Editing IPCC:AR6/WGII/Cross-Chapter-Paper-5 (section)

== CCP5.5 Key Assessment Limitations and Relevant Knowledge Gaps ==

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The assessment presented in this CCP has several limitations, principally in terms of the amount of often fragmented and biased geographic coverage or lack of relevant thematic scope covered in the literature published since AR5 and SROCC. Key assessment limitations and relevant knowledge gaps identified in this CCP fall within the following broad categories: 1) detection and attribution of observed impacts to climate change, 2) limitations and uncertainties associated with predictive models of projected impacts and risks, 3) integrated and systems-oriented research on mountain ecosystem services and their limits under climate change and 4) measurable tracking of adaptation action implemented in mountain regions and their suitability for addressing climate risks. These are summarised in Table CCP5.3. While these limitations and assessment-relevant gaps in knowledge offer important caveats for the interpretation of this assessment; they also highlight prospects to address and improve the evidence basis in future assessments.

'''Table CCP5.3 |''' Summary of key assessment-relevant knowledge gaps and limitations identified in CCP5.

{| class="wikitable"
|-
! colspan="2"| '''Key assessment-relevant knowledge gaps and limitations'''

! '''Relevant WGII report sections'''

|-
| colspan="3"| ''Detection and attribution of observed impacts to climate change''

|-
| Limited amount and scope of literature available on impacts for assessment of detection and attribution to climate change

| * While there is ''high confidence'' on the links between future impacts and risks associated with climate change, there is ''medium evidence'' available on robust detection and attribution of past changes in mountain regions.
* Considerable assessment gaps exist given the limited scope (temporal, spatial or thematic coverage) and number of published studies reporting data and information that capture how mountain social-ecological systems function and their trends over recent decades, which may be applicable for the detection and attribution of changes to climatic change.
* Additionally, there are limitations in current methodologies in terms of including and accounting for other knowledge traditions with respect to the detection and attribution of impacts to climate change in mountain regions (e.g., [[#Chakraborty--2021|Chakraborty and Sherpa, 2021]] ).

| CCP5.2.7,

Figure CCP5.4,

SMCCP5.2

|-
| Consequences of shifting treelines and their interactions with other ecosystem functions

| * The net effects of ongoing climate change with treeline advance and vegetation change on ecosystem carbon exchange, or possible effects on mountain hydrology, remain unresolved in the literature.
* Uncertainties remain regarding the effects of ecosystem-level carbon storage, given that above-ground biomass is higher in forests than in alpine vegetation and (new) trees may change soil carbon fluxes, for instance by introducing new soil organisms, thereby increasing soil carbon flux (e.g., [[#Tonjer--2021|Tonjer et al., 2021]] ).
* The short- and long-term effects of combined warming and changed species cover on mountain soils are complex and insufficiently quantified ( [[#Hagedorn--2019|Hagedorn et al., 2019]] ).

| CCP5.2.1,

CCP1-Biodiversity Hotspots

|-
| colspan="3"| ''Limitations and uncertainties associated with predictive models of projected impacts and risks''

|-
| SSPs

| * There are relevant knowledge gaps in the understanding of future vulnerabilities in mountain social-ecological systems in relation to highly variable and dynamic trends in projected demographic change, socioeconomic development pathways and demand for resources.

| CCP5.3.1; SMCCP5.1

|-
| Species distribution models (SDM)

| * SDMs, which rely on statistical correlations between occurrence records and environmental variables to make spatially explicit predictions, are commonly used to project climate change impacts on mountain ecosystems ( [[#Guisan--2017|Guisan et al., 2017]] ).
* However, they are associated with some limitations that can limit their utility in deriving reliable predictions of future mountain vegetation distributions and, thus, ability to provide a sound basis for mountain nature conservation and climate change adaptation.
* In particular, they only indicate the potential future species distributions based on static relationships between species and predictors in calibration data; in reality, vegetation dynamics will be heavily modulated by phenomena that are commonly overlooked by such models as changing species interactions and competition due to variance in response rates among different species, dispersal limitations and demographic processes ( [[#Scherrer--2020|Scherrer et al., 2020]] ).
* In addition, SDMs are often limited by data availability and therefore tend to omit several environmental factors known to be important for plants, such as soil formation processes, disturbances (e.g., rockfalls, avalanches) and microclimatic conditions ( [[#Scherrer--2011|Scherrer et al., 2011]] ; [[#Enright--2014|Enright, 2014]] ; [[#Mod--2015|Mod et al., 2015]] ; [[#Bråthen--2018|Bråthen et al., 2018]] ).
* More complex dynamic and process-based models are available but still rarely represent all potentially influential vegetation co-variates; applying both model types in conjunction holds potential ( [[#Horvath--2021|Horvath et al., 2021]] ).

