Unstable temperatures significantly increase heat-related mortality risk
Fluctuations in daily temperatures were linked to significant increases in heat-related mortality risk, according to study findings published in The Innovation.
Researchers said it is the first study to their knowledge that evaluated the impact of temperature fluctuations on heat-related mortality.
“Assessing heat-mortality association without consideration of temperature variability may fail to recognize the most severe weather in relation to heat and implement effective early warning systems,” Yuming Guo, MD, PhD, a professor of global environmental health and biostatistics and the head of the Monash Climate, Air Quality Research Unit at Monash University in Australia, said in a press release.
In a global study, Guo and colleagues used the Multi-Country Multi-City Collaborative Research Network to compare data on short-term heat fluctuations and mortality during the warm seasons (the warmest four consecutive months) in 36 countries from 1972 to 2018. In total, 717 locations around the world were assessed through a two-stage time-series design for daily death counts and meteorological data. Temperature variability was based on the standard deviation of the average minimum and maximum temperature for the current day and previous day.
Overall, significant temperature variability during a 24-hour period was linked to more heat-related deaths compared with days when the temperature was stable, according to the researchers. For example, daily temperatures that fluctuated from 25 degrees Celsius to 45 degrees Celsius, and from 33 degrees Celsius to 37 degrees Celsius, represented the same mean temperature of 35 degrees Celsius, but they have “vastly different impacts on mortality,” according to Guo. Days with minimum and maximum temperatures of 25 degrees Celsius and 45 degrees Celsius increased the risk for heat-related deaths vs. days with minimum and maximum temperatures of 33 degrees Celsius and 37 degrees Celsius.
Globally, Guo and colleagues reported a 290% increased risk for heat-related mortality due to high daily temperature variations vs. low daily temperature variations during the study period. Central Europe experienced the greatest increased risk for heat-related mortality due to high temperature variability: 2,853%. In other regions, the increased risk was 145% in North America, 263% in South America, 895% in Central America, 1,382% in Northern Europe, 516% in Southern Europe, 547% in Southeast Asia, 163% in East Asia and 95% in Australia.
“We are living in a warmer and warmer environment that pervasively affects human life and undermines the years of gains in public health,” Guo said. “Human-induced warming has been associated with an increase in frequency and intensity of hot days and increasing heat exposure leads to more sickness and death. Meanwhile, temperatures tend to be more and more unstable (variable) under climate change.”
Heat exposure may stress the cardiovascular and respiratory systems of the aging population, those with underlying conditions and other vulnerable individuals, according to the researchers.
Guo and colleagues said that it is “imperative to raise public awareness of the potential health risks of temperature variability.”
References:
Global study finds unstable temperatures lead to higher heat-related mortality risk – another problem for climate crisis. https://www.eurekalert.org/news-releases/946284. Published March 12, 2022. Accessed March 17, 2022.
Wu Y, et al. Innov. 2022;doi:10.1016/j.xinn.2022.100225.
Perspective
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This study highlights the complexities and uncertainties inherent in the human health response to our changing climate. Modern medicine is built on a stable climate foundation. As this foundation cracks, certainties are falling, risks are shifting and new lines of inquiry are emerging.
Rising temperature presents one of the most direct risks of climate change to human health. As such, heat-related health risks are receiving increasing attention in research. Exposure to heat has been associated with far-reaching health effects, including excess mortality, heat-related illness, renal disease, adverse birth outcomes, congenital anomalies and others.
This study adds important information to our understanding of not only excess mortality but other heat-related health impacts. The finding of temperature variability as a modulator of heat-related mortality risk underscores the critical role of physiologic adaptation in reducing health risks of heat exposure.
Numerous studies have noted geographic differences in vulnerability for diverse heat-related health risks. People in more northern latitudes are generally at higher risk from a given temperature as a result of reduced physiologic adaptation to heat. However, while this is noted, the role of physiologic adaptation is rarely the primary focus of heat illness research. Also, differential vulnerability, whether based on latitude or temperature variability, is generally underappreciated by practitioners.
This paper adds a significant contribution to our understanding of heat vulnerability. Heat illness prevention programs will need to consider variability in warning systems.
The paper also exposes the many uncertainties, and research opportunities, in our understanding of climate change and human health. I appreciate the authors opening this line of inquiry and expect that the role of temperature variability and physiologic adaptation will be the focus of research on other heat-illness risks in the future.
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