Extreme heat: impacts and consequences

Phoenix, Arizona, USA -- extreme heat (2023)

Extreme heat is becoming the “new normal” for many areas of the world. The summer of 2023, for example, has seen some of the hottest days in modern history. Extreme heat is now a regular headline:

How Extreme Heat Affects Workers and the Economy (New York Times)

The heat index reached 152 degrees in the Middle East — nearly at the limit for human survival (The Washington Post)

As heat records fall, how hot is too hot for the human body? (The Conversation)

We are living through Earth’s hottest month on record, scientists say (The Washington Post)

Like many critical issues, extreme temperatures (heat or cold) have wide-ranging ripple effects beyond the direct impacts on animals (including humans) and plants. Places and people that are fortunate enough to escape the worst of the heat or cold may still contend with economic (higher prices, lost productivity, and more) and demographic impacts (including climate migrants).

What does research say about the impacts of extreme heat?

Featured articles:

*Demoury, C., Aerts, R., Vandeninden, B., Bert, V. S., & De Clercq, E.,M. (2022). Impact of Short-Term Exposure to Extreme Temperatures on Mortality: A Multi-City Study in Belgium. International Journal of Environmental Research and Public Health, 19(7), 3763. [PDF] [Cited by]

“According to the World Meteorological Organization (WMO), the past six years have been the warmest ever recorded and global surface temperatures will continue to increase, as well as the frequency and intensity of hot extremes, in the future. With global warming as well as significant excess mortality reported during hot extremes episodes worldwide, heat-related mortality has attracted attention and has been extensively investigated over the last decades.

In light of climate change, health risks are expected to be exacerbated by more frequent high temperatures and reduced by less frequent cold extremes. To assess the impact of different climate change scenarios, it is necessary to describe the current effects of temperature on health. A time-stratified case-crossover design fitted with conditional quasi-Poisson regressions and distributed lag non-linear models was applied to estimate specific temperature-mortality associations in nine urban agglomerations in Belgium, and a random-effect meta-analysis was conducted to pool the estimates. Based on 307,859 all-cause natural deaths, the mortality risk associated to low temperature was 1.32 (95% CI: 1.21–1.44) and 1.21 (95% CI: 1.08–1.36) for high temperature relative to the minimum mortality temperature (23.1 °C). Both cold and heat were associated with an increased risk of cardiovascular and respiratory mortality. We observed differences in risk by age category, and women were more vulnerable to heat than men. People living in the most built-up municipalities were at higher risk for heat. Air pollutants did not have a confounding effect. Evidence from this study helps to identify specific populations at risk and is important for current and future public health interventions and prevention strategies.”

*Grigorieva, E., & Lukyanets, A. (2021). Combined Effect of Hot Weather and Outdoor Air Pollution on Respiratory Health: Literature Review. Atmosphere, 12(6), 790. [PDF] [Cited by]

Association between short-term exposure to ambient air pollution and respiratory health is well documented. At the same time, it is widely known that extreme weather events intrinsically exacerbate air pollution impact. Particularly, hot weather and extreme temperatures during heat waves (HW) significantly affect human health, increasing risks of respiratory mortality and morbidity. Concurrently, a synergistic effect of air pollution and high temperatures can be combined with weather–air pollution interaction during wildfires. The purpose of the current review is to summarize literature on interplay of hot weather, air pollution, and respiratory health consequences worldwide, with the ultimate goal of identifying the most dangerous pollution agents and vulnerable population groups. A literature search was conducted using electronic databases Web of Science, Pubmed, Science Direct, and Scopus, focusing only on peer-reviewed journal articles published in English from 2000 to 2021. The main findings demonstrate that the increased level of PM10 and O3 results in significantly higher rates of respiratory and cardiopulmonary mortality. Increments in PM2.5 and PM10, O3, CO, and NO2 concentrations during high temperature episodes are dramatically associated with higher admissions to hospital in patients with chronic obstructive pulmonary disease, daily hospital emergency transports for asthma, acute and chronic bronchitis, and premature mortality caused by respiratory disease. Excessive respiratory health risk is more pronounced in elderly cohorts and small children. Both heat waves and outdoor air pollution are synergistically linked and are expected to be more serious in the future due to greater climate instability, being a crucial threat to global public health that requires the responsible involvement of researchers at all levels. Sustainable urban planning and smart city design could significantly reduce both urban heat islands effect and air pollution.”

*Guo, Y., Gasparrini, A., Armstrong, B. G., Tawatsupa, B., Tobias, A., Lavigne, E., Coelho,Micheline de Sousa Zanotti Stagliorio, Pan, X., Kim, H., Hashizume, M., Honda, Y., Guo, Y. L., Wu, C., Zanobetti, A., Schwartz, J. D., Bell, M. L., Scortichini, M., Michelozzi, P., Punnasiri, K., . . . Tong, S. (2017). Heat Wave and Mortality: A Multicountry, Multicommunity Study. Environmental Health Perspectives, 125(8), 087006. [PDF] [Cited by]

“BACKGROUND: Few studies have examined variation in the associations between heat waves and mortality in an international context.

OBJECTIVES: We aimed to systematically examine the impacts of heat waves on mortality with lag effects internationally.

METHODS: We collected daily data of temperature and mortality from 400 communities in 18 countries/regions and defined 12 types of heat waves by combining community-specific daily mean temperature ≥90th, 92.5th, 95th, and 97.5th percentiles of temperature with duration ≥2, 3, and 4 d. We used time-series analyses to estimate the community-specific heat wave–mortality relation over lags of 0–10 d. Then, we applied meta-analysis to pool heat wave effects at the country level for cumulative and lag effects for each type of heat wave definition.

