# Appendix TS.All: Aggregated Climate Risk Assessments in WGII AR6

This supplementary material presents the various aggregated risk assessments applied in the WGII AR6. This includes the key risks identified by all the chapters and the way they can be clustered into Representative Key Risks (RKRs) (Section TS.All.1), with a summary of the severity conditions for these RKRs across climate and development pathways, and the interactions among these risks (Section TS.All.2). The assessment of the five Reasons for Concern (RFC), presented in the iconic 'burning embers', provides a complementary cross-cutting impact and risk assessment. This approach is described in Section TS.All.3, along with a comparison with the RKRs (Section TS.All.4). The burning embers for the global and cross-cutting RFCs are complemented by similar depictions for specific regional and thematic concerns (Section SMTS2.1).

## TS.All.1 Key Risks and Representative Key Risks

Regional and sectoral chapters of this report identified 127 key risks that could become severe under particular conditions of climate hazards, exposure and vulnerability (Table SMTS.4). These key risks are assessed to be potentially severe, that is, relevant to the interpretation of dangerous anthropogenic interference (DAI) with the climate system, along levels for warming, exposure/vulnerability and adaptation. Severity has been assessed looking at the magnitude of adverse consequences, the likelihood of adverse consequences, the temporal characteristics of the risk and the ability to respond to the risks. Key risks cover scales from the local to the global, are especially prominent in particular regions or systems and are particularly large for vulnerable sub-groups, especially low-income populations, and already at-risk ecosystems (high confidence). (16.5, Table SM16.4)

These key risks can be represented in eight RKR clusters of key risks relating to low-lying coastal systems; terrestrial and ocean ecosystems; critical physical infrastructure, networks and

services; living standards; human health; food security; water security; and peace and mobility (high confidence) (Table TS. All.1). The assessment of these RKRs, which is presented in detail in Chapter 16, has also been used to organise the synthetic assessment of adaptation options in Chapter 17 and is integrated across various sections in the TS and SPM. (16.5, SM16.2.1, 17.2.1, 17.5.1)

## TS.All.2 Assessment of Severity Conditions for Representative Key Risks

Figure TS.All.1 presents a synthesis of the severity conditions for RKRs by the end of this century. As an illustration of the more specific sets of conditions that result in severe risk for a particular RKR, Figure TS.All.2 provides examples from individual studies of risks to living standards and the conditions under which they could become severe in terms of aggregate economic output, poverty and livelihoods.

The assessment of RKRs demonstrates that severe risk is rarely driven by a single determinant (warming, exposure/vulnerability, adaptation), but rather by a combination of conditions that jointly produce the level of pervasiveness of consequences, irreversibility, thresholds, cascading effects, likelihood of consequences, temporal characteristics of risk and systems' ability to respond (medium to high confidence). In other words, climate risk is not a matter of changing hazards (or climatic impact drivers) only but of the confrontation between changing hazards and changing socioecological conditions.

For most RKRs, potentially global and systemically pervasive risks become severe in the case of high levels of warming, combined with high exposure/vulnerability, low adaptation or both (high confidence). Under these conditions there would be severe and pervasive risks to critical infrastructure (high confidence), to human health from heat-related mortality, to low-lying coastal areas, aggregate economic output and livelihoods (all medium confidence) from armed conflict (low confidence) and to various aspects of food security (with different

<table><caption>Table TS.All.1 | Climate-related representative key risks (RKRs). (16.5, Table 16.6)</caption><thead><tr><td>Code</td><td>RKR</td><td>Scope</td><td>Sub-section assessment of RKR</td></tr></thead><tbody><tr><td>RKR-A</td><td>Risk to low-lying coastal socioecological systems</td><td>Risks to ecosystem services, people, livelihoods and key infrastructure in low-lying coastal areas and associated with a wide range of hazards, including sea level change, ocean warming and acidification, weather extremes (storms, cyclones) and sea ice loss, for example</td><td>16.5.2.3.1</td></tr><tr><td>RKR-B</td><td>Risk to terrestrial and ocean ecosystems</td><td>Transformation of terrestrial and ocean/coastal ecosystems, including change in structure and/or functioning and/or loss of biodiversity</td><td>16.5.2.3.2</td></tr><tr><td>RKR-C</td><td>Risks associated with critical physical infrastructure, networks and services</td><td>Systemic risks due to extreme events leading to the breakdown of physical infrastructure and networks providing critical goods and services</td><td>16.5.2.3.3</td></tr><tr><td>RKR-D</td><td>Risk to living standards</td><td>Economic impacts across scales, including impacts on GDP, poverty and livelihoods, as well as the exacerbating effects of impacts on socioeconomic inequality between and within countries</td><td>16.5.2.3.4</td></tr><tr><td>RKR-E</td><td>Risk to human health</td><td>Human mortality and morbidity, including heat-related impacts and vector-borne and water-borne diseases</td><td>16.5.2.3.5</td></tr><tr><td>RKR-F</td><td>Risk to food security</td><td>Food insecurity and the breakdown of food systems due to climate change effects on land or ocean resources</td><td>16.5.2.3.6</td></tr><tr><td>RKR-G</td><td>Risk to water security</td><td>Risk from water-related hazards (floods and droughts) and water quality deterioration; focus on water scarcity, water-related disasters and risk to Indigenous and traditional cultures and ways of life</td><td>16.5.2.3.7</td></tr><tr><td>RKR-H</td><td>Risks to peace and to human mobility</td><td>Risks to peace within and among societies from armed conflict as well as risks to low-agency human mobility within and across state borders, including the potential for involuntarily immobile populations</td><td>16.5.2.3.8</td></tr></tbody></table>
levels of confidence). Severe risks interact through cascading effects, potentially causing amplification of RKRs over the course of this century (low evidence, high agreement). (Figure TS.All.1) {16.5.2, 16.5.4, Figure 16.10}

