The impact of heat extends far beyond our recognition. In July 2023, a new record for the hottest day globally was set, eclipsing the previous day’s high. California’s Death Valley registered temperatures nearing 130 degrees Fahrenheit, among the highest ever documented.Â
These consequences stem from just a 1-degree Celsius temperature increase—an early signal of a world projected to warm by threefold or more on its current trajectory.
Heat is a unique adversary. In the United States, it outstrips hurricanes, tornadoes, floods, and earthquakes combined in causing deaths. Yet, it’s also a silent assassin, with many of its effects on our bodies shrouded in mystery. Our knowledge remains limited to a fraction of its lethal impact. Moreover, vulnerable groups bear the brunt, disproportionately affecting older individuals, lower-income segments, outdoor laborers, and prisoners—while the rest of society often turns a blind eye from air-conditioned comfort.
In the shadows of heat waves, numerous non-fatal health consequences emerge. The toll compounds with the duration of heat waves, a scenario unfolding this summer worldwide.
Nevertheless, even the most sophisticated metric for comprehending heat’s consequences is flawed. Most health research on heat primarily examines fatalities and, to a lesser extent, hospitalizations. This perspective, as Vivek Shandas, a climate adaptation professor at Portland State University, notes, fails to grasp the extensive harm inflicted on global mental and physical well-being. While discussed studies largely track heat-related deaths, they likely overlook a broader population suffering from heat’s impact, in ways not leading to hospitalization or death.
Physical Toll of Extreme Heat
Cardiovascular Strain
The heart plays a pivotal role in cooling the body during heat stress. This organ comes under immense pressure as temperatures rise. Surprisingly, the majority of heatwave-related deaths don’t result directly from heatstroke-induced organ failure; rather, they’re linked to the heart’s inability to cope.
As temperatures escalate, various body systems work overtime to maintain internal organ temperatures. The heart redirects more blood to the skin, facilitating heat dissipation. Sweating aids this process. However, as individuals age, their efficiency at regulating temperature declines. Their ability to pump sufficient blood per beat, enhance skin blood flow, and sweat for cooling diminishes. With age, not only does the body’s cooling efficiency erode, but older adults may also be on medications that further impede temperature regulation.
Heat’s impact extends to the young and healthy as well. Environmental factors play a role; for example, during the summer of 2023 in Texas, reports indicated several prisoners suffered fatal heart attacks during heatwaves—particularly alarming as air conditioning is absent in two-thirds of the state’s prisons. Shockingly, some of these individuals were just 34 and 35 years old.
Cardiovascular failure fuels debate over heatwave death counts, which often go underreported. To address this gap, health researchers analyze excess mortality to achieve more accurate data.
A study published in Nature Medicine in July found that the 2022 summer’s heatwaves caused over 60,000 deaths in Europe, disproportionately affecting young men and older women. This nearly rivaled the previous record of up to 70,000 excess deaths during Europe’s summer of 2003. During the 2021 heat dome in the Pacific Northwest, official estimates indicated a few hundred deaths; however, the actual toll likely exceeded 1,000.
Respiratory Impact
A significant portion of heatwave-induced excess mortality can be attributed to exacerbated air pollution.
Hot and sunny weather triggers chemical reactions that lead to ground-level ozone formation—a process intensified by heat. Ozone reacts with lung tissue, akin to “sunburn on the lungs,” as described by the American Lung Association.
While the connection between ozone and respiratory health is well-documented, data correlating heatwaves with widespread health consequences is mixed. Hospitals in the UK reported increased respiratory admissions during summer heatwaves. A Finnish study noted a 20 percent rise in hospital admissions for respiratory illnesses during heatwaves. These discrepancies likely stem from variations in reporting practices.
Heat impacts air quality beyond pollutants directly released into the air. High temperatures exacerbate stagnant air, resulting in “heat domes” that trap pollution near the ground. As temperatures rise due to climate change, stagnant days are projected to increase, fostering poor air quality.
Heatwaves indirectly worsen air quality. Heat-induced soil dryness contributes to drought, raising wildfire risks. Wildfires emit particulate matter—a hazardous air pollutant monitored by the EPA’s Air Quality Index.
