Ecosystem changes can be driven by physical factors (e.g., thermal stress), biological responses (e.g., changing ranges), or both, often interacting with stressors from human activities. Multiple stressors, both gradual and episodic, can have complex interactive or amplifying effects on ecosystems (Figure 8.4);17,18 for example, severe hurricanes can heighten forest vulnerability to drought and/or fire.19,20
Many ecosystems are at increased risk of ecosystem tipping points (where rapid and unpredictable conversions to new states occur),22 although it is difficult to predict how, where, and when these changes will occur.23,24 Transformative changes in the composition, structure, function, and other properties of ecosystems result in a new stable state, or regime, with a different combination of species and communities, often resulting in reduced biodiversity and ecosystem services.25,26 Restoring an ecosystem may be difficult or even impossible if a critical threshold or tipping point is crossed and a different system emerges, because changing or restoring the drivers that led to the altered state may not result in a return to the original state (Figure 8.5).27
Ecosystem changes can be gradual or relatively abrupt31 and depend in part on ecosystem characteristics and key species.32 Ecosystems with immobile or long-lived species such as corals or trees can often exhibit abrupt responses because they have limited capacity to keep pace.33,34,35 Ecosystems with higher biodiversity have more species interactions and often exhibit slow changes at first followed by abrupt shifts.15 Multiple stressors can lead to synergistic effects and trigger abrupt changes.36 Examples include the co-occurrence of extreme heat, drought, and invasive grasses (Figure 8.6)22 or wildfires followed by insect infestations (or vice versa; Focus on Western Wildfires).
Vulnerability of ecosystems to climate change depends on exposure to the physical drivers of change and characteristics that affect species’ sensitivity and capacity to adapt.39 Examples of vulnerable ecosystems experiencing transformation are increasingly common (Figure 8.7). There is evidence that ecosystems with higher biodiversity are more resilient in the face of climate change,40,41 indicating that better protection and reduced fragmentation and degradation of ecosystems are potential climate-adaptation strategies.42
Identifying and monitoring species or ecosystem traits that provide early warnings of vulnerability, system-wide decline, or tipping points can assist in reducing risks.26,47,48,49 Numerous long-term monitoring networks (Figure 8.8) have been established in recent decades in direct response to climate and other changes.27,50 Community-led (“citizen”) science efforts such as iNaturalist51 and the USA National Phenology Network,52 alongside community-based monitoring networks53 and Indigenous Knowledge holders (KM 16.3)54 also collect observations across large areas55 and have helped detect altered species distributions, abundances, and phenologies.56,57,58
Climate change and other disturbances that transform ecosystems create growing management challenges.14,59 Building, preserving, or restoring ecosystems is often the most practical and effective resilience strategy;60,61 however, ecosystem transformation may still be inevitable.62 Conventional resource management approaches are often ill-suited for managing uncertainties and related trade-offs.63,64 In contrast, adaptive management iteratively plans, implements, and modifies strategies for managing resources under uncertainty. Successful adaptive management requires an overarching adaptive governance approach that provides institutional structures and decision-making processes for coordinating efforts across scales,65 managing uncertainties and conflicts,66,67 mobilizing diverse knowledges, and addressing stakeholder interests.68,69,70
Decision frameworks designed to anticipate ecosystem transformation can advance adaptative management processes (Figure 8.9).71 As one example, the Resist–Accept–Direct (RAD) framework helps identify conditions where ecosystem management can resist a trajectory of change, accept change, or direct change toward desired future conditions (Figure 8.9).62,72 To engage the “direct” in their RAD planning, Tetlin National Wildlife Refuge in Alaska is combining scenarios, adaptive management, and adaptive pathway planning to engage managers and stakeholders to explore potential transformations, with one focus specifically on subsistence hunting.73
Climate-related stressors and other drivers of global change, such as land-use change, habitat destruction, and overexploitation, can create significant biodiversity changes and losses (Figure 8.1).76,77 Even short-term extreme events such as heatwaves78,79,80 can generate significant species impacts. For example, coral reefs are threatened by cumulative impacts of ocean warming and acidification, marine heatwaves resulting in bleaching and higher susceptibility to diseases, increasingly powerful tropical cyclones causing loss of structural complexity, hypoxia (low oxygen) events, overfishing, and pollution (Figure 8.10a, b; Box 10.1; KMs 9.2, 10.1).81,82,83,84,85,86 Similarly, wildfires (Focus on Western Wildfires)87 can create risks for some species both directly (Figure 8.10c, d) and indirectly through longer-term habitat changes.88