For some RKRs, potentially global and systemically pervasive risks would become severe even with medium to low warming (i.e., 1.5°C-2°C) if exposure/vulnerability is high and/or adaptation is low (medium to high confidence). Under these conditions there would be severe and pervasive risks associated with water scarcity and water-related disasters (high confidence), poverty, involuntary mobility and insular ecosystems and biodiversity hotspots (all medium confidence). {16.5.2}

All potentially severe risks that apply to particular sectors or groups of people at more specific regional and local levels require high exposure/ vulnerability or low adaptation (or both), but they do not necessarily require high warming (high confidence). Under these conditions there would be severe, specific risks to low-lying coastal systems, to people and economies from critical infrastructure disruption, to economic output in developing countries and to livelihoods in climate-sensitive sectors from water-borne diseases, especially in children in low- and middle-income countries, water-related impacts on traditional ways of life and involuntary mobility, for example in small islands and low-lying coastal areas (medium to high confidence). {16.5.2}

Some severe impacts are already occurring (high confidence) and will occur in many more systems before mid-century (medium confidence). Tropical and polar low-lying coastal human communities are experiencing severe impacts today (high confidence), and abrupt ecological changes resulting from mass population-level mortality are already being observed following climate extreme events. Some systems will experience severe risks before the end of the century (medium confidence), for example critical infrastructure affected by extreme events (medium confidence). Food security for millions of people, particularly low-income populations, also faces significant risks with moderate to high warming or high vulnerability, with a growing challenge by 2050 in terms of providing nutritious and affordable diets (high confidence). {16.5.2, 16.5.3}

In specific systems already marked by high exposure and vulnerability, intensive adaptation efforts will not be sufficient to prevent severe risks from occurring under high levels of warming (low evidence, medium agreement). This is particularly the case for some ecosystems and water-related risks (from water scarcity and to Indigenous and traditional cultures and ways of life). {16.5.2, 16.5.3}

Key risks increase the challenges in achieving global sustainability goals (high confidence). The greatest challenges will be from risks to water (RKR-G), living standards (RKR-D), coastal socioecological systems (RKR-A) and peace and human mobility (RKR-H). The most relevant goals are zero hunger (SDG 2), sustainable cities and communities (SDG 11), life below water (SDG 14), decent work and economic growth (SDG 8), and no poverty (SDG 1). Priority areas for regions are indicated by the intersection of hazards, risks and challenges, where, in the near term, challenges to SDGs indicate

probable systemic vulnerabilities and issues in responding to climatic hazards (high confidence). {16.6.1}

Multiple feedbacks between individual risks exist that have the potential to create cascades and then to amplify systemic risks and impacts far beyond the level of individual RKRs (medium confidence), as also reflected in TS.C.11. These are illustrated in Figure TS.All.3, panel A at the RKR level, and in Figure TS.All.3, panel B at the key risk level.

### TS.All.3 Framework and Approach for Assessment of Burning Embers for Reasons for Concern

The RFC framework communicates scientific understanding about accrual of risk in relation to varying levels of warming for five broad categories: risk associated with (a) unique and threatened systems, (b) extreme weather events, (c) distribution of impacts, (d) global aggregate impacts and (e) large-scale singular events. The RFC framework was first developed during the Third Assessment Report along with a visual representation of these risks as 'burning embers' figures, and this assessment framework has been further developed and updated in subsequent IPCC reports including AR5. RFCs reflect risks aggregated globally that together inform the interpretation of dangerous anthropogenic interference with the climate system. (Figure TS.All.1) {16.6.2}

The risk transition or 'ember' diagram illustrates the progression of socioecological risk from climate change as a function of global temperature change, taking into account the exposure and vulnerability of people and ecosystems, as assessed by literature-based expert judgement. The definitions of risk levels used to make the expert judgements are presented in Table TS.All.2 {16.6.2}. Further details are provided in Section 16.6.3. (Figure TS.4)

### TS.All.4 Relationship between Representative Key Risks and Reasons for Concern

The RKRs and RFCs are complementary methods that aggregate individual risks in different ways, as displayed in Figure TS.All.4. They have differences in scale, transitions, timing and treatment of vulnerability and adaptation {16.6.2}
Synthesis of the severity conditions for Representative Key Risks by the end of this century

<figure><img src="image_629.png" /></figure>

**Figure TS.All.1 | Synthesis of the severity conditions for Representative Key Risks (RKRs) by the end of this century.** The figure does not aim to describe severity conditions exhaustively for each RKR, but rather to illustrate the risks highlighted in this report (Sections 16.5.2.3.1 to 16.5.2.3.8). Coloured circles represent the levels of warming (climate), exposure/vulnerability and adaptation that would lead to severe risks for particular key risks and RKRs. Each set of three circles represents a combination of conditions that would lead to severe risk with a particular level of confidence, indicated by the number of black dots to the right of the set, and for a particular scope, indicated by the number of stars to the left of the set. The two scopes are 'broadly applicable', meaning applicable pervasively and even globally, and 'specific', meaning applicable to particular areas, sectors or groups of people. Details of confidence levels and scopes can be found in Section 16.5.2.3. In terms of severity condition levels (Section 16.5.2.3), for warming levels (coloured circles labelled 'C' in the figure), high refers to climate outcomes consistent with RCP8.5 or higher, low refers to climate outcomes consistent with RCP2.6 or lower, and medium refers to intermediary climate scenarios. Exposure-vulnerability levels are determined relative to the range of future conditions considered in the literature. For adaptation, high refers to near maximum potential and low refers to the continuation of today's trends. Despite being intertwined in reality, exposure-vulnerability and adaptation conditions are distinguished to help understand their respective contributions to risk severity. (Figure 16.10)
## Illustrative examples from individual studies of risks to living standards and the conditions under which they could become severe

<figure><img src="image_630.png" /></figure>

### References:

1. Acevedo (2017); 2. Baarsch et al. (2020); 3. Burke et al. (2015); 4. Byers et al. (2018); 5. Carleton and Greenstone (2021); 6. Hallegatte (2017); 7. Hallegatte and Rozenberg (2017);

8. Hoegh-Guldberg (2018); 9. Hsiang et al. (2017); 10. Jafino (2020); 11. Jafino et al. (2020); 12. Kahn (2019); 13. Kalkuhl (2020); 14. Norden (2014); 15. Roy (2018); 16. World Bank (2020)

<figure><img src="image_631.png" /></figure>

**Figure TS.All.2** | Illustrative examples from individual studies of risks to living standards and the conditions under which they could become severe in terms of aggregate economic output, poverty and livelihoods. High, medium and low levels of warming, exposure/vulnerability and adaptation are defined as in Figure TS.All.1.
[Figure 16.9]
## Illustration of some connections across key risks

<figure><img src="image_632.png" /><figcaption>(b) Illustration of interactions at the Key Risk level (e.g. from ecological risk to key dimensions for human societies)</figcaption></figure>

<figure><img src="image_633.png" /></figure>

N.B.: Anthropogenic drivers are not represented as such in panel B, but contribute to all risk considered in this figure

<figure><img src="image_634.png" /></figure>

<footnote>* CIDs are physical climate system conditions (e.g., means, events, extremes) that affect an element of society or ecosystems. Indicated changes are system-dependent and can be detrimental, beneficial, neutral, or a mixture of each. (WGI AR6 SPM)</footnote>

<footnote>** As illustrative suggested rather across than RKR comprehensive, assessments; and qualitative rather than quantitative</footnote>
<table><caption>Table TS.All.4 | Definition of risk levels for reasons for concern. (Table 16.7)</caption><thead><tr><td>Level</td><td>Definition</td></tr></thead><tbody><tr><td>Undetectable (white)</td><td>No associated impacts are detectable and attributable to climate change</td></tr><tr><td>Moderate (yellow)</td><td>Associated impacts are both detectable and attributable to climate change with at least medium confidence, also accounting for the other specific criteria for key risks</td></tr><tr><td>High (red)</td><td>Severe and widespread impacts that are judged to be high on one or more criteria for assessing key risks</td></tr><tr><td>Very high (purple)</td><td>Very high risk of severe impacts and the presence of significant irreversibility or the persistence of climate-related hazards, combined with limited ability to adapt due to the nature of the hazard or impacts/risks</td></tr></tbody></table>

Interconnections between the Key Risks, Representative Key Risks and the Reasons for Concern

<figure><img src="image_635.png" /><figcaption>Figure TS.All.4 | Interconnections among key risks, representative key risks and reasons for concern (Figure 16.13)</figcaption></figure>