finding 7.2 : key-message-7-2

Climate change is altering ecosystem productivity, exacerbating the spread of invasive species, and changing how species interact with each other and with their environment (high confidence). These changes are reconfiguring ecosystems in unprecedented ways (likely, high confidence).

This finding is from chapter 7 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

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.

Description of evidence base:

Primary productivity: Diverse observations suggest that global terrestrial primary production has increased over the latter 20th and early 21st centuries,10bc8ec0-deed-40ff-9d4e-1b202da596bf,9256aa92-5743-4e52-bf45-61646b09cf53,0cdfff8a-93eb-479a-a867-b7c51c08701c,bceda009-3449-4f65-8bd7-4036cef210eb and climate models project continued increases in global terrestrial primary production over the next century.9608fefa-4410-4dec-a7ec-0c3201b618ce,8818342d-683a-4cde-96e8-3087183e69e7 Modest to moderate declines in ocean primary production are projected for most low- to midlatitude oceans over the next century,fa10bfab-8f7c-4d8c-8435-8284a05d78e5,5df44295-7544-4898-817d-7336deed2c48,37519d28-5ca8-4f24-919d-759b277e749a but regional patterns of change are less certain.6917fa32-e7d4-433e-a5ad-81be81d9b77c,fa10bfab-8f7c-4d8c-8435-8284a05d78e5,37519d28-5ca8-4f24-919d-759b277e749a

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;0f046395-da6c-4d4c-adcf-846b68586180,8a208951-0f7c-4eb8-9114-5ec00916198d,c3a35f0a-663c-4eea-84fc-71acad6f3343 for example, small changes in marine primary productivity are likely to result in even larger changes to the biomass of fisheries catch.41f0be78-707a-4169-8838-2446d6587a79

Changes in phenology: Synchronized timing of seasonal events across trophic levels ensures access to key seasonal food sources,b3ed2c28-4717-4cdc-9e8e-5b79a8be84b1,1abd1782-8c41-462c-bd73-e61111765d30 particularly in the spring, and is especially important for migratory species dependent on resources with limited availability and for predator–prey relationships.30fe230f-9dc9-41fc-ad29-e584f1244b95 The match–mismatch hypothesis5c8285d7-fcb9-47f8-ada8-f72e94133879 is a mechanism explaining how climate-induced phenological changes in producers and consumers can alter ecosystem food web dynamics.d0c3b72c-3080-42de-a8e4-dc0edf9d8c56 For example, Chevillot et al.eda98a75-74c7-4b05-a069-6101757a390b found that reductions in temporal overlap of juvenile fish and their zooplankton prey within estuaries, driven by changes in temperature, salinity, and freshwater discharge rates, could threaten the sustainability of nursery functions and affect the recruitment of marine fishes. Secondary consumers may be less phenologically responsive to climate change than other trophic groups,d0c3b72c-3080-42de-a8e4-dc0edf9d8c56 causing a trophic mismatch that can negatively impact reproductive success and overall population levels by increasing vulnerability to starvation and predation.85db98f9-39a3-4123-a48b-d2cd4d3edf28,2e4c198a-04a9-4b31-b760-2a8db74df445 Long-distance migratory birds, which have generally not advanced their phenology as much as lower trophic levels,912dbad9-8981-4cb5-8044-eabf0e563dbf can be particularly vulnerable.47c68570-a805-4d6c-a679-7f8d0332ce36 A recent study found that 9 out of 48 migratory bird species examined did not keep pace with the changing spring phenology of plants (termed green-up) in the period 2001–2012.9c921777-0a90-411f-b3bd-722da79a2fed Trophic mismatch and an inability to sufficiently advance migratory phenology such that arrival remains synchronous with peak resource availability can cause declines in adult survival and breeding success.9c921777-0a90-411f-b3bd-722da79a2fed,2e4c198a-04a9-4b31-b760-2a8db74df445

Invasive species: Changes in habitat and environmental conditions can increase the viability of introduced species and their ability to establish.a4c21da1-a84d-4e9f-bf8d-f6c4f81939a2,db8b5f26-296a-4cd4-8c49-de8ca8c8b39d,3de4eda1-e4b9-47f4-8b90-bb0849d30fd4 Climate change may be advantageous to some nonnative species. Such species are, or could become, invasive, as this advantage might allow them to outcompete and decimate native species and the ecosystem services provided by the native species.

