S y ste m Inte r action and N on -linear it y—Th e N eed fo r C r oss-sector Risk A ssessm ents
Where a system responds linearly and proportionately to warming, there is a better basis for systematic planning. A nonlinear response in a sector or human system is likely instead to raise far greater challenges and should be taken into account for adaptation planning.
Nonlinearities because of Interactions of Impacts Potential interactions of sectoral impacts can introduce a further dimension of nonlinearity into analyses of the potential for significant consequences from global warming. If changes were to be small, it is plausible that there would be few interactions between sectors. For example, a small change in agricultural production might be able to be compensated for elsewhere in another region or system. However, as the scale and number of impacts grow with increasing global mean temperature, interactions between them seem increasingly likely, compounding the overall impact. A large shock to agricultural production resulting from extreme temperatures and drought across many regions would, for example, likely lead to substantial changes in other sectors and in turn be impacted by them. For example, substantial pressure on water resources and changes of the hydrological cycle could ultimately affect water availability for agriculture. Shortages in water and food could in turn impact human health and livelihoods. Diversion of water from ecosystem maintenance functions to meet increased human needs could have highly adverse effects on biodiversity and vital ecosystem services derived from the natural environment. This could cascade into effects on economic development by reducing a population´s work capacity that could, in turn, diminish GDP growth. Nonclimatic factors can interact with impacts to increase vulnerability. For example, increasing demands on resources needed to address the population increase could lead to reduced resilience, if resources are not distributed adequately and equitably. As another example, an aging population will experience higher vulnerability
to particular impacts, such as health risks. Furthermore, such mitigation measures as land-use change to provide for biomass production and incremental adaptation designed for a 2°C world could increase—perhaps exponentially—vulnerability to a 4°C world by increasing land and resource value without guarding against abrupt climate change impacts (Kates et al. 2012). Warren (2011) further stresses that future adaptation measures to projected high impacts, such as changes in irrigation practices to counteract crop failures, might exacerbate impacts in other sectors, such as water availability.
onlinearities because of Cascading N Impacts With the possibility of installed adaptation capacities failing in a 4°C world, infrastructure that plays a key role in the distribution of goods is more exposed to climate change impacts. This could lead to impacts and damages cascading into areas well beyond the initial point of impact. Thus, there is a risk that vulnerability is more widely dispersed and extensive than anticipated from sectoral impact assessment. Projections of damage costs for climate change impacts typically assess the costs of directly damaged settlements, without taking surrounding infrastructure into account. However, in a more and more globalized world that experiences further specialization in production systems and higher dependency on infrastructure to deliver produced goods, damages to infrastructure can lead to substantial indirect impacts. For example, breakdowns or substantial disruption of seaport infrastructure could trigger impacts inland and further down the distribution chain. A better understanding of the potential for such cascading effects, their extent, and potential responses is needed. To date, impacts on infrastructure and their reach has not been sufficiently investigated to allow for a quantitative understanding of the full scope and time frame of total impacts. Such potential examples present a major challenge for future research.
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