Compounding the responses of species to extreme events, the timing of seasonal events such as leaf-out, flowering, migration, spawning, phytoplankton blooms, and egg hatching is changing in response to rising winter and spring temperatures and to the altered timing and amount of snowmelt and rainfall (Figures 8.8, A4.13).58,90,91,92 Changes include earlier flowering and maturity in agricultural crops that affect planting and harvest times,93,94,95,96,97 longer and more intense allergy seasons (KM 14.4),98 and increased pest activity.99,100 Changes are most pronounced at high latitudes and elevations and in urbanized areas.101,102 Phenological mismatches emerge when the timing of activities in interacting species changes at different rates, such as food availability shifting to no longer match a dependent organism’s needs.103,104 Phenological changes are also impacting seasonal carbon cycling105 and increasing vulnerability to spring frost damage (App. 4).106 There are significant economic and social impacts of these changes, including tourism impacts and loss of culturally important species.107,108
Elevational and latitudinal range shifts driven by climate change have already occurred for multiple species (Figure 8.11),109,110,111 with range shifts of marine species more responsive and greater in magnitude than terrestrial ones (KM 10.1; Figure A4.12).112 Mountaintop ranges are shrinking as species shift upslope, with high-elevation ones highly vulnerable.113,114 Milder winters and warmer growing seasons are expected to expand ranges for some species.115,116
Conditions can change over very localized scales, creating complex “mosaic” patterns of environmental stressors.117,118,119,120 Climate refugia occur in locations where environmental conditions are changing more slowly than in surrounding areas121 or where local drivers override more regional-scale processes.122 These refugia are expected to support organisms that can repopulate other depleted areas through dispersal via currents or land corridors123 and are therefore a priority for conservation (Figure 8.12).124,125 Identification of the many existing refugia expected to disappear under climate change is crucial.126,127
Understanding species sensitivities to climate impacts and adaptive capacity can help detect ecological tipping points (KM 8.1).131,132 Large-bodied animals (Box 8.1)133 and species occupying polar habitats are particularly at risk of local extinction due to physiological vulnerabilities.134 In contrast, smaller-bodied species often have more widely variable responses to changing conditions (Figure 8.13).
Disease threats to wildlife, plants, and humans have emerged as a significant climate change risk.142,143,144,145,146,147 Climate change promotes range expansions and population growth of disease-spreading (vector) species, increased host susceptibility via stress, and enhanced pathogen transmission (Table 8.1; KM 15.1),148 with major economic consequences.149,150 Diseases often thrive where other stressors are present; prevalence is projected to further increase as populations and ecosystems become stressed from temperature variation and extreme events, changes in habitats, altered migration patterns and ranges, biodiversity loss, and increases in invasive species (KMs 15.1, 30.4; Figure A4.16).151,152,153,154
Pathogen: Virus
Disease | Affected Organisms |
---|---|
West Nile virus | Birds and mammals |
Viral hemorrhagic septicemia virus | Freshwater and marine fish |
White spot syndrome virus | Aquatic crustaceans |
Tomato spotted wilt virus | Plants |
Pathogen: Bacteria
Disease | Affected Organisms |
---|---|
Furunculosis | Trout and salmon |
Enteric red mouth disease | Freshwater and marine fish |
Citrus greening | Plants |
Pathogen: Fungus
Disease | Affected Organisms |
---|---|
White-nose syndrome | Bats |
Chytridiomycosis | Amphibians |
Rapid ‘Ōhi‘a death | Plants |
Armillaria root rot | Plants |
Pathogen: Parasite
Disease | Affected Organisms |
---|---|
Avian malaria | Birds |
Proliferative kidney disease | Salmon |
Brainworm | Moose, elk, caribou |
Seagrass wasting disease | Aquatic plants |
Pathogen: Unknown
Disease | Affected Organisms |
---|---|
Stony coral tissue loss disease | Corals |
White band disease | Corals |
Colony collapse disorder | Bees |
Climate change has created uncertainty about where and how fast invasive species will spread, but there are both observed cases164 and projections showing expected increases.165 For example, cold-sensitive invasive species such as the kudzu vine (Pueraria montana var. lobata) can spread northward with warming.166 Some invasive species are more successful than natives—particularly certain terrestrial plants167 and aquatic species168—because they better tolerate or more rapidly adapt to changing conditions (Figure 8.15). Yet not all invasive species are favored by climate change; many invasive plants and vertebrates may experience decreased ranges while the ranges of many invasive invertebrates and pathogens are expected to increase.169