| CCP5.2.1

|-
| Quantifiable estimates of monetary costs and potential material losses

| * There is ''limited evidence'' on climate-related risks to economic sectors that are vital for mountain regions, specifically on quantifiable estimates of monetary costs and potential material losses for economic sectors and communities in mountains, adjacent lowlands and other regions dependent on these economic activities.

| CCP5.3.1

|-
| Other model limitations

| * Ecological models that could allow for better forecasts of the effectiveness of EbA as NbS, under different climate scenarios, have not been fully developed ( [[#Seddon--2020|Seddon et al., 2020]] ).

| CCP5.4

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| colspan="3"| ''Integrated and systems-oriented research on mountain ecosystem services and their limits under climate change''

|-
| Water

| * Few assessment-relevant integrative studies are available in the published literature that address relevant aspects of water security, beyond water availability from glacier-fed meltwater, or snow, groundwater and other water stores (e.g., wetlands and sediments). Likewise, few studies address seasonality with respect to a more systems-oriented approach to supply (e.g., water availability) and demand (irrigated agriculture and other multiple uses and user groups).

| CCP5.2.2

Chapter 4

|-
| colspan="3"| ''Measurable tracking of adaptation action implemented in mountain regions and their suitability for addressing climate risks''

|-
| Conditions under which adaptation interventions work against stated goals

| * Few studies report on how adaptation measures and programmes function in mountain contexts that yield the outcomes reported ( [[#McDowell--2020|McDowell et al., 2020]] ).
* Despite transformative processes, to date there is ''limited evidence'' of how knowledge co-production activities support the planning and implementation of successful adaptations in mountain areas.

| CCP5.4.2

|-
| Metrics and heuristics for tracking effectiveness

| * Adaptation responses to intangible losses and loss of cultural values are reported and take different forms, as demonstrated in studies from various world regions ( [[#de%20la%20Riva--2013|de la Riva et al., 2013]] ; [[#Wang--2015|Wang and Qin, 2015]] ; [[#Vander%20Naald--2020|Vander Naald, 2020]] ). However, there is ''limited evidence'' on their adequacy for addressing increasing losses, which remains largely unexplored in the available literature.

| CCP5.3.2.4;

[[IPCC:Wg2:Chapter:Chapter-4#4.4.3|Section 4.4.3.3]]

|-
| Methods and frameworks for monitoring and evaluation

| * Regarding adaptation efforts and effectiveness, there are considerable gaps in adequate monitoring and appropriate evaluation of successful implementation of diverse adaptation measures.
* Across mountain areas, integrated monitoring of key environmental and socioeconomic variables, including international efforts towards the acquisition and sharing of data, offers prospects for supporting the tracking of impacts and adaptation responses, including community-based monitoring initiatives ( [[#Shahgedanova--2021|Shahgedanova et al., 2021]] ; [[#Thornton--2021|Thornton et al., 2021]] ).

| [[IPCC:Wg2:Chapter:Chapter-17#17.5|Section 17.5]] ;

CCP5.4.2

|-
| Feasibility and suitability of adaptation options for managing climate risks

| * The feasibility of adaptation options for managing risks, for example those that could facilitate systems transitions with respect to energy, remains largely unexplored in the literature, with ''limited evidence'' on how projected climate change could impact prospects to develop wind, solar or biomass energy production and use in mountain contexts.
* Given assessments on observed adaptation (Section CCP5.2) and adaptation responses (Section CCP5.4), few studies report a ‘systems approach’ to the study and evaluation of adaptations that combine all relevant aspects of the risk framework (i.e., hazards, exposure and vulnerabilities), including how synergies and trade-offs are considered in context for managing risks.
* There is ''limited evidence'' on the feasibility and long-term effectiveness of adaptation measures to address climate-related impacts and related losses and damages in cities and settlements experiencing changing demographics.

| CCP5.2.2.2; CCP5.4.2; CCP5.4.3

|}

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