Editing IPCC:AR6/WGII/Chapter-12 (section)

== 12.4 Key Impacts and Risks ==

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This section synthesises key risks across the CSA region. It follows the definition and concept of risk given in AR5, distinguishing the risk components, climatic hazards, exposure and vulnerabilities of people and assets ( [[#IPCC--2014|IPCC, 2014]] ). This concept is further developed in AR6, defining key risks as potentially severe risks ( [[IPCC:Wg2:Chapter:Chapter-16#16.5|Section 16.5]] ). Key risks may refer to present or future conditions, with a focus on the 21st century. Both mitigation and adaptation can moderate the extent or severity of risks. The identification and evaluation of risks imply sociocultural values, which may vary across individuals, communities or cultures.

In line with [[IPCC:Wg2:Chapter:Chapter-16|Chapter 16]] of this report, this chapter uses a risk outcome perspective, that is, the focus is on consequences related to risks, which could result from different combinations of hazards, exposure and vulnerabilities. Few studies in the literature focus on severe risks in the CSA region, and scant studies consider specifically and explicitly risk drivers such as level of warming, level of exposure, vulnerability and adaptation.

Criteria for identifying key risks for this chapter include the magnitude of the consequences, in particular the number of people potentially affected; the severity of the negative effects of the risk (e.g., lives threatened, major negative effects on livelihoods, well-being or the economy); the importance of the affected system (e.g., for vital ecosystem services, for large population groups); the irreversibility of either the process leading to the risk or the consequences; and the potential to reduce the risk.

Several of the key risks identified for the CSA region align well with the overarching key risks assessed in AR5 ( [[#Oppenheimer--2014|Oppenheimer et al., 2014]] ) and later in [[#O’Neill--2017|O’Neill et al. (2017)]] , as well as with the representative key risks assessed in [[IPCC:Wg2:Chapter:Chapter-16#16.5|Section 16.5]] of this report. The identified key risks include the following: KR1: risk of food insecurity due to frequent and/or extreme droughts; KR2: risk to life and infrastructure due to floods and landslides; KR3: risk of water insecurity; KR4: risk of severe health effects due to increasing epidemics (in particular vector-borne diseases); KR5: systemic risks of surpassing infrastructure and public service systems capacities; KR6: risk of large-scale changes and biome shifts in the Amazon; KR7: risk to coral reef ecosystems due to coral bleaching; KR8: risks to coastal socioecological systems due to SLR, storm surges and coastal erosion (Table 12.6; Figure 12.11; Table SM12.5).

Identification and assessment of key risks are informed by observed and projected impacts in the different sub-regions of CSA ( [[#12.3|Section 12.3]] ). Figure 12.10 shows a summary of different levels of observed and future impacts per sub-region for different sectors, based on a detailed assessment of climate-change impacts on various systems and components for the corresponding sector (Figure 12.9). This assessment is consistent with and complementary to the assessment in [[#12.3|Section 12.3]] . A synthesis of these impacts (Figure 12.10) indicates the following: Climate change has or will have a major impact on the observed and future decline of Andean glaciers and snow ( ''high confidence'' ) and lead to the degradation of permafrost and destabilisation of related landscapes ( ''medium evidence, high agreement'' ). Water quality is a major concern across the region, but there is ''limited evidence'' of impacts of climate change on water quality as well as on groundwater. Climate change has had a significant impact on terrestrial and freshwater ecosystems in the NWS, SES and SWS sub-regions and a medium impact in the other sub-regions, but the level of confidence varies across sub-regions. Projections indicate a strong impact of climate change on these ecosystems for the future ( ''medium confidence: medium evidence, high agreement'' ). Many aspects and assets of ocean and coastal ecosystems (e.g., mangroves, coral reefs, saltmarshes) were identified as being strongly impacted by climate change, both for observed and future periods ( ''high confidence'' ) ( [[#12.5.2|Section 12.5.2]] ; Figure 12.9).

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[[File:0926daeeebde2b53dbdf237325ccf641 IPCC_AR6_WGII_Figure_12_010.png]]

'''Figure 12.10 |''' '''Synthesis of observed and projected impacts, distinguished for different sectors and each sub-region of CSA.''' Observed impacts relate to the last several decades. Projected impacts represent a synthesis across several emission and warming scenarios, indicative of a time period from the middle to end of the 21st century. For each sector (e.g., health) climate-change impacts are identified as being low, medium or high. The references underlying this assessment can be found in SM12.4.1 and the methodology to complete the synthesis is found in SM12.4.2.