Natural resource managers are implementing adaptation actions including increasing conservation efforts, reducing habitat fragmentation, protecting wildlife corridors, assisting species migration, and expanding protection activities.174 For example, marine protected areas can reduce non-climate stressors like overfishing and facilitate recovery of populations following extreme events like heatwaves, which then benefits recreational and commercial fishing in surrounding areas (KM 28.2).175 Many states now include climate impacts in state wildlife action plans; for example, Massachusetts has identified habitat patches allowing for movement of the threatened Blanding’s turtle and is creating habitats that balance increased drought and other threats.176,177,178
Managing for connectivity can enhance species climate resilience, particularly for wide-ranging and migratory species.179 Priorities include connecting climate refugia, areas of high diversity,123,180 and current and future habitat types.181 For example, resilience strategies for the saltmarsh sparrow (Ammospiza caudacuta), which has declined dramatically due to rising sea levels, include protection of areas expected to convert into future wetlands, use of runnels and other elevation manipulations, and high-marsh restoration.182,183
Assisted migration has been implemented for at-risk species such as the Laysan albatross, Oʻahu tree snail, relict leopard frog, and wolf (Figure 8.16).184 In the Chippewa National Forest in Minnesota, seeds of tree species native to red pine forests but collected 100–200 km to the south—and thus genetically distinct from local populations—are being planted to test assisted migration.185
While protected areas can help species adapt to climate change, these areas are themselves vulnerable;174,187,188,189 many US protected areas are expected to see major shifts in vegetation communities and other species.190 Further, the existing US protected areas system has low overlap with projected climate refugia;191 extending protection to include future habitat suitability for some species may double costs.192 Given continued range shifts, areas with priority species that draw tourists (e.g., bird watchers) will need to refocus as some species become rarer or disappear,193,194 impacting neighboring communities dependent on tourism revenue.
Conflicts (between humans and with wildlife) arising from climate-driven changes in distribution and availability of species and resources are occurring.195,196 For example, some species are moving out of areas set up to conserve them, and range shifts of fish stocks (including across international boundaries) are causing challenges (KM 10.1).197,198 Some adaptation policies (e.g., translocation of nonhuman species into human communities unwilling to coexist with them) may exacerbate conflicts (KM 17.2).199 Adaptive management that prioritizes both climate change response planning and conflict management can reduce negative outcomes.195,200,201
Ecosystem services provide substantial and often economically important contributions to communities, ranging from direct material benefits like food production and clean water to nonmaterial benefits like recreation (Figure 8.17). However, economic valuation alone does not reflect intrinsic or relational values that people hold toward nature;202,203 for example, Tribal and Indigenous Peoples rely on ecosystems for supplies of culturally valuable food, materials for religious ceremonies, and relational links within communities and among generations (KM 16.1).204,205
There are many adverse climate change effects on ecosystem services,207,208 including reduced water availability for human and agricultural uses (KM 4.1), decreased productivity of crop species due to increased pest infestations (KM 11.1), and losses of hazard-mitigating ecosystems like wetlands and coastal shorelines that provide nursery and nesting habitat, recreation, and aesthetic pleasure (Table 8.2; KM 9.2). However, future trends on ecosystem use and benefits are not always clear. For example, rising temperatures can extend seasonal recreational opportunities, but if daily high temperatures exceed 27°–30°C (80.6°–86°F), recreation tends to decrease.209,210
Further, diminished benefits from ecosystem services can also occur based on other factors.211,212 For example, discriminatory planning practices, housing segregation, and racism have created inequitable distributions of services, leading to communities of color experiencing reduced access to benefits like improved air quality or heat reduction (KM 12.2; Figure 12.6).213,214,215 Lack of access often accompanies other environmental harms (e.g., greater exposure to allergens or risks of green gentrification, the displacement of local residents as environmental benefits improve).216,217 Climate change is expected to exacerbate these impacts207 and create further difficulties in addressing environmental racism, highlighting the need for clear management priorities and recognition of diverse values.218,219
