A severe risk to health is the potential for a widespread, substantial worsening of health conditions due to climate change. We measure severity in terms of the magnitude of mortality and morbidity. We consider a severe mortality impact to be a sustained increase in the crude mortality rate  of more than about 2-4 deaths per 10,000 people yr-1. This range of increase is consistent with current mortality impacts with substantial global effects, including traffic fatalities  and the COVID-19 pandemic . We use these global rates as thresholds in all cases, recognising that they reflect substantial variation across regions and sub-populations . Morbidity impacts are measured in numbers of disease cases or hospital admissions. We find that severe health impacts are projected to occur for particular sub-populations and regions where vulnerability is currently high and is assumed to persist into the future; we focus our assessment on these cases. In other cases, literature is either inadequate or does not support severe outcomes.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report