Examples of climate hazards include hydrological droughts, heatwaves and changes in rainfall patterns. Corresponding examples of impacts include increased water scarcity and resulting mortality, people’s inability to work outside due to extreme heat, and river flooding displacing people. The severity of each of these impacts is contingent on the exposure (e.g. the number of people affected, or a country’s degree of reliance on an impacted supply chain) and vulnerability to the corresponding hazard (e.g. access to infrastructure able to supplement water supply, or whether shortage of goods can be compensated from alternative sources) (Figure 1).
Risks can also arise from human responses to climate change that may increase exposure or vulnerability. Social inequality is meanwhile also rising globally, and this may increase vulnerability to risks. Understanding these dynamics is important as countries are ever more integrated in globalized systems, which may increase exposure to ‘cascading’ climate risks.
Exposure refers to the ‘inventory’ of human and natural resources, ecosystems, economic elements and infrastructure, all existing in a given area, that may be impacted by climate hazards. Exposure could be to direct impacts, such as when extreme weather directly impacts local agricultural populations and produce; or indirect, such as when climate change hazard impacts are transmitted from overseas through changes in the movement of goods, finance or people. If people and economic resources are not ‘exposed’ by existing in these potentially dangerous settings, there is no risk from the hazard in question.
Vulnerability defines the propensity of exposed ‘elements’ such as people, their livelihoods and their assets to suffer adverse effects when impacted by hazard events. It is the degree to which natural, human and economic elements may be susceptible to, and unable to cope with, adverse effects of a given climate change hazard when such effects materialize. Again, these vulnerabilities may be to local hazards or to impacts transmitted through the flow of goods, people or finance to a community, affecting the price and availability of goods. Typically, the poorest people in any society are most vulnerable as they have the fewest resources to mitigate the impacts facing them.
Exposures and vulnerabilities to different hazards are inherently related to the socio-economic, political, geographic and environmental contexts in which the elements are situated. In theory, even though climate hazards are increasing, climate risks could simultaneously be decreasing, through effective adaptation measures that reduce exposure, vulnerability and impact. Coping or adaptive capacity is therefore critically important within this context. For instance, Bangladesh and the Netherlands both face sea level rise, but the adaptive capacity in the Netherlands may enable more effective and faster adaptation, and hence decrease the risk to the country. However, the radical uncertainty of the socio-economic and political contexts (as well as the increasing uncertainty of extreme weather due to changing climate) means the overall risk from indirect as well as direct impacts is very difficult to quantify, and therefore has often been downplayed from a risk management perspective.
A systemic, or cascading, climate risk is the probability of a sequence of cascading impacts initially triggered by a climate hazard: from direct impact, to first-order indirect impact, to second-order indirect impact, and so on. Along this chain, or cascade, of impacts, a sequence of vulnerabilities and exposures exist that mediate or expedite the progression of the cascade of impacts. It should be noted that the cascade of impacts can progress in a non-linear manner, as they interact with complex systems, such as regional economies or geopolitical dynamics between countries. Further, as individuals, societies and governments begin adapting, their adaptive measures may themselves in turn become a source of risk.