Ecosystem Service | Potential Climate Impacts | Equity Implications |
---|---|---|
Regulation of Natural Hazards | Coastal marsh retreat is projected due to sea level rise and increased storm activity.220 | Flood risks are often inequitably distributed; for example, property damage risks can be disproportionately higher for Black communities.221 |
Physical and Psychological Experiences | Cold-weather recreational opportunities are projected to decline (e.g., fewer skiing days).209,210,222 | Less green space access in low-income communities and communities of color already results in fewer opportunities for recreation.223,224 |
Water Quantity | Changes in precipitation, snowpack, soil moisture, and evapotranspiration are projected to alter surface and groundwater availability (KM 4.1; Figure A4.7). | Drought often has disparate impacts;225 for example, Tribal reservations in the US Southwest with higher agricultural dependence will be particularly impacted.226 |
Regulation of Air Quality | Street trees provide considerable urban air quality benefits but are vulnerable to drought and heat.227 | Existing tree canopy distribution is inequitable, accounting for greater air pollution228,229,230 associated with legacies of redlining.231 |
Food Production (fisheries) | Aquatic systems are experiencing shifts in species ranges, phenologies, distributions, and productivities.232 | Culturally important species, such as Chinook salmon for Pacific Northwest Tribes, are projected to dramatically decline in the future.233 |
Ecosystem-based mitigation and adaptation opportunities are often called nature-based solutions (NBSs) or natural climate solutions (Figure 8.18).234,235 NBSs support biodiversity and can provide other benefits when managed in collaboration with affected communities and use of local knowledge (KM 21.1). For example, coastal wetland restoration provides both mitigation and adaptation benefits by sequestering carbon and decreasing coastal flooding, wave action, and erosion236 while improving water quality and increasing habitat biodiversity (KM 9.3; Focus on Blue Carbon).237 NBS projects are often very cost-effective, spurring new financing options.238,239
Blue carbon refers to carbon captured by marine and coastal ecosystems, such as mangroves, coastal wetlands, and seagrasses. Coastal ecosystems sequester carbon at a much faster rate than terrestrial ecosystems, and the carbon stored belowground can remain in place for decades to millennia if undisturbed by humans or extreme events.
Read MoreEcosystem-based adaptation is a type of NBS aimed at increasing community resilience to climate change through the use of ecosystems.240,241 Examples include protecting and restoring floodplains to help reduce flood impacts242 or helping farmers cope with drought through soil conservation measures.243 There are high returns on investments to restore coastal ecosystems in particular, since US coral reefs provide estimated adaptation benefits of more than $1.8 billion annually (dollar year not provided).244,245 These approaches can also have positive equity benefits when designed with local participation and buy-in through collaborative approaches (KM 31.4).246,247,248,249,250,251
Current and future opportunities for NBSs exist across the US, particularly for mitigation solutions focused on protecting and increasing carbon storage by natural ecosystems (Figures 6.6, 8.19; Focus on Blue Carbon).255 Planning for future protected areas for both climate and biodiversity could emphasize areas that not only hold large amounts of carbon but also help species adapt,256 recognizing the important role that many animal species play in carbon cycling.257 However, NBSs themselves are also vulnerable to rising temperatures, sea level rise, and other climate impacts.258
NBSs that involve restoring degraded ecosystems can improve resilience260 and increase provision of ecosystem services.261 Ideally, restoration is designed to recover a range of potential benefits.262,263 However, multiple services cannot necessarily be maximized simultaneously, as focusing on one ecosystem service at the expense of other benefits leads to trade-offs.264,265,266 Larger-scale restoration efforts are generally more successful when connected to local priorities,267 including their use in addressing environmental inequities (Box 8.2).268
Tribal forestry programs throughout the US provide exemplary models of Indigenous land management practices that showcase Tribes’ ability to balance sustainable environmental stewardship, fulfilling the social, ecological and economic needs of their communities.269 The “anchor forests” concept, in which Tribes are at the center of multiple landownerships and serve as the primary hub for providing forest management infrastructure, is one effective approach. Such initiatives maximize concepts of Tribal sovereignty and Indigenous Knowledge to restore forests at the pace and scale needed to mitigate and adapt to rapid climate change.270 Furthermore, traditional and contemporary Indigenous management practices that support both cultural and spiritual relationships with nature and an equitable climate transition can serve as critical pathways to sustaining ecosystems (KMs 7.3, 16.1).271 Incorporating local knowledge and Indigenous Peoples in the co-development of restoration activities can produce considerable benefits.272
