Editing IPCC:AR6/WGII/Chapter-11 (section)

=== 11.5.1 Cascading, Compounding and Aggregate Impacts ===

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==== 11.5.1.1 Observed Impacts ====

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Climate impacts are cascading, compounding and aggregating across sectors and systems due to complex interactions ( ''high confidence'' ) ( [[#Pescaroli--2016|Pescaroli and Alexander, 2016]] ; [[#Challinor--2018|Challinor et al., 2018]] ; [[#Zscheischler--2018|Zscheischler et al., 2018]] ; [[#Steffen--2019|Steffen et al., 2019]] ; [[#AghaKouchak--2020|AghaKouchak et al., 2020]] ; [[#CoA--2020e|CoA, 2020e]] ; [[#Lawrence--2020b|Lawrence et al., 2020b]] ; [[#Simpson--2021|Simpson et al., 2021]] ) (Boxes 11.1, 11.3, 11.4, 11.5 and 11.6). Cascading impacts propagate via interconnections and systemic factors, including supply chains, shared reliance on connected biophysical systems (e.g., water catchments and ecosystems), infrastructure, essential goods and services and the exercise of governance, leadership, regulation, resources and standard practices (e.g., in planning and building codes), including lock-in of past decisions and experience ( [[#CSIRO--2018|CSIRO, 2018]] ; [[#Lawrence--2020b|Lawrence et al., 2020b]] ). The capacity of critical systems such as information, communication and technology, water infrastructure, health care, electricity and transport networks, is being stretched, with impacts cascading to other systems and places, exacerbating existing hazards and generating new risks ( [[#Cradock-Henry--2017|Cradock-Henry, 2017]] ) (11.3.6; 11.3.10; Box 11.1). Temporal or spatial overlap of hazards (e.g., drought, extreme heat and fire; drought followed by extreme rainfall) are compounding impacts ( [[#Zscheischler--2018|Zscheischler et al., 2018]] ) and affecting multiple sectors.

Extreme events such as heatwaves, droughts, floods, storms and fires have caused deaths and injuries ( [[#Deloitte--2017a|Deloitte, 2017a]] ) (11.3.5.1), and affected many households, communities and businesses via impacts on ecosystems, critical infrastructure, essential services, food production, the national economy, valued places and employment. This has created long-lasting impacts (e.g., mental health, homelessness, health incidents and reduced health services) ( [[#Brown--2017|Brown et al., 2017]] ; [[#Brookfield--2018|Brookfield and Fitzgerald, 2018]] ; [[#Rychetnik--2019|Rychetnik et al., 2019]] ) and reduced adaptive capacity ( [[#Friel--2014|Friel et al., 2014]] ; [[#O’Brien--2014|O’Brien et al., 2014]] ; [[#Ding--2015|Ding et al., 2015]] ; [[#CoA--2020e|CoA, 2020e]] ) (Box 11.1, Box 11.3, 11.3.1–11.3.10).

In New Zealand, extreme snow, rainfall and wind events have combined to impact road networks, power and water supplies and have impeded interdependent wastewater and stormwater services and business activities ( [[#Deloitte--2019|Deloitte, 2019]] ; [[#Lawrence--2020b|Lawrence et al., 2020b]] ; [[#MfE--2020a|MfE, 2020a]] ) (Box 11.4). Community and infrastructure services are periodically disrupted during extreme weather events, triggering impacts from the interdependencies across enterprises and individuals ( [[#Glavovic--2014|Glavovic, 2014]] ; [[#Paulik--2021|Paulik et al., 2021]] ).

Slow-onset climate change impacts have also had cascading and compounding effects. For example, degradation of the GBR by ocean heating, acidification and non-climatic pressures ( [[#Marshall--2019|Marshall et al., 2019]] ), repeated pluvial, fluvial and coastal flooding of some settlements ( [[#Paulik--2019a|Paulik et al., 2019a]] ; [[#Paulik--2020|Paulik et al., 2020]] ), long droughts and water insecurity in rural communities ( [[#Tschakert--2017|Tschakert et al., 2017]] ) and the gradual loss of species and ecological communities have caused substantial ecological, social and economic losses. Indigenous Peoples have especially been impacted by multiple and complex losses ( [[#Johnson--2021|Johnson et al., 2021]] ) (11.4).

