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

===== 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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