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[[File:cb055551d9b79a45ff83453b896fa5ff IPCC_AR6_WGII_Figure_12_011.png]]

'''Figure 12.11 |''' '''Synthesis of key risks for the CSA region.''' The base map indicates the mean temperature change between the SSP2 4.5 scenario using CMIP6 model projections for 2081–2100 and a baseline period of 1986–2005 (WGI AR6 Atlas, [[#Gutiérrez--2021|Gutiérrez et al., 2021]] ).

In most sub-regions, crop, livestock, fisheries and food systems in general show medium to high impacts of climate change over the observed period, as does the remaineder of the 21st century ( ''medium confidence: medium evidence, high agreement'' ). For some sub-regions, the available literature does not allow for an assessment of impacts on various human systems, including cities and infrastructure, health, poverty, livelihoods, migration, conflicts and IKLK, especially for future time periods. This points to important knowledge gaps about climate-change impacts on human systems. The indication of high impacts on several human systems and sub-regions points to the need to close these knowledge gaps.

Assessment of key observed and projected impacts and risks shows that in the CSA region several systems are already approaching critical thresholds under current warming levels, in particular glaciers in the Andes, coral reefs in CA ( ''high confidence'' ) and ocean and coastal ecosystems in virtually all sub-regions ( ''medium confidence: medium evidence, high agreement'' ). Some systems could cross these thresholds with different levels of reversibility depending on the degree of future warming, that is, glaciers in the Andes and coral reefs in CA, which will show partial but irreversible loss already under low levels of warming (RCP2.6) ( ''high confidence'' ). The risk of large-scale ecological changes and biome shifts of the Amazon rainforest, that is, a transition from tropical forest into other biomes such as seasonal forest or savannah, is now assessed with ''medium confidence'' , with the extent of the changes depending on the level of future warming and non-climatic drivers (land use change, deforestation, forest fire practices).

Systemic risks where critical infrastructure and public service system capacities are surpassed due to storms, floods and epidemics, with cascading impacts through vulnerable systems and populations and economic sectors, have the potential to affect large parts of populations and are therefore of major concern ( ''medium confidence: limited evidence, high agreement'' ). The COVID-19 crisis has exposed the existing vulnerabilities in important systems, in particular health systems and public services ( [[#Phillips--2020|Phillips et al., 2020]] ). However, tipping points in social systems are poorly understood ( [[#Bentley--2014|Bentley et al., 2014]] ; [[#Milkoreit--2018|Milkoreit et al., 2018]] ), and there is ''limited evidence'' to inform understanding about which level of compound climatic, environmental and socioeconomic stressors social systems will withstand in CSA.

Overall, most key risks and their severity and extent are strongly driven and determined by system exposure, vulnerability and adaptive capacity. In particular, the high vulnerability of large populations, infrastructure and service systems, such as health, food and energy production and supply, are important factors, along with high levels of inequality and poor governance, for creating and increasing key risks ( ''high confidence'' ). Prevailing low levels of available information and understanding exacerbate the uncertainties surrounding key risks and so pose limitations to adaptation. An example is CA, with its high levels of vulnerability and exposure, but there is ''limited evidence'' and understanding on impacts and risks, making this region susceptible to inappropriate adaptation to expected future climate-change impacts.

'''Table 12.6 |''' Synthesis of key risks identified and assessed for Central and South America region

{| class="wikitable"
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! '''Consequence that would make the risk severe'''

! '''Associated changes in hazards'''

! '''Associated changes in exposure'''

! '''Associated changes in vulnerability'''

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| colspan="3"| '''1. Risk of food insecurity due to frequent/extreme droughts'''

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| Substantial decrease in yield for key crops, disruption of food provision chains, reduced capacity or production of goods, reduced food security and increased malnutrition.

| More frequent and/or longer drought periods; decrease in annual rainfall, severe decrease in rainfall at onset of rainy season; desertification of semiarid regions.

| More people exposed to food insecurity due to spatially more extensive drought, high population growth rate (including rural areas) and greater population dependence on agricultural goods.

| Reduced capacity of farmers (especially small-scale) to adapt to changing climatic conditions; soil degradation, insufficient government support of adaptation measures, financial contributions, infrastructure, insurance, and research efforts; inefficient water management.

|-
|
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| colspan="3"| '''2. Risk to life and infrastructure due to floods and landslides'''

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| Death and severe health effects, disruption of critical infrastructure and service systems.

| More frequent and severe storms and heavy precipitation events; changing snow conditions and thawing permafrost; retreating glaciers, formation of glacier lakes, increased GLOF hazard.

| More people exposed to floods and landslides due to changing hazards, land use and increased population; occupation of more risk-prone areas such as flood plains and steep slopes.

| Low-income and marginal populations and low resilience of infrastructure and critical service systems; limited government support through insurance, monitoring, EWSs and recovery.