Invasive species’ impacts on ecosystems are likely to have a greater negative impact on human communities that are more dependent on the landscape/natural resources for their livelihood and cultural well-being.99e9a2aa-b071-47fd-906d-81fd55914789,910c93dd-8d84-425b-82f2-6c5b0f516ddd Thus rural, ranching, fishing, and subsistence economies are likely to be negatively impacted. Some of these communities are economically vulnerable (for example, due to low population density, low median income, or reduced tax revenues) and therefore have limited resources and ability to actively manage invasive species.e76faf3a-3cf2-4bf0-8a17-ae8c22ca63c6,156e9522-db7e-400d-8a0b-8f0e7a2087ce Climate change and invasive species have both been recognized as two of the most significant issues faced by natural resource managers.c65ce3aa-364c-4301-82c4-301e750e2fd5,33e13829-9f3d-400e-9be7-4f3c6b16b41b For example, the invasive cheatgrass (Bromus tectorum) is predicted to increase in abundance with climate change throughout the American West, increasing the frequency of major economic impacts associated with the management and rehabilitation of cheatgrass-invaded rangelands.e421a79e-a529-48bf-872a-cb3422ebad9e,a1cef8d8-44ab-4b68-b13f-5bdb5db91f3a Ecological and economic costs of invasive species are substantial, with global costs of invasive species estimated at over $1.4 trillion annually.c65ce3aa-364c-4301-82c4-301e750e2fd5 Annual economic damages from climate change are complex and are projected to increase over time across most sectors that have been examined (such as coral reefs, freshwater fish, shellfish) (Ch. 29: Mitigation, Figure 29.2).

Species interactions and emergent properties: Human-caused stressors such as land-use change and development can also lead to novel environmental conditions and ecological communities that are further degraded by climate impacts (Ch. 11: Urban, KM 1) .7406884d-2302-4644-aa50-12ed8baf4fd7,506759aa-765f-4007-a678-17d69d139e39 Studies of emergent properties have progressed from making general predictions to providing more nuanced evaluations of behavioral mechanisms such as adjusting the timing of activity levels to avoid heat stress f52a5afb-23aa-4868-9a04-f6d45436198f,f560cd89-0ad2-4ec7-bade-0a2b248e6f01,7f9410be-e7d7-476c-a517-5af0904740a7 and predation,a7860146-7a14-4d34-8217-4ab0c4afd673 tolerances to variable temperature fluctuations and water availability,fd60b5d9-7670-4652-b00a-e37ff0891f00,64780ef3-81ff-4ecd-ad73-47b64be0565a,0f2bb63f-d2da-4853-87b7-d8f732f57e8e,a379e313-10fb-44e6-b6b2-6967ef43241f adaptation to changes,0f2bb63f-d2da-4853-87b7-d8f732f57e8e,a3e217ec-2e9e-4b6b-b113-dfde9e54ea5f turnover in community composition,6e6cd811-f193-4b44-8bb7-f65b8c43f5fe,00b388e8-5db4-4aa7-acbb-c1c8237aa4bd and specific traits such as dispersal ability.7843f759-b2e4-4298-a2cb-eda2a2d35a9e,e3cd2dc9-3bb4-422a-a2d4-a55ca8651758

Changes in community composition vary relative to invasion rates of new species, local extinction, and recruitment and growth rates of resident species, as well as other unknown factors.00b388e8-5db4-4aa7-acbb-c1c8237aa4bd In some cases, such as Pacific Northwest forests, community turnover has been slow to date, likely due to low exposure or sensitivity to the direct and indirect impacts of climate change,6e6cd811-f193-4b44-8bb7-f65b8c43f5fe while in other places, like high-latitude systems, dramatic shifts in community composition have been observed.23eba59a-13f9-4881-8bb7-f07677d5e8db Differential responses within and across communities are expected due to individual sensitivities of community members. For example, as a result of the uncertainties associated with range shifts, the impact of individual species’ range shifts on ecosystem structure and function and the potential for the creation of novel community assemblages have medium certainty. The interplay of physical drivers resulting in range shifts and the ways in which interactions of species in new assemblages shape final outcomes affecting ecosystem dynamics is uncertain, although there is more certainty in how ecosystem services will change locally. There is still high uncertainty in the rate and magnitude at which community turnover will occur in many systems; still, there is widespread agreement of high turnover and major changes in age and size structure with future climate impacts and interactions with other disturbance regimes.6e6cd811-f193-4b44-8bb7-f65b8c43f5fe,00b388e8-5db4-4aa7-acbb-c1c8237aa4bd,23eba59a-13f9-4881-8bb7-f07677d5e8db