The chapter lead author, coordinating lead author, and agency chapter lead authors discussed the Fourth National Climate Assessment (NCA4) ecosystems chapter and brainstormed topics that had emerged since then or were not well covered. The chapter lead author also pulled out key gaps identified from the US Global Change Research Program assessment review document and public comments. A tentative list was compiled of authors with expertise in ecosystems, biodiversity, and ecosystem services; marine, freshwater, and terrestrial systems covering NCA regions; and ecosystem types. The final author team comprised a mix of federal agency scientists and academic experts with varying experience in assessments and past NCAs. Key Messages were developed by the full author team through virtual meetings from fall 2021 through spring 2022, with additional inputs from a public engagement workshop held in January 2022, in which over 100 people participated virtually to suggest topics for review by the chapter. A Youth Dialogues public engagement workshop was held online in February 2022 in partnership with the Youth Environmental Alliance in Higher Education and Rutgers Climate Institute. Federal agency reviews in summer 2022 provided further suggestions for improvement, as did additional public comments and the National Academies review in spring 2023. At the April 2023 in-person meeting in Washington, DC, the author team collectively discussed the wording and confidence levels for the three Key Messages to ensure consensus around the statements.
Since NCA4, a plethora of research has been published describing how ecosystems are changing or are expected to change further in the face of climate change and other stressors, along with numerous specific species and ecosystem services impacts. The evidence base for this report is therefore heavily weighted to peer-reviewed journal articles published in the last five years.
Climate change, together with other stressors, is driving transformational changes in ecosystems, including loss and conversion to other states, and changes in productivity . These changes have serious implications for human well-being . Many types of extreme events are increasing in frequency and/or severity and can trigger abrupt ecosystem changes . Adaptive governance frameworks, including adaptive management, combined with monitoring can help to prepare for, respond to, and alleviate climate change impacts, as well as build resilience for the future .
Read about Confidence and Likelihood
Many examples of regime shifts resulting from transformative changes are already documented, and the evidence base is strong across multiple ecosystem types,273 including forest transformations to grassland or woodland following increased wildfires; widespread die-off of pinyon pines from drought and bark beetle infestations; and shifts from healthy kelp forests to urchin barrens due to epizootic disease and marine heatwaves in nearshore marine environments.144,274,275,276,277,278,279,280 Overall, regime shifts of temperate ecosystems toward more subtropical ones at their southern limits are expected in response to future decreases in the frequency and intensity of extreme cold events.45 For example, mangrove forests in Florida and along the Gulf Coast are projected to expand northward into present-day salt marshes.43
Systematic biodiversity surveys, digitized museum records, and long-term automated data collection have all demonstrated the importance of multiple methods of monitoring of environmental changes through strong evidence bases.281,282,283,284
The ability to predict ecological responses to changing climate conditions remains a key gap for most ecosystems because of complex interactions among species, the potential for adaptation (through both evolutionary responses and human activity), and the intersection of climate change with other drivers of change.36,285,286 For example, warmer temperatures can lead not only to increased forest regeneration and tree growth but also to increased mortality of older trees through wildfires, insects, and disease, with the resulting net impacts highly uncertain.287 Warmer winters are generally expected to benefit forest pests,288 but complex interactions among pests, their hosts, and other disturbances can make the combined effects more muted than otherwise expected.289,290,291 Recent research suggests that multiple disturbances can have counteracting effects, although patterns are not always clear, and sometimes intensified combined effects (synergies) also occur.292,293
