Editing IPCC:AR6/WGII/Chapter-16 (section)

=== 16.6.1 Key Risks and Sustainable Development ===

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The United Nations 2030 Agenda for Sustainable Development, and the SDGs ( [[#UN--2015|UN, 2015]] ), since 2015, have become an important vision for the United Nations member countries (Chimhowu, 2019) as well as for corporations to contribute towards sustainable growth ( [[#UNDP--2016|UNDP et al., 2016]] ; [[#Ike--2019|Ike et al., 2019]] ; [[#van%20der%20Waal--2020|van der Waal and Thijssens, 2020]] ). Climate change risks, as embodied in the RKR and RFCs, can affect attainment of the SDGs and have consequences for lives and livelihoods (related to SDGs 1, 4, 8 and 9), health and well-being (related to SDGs 2, 3 and 6), ecosystems and species (related to SDGs 6, 14 and 15), economic (related to SDGs 1, 8 and 12), social and cultural assets (related to SDGs 5, 10, 11, 16 and 17), services including ecosystem services (related to SDGs 6, 7, 11, 12, 14 and 15), and infrastructure (related to SDGs 6, 7, 9, 11 and 12). This section assesses the level of linkages between key risks with sustainable development, in terms of the SDG targets and indicators. This informs on the key risks which are most relevant to consider with respect to the attainment of the SDGs.

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==== 16.6.1.1 Links between Key Risks and Sustainable Development Goals ====

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Within the AR6 cycle, the three IPCC Special Reports have all considered the relationships between climate change impacts and actions and the SDGs. SR15 discussed priorities for sustainable development in relation to climate adaptation efforts ( [[IPCC:Wg2:Chapter:Chapter-5#5.3.1|Section 5.3.1]] , SR15); synergies and trade-offs of climate adaptation measures ( [[IPCC:Wg2:Chapter:Chapter-5#5.3.2|Section 5.3.2]] , SR15); and the effect of adaptation pathways towards a 1.5°C warmer world ( [[IPCC:Wg2:Chapter:Chapter-5#5.3|Section 5.3.3]] SR15). The SRCCL considered impacts of desertification on SDGs 1 (no poverty), 2 (zero hunger), 13 (climate), 15 (life on land) and 5 (gender) ( [[#IPCC--2019a|IPCC, 2019a]] , Figure 3.9). Trade-offs and synergies between SDGs 2 (zero hunger) and 13 (climate action) at the global level were recognised ( [[#IPCC--2019a|IPCC, 2019a]] , [[IPCC:Wg2:Chapter:Chapter-5#5.6|Section 5.6.6]] , Figure 5.16). Various integrated response options, interventions and investments were also evaluated within the SDG framework ( [[#IPCC--2019a|IPCC, 2019a]] , [[IPCC:Wg2:Chapter:Chapter-6#6.4.3|Section 6.4.3]] ). The SROCC (Chapter 5) concluded that climate change impacts on the ocean, overall, will negatively affect achieving the SDGs, with 14 (life below water) being most relevant ( [[#Singh--2019|Singh et al., 2019]] ).

Many linkages between SDG 13 (climate action) and other SDGs have been identified ( ''very high confidence'' ) ( [[#Blanc--2015|Blanc, 2015]] ; [[#Kelman--2015|Kelman, 2015]] ; [[#Northrop--2016|Northrop et al., 2016]] ; [[#Hammill--2017|Hammill and Price-Kelly, 2017]] ; [[#ICSU--2017|ICSU, 2017]] ; [[#Mugambiwa--2017|Mugambiwa and Tirivangasi, 2017]] ; [[#Dzebo--2018|Dzebo et al., 2018]] ; [[#Major--2018|Major et al., 2018]] ; [[#Nilsson--2018|Nilsson et al., 2018]] ; [[#Sanchez%20Rodriguez--2018|Sanchez Rodriguez et al., 2018]] ). In addition, interactions between different climate change actions and SDGs, and interactions among SDGs themselves, have also been assessed ( [[#Nilsson--2016|Nilsson et al., 2016]] ; [[#IPCC--2018a|IPCC, 2018a]] ; [[#McCollum--2018|McCollum et al., 2018]] ; [[#Fuso-Nerini--2019|Fuso-Nerini et al., 2019]] ; [[#IPCC--2019b|IPCC, 2019b]] ; [[#Cernev--2020|Cernev and Fenner, 2020]] ). The Cross-Chapter Box GENDER in [[IPCC:Wg2:Chapter:Chapter-18|Chapter 18]] assessment indicates the importance of gender considerations in achieving success and benefits in adaptation efforts. Aligning climate change adaptation to the SDGs could bring potential co-benefits and increased efficiency in funding, and reduce the gap between adaptation planning and implementation ( ''very high confidence'' ) ( [[#IPCC--2018a|IPCC, 2018a]] ; [[#Sanchez%20Rodriguez--2018|Sanchez Rodriguez et al., 2018]] ; [[#IPCC--2019b|IPCC, 2019b]] ; [[#IPCC--2019a|IPCC, 2019a]] ).

Progress towards meeting the SDGs has been recognised to be able to reduce global disparities and support more climate resilient development pathways (IPCC WGII AR5, Chapter 13, p. 818; discussed further in Chapter 18). Nevertheless, we are still lagging in achieving the 2030 Goals ( [[#OECD--2019|OECD, 2019]] ; [[#Sachs--2021|Sachs et al., 2021]] ), and this affects societal vulnerability, readiness and risk response capacities ( [[#IPCC--2019a|IPCC, 2019a]] , Chapters 6, 7, Chapters 6 and 8, this report). We assess the risk literature for linkages between key risks (grouped by RKRs) and the indicators of the SDGs ( [[#UN--2015|UN, 2015]] ) using text analysis (details in SM16.5) to identify the potential level of effect of different risks on the SDGs. Some 940 documents were analysed. The SDG status is associated with projected climate hazards, also called climatic impact drivers (CIDs) ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ) (panel a), and RKRs (panel c), summarising hazard and exposure with vulnerability aspects, as expressed by challenges in achieving the SDGs (panel d), on a regional level (Figure 16.12).

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[[File:b841e572052129fd154aa12623b9c0db IPCC_AR6_WGII_Figure_16_012.png]]

'''Figure 16.12 |''' '''Linkages between the projected climatic impact drivers (CIDs) by region, Sustainable Development Goals (SDGs) by region, and the representative key risks (RKRs).'''

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==== 16.6.1.2 Results, Implications and Gaps ====

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Linkages between the 17 SDGs and the eight RKRs (Figure 16.12 bottom left panel) are mapped to the regional SDG status (Figure 16.12 bottom right panel) and related to the CIDs (Figure 16.12 top left panel). Interconnections between CIDs and RKRs are complicated by the possibility of concurrent weather events, extremes and longer-term trends. Risks are compounded by existing vulnerabilities ( [[#Iwama--2016|Iwama et al., 2016]] ; [[#Thomas--2019b|Thomas et al., 2019b]] ; [[#Birkmann--2021|Birkmann et al., 2021]] ) and cascading consequences ( [[#Pescaroli--2015|Pescaroli and Alexander, 2015]] ; [[#Pescaroli--2018|Pescaroli and Alexander, 2018]] ; [[#Yokohata--2019|Yokohata et al., 2019]] ) (see, for example, Sections 3.4.3.5, 5.12, 6.2.6, 7.2.2.2) as well as interactions. The level of challenges faced in attaining the SDGs is one metric for assessing vulnerability and lack of capacity to manage risks ( [[#Cernev--2020|Cernev and Fenner, 2020]] ). Other metrics are also available ( [[#Parker--2019|Parker et al., 2019]] ; [[#Garschagen--2021b|Garschagen et al., 2021b]] ; [[#Birkmann--2022|Birkmann et al., 2022]] ). From Figure 16.12, aside from SDG13 (climate action), the strongest connections and risk challenges are with zero hunger (SDG2), sustainable cities and communities (SDG11), life below water (SDG14), decent work and economic growth (SDG8), no poverty (SDG1), clean water and sanitation (SDG6) and good health and well-being (SDG3) ( ''high confidence'' ). Other SDGs have strong linkages with specific RKRs, for example, terrestrial and marine ecosystems with life on land (SDG15); infrastructure (RKR-C) with industry, innovation and infrastructure (SDG9) and affordable and clean energy (SDG7); living standards (RKR-D) with gender equality (SDG5); and peace and human mobility (RKR-H) with peace, justice and strong institutions (SDG 16) ( ''high confidence'' ).