Climate-induced warming is predicted to increase overlaps between some species that would normally be separated in time. For example, tree host species could experience earlier bud burst, thus overlapping with the larval stage of insect pests; this increase in synchrony between normally disparate species can lead to major pest outbreaks that alter community composition, productivity, ecological functioning, and ecosystem services.eb499fee-65b6-4fb6-80cf-a09dd60561c4 Direct climate impacts, such as warmer winters and drought-induced stress on forests, can interact with dynamics of pest populations to render systems more susceptible to damage in indirect ways. In the case of the bark beetle, for example, forests that have experienced drought are more vulnerable to damage from beetle attacks.678c7f6b-c6d0-4634-b4e0-c46db5544fa0,8252d3e9-6de4-4d92-942a-69ffa9769fc1 Other potential outcomes of novel species assemblages are changes in energy and nutrient exchange (for example, altered carbon use in streams as new detritus-feeding or predator communities emerge)516db32d-e3f6-49b3-a09e-e9045b101703 and respiration6bd72e09-4468-471b-be39-4df7a98a4274 within and among ecological communities. Abrupt and surprising changes or the disruption of trophic interactions have the potential for negative and irreversible impacts on food webs and ecosystem productivity that supports important provisioning services including fisheries and forest harvests for food and fiber. Abrupt changes in climate have been observed over geological timescales and have resulted in mass extinctions, decreased overall biodiversity, and ecological communities largely composed of generalists.7843f759-b2e4-4298-a2cb-eda2a2d35a9e

New information and remaining uncertainties:

Primary productivity: There is still high uncertainty in how climate change will impact primary productivity for both terrestrial and marine ecosystems. For terrestrial systems, this uncertainty arises from an incomplete understanding of the impacts of continued carbon dioxide increases on plant growth;388e7305-fea3-40ad-a42f-55fccb5fa0df,97e8245e-ac65-48cf-ac9d-0465a19a9799,b88c574e-62bc-459d-b08e-5a68fcd4c8d0 underrepresented nutrient limitation effects;76e702ad-9c8a-4513-b7b1-eafb1c210e16 effects of fireea8d831c-6b6b-4f8c-9b60-f17bab43660e and insect outbreaks;df19cf82-b4eb-4281-a379-2f1863e7142f and an incomplete understanding of the impacts of changing climate extremes678c7f6b-c6d0-4634-b4e0-c46db5544fa0,fadd37a9-ff7d-4f34-b6ca-48239412e097 on primary production. Direct evidence for declines in marine primary production is limited. The suggestion that phytoplankton pigment has declined in many ocean regions,973493c4-7e62-481c-91ce-abd7168bc05e indicating a decline in primary production, was found to be inconsistent with primary production time series1cf715d6-2886-4040-b417-d01f752924c4 and potentially sensitive to analysis methodology.6da1e4ed-56e9-4ccf-beb9-b6502466f874,8a1602bc-f6fb-4a26-a0f3-47f5f2956654,05d7d6ad-e0ce-4ed6-8ba6-b7821ecfa9da Subsequent work accounting for methodological criticisms still argued for a century-scale decline in phytoplankton pigment but acknowledged large uncertainty in the magnitude of this decline and that some areas show marked increases.7efd3ca6-6c9d-4beb-99db-6423fe43a134 There is growing consensus for modest to moderate productivity declines at a global scale in the marine realm.fa10bfab-8f7c-4d8c-8435-8284a05d78e5,5df44295-7544-4898-817d-7336deed2c48,37519d28-5ca8-4f24-919d-759b277e749a Considerable disagreement remains at regional scales.fa10bfab-8f7c-4d8c-8435-8284a05d78e5 For both the terrestrial and marine case, however, projections clearly support the potential for marked primary productivity changes.

Phenology: Models of phenology, particularly those leveraging advanced statistical modeling techniques that account for multiple drivers in phenological forecasts,416437c8-7830-491a-9903-c1054cff913a enable extrapolation across space and time, given the availability of gridded climatological and satellite data.3307a62c-ed45-4399-bcb9-f77e71b1e626,63774c1b-c5e4-47f9-96fc-6033a46c208f,197d5564-21cc-4988-b6ed-33d48bc2b2f0,42b95a9f-a33b-4c2a-a298-ba26f9f2dd6a However, effective characterization of phenological responses to changes in climate is often constrained by the availability of adequate in situ (ground-based) organismal data. Experimental manipulation of ecological communities may be insufficient to determine sensitivities; for example, E. M. Wolkovich et al. 20127cd64f08-0c6d-4e1d-928e-6b0126d015a8 compared observational studies to warming experiments across four continents and found that warming predicted smaller advances in the timing of flowering and leafing by 8.5- and 4.0-fold, respectively, than what has been observed through long-term observations.