There are a number of gaps in comprehensive, long-term ecological monitoring to detect changes and to predict the risks of future climate change.48 Improved knowledge of biological response mechanisms that drive ecological changes36 will enable better anticipation of ecosystem shifts, especially for systems dominated by long-lived species and where impacts emerge after a time lag;294,295 this makes eliminating monitoring gaps (e.g., in Arctic and ocean regions) critical. Community monitoring programs are promising but can be biased (e.g., lack of uniform sampling) toward particular regions or species.296
While adaptive management is widely considered an effective approach for managing uncertainty through learning in order to conserve, manage, and restore ecosystems and species populations,297 successful implementation is limited by the lack of effective monitoring mechanisms,298 challenges in dealing with uncertainty, and lack of appropriate institutional mechanisms for its implementation, among other problems.299,300,301,302 As a result, an adaptive governance approach is increasingly understood as a broader and more promising mechanism for addressing the social and institutional requirements of adaptive management while also facilitating social–ecological transformation.300,303 However, the adaptive governance approach also has its own conceptual and implementation challenges that need to be addressed in order to enhance success, given insufficient evidence on effective implementation298 and questions about its capacity to bring about transformational changes.304 There is also potential for undesirable outcomes, such as inadequate consideration of power and social equity issues.305,306,307,308 Moreover, there are gaps in research on enhancing the transition process toward adaptive management and governance and associated outcomes,309 as well as lack of clarity on the synergies and trade-offs among determinants of the capacity for adaptation and transformation.310,311
A growing body of empirical field studies and monitoring programs shows that climate change, in concert with other stressors, is driving transformational changes across many ecosystems and that changes will accelerate with continued warming (very likely, high confidence). Given the growing impacts of ecosystem change, the serious implications for human well-being were also considered very likely, and the authors assessed high confidence, given the empirical studies across multiple ecosystems (i.e., not just projections) showing that a range of well-being impacts are already being experienced across economic, cultural, and social systems. As Chapter 2 has indicated, extreme events are increasing in frequency and/or severity, and these events are more frequently implicated in abrupt ecosystem changes; but because of limited studies examining the direct correlation of extreme events on abrupt ecosystem transformations, the authors assessed only medium confidence. The authors also note that adaptive governance frameworks, adaptive management, and monitoring all play a role in helping to cope with climate changes; but given the paucity of evidence of long-term impacts of adaptive governance, the authors assessed only medium confidence.
The interaction of climate change with other stressors is causing biodiversity loss, changes in species distributions and life cycles, and increasing impacts from invasive species and diseases, all of which have economic and social consequences . Future responses of species and populations will depend on the magnitude and timing of changes, coupled with the differential sensitivity of organisms; species that cannot easily relocate or are highly temperature sensitive may face heightened extinction risks . Identification of risks (e.g., extreme events) will help prioritize species and locations for protection and improve options for management .
Read about Confidence and Likelihood
Shifts in species ranges in response to changing climate occur across a wide range of species and are expected to accelerate.312,313 The evidence base is strong across a wide range of marine, plant, invertebrate, reptile, bird, and mammal species; selected examples are shown in Figure 8.11, but many more exist. Further, there is strong evidence for the patterns of range shifts differing among types of species; for example, multiple studies have shown that marine species have expanded their ranges more readily than terrestrial species, with shifts in distributions occurring more quickly as well,314,315 whereas terrestrial species tend to have greater behavioral adaptations and less physiological sensitivity to temperature changes.316,317,318
The evidence base of documented responses in the timing of life cycles to climate change is strong, ranging from earlier flowering dates in many parts of the country, to shifts in hibernation of mammals, to timing of egg laying of frogs.319,320 Very rapid changes can be easily observed, for example, in short-lived plants that have high turnover rates and more rapid genetic adaptation,321 lending strength to the evidence base.