Pregnancy and Heat
Extreme heat adversely affects pregnant individuals and fetuses, correlating with premature birth and low birth weight. Heat strains the cardiovascular system, which is already working overtime during pregnancy.
Pregnant individuals face challenges cooling down, leading to symptoms like fatigue, muscle cramps, dizziness, and dehydration, potentially escalating to life-threatening heatstroke.
Heat’s impact isn’t uniform across pregnant populations. Black women, in particular, face higher risks, as demonstrated by a study examining 60,000 California births between 1996 and 2006. The study linked a 10-degree temperature rise to a 9 percent increase in deliveries before 37 weeks. Broader research supports this, revealing that every 1-degree Celsius temperature increase correlates with a 5 percent rise in preterm births and stillbirths across 24 countries.
Sleep Disturbances Due to Heat
Oddly enough, the deadliest effects of heat are felt overnight.
During sleep, the body’s internal temperature naturally drops to facilitate rest. This process involves redistributing core heat to extremities, aiding sleep onset. Ambient temperature significantly affects this process. Unable to cool down, the heart works harder after a day of heightened strain.
Ironically, summer nights are warming faster than days due to climate change. The National Oceanic and Atmospheric Administration notes that since 1895, summer overnight lows in the US are warming almost twice as fast as afternoon highs. Urban heat islands exacerbate this phenomenon.
Sleep quality is closely tied to temperature. Higher room temperatures lead to disrupted sleep, with hotter rooms linked to shorter REM sleep—an aspect associated with memory, motor skills, and emotional regulation.
Emotional and Mental Impact
Heat’s impact transcends the physical realm, affecting emotions, learning, stress, and anxiety. The precise mechanisms behind these effects remain elusive. While causation shouldn’t be conflated with correlation, alternative theories abound: compromised sleep quality could underlie many issues; unknown bodily processes may be at play; coping with heat and high AC bills could exacerbate anxiety; or shifts in society’s rhythms might magnify these problems.
Nonetheless, research consistently highlights a correlation between heat and overall well-being. Heatwaves lead to increased emergency room visits, suicide rates, and a surge in violent crimes.
Learning is also impaired. High temperatures influence cognitive function, stamina, and memory. A study analyzing standardized international exam scores discovered that temperatures above 80 degrees Fahrenheit affected academic performance. The correlation between high temperatures and diminished academic capabilities underscores heat’s capacity to hinder learning.
Heat can also reshape decision-making at all societal levels during heat waves. A study published in the American Economic Journal: Applied Economics revealed that US immigration judges issued harsher judgments during hotter temperatures. This suggests that decisions are influenced by heat even within climate-controlled courtrooms. Elevated temperatures have also been linked to altered risk perceptions, potentially contributing to riskier behavior among individuals caught off-guard by heat.
Undisclosed Toll: The “Human Face of Heat”
Heat ravages mental, emotional, and physical health. However, there’s a dearth of answers regarding how altering responses could minimize these effects.
Interdisciplinary collaboration has emerged in heat research, uniting social scientists, climate experts, architects, and designers to tackle complex questions surrounding human behavior, mental health, and medicine. Daniel Vecellio, a climate and health scholar at George Mason University, highlights the necessity of this combined approach.
Nonetheless, the mystery shrouding activities within homes looms large. A study in Portland, Oregon, equipped 53 homes with sensors, revealing temperatures in public housing failing to dip below 85 degrees even when air conditioning was on full blast throughout the night.
Inadequate knowledge often hampers officials’ responses to heat waves. Immediate interventions, such as providing energy bill assistance, could offer more effective relief than current strategies like cooling centers and water provisions.
Even if we uncover the intricacies of the body’s response to heat waves, much remains unknown about how individuals truly cope. One certainty is that we’ve just scratched the surface of these consequences, set to unfold on a global scale. The heat will only intensify from here on out. The best way to keep your athletes safe is to have good heat policies in place and to follow their guidance.
The National Athletic Trainers’ Association has several heat-related consensus and position statements: