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

==== 16.5.3.2 Exposure and Vulnerability Trends ====

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Development pathways describe plausible alternative futures of societal change and are critical to future risks because they affect outcomes of concern both through non-climate and climate-related channels ( ''very high confidence'' ).

Studies illustrating sensitivity to development pathways typically do so by contrasting projected impacts for the same climate pathway or temperature level but different levels of socioeconomic exposure and vulnerability, for example based on SSPs ( [[#O’Neill--2014|O’Neill et al., 2014]] ; [[#Van%20Vuuren--2014|Van Vuuren et al., 2014]] ). Or, they infer sensitivity to future development pathways based on differences in impacts across current populations with different levels of exposure or vulnerability. We refer to future conditions based on SSPs 1 or 5 as ‘low exposure’ or ‘low vulnerability’ conditions, and those based on SSPs 3 or 4 as ‘high exposure’ or ‘high vulnerability’ conditions ( [[#O’Neill--2014|O’Neill et al., 2014]] ; [[#van%20Vuuren--2014|van Vuuren and Carter, 2014]] ).

A wide range of climate change impacts depend strongly on development pathway ( ''high confidence'' ). A low (relative to high) exposure future, determined by limited population growth and urbanisation, results in about 30% fewer people exposed to extreme heat globally ( [[#Jones--2018b|Jones et al., 2018b]] ) and about 50% fewer in Africa ( [[#Rohat--2019a|Rohat et al., 2019a]] ), similar to the effect of a medium versus high level of global warming. Low-exposure conditions also reduce the fraction of the population in Europe at very high risk of heat stress from 39% to 11% ( [[#Rohat--2019b|Rohat et al., 2019b]] ). Demographic differences lead to a reduction in the global population exposed to mosquitos acting as viral disease vectors by more than half ( [[#Monaghan--2018|Monaghan et al., 2018]] ) and exposure to wildfire risk by nearly half ( [[#Knorr--2016|Knorr et al., 2016]] ).

Studies are increasingly going beyond exposure to incorporate future vulnerability, finding that it is often the dominant determinant of risk ( ''high confidence'' ). A low (relative to high) vulnerability future reduces the risk to global poverty by an order of magnitude, robustly across approaches that account for macroeconomic growth, structural change in the economy, inequality, and access to infrastructure services ( [[#Hallegatte--2017|Hallegatte and Rozenberg, 2017]] ), or for the exposure of vulnerable populations to multi-sector climate-related risks ( [[#Byers--2018|Byers et al., 2018]] ). A low (relative to high) vulnerability future also reduces the global mean number of temperature-attributable deaths in 2080–2095 due to enteric infections by an order of magnitude (from &gt;80,000 to &lt;7000; ( [[#Chua--2021|Chua et al., 2021]] )). Low future socioeconomic vulnerability to flooding reduces global fatalities and economic losses by 69–96% ( [[#Jongman--2015|Jongman et al., 2015]] ). Low vulnerability as measured by indicators including per capita GDP, education, governance, water demand and storage potential reduces water insecurity by a factor of three ( [[#Koutroulis--2019|Koutroulis et al., 2019]] ). A scenario with reduced barriers to trade reduces the number of people at risk of hunger due to climate change by 64% ( [[#Janssens--2020|Janssens et al., 2020]] ). Structural transformation of the economy (shift of the workforce from highly exposed sectors such as agriculture and fishing to less exposed sectors such as services) lowers GDP impact projections by 25–30% in today’s developing countries by 2100 ( [[#Acevedo--2017|Acevedo et al., 2017]] ).

The IPCC SRCCL supports the importance of societal conditions to climate-related risk ( [[#Hurlbert--2019|Hurlbert et al., 2019]] ), concluding that risks of water scarcity in drylands (i.e., desertification), land degradation and food insecurity are close to High [[#footnote-000|3]] beginning at 1.5°C under high-vulnerability conditions (SSP3), but remain close to Moderate up to slightly above 2°C for low-vulnerability conditions (SSP1). Specifically, risk of water scarcity in drylands (i.e., desertification) at 1.5°C warming is reduced in low vulnerability (relative to high vulnerability) conditions from High to Medium. Similarly, under a 2°C warming, risk is reduced from High to Moderate for food security and High to Moderate-to-High for land degradation.

While climate change will increase risk to society and ecosystems, future exposure and vulnerability conditions will also greatly impact outcomes of concern directly. Global economic damages to coastal assets from tropical cyclones are projected to increase by more than 300% due to coastal development alone, a much larger effect than projected climate change impacts through 2100 even in RCP8.5 ( [[#Gettelman--2018|Gettelman et al., 2018]] ). Similarly, global crop prices are more than three times more sensitive to alternative assumptions about changes in production technologies and demand than to alternative climate outcomes ( [[#Ren--2016|Ren et al., 2016]] ). Future water scarcity is driven mainly by both demographic change and socioeconomic changes affecting water demand and management. A measure of between-country inequality (Gini coefficient) would decline by more than 50% this century in low-vulnerability conditions, but would double in a high-vulnerability future ( [[#Crespo%20Cuaresma--2017|Crespo Cuaresma, 2017]] ), outweighing the effect of climate ( [[#Taconet--2020|Taconet et al., 2020]] ). Similarly, the global prevalence of armed conflict will roughly double this century in a high-vulnerability future, whereas it will drop by half in a low-vulnerability future ( [[#Hegre--2016|Hegre et al., 2016]] ). In Sub-Saharan Africa, assumptions about governance and political rights are estimated to be far more important to the future risk of violent conflict than climate change ( [[#Witmer--2017|Witmer et al., 2017]] ).

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