Long-term studies (i.e., decades) are needed to discern the fingerprints of climate change on long-lived animals,322 which can be challenging. But some impacts are in evidence; for example, sea level rise is expected to impact nesting site availability and quality for sea turtles, while warming temperatures can affect sex ratio of offspring.323,324 Refugia have potential to mitigate some extinction risks for species able to take advantage of them, but the evidence base is fairly new. Further, emerging modeling studies have indicated that these areas, too, are at risk; for example, Ebersole et al. (2020)127 found that under a 4°C (7.2°F) warming scenario, there was a >50% probability that refugia for freshwater fish species would decrease in area by 42%–77% by 2070.
Disease risks are occurring as a result of many factors and across different hosts and pathogens; given the large number of potential risks, meta-analyses have been helpful in providing overviews of the evidence base. One comprehensive review of infectious diseases spread between humans and animals found that 58% of diseases worldwide have been exacerbated by climate change (e.g., warming, altered precipitation, and floods).154 Only 16% of diseases were diminished by climate change. A global analysis of thousands of wildlife populations indicated that climate warming exacerbates wildlife disease throughout the temperate zone worldwide and is expected to increase wildlife disease in the United States.325 A different global analysis of 6,801 ecological assemblages demonstrated that human-dominated ecosystems strongly favored animal species that host human disease pathogens while decreasing the presence of non-host animals,326 a strong evidence base for the finding that stressed ecosystems tend to experience more disease risk.153 Many empirical examples of ongoing disease outbreaks—e.g., fish kills and large-scale coral disease outbreaks following coral bleaching events—have increased in number and are evidence of perturbed aquatic systems where disease stresses are exacerbated by warming.144,146 The well-documented catastrophic declines in amphibian populations caused by the invasive chytrid fungus Batrachochytrium dendrobatidis have also been well linked to warming conditions.327
The speed and extent of some species range shifts remain uncertain. Climate envelope models use current relationships among species ranges and climatic characteristics to project how ranges may shift in the face of climate change,328 yet they necessarily assume that climate is the main constraint on ranges and that species rapidly respond. In reality, species responses can be slowed and limited by dispersal ability, natural and human-created barriers, and species interactions.329,330
Moreover, climate change is expected to present organisms with novel environmental conditions, making predictions based on historical relationships problematic.331 Specifically, improving such predictions would require a better understanding of the degree to which range shifts occur due to longer-term climatic changes versus periodic extreme weather events such as heatwaves brought on by those climatic changes.86
While climate refugia are increasingly discussed in the literature, they are themselves vulnerable to climate impacts, and there is uncertainty about their persistence and resilience.126,127
The individual and variable responses of species to climate change is expected to disrupt important biological interactions. Many risks posed by emerging mismatches among interacting species remain unclear,332 as do needed management responses to reduce economic and social impacts.
Impacts of climate change on species health are complex and difficult to generalize across systems;291 for example, the role of climate change among other drivers of the spread of tick-borne diseases, like changes in land use or human behavior, remains a topic of some debate.152,156
Studies showing that invasives could be limited in response to climate change are based mostly on studies of terrestrial species whose range shifts are often limited by oceans,169 indicating that more research is needed on different types of species to improve projections.
There is high confidence that the interaction of climate change with other stressors will very likely lead to biodiversity loss, changes in species distribution and life cycles, and increasing impacts from invasives and diseases, given a very well-documented range of species changes across multiple ecosystem types, as well as clear economic and social consequences in many regions already experiencing these impacts. The evidence is strong, and the authors assessed high confidence that some species, particularly those that cannot easily relocate and those that are highly temperature sensitive, are facing heightened extinction risks, and that these are very likely, given that some species populations are already in serious decline at current levels of warming. Policy actions to help species adapt were assessed, and what they have in common is a clear identification of risks and prioritization of species and locations for protection. The evidence base for these policy actions is clear, and the authors have high confidence that such actions can expand and improve options for management.
Climate change is having variable and increasing impacts on ecosystem services and benefits, from food production to clean water to carbon sequestration, with consequences for human well-being . Changes in availability and quality of ecosystem services, combined with existing social inequities, have disproportionate impacts on certain communities . Equity-driven nature-based solutions, designed to protect, manage, and restore ecosystems for human well-being, can provide climate adaptation and mitigation benefits .
