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

=== 16.6.4 Summary ===

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The updated RFCs show that transitions between levels of risk are now assessed to occur at lower levels of global warming than in previous assessments ( ''high confidence'' ), levels of confidence in assigning transitions have generally increased, evidence on the potential for adaptation to adequately address risks at different warming levels remains limited, and transitions from high to very high levels of risk have been assessed for all five RFCs, compared with just two RFCs in AR5, together showing how literature published since AR5 is informing us on our future climate risks.

* In particular, risks to unique and threatened systems (RFC1) are now assessed to be already at a high level today, as compared with a moderate level in previous assessments, and transition to a very high level is assessed to occur beginning at 1.2°C, passing through a median value of 1.5°C, and completing the transition at 2.0°C warming ( ''high confidence'' ).
* Risks associated with extreme weather events (RFC2) are assessed to have begun to transition to a high level already when global warming reached 1°C, with that transition projected to complete for a warming of 1.5°C ( ''high confidence'' ). Newly in AR6, a transition between high and very high levels of risk was assessed to lie at 2.0°C warming for RFC2 (range 1.8–2.5°C).
* For risks associated with the distribution of impacts (RFC3), there is now ''high confidence'' that a transition to moderate risk has already occurred, and the transition to high risk is now projected to occur between 1.5°C and 2.0°C warming with ''medium confidence'' . Furthermore, a transition from high to very high risk is provided for the first time in this AR6 assessment, between 2.0°C and 3.5°C warming ( ''medium confidence'' ) ''.''
* Global aggregate impacts (RFC4) are assessed to have begun to transition to a moderate level already when global warming reached 1°C, and are projected to transition to a high level with warming of 1.5–2.5°C (median 2°C) with ''medium confidence.'' An assessment of a transition to very high risk is provided for the first time in AR6, over the range 2.5–4.5°C with ''low confidence'' .
* Risks associated with large-scale singular events are assessed to have already completed transitioning to moderate with 1°C warming ( ''high confidence'' ), with a transition to high risk between 1.5°C and 2.5°C (median 2°C) ( ''medium confidence'' ). An assessment of a transition to very high risk is provided for the first time in AR6, over the range 2.5–4.5°C with ''low confidence'' .

In summary, risks to unique and threatened systems (RFC1) are higher at recent and projected levels of warming than assessed previously ( ''very high confidence'' ); risks associated with extreme weather events (RFC2) are assessed comparably to AR5 and SR15 at recent and low levels of warming, but notably much higher at projected warming above 1.8°C ( ''medium confidence'' ); risks associated with distribution of impacts (RFC3) and global aggregate impacts (RFC4) are similar to SR15 and higher than AR5 above 2°C ( ''medium confidence'' ); and those associated with large-scale singular events (RFC5) are similar to SR15 and higher at both recent and projected warming than AR5 ( ''medium confidence'' ).

Limiting global warming to 1.5°C would ensure risk levels remain moderate for RFC3, RFC4 and RFC5 ( ''medium confidence'' ), but risk for RFC2 would have transitioned to a high risk at 1.5°C and RFC1 would be well into the transition to very high risk ( ''high confidence'' ). Remaining below 2°C warming (but above 1.5°C) would imply that risk for RFC3 through 5 would be transitioning to high, and risk for RFC1 and RFC2 would be transitioning to very high ( ''high confidence'' ) ''.'' By 2.5°C warming, RFC1 will be in very high risk ( ''high confidence'' ) and all other RFCs will have begun their transitions to very high risk ( ''medium confidence'' for RFC2, RFC3 and RFC4, ''low confidence'' for RFC5 '')'' . These highest levels of risk are associated with an irreversible component, such that some impacts would persist even were global temperatures to subsequently decline in an ‘overshooting’ scenario.

Lack of evidence on the potential for adaptation to adequately reduce risk is a critical gap in our ability to assess global risk transitions at the RFC level, but not the only gap. In some cases, such as RFC1, the widespread nature and rapid speed of the escalating risks, in combination with limited ability to adapt, means that transitions to high risk may occur despite medium or even high levels of adaptation. Risks that are largely natural and not widely mediated by human vulnerability are thus less likely to have risk transitions that shift under higher societal adaptation. Risk transitions that are mediated through human systems, such as distribution impacts, for example, are more likely to shift in response to adaptation as impacts are strongly mediated through vulnerability within human systems, but such a shift is difficult to quantify given knowledge gaps in the literature ( [[#16.3|Section 16.3]] ). However, in some circumstances, expanded global adaptation could slow some of these transitions ( ''low confidence'' ); in the case of RFC2, RFC3 and RFC4, the literature suggests that coordinated global adaptation could increase the global temperature at which risks transition from moderate to high, for example the prevention of mortality associated with heat stress within RFC2.

A higher level of adaptation, applied globally and effectively, could have larger benefits for several RFC, either postponing the onset of a high level of risk until a higher level of warming is reached (and allowing time for mitigation efforts) or allowing a system to survive a temporary overshoot of a lower temperature threshold. Adaptations are likely to have significant potential to reduce risks ( [[#Magnan--2021|Magnan et al., 2021]] ), in particular for risks mediated through human systems. However, there is ''limited evidence'' available to assess the extent to which current or potential adaptations are or would be adequate in reducing climate risks at different levels of warming, and adaptation implications for risk transitions will be highly localised. Pathways and opportunities for risk management and adaptation actions with transformational potential are discussed in Chapter 17, together with enabling factors, governance frameworks, financing, success factors, and monitoring and evaluation discussed in Chapter 18, supporting sustainable system transitions and leading to options for climate resilient development pathways.

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