On a global scale, priority areas for regions can be evaluated from the intersection of climate hazards, risks and the level of challenges in SDG attainment ( [[#Moyer--2020|Moyer and Hedden, 2020]] ; [[#Sachs--2021|Sachs et al., 2021]] ). The greatest linkages and effects on the SDGs will be due to risks to water (RKR-G), living standards (RKR-D), coastal socio-ecological systems (RKR-A) and peace and human mobility (RKR-H) ( ''high confidence'' ) (details in SM16.5).

In particular, coastal socio-ecological systems (RKR-A), living standards (RKR-D), food security (RKR-F), water security (RKR-G) and peace and human mobility (RKR-H), have strong linkages with SDG 2 (zero hunger), for which there are significant to major challenges for all regions ( ''high confidence'' ). Almost all the RKRs are strongly linked to SDGs 8 (decent work and economic growth) and 11 (sustainable cities and communities) ( ''high confidence'' ), where regions such as Africa, Asia, and Central and South America face significant to major challenges in attaining targets. All regions also face major to significant challenges affecting SDGs 14 (life below water) and 15 (life on land), which relate to terrestrial and ocean ecosystems (RKR-B) ( ''high confidence'' ).

The analysis of RKR linkages to SDGs is also useful in identifying gaps and susceptibilities, especially for developing future climate resilient development targets. This aspect is discussed further in Chapter 18. Gaps may arise as SDG targets and indicators are not specifically focused on systems affected by climate change risks or impacts. For example, in the SRCCL [[IPCC:Wg2:Chapter:Chapter-7#7.1.2|Section 7.1.2]] , [[#Hurlbert--2019|Hurlbert et al. (2019)]] noted the absence of an explicit goal for conserving freshwater ecosystems and ecosystem services in the SDGs. Such gaps ( [[#Tasaki--2015|Tasaki and Kameyama, 2015]] ; [[#Guppy--2019|Guppy et al., 2019]] ) are inevitable as the current SDG targets and indicators focus on overall sustainable development. As another example, projected increases in frequency and intensity of hot temperature extremes are likely to result in increased heat-related illness and mortality, yet heat extremes are not called out as an SDG indicator under SDGs 3 (good health and well-being) or 13 (climate action). The gaps on climate-related metrics for impacts on health are just beginning to be evaluated ( [[#Lloyd--2019|Lloyd and Hales, 2019]] , see also [[IPCC:Wg2:Chapter:Chapter-7#7.1.6|Section 7.1.6]] ). The current SDG 13 (climate action) targets also do not specifically track the possibility of differential impacts on society from disasters and extreme weather events (RFC2). For example, the first indicator ( [[IPCC:Wg2:Chapter:Chapter-13#13.1.1|Section 13.1.1.1]] ), ‘Number of deaths, missing persons and directly affected persons attributed to disasters per 100,000 population’, does not include any requirement for disaggregated data, unlike several other socioeconomic and population SDG indicators, making it difficult to track the different effects that climate-related disasters are expected to have on men, women and children across different segments of society, relevant for distributional impacts (RFC3) (see also [[IPCC:Wg2:Chapter:Chapter-8#8.3|Section 8.3]] , Cross-Chapter Box GENDER in Chapter 18). The risk consequences identified and discussed in each RKR ( [[#16.5.2|Section 16.5.2]] ) provide useful entry points for identifying indicators and metrics for monitoring and evaluating specific impacts of key climate change risks. In addition, the sector and region chapters have considered various adaptation responses relevant to the SDGs (see, for example, Sections 3.6, 4.7.5, 5.13.3, 8.2.1.6, 10.6.1, 13.11.4, 14.6.3) with relevant metrics for evaluation.

In summary, key risks, and the consequences arising from them, are directly linked to and will affect specific indicators of the SDGs ( ''high confidence'' ). They also will be indirectly linked to, and thus affect, the SDGs overall, due to the interactions between the key risks ( [[#16.5|Section 16.5]] ) and between the SDGs themselves ( ''very high confidence'' ). These results support previous findings that climate change impacts pose a risk to achieving sustainability ( [[#Ansuategi--2015|Ansuategi et al., 2015]] ; [[#Chirambo--2016|Chirambo, 2016]] ; [[#ICSU--2017|ICSU, 2017]] ; [[#Pradhan--2017|Pradhan et al., 2017]] ; [[#Gomez-Echeverri--2018|Gomez-Echeverri, 2018]] ; [[#IPCC--2018a|IPCC, 2018a]] ; [[#IPCC--2019b|IPCC, 2019b]] ; [[#IPCC--2019a|IPCC, 2019a]] ; [[#Cernev--2020|Cernev and Fenner, 2020]] ). Not all observed or expected consequences arising from the key risks are fully captured by the SDG indicators, nor were they designed to be. Therefore, for monitoring and assessing the climate risk impacts, it is useful to consider specific climate change impact indicators and metrics ( [[#Enenkel--2020|Enenkel et al., 2020]] ) to capture any realised impacts.

In the near term, the strength of connection between the RKRs and the SDGs, with respect to existing SDG challenges, indicate probable systemic vulnerabilities and issues in responding to climatic hazards ( [[#UN-IATFFD--2019|UN-IATFFD, 2019]] ; Leal [[#Filho--2020|Filho et al., 2020]] ; [[#Weaver--2020|Weaver et al., 2020]] ; [[#Tiedemann--2021|Tiedemann et al., 2021]] ) ( ''high confidence'' ). In the medium to long term (associated with global warming levels of between 2°C and 2.7°C under SSP2–4.5 scenario), if such vulnerabilities and challenges cannot be substantially reduced, the hazards and risks resulting from the projected CIDs (Figure 16.12b, c) will further stress systems relevant for sustainable development, based on current experience of the COVID-19 pandemic ( [[#UN-IATFFD--2021|UN-IATFFD, 2021]] , see also Cross-Chapter Box COVID in Chapter 7; Sections 8.2, 8.3) ( ''medium confidence'' , based on ''medium evidence'' , ''high agreement'' ).

The potential impacts of the various climate hazards, the occurrence of extreme events, and the projected trends of climate hazards give rise to complex risks for ecological and human systems, which are compounded by the exposure, vulnerability and sustainability challenges faced in different regions of the world. The potential global consequences are elaborated in the next section, which describes the framework and approach for the assessment of the five RFCs.

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===== Relationship between RKRs and RFCs =====

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RFCs reflect risks aggregated globally that together inform the interpretation of DAI with the climate system. The five RFC categories are maintained as previously defined for consistency with earlier assessments. Compared with the synthesis of risk across RKRs in [[#16.5|Section 16.5]] , we note that the RKRs and RFCs are complementary methods that aggregate individual risks into different but interconnected categories (Figure 16.13).

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[[File:d61d135c63b44321897e7579fcdb6a3d IPCC_AR6_WGII_Figure_16_013.png]]

'''Figure 16.13 |''' '''Interconnections between the key risks, representative key risks and Reasons for Concern.'''

We draw important distinctions between RFC and RKR. First, RFCs assess risks that might be of global concern, while RKRs also include risks that may be of concern only locally or for specific population groups (Figure 16.13). RFCs focus on the full range of increasing risk, and locate transitions between four categories of risk: undetectable, moderate, high, and very high. RKRs focus on severe risks, and attempt to elaborate when/where severe impacts may occur. RKR assessments focus on the conditions under which some risks would become severe over the course of this century, while RFCs evaluate changes in risk levels against gradual increase in temperature levels. The RKR analysis used specific definitions of severity including quantified thresholds where possible, and this is distinct from the approach based on the combined elements of risk used in the RFC expert elicitation process. Severity as defined in the RKRs is associated with high or very high risk levels but does not align precisely with either of those categories, and a further difference arises from a more explicit emphasis on irreversibility and adaptation limits in the very high risk category in the RFCs. Thus, RKR and RFC neither map directly to one another in terms of content, nor in terms of the response metric.

The treatment of vulnerability and adaptation is different in the RKR and RFC assessments. The RKR assessment considered specifically three alternative levels of vulnerability, whereas the RFC process did not explicitly differentiate risk by level of vulnerability. Therefore, the global warming levels at which the various RKR assessments identify risk of severe impacts are not directly comparable to risk transitions identified in the RFC assessments. In addition, RKRs consider implications of low versus high adaptation in order to illustrate the potential role of ambitious adaptation efforts to limit risk severity; RFCs consider risks in a no/low adaptation scenario only, although there is some discussion of the potential role of adaptation in assessing the transition to very high risk. Last, both RKRs and RFCs focus on the 21st century scale, though recognising risk will continue to increase after 2100, but treat this timing issue differently: RKRs assess severe risks over the course of this century and distinguish risks that are already severe, that will become severe by the mid-century, or that will become severe by the end of the century; while RFCs assess risk level irrespective of their timing, but according to different temperature levels.

Many of the elements of risk which contribute to RKRs also contribute to risk within one or more RFCs. In turn, elements of risk within some RFCs, such as extreme weather and changes in the Earth system contribute to risk within one or more RKR. Hence, RFCs may incorporate elements of many different RKRs, and vice versa. There are therefore common elements between some particular RKRs and RFCs: for example, risks to terrestrial and ocean ecosystems (RKR-B) contribute strongly to RFC1 (Unique and Threatened Systems) and RFC4 (Global Aggregate Impacts), while RFC2 (extreme weather events) has implications for all RKRs, including direct linkages with critical physical infrastructure, networks and services (RKR-C). Furthermore, risks emerging from the interaction of RKRs also contribute to the RFCs, but are only qualitatively described in [[#16.5.4|Section 16.5.4]] . For example, the effects of risks to terrestrial and ocean ecosystems (RKR-A) affect living standards and equity (RKR-C), as does the associated decline in ecosystem services which then impacts livelihoods (RKR-D).

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===== Elicitation Methodology =====

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The method used to develop judgements on levels of risk builds on the approach described in WGII AR5 Chapter 19 ( [[#Oppenheimer--2014|Oppenheimer et al., 2014]] ) and outlined in more detail in the work of [[#O’Neill--2017|O’Neill et al. (2017)]] , while integrating advances in the AR6 SRs including expert judgement (SRCCL, [[#Zommers--2020|Zommers et al., 2020]] ). We provide further details on the underlying judgements of risk level compared with previous assessments by indicating key risk criteria associated with each judgement: magnitude of adverse consequences, likelihood of adverse consequences, temporal profile of the risk, and ability to respond to the risk ( [[#16.5.1|Section 16.5.1]] ). The definitions of risk levels used to make the expert judgements are presented in Table 16.7 ( [[#16.5.1|Section 16.5.1]] ).

'''Table 16.7 |''' Definition of risk levels for Reasons for Concern.

{| class="wikitable"
|-
! Level

! Definition

|-
| Undetectable (white)

| No associated impacts are detectable and attributable to climate change.

|-
| Moderate (yellow)

| 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.

|-
| High (red)

| Severe and widespread impacts that are judged to be high on one or more criteria for assessing key risks.

|-
| Very high (purple)

| 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.

|}

A brief summary of the framework that was used to carry out the risk assessment, synthesis and expert elicitation is presented here, and details are provided in SM16.6. Expert judgements about the qualitatively defined levels of risk (i.e., undetectable, moderate, high, and very high) reached at various levels of global average warming are informed by evidence of observed impacts illustrated in [[#16.2|Section 16.2]] and variations in individual key risks under different scenarios of climate change, socioeconomics and adaptation effort in [[#16.5|Section 16.5]] . We follow the methodological advances from SRCCL [[IPCC:Wg2:Chapter:Chapter-7|Chapter 7]] ( [[#Hurlbert--2019|Hurlbert et al., 2019]] ), which used an expert elicitation protocol for developing the burning embers ( [[#Zommers--2020|Zommers et al., 2020]] ). Specifically, we used expert participants from within the AR6 author team and a protocol based on the modified Delphi technique ( [[#Mukherjee--2015|Mukherjee et al., 2015]] ) and the Sheffield Elicitation Framework ( [[#Oakley--2010|Oakley and O’Hagan, 2010]] ; [[#Gosling--2018|Gosling, 2018]] ). This approach (Figure 16.14) includes a two-round elicitation process with a first round of independent anonymous judgements about the global warming level at which risk levels transition from one to the next, and a final round of group discussion and deliberation to develop consensus. The results are then reported, and additional references are made to findings from other relevant chapters in this report. Then, authors who had not participated in the elicitation as part of independent appraisal review the results.

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[[File:ec25942263bc47b0c7ff54998c9a0336 IPCC_AR6_WGII_Figure_16_014.png]]

'''Figure 16.14 |''' '''Expert elicitation approach for assessment of RFC risk level transitions.''' A more detailed description of the methodology used in this elicitation is provided in SM16.6.

The resulting risk transition or ‘ember’ diagram illustrates the progression of socio-ecological 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. [[#16.6|Section 16.6.3]] presents these diagrams for each RFC, providing information about the most important literature-based evidence that experts used to make their judgements. Similar assessments for selected individual KRs are discussed in Chapters 2, 7, 9, 12, 13 and 14.

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===== Representation of warming levels =====

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The RFC assessment reflects the latest understanding of warming reported in WGI AR6. Global surface temperature was 1.09 [0.95 to 1.20]°C higher in 2011–2020 than 1850–1900, with stronger warming over land (1.59 [1.34 to 1.83]°C) than over the ocean (0.88 [0.68 to 1.01]°C) (WGI AR6 Cross Chapter Box 2.3 Table 1, Eyring et al. in [[#Gulev--2021|Gulev et al., 2021]] ). Warming levels are commonly reported and studied in the impacts literature using two scales of spatially averaged temperature rise, global surface air temperature (GSAT), commonly produced by General Circulation Models (GCMs) when projecting climate changes, and global mean surface temperature (GMST), commonly used in empirical studies. Both have the same reference point of pre-industrial of 1850–1900. The ember diagrams presented here use GSAT, which is consistent with most literature of projected risk (largely based on the output of climate models). To the extent that the embers also draw on the observed impacts literature using GMST, this potential variation is minimal as the average levels of GSAT and GMST have been shown to match closely (for further discussion on this, see Cross-Chapter Box CLIMATE in Chapter 1). Hence, the diagrams are presented with a single ''y'' -axis representing global temperature change, generally referring to global temperature rise irrespective of when it occurs; however, the majority of the literature assessed considers alternative levels of warming during the 21st century. For example, a warming level of 2°C might occur in the 2050s, in the 2080s or in 2100 (see next section).

Furthermore, climate-related hazards associated with each of the RFCs are assessed in WGI AR6 Cross-Chapter Box 12.1 Table 1 ( [[#Tebaldi--2021|Tebaldi et al., 2021]] ), which synthesises information from various chapters of WGI on 35 such hazards according to global warming levels (GWLs) to inform understanding of their potential changes and associated risks with temperature levels in general.

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===== Temporal dimension =====

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When are the risks shown in the embers projected to occur? The issues associated with assessing transient risks are discussed in Chapter 3, SR15 ( [[#IPCC--2018a|IPCC, 2018a]] ). Some of the literature, however, does explore the dynamics within human and natural systems (i.e., the way in which systems respond when a transient level of warming is first reached, and then further, how they continue to develop if that transient level of warming is then maintained indefinitely). We note that this important factor is captured in the RFC assessment (and ember diagrams), since the timing of risk accrual is one of the criteria for the assessment of the level of risk ( [[#16.5.1|Section 16.5.1]] ). Risks that are known to evolve only over very long-time scales contribute less to the level of risk than those which are known to occur rapidly. This is because SLR also depends on the dynamics of global warming, including the rate of change of radiative forcing, and time lags of several decades, including between atmospheric and ocean warming, and in reaching equilibrium sea level state ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ). However, longer-term risks that would arise if those transient temperatures were maintained are also included, and this is particularly important in RFC5 (large-scale singular events). Note that risks that take place over a very long time scale are considered to be of lower concern than more imminent risks. However, changes of very large magnitude can still be very important even if far away in time, especially if these changes are irreversible (or reversible only on extremely long time scales) (see [[#16.5.1|Section 16.5.1]] ).

Although the embers do not indicate the decade in which certain risks are projected to occur, clearly this depends strongly on the level of mitigation action as well as the degree of adaptation. Hence, the ember diagram (Figure 16. 15 ) is shown alongside a graphic illustrating possible global temperature time series emerging from alternative future scenarios assessed by WGI AR6 which imply different levels of mitigation effort. For example, in a scenario with a high level of mitigation effort (SSP1–1.9) reaching net zero emissions in the 2050s, it is ''extremely likely'' that global warming remains below 2°C and more than 50% ''likely'' that it will remain below 1.6°C (AR6 WGI 4.3.1.1, [[#Meinshausen--2020|Meinshausen et al., 2020]] ). On the other hand, a level of 2°C warming is ''extremely likely'' to be exceeded during the 21st century under the three scenarios assessed by WGI AR6 in which GHG emissions do not fall below current levels before mid-century (i.e., SSP2–4.5, SSP3–7.0, SSP-8.5) (WGI AR6 4.3.1.1, [[#Lee--2021|Lee et al., 2021]] ). WGI AR6 has assessed that ‘global surface temperature averaged over 2081–2100 is ''very likely'' to be higher by 1.0°C–1.8°C under the lowest CO 2 emission scenario considered in this report (SSP1–1.9) and by 3.3°C–5.7°C under the highest CO 2 emission scenario (SSP5–8.5)’. However, almost all scenarios assessed by IPCC AR6 WGI reach 1.5°C global warming level in the early 2030s (WGI AR6 SPM, [[#IPCC--2021|IPCC, 2021]] ).

