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

===== Key risks across climate and development pathways =====

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'''Regional and sectoral chapters of this report identified over 120 key risks (KRs) that could become severe under particular conditions of climate hazards, exposure, and vulnerability. These key risk are represented in eight so-called Representative Key Risks (RKRs) clusters of key risks relating to low-lying coastal systems; terrestrial and ocean ecosystems; critical physical infrastructure, networks and services; living standards; human health; food security; water security; and peace and human mobility (''' '''''high confidence''''' ''').''' A key risk is defined as a potentially ‘severe’ risk, that is, one that is relevant to the interpretation of dangerous anthropogenic interference (DAI) with the climate system. Key risks cover scales from the local to the global, are especially prominent in particular regions or systems, and are particularly large for vulnerable subgroups, especially low-income populations, and already at-risk ecosystems ( ''high confidence'' ). The conditions under which RKRs would become severe have been assessed along levels for warming, exposure/vulnerability, and adaptation: for warming, high refers to climate outcomes consistent with RCP8.5 or higher, low refers to climate outcomes consistent with RCP2.6 or lower, and medium refers to outcomes for scenarios between RCPs 2.6 and 8.5; exposure/vulnerability levels are relative to the range of future conditions considered in the literature; for adaptation, high refers to near maximum potential and low refers to the continuation of today’s trends (and Sections 6.5.2.1, 16.5.2.2, SM16.7.4).

'''For most Representative Key Risks (RKRs), potentially global and systemically pervasive risks become severe in the case of high warming, combined with high exposure/vulnerability, low adaptation, or both (''' '''''high confidence''''' ''').''' Under these conditions, there would be severe and pervasive risks to critical infrastructure ( ''high confidence'' ) and to human health from heat-related mortality, to low-lying coastal areas, aggregate economic output, and livelihoods (all ''medium confidence'' ), of armed conflict ( ''low confidence),'' and to various aspects of food security (with different levels of confidence). Severe risks interact through cascading effects, potentially causing amplification of RKRs over the course of this century ( ''limited evidence'' , ''high agreement'' ). {16.5.2.3, 16.5.2.4, 16.5.4, Figure 16.10}

'''For some RKRs, potentially global and systemically pervasive risks would become severe even with medium to low warming (i.e., 1.5–2°C) if exposure/vulnerability is high and/or adaptation is low (''' '''''medium''''' '''to''' '''''high confidence''''' ''').''' Under these conditions, there would be severe and pervasive risks associated with water scarcity and water-related disasters ( ''high confidence'' ), poverty, involuntary mobility, and insular ecosystems and biodiversity hotspots (all ''medium confidence'' ). {16.5.2.3, 16.5.2.4}

'''All potentially severe risks that apply to particular sectors or groups of people at more specific regional and local levels require high exposure/vulnerability or low adaptation (or both), but do not necessarily require high warming (''' '''''high confidence''''' ''').''' Under these conditions, there would be severe, specific risks to low-lying coastal systems, to people and economies from critical infrastructure disruption, economic output in developing countries, livelihoods in climate-sensitive sectors, waterborne diseases especially in children in low- and middle-income countries, water-related impacts on traditional ways of life, and involuntary mobility for example in small islands and low-lying coastal areas ( ''medium'' to ''high confidence'' ). {16.5.2.3, 16.5.2.4}

'''Some severe impacts are already occurring (''' '''''high confidence''''' ''') and will occur in many more systems before mid-century (''' '''''medium confidence''''' ''').''' Tropical and polar low-lying coastal human communities are experiencing severe impacts today ( ''high confidence'' ), and abrupt ecological changes resulting from mass population-level mortality are already observed following climate extreme events. Some systems will experience severe risks before the end of the century ( ''medium confidence'' ), for example critical infrastructure affected by extreme events ( ''medium confidence'' ). Food security for millions of people, particularly low-income populations, also faces significant risks with moderate to high warming or high vulnerability, with a growing challenge by 2050 in terms of providing nutritious and affordable diets ( ''high confidence'' ). {16.5.2.3, 16.5.3}

