In recent weeks, the world has experienced extreme heat waves, particularly in the United States, China, and Europe. However, researchers are raising awareness about a chronic form of heat exposure that can last for months without reaching the threshold of a heat wave, particularly in urban areas like Miami and Phoenix. This sustained high temperature can lead to serious health issues, including kidney dysfunction, sleep apnea, and mental health problems such as depression. According to Mayra Cruz, a climate and health researcher at the University of Miami, there is a startling lack of research focused on the cumulative health impacts of prolonged exposure to heat, which is concerning amid the ongoing climate crisis.
The effects of chronic heat are particularly alarming for vulnerable families who lack air conditioning, as highlighted by urban planner Victoria Turner from UCLA. In families where a mother is pregnant and children are exposed to high temperatures at home and school, the consequences can affect their physiological development. These conditions raise issues about public health, especially for those without the means to find respite from the heat. Moreover, chronic exposure can amplify existing health issues, making it essential to understand these impacts in the context of climate change.
Conventional definitions of heat waves often hinge on daily temperature thresholds based on historical averages. In tropical and subtropical areas, these baseline temperatures may already be dangerously high. For instance, in Miami, the heat index can reach 32°C (90°F) for half the year. The agricultural sector has provided some of the strongest evidence linking chronic heat to health issues, particularly among workers in Central America, where consistent hot conditions have led to chronic kidney disease. Studies indicate that providing hydration and shade can mitigate these health risks, illustrating the critical relationship between heat exposure, hydration, and health outcomes.
While some might argue that data on heat-related deaths shows no higher mortality rates in regions with consistently high temperatures, experts caution against such assumptions. Kristie Ebi, a climate and health researcher at the University of Washington, notes the scant research into chronic heat’s risks, pointing out that baseline heat can worsen existing health conditions. As intensive care physician Pope Mosely observes, heat functions as a “force multiplier” for chronic ailments, particularly those related to blood flow and inflammation. Such conditions can worsen substantially under heat stress, as the body grapples with how to manage blood distribution.
Chronic heat not only affects physical health but also has significant implications for sleep and mental well-being. Urban environments, with their heat-retaining infrastructure, prevent nighttime temperatures from cooling, disrupting sleep patterns. Studies show that high night temperatures correlate with increased rates of sleep apnea and can lead to significant annual losses in sleep hours. These recurring sleep disturbances complicate cardiometabolic health and overall quality of life, as noted by sleep health researcher Bastien Lechat from Flinders University in Australia.
Moreover, mental health issues are compounded by heat, as chronic exposure may exacerbate stress and anxiety disorders. A study of U.S. high school students found that warmer school days negatively affected academic achievement, emphasizing how chronic heat may erode cognitive functioning. Vulnerable populations, who often lack access to cooling resources, bear the brunt of these health risks, underscoring the urgent need for targeted research and interventions that address chronic heat exposure and its far-reaching consequences, particularly for those who are most at risk.
In light of these findings, experts like Cruz advocate for more research focused on the health impacts of chronic heat exposure. As climate change continues to amplify the frequency of hot days, understanding and addressing these health implications becomes increasingly crucial. The lack of attention to populations most affected by chronic heat highlights a critical gap in public health research that must be urgently addressed to safeguard health in a warming world.