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===== Temperature overshoot =====

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The concept of temperature overshoot, defined as ‘exceedance of a specified global warming level followed by a decline to or below that level during a specified period of time’ is a relevant consideration for this RFC risk assessment; however, the effect of overshoot has not explicitly been considered in the burning ember assessment because of the limited literature basis. However, despite the lack of directly assessed overshoot scenarios, the current literature provides several salient examples of irreversible changes that are projected to occur once global temperatures reach a particular level. For example, coral reefs are unable to survive repeated bleaching events that are too close together, leading to irreversible loss of the reefs even if bleaching were to cease (see [[#16.6|Section 16.6.3.1]] RFC1). Species extinction is irreversible, and [[IPCC:Wg2:Chapter:Chapter-2|Chapter 2]] assesses that, at ~1.6°C, &gt;10% of species are projected to become endangered as compared with &gt;20% at ~2.1°C (median), representing high and very high biodiversity risk, respectively ( ''medium confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-2#2.5.4|Section 2.5.4]] ). Similarly, WGI AR6 finds that ‘Over the 21st century and beyond, abrupt and irreversible regional changes in the water cycle, including changes in seasonal precipitation, streamflow and aridity, cannot be excluded’. Thus, information about irreversibility provides information about the potential outcome of temperature overshoot scenarios. Other types of losses, such as loss of human or species life, are irreversible even if the loss process ceases in the future. The less resilient a system is, the more likely it is to suffer irreversible damage during a temperature overshoot; the more resilient it is, the more likely it is to be able to withstand the overshoot or recover afterwards. Very high levels of risk, as assessed here in the RFC, are associated with a wide range of criteria for risk assessment including irreversibility. While not all very high risks are irreversible, in general, risks reaching a very high level include a component of irreversible risks that would persist during and after an overshooting of a given temperature level.

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===== Risks associated with socioeconomic development, mitigation and maladaptation =====

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The ember diagrams in Figure 16. 15 capture only the risks arising from exposure of vulnerable socio-ecological systems to climatic hazards across a range of socioeconomic futures. They do not capture any risk component arising solely from changes in population or level of development. Importantly, they also do not capture additional risks that may arise from the human response to climate change, including climate change mitigation or unintended negative consequences of adaptation-related responses (i.e., maladaptation) ( [[IPCC:Wg2:Chapter:Chapter-17#17.5.1|Section 17.5.1]] ). Such risks are discussed in SRCCL Chapter 7, for example, adverse effects of the very large-scale use of land and water for primary bioenergy production on food production and biodiversity ( [[#Hurlbert--2019|Hurlbert et al., 2019]] ). Contributions of mitigation or maladaptation to risk can be important, however, and are discussed further in the context of specific RFCs in [[#16.6|Section 16.6.3]] . In general, such components of risk are difficult to quantify, and can be minimised by good design of climate change mitigation and adaptation. Thus, the effect is excluded from the ember diagrams to allow a clearer representation of the accrual of climate change risk with global warming.

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===== Emergent risk =====

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AR5 [[#Oppenheimer--2014|Oppenheimer et al. (2014)]] defined ‘emergent risk’ as a risk that arises from the interaction of phenomena in a complex system. While emergent risk is a relevant consideration for this RFC risk assessment, this type of risk has not been explicitly accounted for in the burning ember assessment because of the limited literature basis. Unlike known or identified risks, emergent risks are characterised by the uncertainty of consequences and/or probabilities of occurrence. The International Risk Governance Council (IRGC) suggests three categories of emergent risks: (1) high uncertainty and a lack of knowledge about potential impacts and interactions with risk-absorbing systems; (2) increasing complexity, emergent interactions and systemic dependencies that can lead to nonlinear impacts and surprises; and (3) changes in context (for example, social and behavioural trends, organisational settings, regulations, natural environments) that may alter the nature, probability and magnitude of expected impacts. Feedback processes between climatic change, human interventions involving mitigation and adaptation actions, and processes in natural systems can be classified as emergent risks if they pose a threat to human security.

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