southwest United States in recent years.140,141,142 Modest to moderate declines in ocean primary production are projected for most low- to midlatitude oceans over the next century,143,144,145 but regional patterns of change are less certain.60,143,145 Most models project increasing primary productivity in the Arctic due to decreasing ice cover. This trend is supported by satellite-based observations of the primary productivity–ice cover relationship over the last 10–15 years.146,147,148 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.149,150,151 For example, small changes in marine primary productivity are likely to result in even larger changes to the biomass of fisheries catch.152
Varying phenological responses to climate change can also impact the food web and result in altered species interactions and resource mismatch.17,153 Such mismatches can decrease the fitness of individuals, disrupt the persistence and resilience of populations, alter ecosystems and ecosystem services, and increase the risk of localized extinctions.16,26,113,154,155 In marine ecosystems, rapid phenological changes at the base of the food web can create a mismatch with consumers,156 disrupting the availability of food for young fish and changing the food web structure.24,156 In both terrestrial and aquatic environments, migratory species face the potential for resource mismatch. For example, a majority of migratory songbirds in North America have advanced their phenology in response to climate change, but for several species, such as the yellow-billed cuckoo and the blue-winged warbler, these changes have been outpaced by advancing vegetation in their breeding grounds and stopover sites.28 The resulting mismatch between consumers and their food or habitat resources can result in population declines.155
In addition to changes in productivity and phenology, novel species interactions as a result of climate change can cause dramatic and surprising changes. For example, range expansions of tropical herbivorous fishes have changed previously kelp-dominated systems into kelp-free sites.157 These novel combinations of species are expected to outcompete and potentially eliminate some native species, posing a significant threat to the long-term stability of iconic ecosystems and the services they provide.157 A recent survey of 136 freshwater, marine, and terrestrial studies suggests that species interactions are often the immediate cause of local extinctions related to climate change.158
Climate change impacts to ecosystem properties are difficult to assess and predict because they arise from multiple and complex interactions across different levels of food webs, habitats, and spatial scales. Modeling and experimental studies are some of the few ways to assess complicated ecological interactions, especially in marine systems where direct observations of plants, fish, and animals are difficult.67,159,160,161 There is strong consensus that trophic mismatches and asynchronies will occur, yet these are mostly predicted consequences, and few examples have been documented.13,84,162,163 While theory and management principles for novel ecosystems are new, strongly debated, and largely descriptive, they are also crucial for understanding and anticipating widespread ecosystem changes in the future.164,165,166 For example, it remains largely uncertain which members of historical ecological communities and ecosystems will adapt in place or move into new locations to follow optimal ecological and environmental conditions.167 Such uncertainties complicate management decisions regarding where and when human intervention is advisable to assist persistence.
It is also unclear how the restructuring of ecosystems will manifest in terms of the functioning and delivery of ecosystem services.167,168 For example, along the Northeast Atlantic coast, native fiddler and blue crabs have shifted their ranges north and are now found in New England coastal habitats where they were previously absent.169,170 These two species join an assemblage of native and invasive crab species, which are responding to changes in environmental and ecological conditions in different ways. In some locations, purple marsh crabs are benefiting from lower abundances of blue crabs and other predators, in part due to overfishing; this results in population explosions of purple marsh crabs that damage marsh habitats through herbivory (plant eating) and burrowing activities.171 Because salt marshes provide a range of ecosystem services, including coastal protection, erosion control, water purification, carbon sequestration, and maintenance of fisheries, marsh destruction can negatively impact human communities.172 Thus, climate impacts to ecosystems can have important consequences for ecosystem services and the people who depend on them.
