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

==== 16.1.3.4 What Future Risks Are of Greatest Concern? ====

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The fourth and final element of the chapter is the question about the risks we face, and which ones we should be most concerned about. This is addressed in Sections 16.5 and 16.6.

[[#16.5.1|Section 16.5.1]] presents a full discussion of ‘key risks’, synthesised from across all chapters, defined as those risks that are potentially severe and therefore especially relevant to the interpretation of ‘dangerous anthropogenic interference with the climate system’ in the terminology of UNFCCC Article 2.

In 2015, the Paris Agreement established the goal of ‘holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C above pre-industrial levels’. However, assessment of key risks across a range of future warming levels remains a high priority for several reasons: (1) understanding risks at higher levels of warming can help prepare for them, should efforts to limit warming be unsuccessful ( [[#UNEP--2017|UNEP, 2017]] ); (2) understanding risks at higher levels can inform the benefits of limiting warming to lower levels; (3) in addition, there is continued debate about whether warming limits should be at or rather somewhere below 2°C (in particular at 1.5°C); and (4) there is a more explicit recognition that key risks can result not only from increased warming, but also from changes in the exposure and vulnerability of society, and from a lack of ambitious adaptation efforts. Thus, relatively limited warming does not automatically imply that key risks will not occur. In assessing key risks, we have applied four criteria: magnitude of adverse consequences, likelihood of adverse consequences, temporal characteristics of the risk, and ability to respond. Of course, this is an aggregated approach to what is dangerous; it should be noted that in practice, ‘dangerous’ will occur at a myriad of temperature levels depending on who or what is at risk (and their circumstances), geographic scale and time scale.

A new element is that we particularly look at a set of eight ‘representative key risks’ that exemplify the underlying set of key risks identified in the earlier chapters: risk to the integrity of low-lying coastal socio-ecological systems, risk to terrestrial and ocean ecosystems, risk to critical physical infrastructure and networks, risk to living standards (including economic impacts, poverty and inequality), risk to human health, risk to food security, risk to water security, and risk to peace and human mobility ( [[#16.5.2.3|Section 16.5.2.3]] ).

Another increased focus relates to the issue of compound risks. This includes risks associated with compound hazards (Working Group I AR6 Chapter 11, [[#Seneviratne--2021|Seneviratne et al., 2021]] ), but also implications for future risk when repeated impacts erode vulnerability, as well as through transboundary effects (including effects both from one system to a neighbouring one, as well as from one system to a distant one), also discussed in the cross-chapter box on inter-regional risks and adaptation (Cross-Chapter Box INTEREG in this Chapter).

[[#16.6|Section 16.6]] maps the representative key risks in [[#16.5|Section 16.5]] to the SDGs, noting both direct and indirect implications for climate resilient development as assessed in Chapter 18.

Finally, [[#16.6|Section 16.6]] presents an updated assessment of the so-called Reasons for Concern (RFC): risks related to unique and threatened systems, extreme events, distribution of impacts, aggregate impacts (including the cross-chapter box on the global economic impacts of climate change and the social cost of carbon, Cross-Working Group Box ECONOMIC) and the risk of irreversible and abrupt transitions.

The AR4 and AR5 each also evaluated the most important climate risks, framed firstly in terms of the state of knowledge relevant to Article 2 of the UNFCCC. The TAR first synthesised this knowledge in five RFCs. AR4 identified a set of ‘key vulnerabilities’ and provided an update of the RFCs. AR5 further refined a new risk framework developed in the IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX), and used it to assess ‘key risks’ and provide another update of the overarching RFCs, drawing as well on Cramer et al.’s (2014) assessment of observed changes.

Our risk assessment also further builds on risk assessments from the Special Reports that are part of the AR6 cycle, that is, SR15, SRCCL and SROCC. While since AR4 the RFC assessment framework has remained largely consistent, refinements in methodology have included the consideration of different risks, the role of adaptation, use of confidence statements, more formalised protocols and standardised metrics ( [[#Zommers--2020|Zommers et al., 2020]] ). In subsequent assessment cycles, the risk level at a given temperature has generally increased, reflecting accumulating scientific evidence ( [[#Zommers--2020|Zommers et al., 2020]] ).

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