'''In specific systems already marked by high exposure and vulnerability, high adaptation efforts will not be sufficient to prevent severe risks from occurring under high warming (''' '''''limited evidence''''' ''',''' '''''medium agreement''''' ''').''' This is particularly the case for some ecosystems and water-related risks (from water scarcity and to indigenous and traditional cultures and ways of life). {16.5.2.3, 16.5.2.4, 16.5.3}

'''Interconnectedness and globalisation establish pathways for the transmission of climate-related risks across sectors and borders, for instance through trade, finance, food and ecosystems (''' '''''high confidence''''' ''').''' Examples include semiconductors, global investments, major food crops like wheat, maize and soybean, and transboundary fish stocks. There are knowledge gaps on the need for, effectiveness of, and limits to adaptation to such inter-regional risks. { [[#cross-chapter-box-intereg|Cross-Chapter Box INTERREG]] in this Chapter }

'''Key risks increase the challenges in achieving global sustainability goals (''' '''''high confidence''''' ''').''' The greatest challenges will be from risks to water (RKR-G), living standards (RKR-D), coastal socio-ecological systems (RKR-A) and peace and human mobility (RKR-H). The most relevant goals are zero hunger (Sustainable Development Goal [SDG] 2), sustainable cities and communities (SDG11), life below water (SDG14), decent work and economic growth (SDG8), and no poverty (SDG1). Priority areas for regions are indicated by the intersection of hazards, risks and challenges, where, in the near term, challenges to SDGs indicate probable systemic vulnerabilities and issues in responding to climatic hazards ( ''high confidence'' ). {16.6.1}

The scale and nature of climate risks is partly determined by the responses to climate change, not only in how they reduce risk, but also how they may create other risks (sometimes inadvertently, and sometimes to others than those who implement the response, in other places, or later in time).

'''Solar radiation modification (SRM) approaches have potential to offset warming and ameliorate other climate hazards, but their potential to reduce risk or introduce novel risks to people and ecosystems is not well understood (''' '''''high confidence''''' ''').''' SRM effects on climate hazards are highly dependent on deployment scenarios, and substantial residual climate change or overcompensating change would occur at regional scales and seasonal time scales ( ''high confidence'' ). Due in part to limited research, there is ''low confidence'' in projected benefits or risks to crop yields, economies, human health or ecosystems. Large negative impacts are projected from rapid warming for a sudden and sustained termination of SRM in a high-CO 2 scenario ( ''high confidence'' ). SRM would not stop CO 2 from increasing in the atmosphere or reduce resulting ocean acidification under continued anthropogenic emissions ( ''high confidence'' ). There is ''high agreement'' in the literature that for addressing climate change risks SRM is, at best, a supplement to achieving sustained net zero or net negative CO 2 emission levels globally. Co-evolution of SRM governance and research provides a chance for responsibly developing SRM technologies with broader public participation and political legitimacy, guarding against potential risks and harms relevant across a full range of scenarios. { [[#cross-working-group-box-srm|Cross-Working Group Box SRM]] }

'''Recent global estimates of the economic cost of climate impacts exhibit significant spread and generally increase with global average temperature, as well as vary by other drivers, such as income, population and composition of the economy (''' '''''high confidence''''' ''').''' The wide variation across disparate methodologies does not allow a robust range of damage estimates to be identified with confidence, though the spread of estimates increases with warming in all methodologies, indicating higher risk (in terms of economic costs) at higher temperatures ( ''high confidence'' ). Reconciling methodological variance is a priority for facilitating use of different lines of evidence; however, that some new estimates are higher than the AR5 range indicates that global aggregate economic impacts could be higher than previously assessed ( ''low confidence'' due to the lack of robustness and comparability across methodologies). { [[#cross-working-group-box-economic|Cross-Working Group Box ECONOMIC]] in Chapter 16 }

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