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==== 11.5.1.2 Projected Impacts ====

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Cascading, compounding and aggregate impacts are projected to grow due to a concurrent increase in heatwaves, droughts, fires, storms, floods and sea level ( ''high confidence'' ) ( [[#CSIRO--2020|CSIRO, 2020]] ; [[#Lawrence--2020b|Lawrence et al., 2020b]] ). Urban wastewater, stormwater and water supply systems are particularly vulnerable in New Zealand ( [[#Paulik--2019a|Paulik et al., 2019a]] ; [[#Hughes--2021|Hughes et al., 2021]] ) to pluvial flooding (Box 11.4) and to sea level rise (SLR) (Box 11.6), with flow-on effects to settlements, insurance and finance sectors, and governments ( [[#Lawrence--2020b|Lawrence et al., 2020b]] ). Furthermore, consecutive heavy rainfall events in late summer and autumn, following drought conditions in low-lying modified wetland areas, have implications for the operation of flood control infrastructure as increased rainfall intensity, land subsidence and sea level rise (SLR) compound and result in the retention of floodwaters ( [[#Pingram--2021|Pingram et al., 2021]] ).

In Australia, the aggregate loss of wealth due to climate-induced reductions in productivity across agriculture, manufacturing and service sectors is projected to exceed AUD$19 billion by 2030, AUD$211 billion by 2050 and AUD$4 trillion by 2100 for RCP8.5 ( [[#Steffen--2019|Steffen et al., 2019]] ) (Table 11.13). Projected impacts also cascade across national boundaries via value chains, markets, movement of humans and other organisms and geopolitics (e.g., migration from near-neighbours as a pathway for adaptation, mobile climate-sensitive diseases and changes in production and trade patterns) ( [[#Lee--2018|Lee et al., 2018]] ; [[#Nalau--2018|Nalau and Handmer, 2018]] ; [[#Schwerdtle--2018|Schwerdtle et al., 2018]] ; [[#Dellink--2019|Dellink et al., 2019]] ). The scale of impacts is projected to challenge the adaptive capacity of sectors, governments and institutions ( [[#Steffen--2019|Steffen et al., 2019]] ), including the insurability of assets and risks to lenders ( [[#Storey--2017|Storey and Noy, 2017]] ).

'''Table 11.13 |''' Economy-wide projected costs (AUD$) of climate change in Australia. (Estimates are not comparable across studies because different methods have been used. Estimates for later in the century are speculative because both impacts and adaptation are uncertain.)

{| class="wikitable"
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! Impact

! 2030

! 2050

! 2090

! Reference

|-
| Damage-related loss of property value in Australia

| $571 billion

| $611 billion

| $770 billion

| ( [[#Steffen--2019|Steffen et al., 2019]] )

|-
| Property damage in Australia

|
| $91 billion/year

| $117 billion/year

| ( [[#Steffen--2019|Steffen et al., 2019]] )

|-
| Loss of asset value of road infrastructure (including freeways, main roads and unsealed roads) in Australia at risk of a SLR of 1.1 m by 2100

|
| $46–60 billion

| ( [[#DCCEE--2011|DCCEE, 2011]] )

|-
| Loss of asset value of rail and tramway infrastructure in Australia at risk of a SLR of 1.1 m by 2100

|
| $4.9–6.4 billion

| ( [[#DCCEE--2011|DCCEE, 2011]] )

|-
| Loss of asset value of residential buildings in Australia at risk of a SLR of 1.1 m by 2100 (2008 replacement value)

|
| $51–72 billion

| ( [[#DCCEE--2011|DCCEE, 2011]] )

|-
| Loss of asset value of light industrial buildings (used for warehousing, manufacturing and assembly activities and services) in Australia at risk of a SLR of 1.1 m by 2100

|
| $4.2–6.7 billion

| ( [[#DCCEE--2011|DCCEE, 2011]] )

|-
| Loss of asset value of commercial buildings (used for wholesale, retail, office and transport activities) in Australia at risk of a SLR of 1.1 m by 2100 (2008 replacement value)

|
| $58–81 billion

| ( [[#DCCEE--2011|DCCEE, 2011]] )

|-
| Accumulated loss of wealth due to reduced agricultural productivity and labour productivity

| $19 billion

| $211 billion

| $4.2 trillion

| ( [[#Steffen--2019|Steffen et al., 2019]] )