RESULTS: Heat waves of all definitions had significant cumulative associations with mortality (increased risk of death) in all countries but varied by community. The higher the temperature threshold used to define heat waves, the higher heat wave associations on mortality. However, heat wave duration did not modify the impacts. The association between heat waves and mortality appeared acutely and lasted for 3 and 4 d. Heat waves had higher associations with mortality in moderate cold and moderate hot areas than cold and hot areas. There were no added effects of heat waves on mortality in all countries/regions, except for Brazil, Moldova, and Taiwan. Heat waves defined by daily mean and maximum temperatures produced similar heatwave–mortality associations, but not daily minimum temperature.

CONCLUSIONS: Results indicate that high temperatures create a substantial health burden, and effects of high temperatures over consecutive days are similar to what would be experienced if high temperature days occurred independently. People living in moderate cold and moderate hot areas are more sensitive to heat waves than those living in cold and hot areas. Daily mean and maximum temperatures had similar ability to define heat waves rather than minimum temperature.”

*Ratter-Rieck, J., Roden, M., & Herder, C. (2023). Diabetes and climate change: current evidence and implications for people with diabetes, clinicians and policy stakeholders. Diabetologia, 66(6), 1003-1015. [PDF]

“Climate change will be a major challenge for the world’s health systems in the coming decades. Elevated temperatures and increasing frequencies of heat waves, wildfires, heavy precipitation and other weather extremes can affect health in many ways, especially if chronic diseases are already present. Impaired responses to heat stress, including compromised vasodilation and sweating, diabetes-related comorbidities, insulin resistance and chronic low-grade inflammation make people with diabetes particularly vulnerable to environmental risk factors, such as extreme weather events and air pollution. Additionally, multiple pathogens show an increased rate of transmission under conditions of climate change and people with diabetes have an altered immune system, which increases the risk for a worse course of infectious diseases. In this review, we summarise recent studies on the impact of climate-change-associated risk for people with diabetes and discuss which individuals may be specifically prone to these risk conditions due to their clinical features. Knowledge of such high-risk groups will help to develop and implement tailored prevention and management strategies to mitigate the detrimental effect of climate change on the health of people with diabetes.

Many factors can affect the physiological response to heat. Among the individuals most vulnerable to extreme heat are infants and people older than 65 years, people living in urban environments and individuals with chronic diseases. Both factors of the external (e.g. built, social and physico-chemical environment) and internal (e.g. proteome, microbiome, metabolome) exposome will, therefore, determine vulnerability to climate change. Partially owing to impaired responses to heat stress, but also because of comorbidities like cardiovascular disease and chronic kidney disease, people with diabetes are particularly susceptible to the risks of high ambient temperatures and heatwaves.” 

*da Silva, I., Hei Wikuats, C. F., Hashimoto, E. M., & Martins, L. D. (2022). Effects of Environmental and Socioeconomic Inequalities on Health Outcomes: A Multi-Region Time-Series Study. International Journal of Environmental Research and Public Health, 19(24), 16521. [PDF]

  • The maximum temperature and relative humidity are the variables of greatest risk for cardiovascular diseases.
  • The minimum temperature represents the highest risk variable for respiratory diseases.
  • Mental diseases are influenced by extreme temperatures.
  • The relative risk varied among regions as a function of the socioeconomic conditions and climate.

The gradual increase in temperatures and changes in relative humidity, added to the aging and socioeconomic conditions of the population, may represent problems for public health, given that future projections predict even more noticeable changes in the climate and the age pyramid, which require analyses at an appropriate spatial scale. To our knowledge, an analysis of the synergic effects of several climatic and socioeconomic conditions on hospital admissions and deaths by cardiorespiratory and mental disorders has not yet been performed in Brazil. Statistical analyses were performed using public time series (1996–2015) of daily health and meteorological data from 16 metropolitan regions (in a subtropical climate zone in South America). Health data were stratified into six groups according to gender and age ranges (40–59; 60–79; and ≥80 years old) for each region. For the regression analysis, two distributions (Poisson and binomial negative) were tested with and without zero adjustments for the complete series and percentiles. Finally, the relative risks were calculated, and the effects based on exposure–response curves were evaluated and compared among regions. The negative binomial distribution fit the data best. High temperatures and low relative humidity were the most relevant risk factors for hospitalizations for cardiovascular diseases (lag = 0), while minimum temperatures were important for respiratory diseases (lag = 2 or 3 days). Temperature extremes, both high and low, were the most important risk factors for mental illnesses at lag 0. Groups with people over 60 years old presented higher risks for cardiovascular and respiratory diseases, while this was observed for the adult group (40-59 years old) in relation to mental disorders. In general, no major differences were found in the results between men and women. However, regions with higher urbanization levels presented risks, mainly for respiratory diseases, while the same was observed for cardiovascular diseases for regions with lower levels of urbanization. The Municipal Human Development Index is an important factor for the occurrence of diseases and deaths for all regions, depending on the evaluated group, representing high risks for health outcomes (the value for hospitalization for cardiovascular diseases was 1.6713 for the female adult group in the metropolitan region Palmas, and the value for hospitalization for respiratory diseases was 1.7274 for the female adult group in the metropolitan region Campo Mourão). In general, less developed regions have less access to adequate health care and better living conditions.”

For more information, please search Science Primary Literature (database).

Questions? Please let me know (engelk@grinnell.edu).