Climate change is affecting the availability and delivery of ecosystem services to society through altered provisioning, regulating, cultural, and supporting services.95
A reduced supply of critical provisioning services (food, fiber, and shelter) has clear consequences for the U.S. economy and national security and could create a number of challenges for natural resource managers.104 Although an extended growing season resulting from phenological shifts may have positive effects on the yield and prices of particular crops,173 net changes to agricultural productivity will vary regionally (Figure 7.6) and will be affected by other climate change impacts, such as drought and heat stress.174,175 In addition, early springs with comparatively late (but climatically normal) frosts can directly affect plant growth and seed production and indirectly disrupt ecosystem services such as pollination. By the middle of this century, early onset of spring could occur one out of every three years; however, if the date of last freeze does not change at the same rate, large-scale plant damage and agricultural losses, 176,177,178 as well as changes to natural resource markets,119 are possible. Shellfish harvests are also projected to decline significantly through the end of the century due to ocean acidification, with cumulative estimated losses of $230 million under RCP8.5 and $140 million under RCP4.5 (discounted at 3%) (see the Scenario Products section of App. 3 for more information on scenarios).104
The degree to which climate change alters species’ ranges can create jurisdictional conflict and uncertainty.97 For example, fisheries management is typically done within defined boundaries and governed by local or international bodies, and terrestrial resource extraction typically occurs on private property or leased public lands with legislated boundaries.180 Local extinctions and range shifts of marine species have already been documented (Ch. 9: Oceans, KM 2), as species’ ranges shift with changing habitat and food conditions. Some species have moved out of historical boundaries and seasonal areas and into places that have no policy, management plan, or regulations in place to address their presence and related human use. Furthermore, unique life histories and genetic resources will likely be lost altogether as range shifts and the spread of invasive species interact with ecological complexity. Examples include loss of genetic diversity and the evolution of traits that increase rates of dispersal.181,182 Managers may also need to respond to an alteration in the timing of spawning and migration of fish species in order to avoid overly high levels of fish mortality.183
Climate change can affect important regulating services such as the capture and storage of carbon,126 which can help reduce greenhouse gas concentrations in the atmosphere and thereby contribute to climate change mitigation.184 Climate change impacts, such as changes to the range and abundance of vegetation, to the incidence of wildfire and pest outbreaks, and to the timing and species composition of phytoplankton blooms, can all impact carbon cycling and sequestration (Ch. 5: Land Changes, KM 1; Ch. 6: Forests, KM 2; Ch. 9: Oceans, KM 2; Ch. 29: Mitigation, Box 29.1). Disease regulation is also an important ecosystem service that can be impacted by climate change. Pests and diseases are expected to expand or shift their ranges as the climate warms, and the evolution of immune responses will be important for both human and animal health (Ch. 18: Northeast, KM 4; Ch. 21: Midwest, KM 4; Ch. 26: Alaska, KM 3; Ch. 6: Forests, KM 1; Ch. 14: Human Health, KM 1).185,186 Other examples of regulating ecosystem services that could be impacted by climate change include coastal protection from flooding and storm surge by natural reefs (Ch. 8: Coastal, KM 2),187 the supply of clean water (Ch. 3: Water, KM 1)188 and controls on the timing and frequency of wildfires (Ch. 6: Forests, KM 1).189
Some cultural ecosystem services are also at risk from climate change. By the end of the century (2090), cold water recreational fishing days are predicted to decline, leading to a loss in recreational fishing value of $1.7 billion per year under RCP4.5 and $3.1 billion per year under RCP8.5 by 2090.104 Climate change is also predicted to shorten downhill and cross-country ski seasons.104 In northwestern Wyoming and western Montana, the cross-country ski season is projected to decline by 20%–60% under RCP4.5 and 60%–100% under RCP8.5 by 2090 (Ch. 22: N. Great Plains, KM 3). Climate change also threatens Indigenous peoples’ cultural relationships with ancestral lands (Ch. 15: Tribes, KM 1). In addition, biodiversity and ecosystems are valuable to humans in and of themselves through their “existence value,” whereby people derive satisfaction and value simply from knowing that diverse and healthy ecosystems exist in the world.190 For example, a recent study found that the average U.S. household is willing to pay $33–$73 per year for the recovery or delisting of one of eight endangered or threatened species they studied.191 However, climate change could have a positive impact on recreational activities that are more popular in warmer weather. For example, demand for biking, beachgoing, and other recreational activities has been projected to increase as winters become milder.95,192
Finally, 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.48,193 Novel species assemblages associated with climate change can result in changes to energy and nutrient exchange (for example, altered carbon use in streams as new detritus-feeding or predator communities emerge) within and among ecological communities.193 Because supporting services underpin all other ecosystem services, climate-induced changes to these services can have profound effects on human well-being.
Climate change is affecting valued resources and ecosystem services in complex ways, as well as challenging existing management practices. While natural resource management has traditionally focused on maintaining or restoring historical conditions, these goals and strategies may no longer be realistic or effective as the climate changes.194 Climate-driven changes are most effectively managed through highly adaptive and proactive approaches that are continually refined to reflect emerging and anticipated impacts of climate change (Ch. 28: Adaptation, Figure 28.1).194 Decision support tools, including scenario planning195,196,197 and structured decision-making,198 can help decision-makers explore broad scenarios of risk and develop actions that account for uncertainty, optimize tradeoffs, and reflect institutional capacity.