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| Wind damage to dwellings in Cairns, Townsville, Rockhampton and south-east Queensland (assuming a 4% discount rate)

| $3.8 billion

| $9.7 billion

| $20 billion

| ( [[#Stewart--2011|Stewart and Wang, 2011]] )

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| Damage to Australian coastal residential buildings due to SLR (A1B scenario, 3.5°C global warming)

|
| $8 billion

| ( [[#Wang--2016|Wang et al., 2016]] )

|}

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==== 11.5.1.3 Adaptation ====

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Coordinating adaptation strategies and addressing underlying exposure and vulnerability can increase resilience to cascading, compounding and aggregate impacts ( ''high confidence'' ) (Table 11.17; 11.7.3). Systems understanding, network analysis, stress testing, spatial mapping, collaboration, information sharing and interoperability across states, sectors, agencies and value chains, as well as national-scale facilitation, can increase adaptive capacity ( [[#Espada--2015|Espada et al., 2015]] ; [[#CoA--2020e|CoA, 2020e]] ; [[#Cradock-Henry--2020b|Cradock-Henry et al., 2020b]] ; [[#Jozaei--2020|Jozaei et al., 2020]] ). Greater system diversity, modularity, redundancy, adaptability and decentralised control can reduce the risk of cascading failures and system breakdown ( [[#Sinclair--2017|Sinclair et al., 2017]] ; [[#Sellberg--2018|Sellberg et al., 2018]] ). Addressing existing vulnerabilities in systems can reduce susceptibility and improve the resilience of interdependent systems (11.7.3). Multi-level leadership, including national and sub-national policies, laws and finance can reduce and manage aggregate risks supported by the enablers in Table 11.17.

Anticipatory governance and agile decision-making can build resilience to cascading, compounding and aggregate impacts ( ''high confidence'' ) ( [[#Boston--2016|Boston, 2016]] ; [[#Deloitte--2016|Deloitte, 2016]] ; [[#Steffen--2019|Steffen et al., 2019]] ; [[#CoA--2020e|CoA, 2020e]] ; [[#CSIRO--2020|CSIRO, 2020]] ; [[#Lawrence--2020b|Lawrence et al., 2020b]] ; [[#MfE--2020c|MfE, 2020c]] ). There is uncertainty about whether standard integrated assessment models can estimate cascading and compounding impacts across systems and sectors, but systems methodologies and social network analysis hold promise ( [[#Stoerk--2018|Stoerk et al., 2018]] ; [[#Cradock-Henry--2020b|Cradock-Henry et al., 2020b]] ). Interventions at the landscape, building and individual scales can reduce the negative health effects of current and future extreme heat, if integrated in well-communicated heat action plans with robust surveillance and monitoring ( [[#Jay--2021|Jay et al., 2021]] ).

In Australia, the National Disaster Risk Reduction Framework ( [[#CoA--2018b|CoA, 2018b]] ), National Recovery and Resilience Agency and Australian Climate Service (CoA, 2021) can provide some support for adaptation across multiple sectors. New Zealand has effective partnerships across critical infrastructure through lifelines groups, but organisational silos and lack of stress testing of plans hamper coordinated decision-making during crises and for adaptation ( [[#Brown--2017|Brown et al., 2017]] ; [[#Lawrence--2020b|Lawrence et al., 2020b]] ). The New Zealand national risk assessment, national adaptation plan, forthcoming Climate Change Adaptation Act and monitoring of adaptation progress by the Climate Change Commission provide a framework for anticipating climate change risks ( [[#MfE--2020a|MfE, 2020a]] ).

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