Box Introduction.1 Risk and the Management of an Uncertain Future Edit Share

Climate change exposes people, societies, economic sectors and ecosystems to risk. Risk is the potential for consequences when something of value is at stake and the outcome is uncertain, recognizing the diversity of values. {WGII SPM Background Box SPM.2, WGIII 2.1, SYR Glossary}

Risks from climate change impacts arise from the interaction between hazard (triggered by an event or trend related to climate change), vulnerability (susceptibility to harm) and exposure (people, assets or ecosystems at risk). Hazards include processes that range from brief events, such as severe storms, to slow trends, such as multi-decade droughts or multi-century sea level rise. Vulnerability and exposure are both sensitive to a wide range of social and economic processes, with possible increases or decreases depending on development pathways. Risks and co-benefits also arise from policies that aim to mitigate climate change or to adapt to it. (1.5)

Risk is often represented as the probability of occurrence of hazardous events or trends multiplied by the magnitude of the consequences if these events occur. Therefore, high risk can result not only from high probability outcomes but also from low probability outcomes with very severe consequences. This makes it important to assess the full range of possible outcomes, from low probability tail outcomes to very likely outcomes. For example, it is unlikely that global mean sea level will rise by more than one meter in this century, but the consequence of a greater rise could be so severe that this possibility becomes a significant part of risk assessment. Similarly, low confidence but high consequence outcomes are also policy relevant; for instance the possibility that the response of Amazon forest could substantially amplify climate change merits consideration despite our currently imperfect ability to project the outcome. (2.4, Table 2.3) {WGI Table 13.5, WGII SPM A-3, 4.4, Box 4-3, WGIII Box 3-9, SYR Glossary}