The majority of terrestrial plant phenological research to date has focused on patterns and variability in the onset of spring, with far fewer studies focused on autumn.f773b2e9-428c-455b-82f9-a4dbf065d44b However, autumn models have large biases in describing interannual variation.f707c003-8d84-4a07-9136-17693ece0969,75297381-3981-400f-9fd1-1cfc7e3b408e Additional research is needed on autumnal responses to environmental variation and change, which would greatly expand inferences related to the carbon uptake period, primary productivity, nutrient cycling, species interactions, and feedbacks between the biosphere and atmosphere.b5b2510c-671b-43d8-96ab-e059264d2b10,42539f88-a4ae-4b6f-88cc-5f763487644e,9d22793a-3188-4520-81c8-00a060b88ea8,661efe0c-864b-4017-b96d-76a5ffcb1b05 While broad-based availability of phenological data has improved greatly in recent years, more extensive, long-term monitoring networks with consistently implemented protocols would further improve scientific understanding of phenological responses to climate change and would better inform management applications.2da0bf82-d492-47e5-b45d-7d0c2f5e9267

Invasive species: There is some uncertainty in knowing how much a nonnative species will impact an environment, if and when it is introduced, although there are methods available for estimating this risk.1e9b900d-0a4c-428e-9e76-8b97858a3800,07317e2c-abb0-4ec8-8d32-e0edcf69d82a For example, the U.S. Department of Agriculture conducts Weed Risk Assessment,811c9201-dba3-40ca-b91f-d0434e586228 and the U.S. Fish and Wildlife Service publishes Ecological Risk Screening Summaries ( New technologies, such as genetic engineering, environmental DNA, and improved detection via satellites and drones, offer promise in the fight against invasive species.bb0bd25d-6d90-4336-95d4-6dde685079ce New technologies and novel approaches to both invasive species management and mitigation and adapting to climate change could reduce negative impacts to livelihoods, but there is some uncertainty in whether or not the application of new technologies can gain social acceptance and result in practical applications.

Species interactions and emergent properties: Climate change impacts to ecosystem properties are difficult to assess and predict, because they arise from interactions among multiple components of each system, and each system is likely to respond differently. One generalization that can be made arises from fossil records, which show climate-driven mass extinctions of specialists followed by novel communities dominated by generalists.7843f759-b2e4-4298-a2cb-eda2a2d35a9e Although there is widespread consensus among experts that novel interactions and ecosystem transitions will result from ecological responses to climate change,e3cd2dc9-3bb4-422a-a2d4-a55ca8651758 these are still largely predicted consequences, and direct evidence remains scarce; thus, estimates of how ecosystem services will change remain uncertain in many cases.7406884d-2302-4644-aa50-12ed8baf4fd7,7843f759-b2e4-4298-a2cb-eda2a2d35a9e,ed131239-ef2e-42a8-8411-4f82623f9a1f,e3806275-d9a5-4c0a-9e20-7acda7390db6,902375a2-1324-48f2-b66f-bdd52542bfb6,4d7f374e-55ce-4438-9edc-66d2588871da,3f87d74e-c4af-46bc-aee3-67ed7e37dd1e,506759aa-765f-4007-a678-17d69d139e39,a3e217ec-2e9e-4b6b-b113-dfde9e54ea5f,ff1f13b1-f469-424d-a206-eafc06bfd775,bcbdf42d-2c19-4836-9ccf-6f1bedb625de Modeling and experimental studies are some of the few ways to assess complicated ecological interactions at this time. New and more sophisticated models that can account for multispecies interactions, community composition and structure, dispersal, and evolutionary effects are still needed to assess and make robust predictions about system responses and transitions.4d7f374e-55ce-4438-9edc-66d2588871da,a3e217ec-2e9e-4b6b-b113-dfde9e54ea5f,ff1f13b1-f469-424d-a206-eafc06bfd775

High uncertainty remains for many species and ecosystems due to a general lack of basic research on baseline conditions of biotic interactions; community composition, structure, and function; and adaptive capacity; as well as the interactive, synergistic, and antagonistic effects of multiple climate and non-climate stressors.7843f759-b2e4-4298-a2cb-eda2a2d35a9e,e3806275-d9a5-4c0a-9e20-7acda7390db6,bcbdf42d-2c19-4836-9ccf-6f1bedb625de Improved understanding of predator–prey defense mechanisms and tolerances are key to understanding how novel trophic interactions will manifest.a379e313-10fb-44e6-b6b2-6967ef43241f

Assessment of confidence based on evidence:

There is high confidence that climate-induced changes are occurring within and across ecosystems in ways that alter ecosystem productivity and how species interact with each other and their environment.

There is high confidence that such changes can likely create mismatches in resources, facilitate the spread of invasive species, and reconfigure ecosystems in unprecedented ways.

Regions Covered

Related NASA GCMD keywords

References :

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