There is nearly universal evidence that non-optimal ambient temperatures increase mortality , with notable heterogeneity only in the shape of the temperature-mortality relationship across geographical regions but often sharply growing relative risks at the outer 5% of the local historical temperature distributions . Significant advances have been made since AR5 regarding the analysis of temperature- related excess mortality in previously under-researched regions, such as developing countries and tropical climates . Progress has also been made with regard to temporal changes in temperature-related excess mortality and underlying population vulnerability over time. Heat-attributable mortality fractions have declined over time in most countries owing to general improvements in health care systems, increasing prevalence of residential air conditioning, and behavioural changes. These factors, which determine the susceptibility of the population to heat, have predominated over the influence of temperature change . Important exceptions exist, for example, where unprecedented heatwaves have occurred recently.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report