By definition, extreme events are rare, which means the quality and quantity of data, and the availability of analyses of these data, can be limited for some events. Nevertheless, observations since 1950 confirm that the frequency, intensity, spatial extent, and duration of some extreme weather and climate events have changed. Projected changes under different emissions scenarios generally are similar over the coming decades because of the inertia in the climate system, with the projected changes relatively small compared with natural climate variability. Projections of climate change-related alterations in weather and climate events for the end of the century, relative to the end of the last century, are highly uncertain.
Projections include substantial increases in temperature extremes, with higher temperatures when extremes occur. At the global scale, it is virtually certain that increases in the frequency and magnitude of warm daily temperature extremes will occur. It is very likely that the length, frequency, and/or intensity of heatwaves will increase over most land areas. Depending on the region and emissions scenario, extreme daily maximum temperatures that currently occur once in 20 years will likely increase by about 1°C to 3°C by mid-21st century. Based on the A1B and A2 emissions scenarios, a 1-in-20 year hottest day is likely to become a 1-in-2 year event by the end of the century in most regions. Less warming is projected under the B1 scenario.
The impacts of similar strength weather and climate events in different regions have very different consequences. With high vulnerability, even minor events can result in extreme impacts. Conversely, a strong weather or climate event can affect locations with low vulnerability. A wide range of factors influences exposure and vulnerability, including socioeconomic development, characteristics of the affected population, etc. Therefore, policies and measures are most effective when tailored to the local context.
Health researchers and public health specialists can incorporate projections of changes in extreme events into program development, implementation, and monitoring, considering how to most effectively address changing climate risk profiles in current and new policies and measures to minimize future potential health impacts. For example, heatwave early warning systems can be structured to consider changing seasonality, peak temperatures, length of heatwaves, outreach materials to vulnerable groups, etc. Explicitly designing adaptation options to iteratively manage risks will help reduce health risks under new climate futures.