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| '''3. Risk of water insecurity'''

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| Seasonal water availability change and decline due to glacier shrinkage, snow cover change, more pronounced dry periods and poor or failed water management and governance.

| Glacier shrinkage, snow cover change, more pronounced dry periods, precipitation and circulation changes.

| Increase in population dependent on contribution of glacier/snow melt, especially during drought conditions; increased demand from intensification of agriculture, mining, hydropower and urbanisation.

| Unequal water consumption systems, failed water management and government capacities, low water infrastructure efficiency, growing urban areas.

|-
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| colspan="4"| '''4. Risk of severe health effects due to increasing epidemics (in particular vector-borne diseases)'''

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| Increased rate of epidemics of vector-borne diseases (malaria, dengue, Zika, leishmaniasis) together with diarrheal diseases. Severe health effects and damage to health systems in countries with low adaptive capacity and where original endemicity is high and control status poor.

| Higher temperatures increase the geographical range of vectors, leading to expansion of climate suitable areas.

| Increased population density and mobility through urbanisation results in high transmission rate. Increased population exposed to arboviruses due to expansion of vectors, including higher altitudes and latitudes.

| Poor sanitation conditions, particularly in low-income communities and for Indigenous Peoples. Insufficient coverage of appropriate water provision and sewage systems. Low structural or economic capacity to cope; underfunding of health systems. Increase in infections can increase incidence of more severe forms of dengue.

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| colspan="3"| '''5. Systemic risks of surpassing infrastructure and public service systems capacities'''

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| Breakdown of public service systems, including infrastructure and health services due to cascading impacts of natural hazards and epidemics, affecting a large part of the population.

| Higher frequency and magnitude of climate-related events (storms, floods, landslides), together with an increase in spatial and temporal distribution of pathogens/vectors for malaria, dengue, Zika and leishmaniasis.

| More people and infrastructure exposed to climate/weather events; increase in population exposed to arboviruses due to spatial expansion of vectors.

| Increasing vulnerability of public service and infrastructure systems; insufficient disaster management; little improvement, maintenance and expansion of public healthcare systems; low system resilience.

|-
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| colspan="3"| '''6. Risk of large-scale changes and biome shifts in Amazon'''

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| Transition from tropical forest into other biomes such as seasonal forest or savannah through forest degradation and deforestation; risk of shifting from carbon sink to source.

| More frequent, stronger and more persistent drought periods; temperature increase and reduction in annual rainfall.

| Reduced availability of natural sources for local people; land use and land cover change (mining, deforestation); loss of biodiversity and ecosystem services; health impacts from increased forest fires particularly for Indigenous Peoples.

| Strong dependence on non-climatic drivers, in particular land use change, deforestation, forest fire practices; low capacity to monitor and control deforestation.

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| colspan="3"| '''7. Risk to coral reef ecosystems due to coral bleaching'''

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| Degradation and possible death of Mesoamerican coral reef, the second largest reef in the world; severe damage to habitat for marine species, degrading coastal protection and other ecosystem services, decreased food security from fisheries, lack of income from tourism.

| Ocean SST increase, lowered seawater pH and carbonate levels due to increased atmospheric CO 2 levels, leading to ocean acidification and coral bleaching.

| Continued exposure to increased atmospheric CO 2 levels and SSTs together with destruction from coastal development, fishing practices and tourism.

| Ecosystem highly sensitive to water temperature and pH fluctuations; high levels of negative human interference with reefs including runoff and pollution.

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| colspan="4"| '''8. Risks to coastal socioecological systems due to SLR, storm surges and coastal erosion'''

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| Coastal flooding and erosion causing severe damage to coastal population and infrastructure; loss of fisheries, reef degradation and decline in coastal protection due to increased storm surges and waves;saltwater intrusion and land subsidence.

| High continuing trajectories of SLR; More intense and persistent coastal flooding, saltwater intrusion, coastal erosion.

| Coastal population growth; increased number of people, infrastructure and services (coastal tourism) exposed; need for relocation of millions of people.

| Poor planning in coastal development and infrastructure, disproportionate vulnerability and limited adaptation options for rural communities and Indigenous Peoples, increasing urbanisation in coastal cities; significant economic losses and unemployment from declining tourism.

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