UCアーバインが主導する学際的なチームが熱中症対策に挑む(UC Irvine-led interdisciplinary team delves into a heated debate about humidity)


2023-05-31 カリフォルニア大学校アーバイン校(UCI)



暑さに関連する健康被害における湿度の役割: 熱い議論 Humidity’s Role in Heat-Related Health Outcomes: A Heated Debate

Jane W. Baldwin,Tarik Benmarhnia,Kristie L. Ebi,Ollie Jay,Nicholas J. Lutsko, andJennifer K. Vanos
Environmental Health Perspectives  Published:31 May 2023

Figure 1A is a set of two ribbon plus line graphs titled Earth with climate change, plotting negative to positive (y-axis) across past and future (x-axis) for temperature and humidity. Figure 1B is a set of two illustrations. On the top, inside an arrow pointing right, an illustration depicts epidemiology where a human stick figure is kneeling down owing to sun exposure equaling a function of high temperature exposures. At the bottom, inside an arrow pointing right, an illustration depicts physiology where a human stick figure is kneeling down owing to sun exposure equaling a function of shorter-duration exposures to both high temperature and humidity (among other variables). Figure 1C is a ribbon plus line graph titled projected health risks, plotting negative to positive with a human stick figure kneeling down owing to sun exposure (y-axis) across past to future (x-axis) for physiology based and epidemiology based.


As atmospheric greenhouse gas concentrations continue to rise, temperature and humidity will increase further, causing potentially dire increases in human heat stress. On physiological and biophysical grounds, exposure to higher levels of humidity should worsen heat stress by decreasing sweat evaporation. However, population-scale epidemiological studies of heat exposure and response often do not detect associations between high levels of humidity and heat-related mortality or morbidity. These divergent, disciplinary views regarding the role of humidity in heat-related health risks limit confidence in selecting which interventions are effective in reducing health impacts and in projecting future heat-related health risks.

Via our multidisciplinary perspective we seek to a) reconcile the competing realities concerning the role of humidity in heat-related health impacts and b) help ensure robust projections of heat-related health risks with climate change. These objectives are critical pathways to identify and communicate effective approaches to cope with present and future heat challenges.

We hypothesize six key reasons epidemiological studies have found little impact of humidity on heat–health outcomes: a) At high temperatures, there may be limited influence of humidity on the health conditions that cause most heat-related deaths (i.e., cardiovascular collapse); b) epidemiological data sets have limited spatial extent, a bias toward extratropical (i.e., cooler and less humid), high-income nations, and tend to exist in places where temporal variations in temperature and humidity are positively correlated; c) analyses focus on older, vulnerable populations with sweating, and thus evaporative, impairments that may be further aggravated by dehydration; d) extremely high levels of temperature and humidity (seldom seen in the historical record) are necessary for humidity to substantially impact heat strain of sedentary individuals; e) relationships between temperature and humidity are improperly considered when interpreting epidemiological model results; and f) sub-daily meteorological phenomena, such as rain, occur at high temperatures and humidity, and may bias epidemiological studies based on daily data. Future research must robustly test these hypotheses to advance methods for more accurate incorporation of humidity in estimating heat-related health outcomes under present and projected future climates. https://doi.org/10.1289/EHP11807