Systems that are already degraded or stressed from non-climate stressors have lower adaptive capacity and resilience (Ch. 28: Adaptation, KM 3); therefore, some of the most effective actions that managers can take are to strategically restore and conserve areas that support valued species and habitats. However, these actions will be most effective when they consider future conditions in addition to historical targets.4 New guidance on habitat restoration actions that can help to reduce impacts from climate change199,200,201 is now being incorporated into regional and local restoration plans (Ch. 24: Northwest, KM 2). Limiting the spread of invasive species can also help maintain biodiversity, ecosystem function, and resilience.202,203,204 In 2016, the U.S. Federal Government recommended specific management actions for the early detection and eradication of invasive species.205
Understanding and reestablishing habitat connectivity across terrestrial, freshwater, and marine systems are other key components in helping ecosystems adapt to changing environmental conditions.45,46,201,206 Identifying and conserving climate change refugia (that is, areas relatively buffered from climate change that enable persistence) in ecological corridors can help species stay connected.207,208 For example, areas of particularly cold water have been identified in the Pacific Northwest that, if well-connected and protected from other stressors, could act as critical habitat for temperature-sensitive salmon and trout populations.209,210,211 More active approaches like assisted migration, whereby species are actively moved to more suitable habitats, and genetic rescue, where genetic diversity is introduced to improve fitness in small populations,212 may be considered for species that have limited natural ability to move or that face extreme barriers to movement due to habitat fragmentation and development (Ch. 5: Land Changes, “State of the Sector” and KM 2).124 For any assisted migration, there could be unforeseen and unwanted consequences. Developing policies to analyze and manage the potential consequences of assisted migration would not guarantee successful outcomes, but is likely to minimize unintended consequences.213,214
Climate change impacts have been incorporated into national and regional management plans that seek to mitigate harmful impacts and to address future management challenges, while also accounting for other non-climate stressors. Federal agencies with responsibilities for natural resource management are increasingly considering climate change impacts in their management plans, and many have formulated climate-smart adaptation plans for future resource management (such as the National Oceanic and Atmospheric Administration [NOAA], National Park Service [NPS], and U.S. Fish and Wildlife Service [USFWS]).215,216,217,218,219,220 For example, the National Marine Fisheries Service recognizes climate change as a specific threat to marine resources, has developed regional action plans (e.g., Hare et al. 2016221), and is undertaking regional vulnerability analyses to incorporate climate change impacts in decision-making.129,215,217 Agencies within the Department of the Interior are also increasingly developing and using climate change vulnerability assessments as part of their adaptation planning processes.222 For example, USFWS has considered climate change in listing decisions, biological opinions, and proposed alternative actions under the Endangered Species Act (e.g., USFWS 2008, 2010223,224). In addition, federal agencies have been challenged to develop policies and approaches that consider ecosystem services and related climate impacts within existing planning and decision frameworks.225 For example, ecosystems can be managed to help mitigate climate change through carbon storage on land and in the oceans (Ch. 29: Mitigation, Box 29.1; Ch. 5: Land Changes, KM 1)200,226,227 and to buffer ocean acidification,228 which could help reduce pressure on ecosystems. USFWS has been acquiring and restoring ecosystems to increase biological carbon sequestration since the 1990s.229
At the local and regional levels, efforts to restore ecosystems, increase habitat connectivity, and protect ecosystem services are gaining momentum through collaborations among state and tribal entities, educational institutions, nongovernmental organizations, and partnerships. For example, the Great Lakes Climate Adaptation Network, NOAA’s Great Lakes Integrated Sciences and Assessments Program, the Huron River Watershed Council, and five Great Lakes cities worked together to develop a vulnerability assessment template that incorporates adaptation and climate-smart information into city planning (Ch. 21: Midwest, Case Study “Great Lakes Climate Adaptation Network”). Significant work remains, however, before climate change is comprehensively addressed in natural resource management at local and national scales. Improved projections of climate impacts at local and regional scales would likely improve ecosystem management, as would predictive models to inform effective adaptation strategies.230,231,232 Yet such tools are often hampered by a lack of sufficient data at the appropriate scale.232 In addition, institutional barriers (such as a focus on near-term planning, fixed policies and protocols, jurisdictional restrictions, and an established practice of managing based on historical conditions) have constrained agencies from comprehensively accounting for climate impacts.194 Finally, more rigorous evaluation of adaptation efforts would allow managers to fully assess the effectiveness of proposed adaptation measures.194
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.