Read about Confidence and Likelihood
There is strong evidence that communities of color experience greater air pollution inequity228,229,230,231 compared to White communities and have reduced and/or less high-quality access to green space, trees, and other ecosystems that buffer these impacts. Limited access to resources and services also extends to those with limited income or wealth (also known as economic capacity), and these factors interact with race and other social hierarchies, including power, in complex ways.333
There is strong evidence at the global level that warming and carbon dioxide fertilization effects have already altered some ecosystem services, such as coastal carbon storage and ecosystem biodiversity, as noted in the recent Intergovernmental Panel on Climate Change report.2 For the US, while not all ecosystem services have been quantitatively assessed for climate impacts, those that have been show either currently observable declines (e.g., nearly 40% of pollinator-dependent crops in the US suffer from low pollinator abundance)334 or projections of future decline (e.g., reduced outdoor recreation opportunities by 2050).210
Evidence for the effectiveness of restoration at improving ecosystem service benefits is growing as more landscape-scale restoration is undertaken across multiple ecosystems.263 Additionally, valuation of ecosystem services benefits has proven to be a strong driver of new restoration programs, as it helps identify potential ecosystems to manage or restore (e.g., how health benefits can be obtained from restoration of vegetated terrestrial systems).262
There remain challenges in measuring, monitoring, and evaluating the impacts and effectiveness of many ecosystem services.335 In the US, urban spaces continue to be under-researched, especially in communities of color, despite often being biodiverse environments;336 and current research is usually limited to city-specific case studies of ecosystem services measurements and analyses, with less focus on comparative work.248,337 Furthermore, many city planning documents do not include climate change adaptation practices regarding cultural services or environmental injustice in ways that translate to implementation338 and instead focus on physical and natural resources, costs, or logistics.247 Research that engages communities, residents, and small organizations in identifying and designing measurements, valuation, and management criteria is a persistent gap, given the continuing lack of resident participatory research and community science in identifying problems and implementing solutions. A few studies have connected multiple types of urban ecosystem services from a theoretical planning point of view,248,337,339 but integrating justice into ecosystem service practices by prioritizing community needs, aligning methods of assessment and criteria to goals, and addressing environmental racism is a critical gap.247
There are few examples of ecological restoration practices designed to be resilient to climate change,340,341 with particular challenges around making decisions about what needs to be “restored”342 and to what conditions or baseline, as well as how to minimize vulnerability to extreme climate events that may be unprecedented in recent history. There can be spatial disconnects between where restoration actions need to be implemented and where ecosystem service improvements will be observed,343 and the economic cost of restoration efforts and stakeholder preferences for desired states can prevent recovery efforts.344
NBSs could cause risks of undesirable outcomes if they entail ecosystem transformations or species introductions over large areas of land; thus, they require careful study prior to implementation to avoid exacerbation of environmental and social injustices.345,346 There are increasing cases of poorly designed NBSs and rising concern over second-order effects, like green gentrification.216,217 However, there are considerable research gaps regarding how to avoid these outcomes. Evidence suggests that more stakeholder engagement in carbon removal projects and policies could help maximize adaptation benefits,347 but this is an area of ongoing research.
There is high confidence that climate is having variable and growing impacts on many ecosystem services, based on an expanding literature containing many regional examples. These changes are assessed as very likely, given the existing levels of warming in areas where impacts have already been observed. There is high confidence that these changes in availability and quality of ecosystem services, when combined with existing social inequities that are also well documented, will result in disproportionate impacts on some communities. These disproportionate impacts were assessed as very likely, given that impacts are already visible, particularly in urban areas. The authors assessed it to be likely that nature-based solutions designed to be equitable can provide multifunctional benefits for climate adaptation and mitigation, although there is only medium confidence that current examples of nature-based solutions are able to fully address mitigation and adaptation needs in an equitable manner, given a growing body of evidence that poorly designed or inequitable nature-based solutions do continue to be implemented in some places.
Virtually Certain | Very Likely | Likely | As Likely as Not | Unlikely | Very Unikely | Exceptionally Unlikely |
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99%–100% | 90%–100% | 66%–100% | 33%–66% | 0%–33% | 0%–10% | 0%–1% |
Very High | High | Medium | Low |
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