Editing IPCC:AR6/WGII/Chapter-1 (section)

==== 1.3.1.1 The Nature of Climate Risk as Assessed in this Report ====

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Greater understanding of climate-related risks is emerging; however, there are important shortcomings in the information for some regions and sectors, and for developing versus developed countries. These risks assume significance in interaction with the cultures, values, ethics, identities, experiences, and knowledge systems of affected communities and societies, as well as their governance, finances, capabilities and resources. The key risk assessment in the IPCC AR5 informed the long-term temperature goal in the 2015 Paris Agreement—limiting the increase in global mean temperature to well below 2°C and pursuing efforts towards limiting warming to 1.5°C ( [[#Oppenheimer--2014|Oppenheimer et al., 2014]] ; [[#Pachauri--2014)|Pachauri et al., 2014)]] . The IPCC Special Report on Global Warming of 1.5°C, responding to an invitation by UNFCCC, used new scientific information to provide a specific risk assessment associated with the ambitious warming levels targeted by the Paris Agreement ( [[#Hoegh-Guldberg--2019|Hoegh-Guldberg et al., 2019]] ). The Special Reports on Oceans and Land further advanced the methods of transparent risk assessment ( [[#Zommers--2020|Zommers et al., 2020]] ). The current assessment expands significantly from the previous reports, aiming to inform and advance understanding of the following core themes: (a) the ways changes in vulnerability and exposure modulate risks of climate change impacts and risk complexity in addition to warming; (b) the knowledge basis relevant to continued refinement of temperature goals; (c) the effectiveness of adaptation solutions; (d) the management of risks at higher levels of warming, should ambitious climate change mitigation be unsuccessful, including limits to adaptation; and (e) the benefits of climate change mitigation and emissions reductions (Section 16.1).

This report evaluates key risks—potentially severe risks—meriting society’s full attention globally and regionally across sectors, in order to inform judgements about dangerous anthropogenic interference with the climate system ( [[#Oppenheimer--2014|Oppenheimer et al., 2014]] ; [[#Mach--2016|Mach et al., 2016]] ; see also Sections 16.1.2; 16.4; WGI Section 1.2.4.1). As described detail in Chapter 16, evaluation of key risks is based on expert judgement applied to all relevant lines of evidence, with a focus on the role of societal values in determining the importance of a risk. Specific criteria considered relate to the magnitude of adverse consequences, including the potential for irreversibility, thresholds, or cascading effects; the likelihood of adverse consequences; the timing of the risk; and the ability to respond to the risk (Section 16.5.1).

The key risk assessment conveys increasing urgency given the growing visibility of climate change impacts in the current world (Sections 1.1; 16.1). Representative key risks emerging across sectors and regions include risks to coastal socio-ecological systems and terrestrial and ocean ecosystems; risks associated with critical infrastructure, networks and services; risks to living standards and human health; risks to food and water security; and risks to peace and migration (Section 16.5). Compared to the AR5, the emphasis on human dimensions of key climate-related risks has continued and increased, for instance, the potentially severe impacts for cultural heritage ( [[#IPCC--2014c|IPCC, 2014c]] ; Pachauri et al., 2014; see also Section 16.4). These human dimensions are essential for understanding vulnerability, impacts and risks central to ensuring human well-being, human security, sustainable development and poverty reduction in a changing climate.

To encompass the nature of climate risk, IPCC assessment since the Third Assessment Report has used five overarching domains, named ‘reasons for concern’, to assess increasing risk for societies and ecosystems under climate change ( [[#IPCC--2014b|IPCC, 2014b]] ; [[#O’Neill--2017|]] [[#O’Neill--2017|O’Neill et al., 2017]] ; see also Section 16.5; WGI Section 1.2.4.1). The reasons for concern approach has enabled evidence to be combined with expert judgement, in order to provide a holistic assessment across multiple lines of evidence ( [[#O’Neill--2017|]] [[#O’Neill--2017|O’Neill et al., 2017]] ). The approach also respects the uncertainties inherent to climate risk and highlights the ways in which values are relevant in connecting scientific knowledge to societal decision making and risk management. The different reasons for concern underscore that there is no single metric that can reflect all dimensions of climate-related risk and the diversity of consequences for lives and livelihoods, health and well-being, economic and sociocultural assets, infrastructure and ecosystems ( [[#Mach--2017|Mach and Field, 2017]] ; see also Section 1.4.1.2).

The AR6 Reasons for Concern framework enables integration across key risks and representative key risks, including how risks vary with the magnitude of global warming, socioeconomic development pathways and levels of adaptation (Section 16.6). Risk levels are determined through a formal elicitation approach for both representative key risks and reasons for concern, following the authors’ assessment of the literature. The reasons for concern consider ''unique and threatened systems'' (RFC1), such as coral reefs or Arctic Sea ice systems that have especially high vulnerability and low capacity to adapt. They also include the role of ''extreme weather events'' (RFC2), such as heat waves, heavy rain, drought, coastal flooding or wildfires. The reasons for concern address both the ''distributional'' and the ''aggregate impacts'' of climate change (RFC3, RFC4), including the unfairness factor for populations that have contributed little in terms of historic emissions but that are disproportionately vulnerable to the impacts of a changing climate. The final reason for concern relates to ''large-scale singular events'' , nonlinearities and tipping points (RFC5), including ice sheet collapse and ecosystem regime shifts.

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'''Figure 1.3 |''' '''Different interactions can decrease or increase climate-related risks.''' Key examples include interactions '''(a)''' among sectors, '''(b)''' through time, '''(c)''' across regions, or '''(d)''' between impacts and responses. The specific interactions indicated within each panel of this figure are illustrative, not comprehensive or indicative of relative importance. Source: (Simpson et. al. 2021)

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