Dr. Michael DeSanctis, PhD, LP, ABPP, DBSM June 2021
I was moved to write this blog out of my concern for the rapid and continuing transformations in our global climate and the impact of the changing physical environment on human wellness, sleep and other recurring and necessary life processes. Environmental scientists have measured increases in global temperature that are reaching unprecedented levels relative to 30-year averages for given locales. I can offer my perspective as a mental health clinician and long-time observer of weather and climate, having studied the hypothesized correlation of daily meteorological variables with measured mood and reaction time nearly 40 years ago (DeSanctis, 1982).
Climate reflects the longitudinal sum of all weather activity in a given locale, region or continent. Established research findings have increaslingly suggested a relationship between rises in average ambient temperature and more frequent episodes of aggression and irritability in human beings. A clearly defined neurobiologic pathway linking high air temperatures and specific aggressive, acting-out behaviors does not yet exist; however, we do understand that serotoninergic activity in brain circuits may be a mediating factor (cf. Tiihonen et al, 2017). Dysregulation of central serotonin metabolism may trigger negative emotional states, including anxiety, and could adversely impact sleep onset and/or maintenance.
Felix Gad Sulman, a physician and bio-climatologist, discussed at least 3 broad categories of somatic reactions to pronounced spikes in temperature, generated by the Sharav, a hot, dry easterly wind blowing toward the Mediterranean, similar to the Santa Ana wind in southern California. (Sulman, 1976). Prolonged exposure to hot dry environments, particularly in excess of the typical weather variation in high and low temperatures, was thought to reduce catecholamine activity, promote serotonin release and raise the risk of overactive thyroid. Some of the aggregate impacts include fatigue, reduced concentration, insomnia, enhanced sensitivity to heat or cold, and paradoxical restlessness.
On a more micro level, sustained high daily temperatures – e.g., 10-20 degrees above local norms or climate records, spanning weeks or months, involving both nocturnal and diurnal readings – impose great strain on power grids attempting to maintain adequate cooling in residential spaces. Without A/C or evaporative cooling, indoor temperatures can quickly rise to intolerable and dangerous levels. This issue is especially relevant to those living in densely crowded urban spaces with considerable masonry and blacktop, and relatively few trees, where there is minimal shade or opportunities for a nocturnal cool-down. Sleep can be a casualty of this measured change in typical temperatures for a particular locality.
Optimum temperatures in a sleeping quarter should be in the 60s Fahrenheit at night. Without AC systems running at efficient levels, or open windows the air in the bedroom becomes stuffy and overheated, taxing our hypothalamic-based thermoregulatory system. We may experience downstream states of arousal, restlessness or anxiety inhibiting sleep onset and undermining sleep continuity. Open windows mean outside noises become more salient, leaking more light into the bedroom. Loss of restorative sleep undermines our ability to adapt to increased thermal stress.
Research by Zheng, Li & Wang (2019) examined the effects of high temperature on the physiology of sleep among college-age students. Their study determined that 36 and 38 degrees Centigrade correlated with worse sleep outcomes, involving compromised sleep duration and shallower sleep. Better outcomes for sleep occurred when ambient temperatures were measured at 32 C or 28C. If the central nervous system is busy thermoregulating to keep cool, through perspiration, obtaining a glass of water or removal of blankets, it stands to reason that sleep would suffer. Dehydration can adversely impact sleep onset as well as continuity.
Subjectively, I recall many a sultry summer night as a child, struggling to sleep in a converted attic room, with a loud floor fan blowing warm air around. When a cool front regime arrived, and the heat and humidity dissipated, sleep was more restorative and pleasant.
Another weather-related factor that can be associated with rising temperatures is higher dew point, the measure of how much water vapor is saturating the air. Prolonged exposure to elevated dewpoints combined with high temperatures pre-dispose to daytime heat exhaustion due to less efficient internal cooling, negating the effects of restorative nocturnal sleep.
Adding to thermal environmental stress, and consistent with scientific predictions about extreme weather in a global warming scenario, is the spectre of flooding from violent downpours and prolonged periods of rainy weather, as experienced this spring in our Gulf states. Flashfloods imperil people in their homes, raise the risk of mudslides, destroy precious belongings, and leave people feeling very vulnerable and unsafe in their most private of living spaces. People have experienced nightmares about water in their basements, and the mere prospect of severe flooding triggers anticipatory anxiety and apprehension. The forecast of a dam at risk for collapsing, or further relentless flooding rains, feeds into round-the-clock hyperarousal states.
Those living in fire-prone areas of the West Coast and adjacent intermountain region dwell with the ever-present fear of wildfire and the mortal threat to oneself and family. Sleep may be a casualty of this elevated risk state in one’s environment, as e-devices and radios are targeted by periodic public service warnings of high fire danger.
With a greater proportion of the US population repeatedly exposed to extreme weather, the possibility of acute post-traumatic emotional and behavioral reactivity exists in at-risk communities, especially on the heels of the COVID-19 pandemic. Dreams become more turbulent and unsettling, and baseline anxiety and hypervigilance erode sleep quality as hyper-aroused brain structures and brain wave signatures promote wakefulness even in the midst of slumber.
In the emerging post-COVID-19 world, intentionally cultivating daily habits of wellness, lifestyle modifications and application of sleep hygiene practices, including awareness of one’s basic circadian cycle, provide some degree of resilience in the face of unanticipated weather emergencies triggered by climate change. Alterations in climate bring into sharp focus the important link between physical environmental states and situational, as well as chronic states of somatic and psychological distress- a process mediated by neuro-hormonal/biochemical processes manifested in disturbances of sleep, wakefulness and behavior.
DeSanctis, M. (1982). The biopsychology of the weather matrix: An evaluation of psychomotor behavior and mood states as a function of ionization polarity and cognitive-personality dimensions. Dissertation Abstracts International, 43(4).
Sulman, F. G. (1976). Health, Weather and Climate. Basel, Switzerland: S. Karger.
Tiihonen, J., Halonen, P., Tiihonen, L. et al. (2017). The Association of Ambient Temperature and Violent Crime. Sci Rep 7, 6543. https://doi.org/10.1038/s41598-017-06720-Z
Zheng, G., Ke, L. & Wang, Y. (2019). The effects of high temperature weather on human sleep quality and appetite. International Journal Environmental Research and Public Health. January, 16(2), 270.
Published online: 2019 Jan 18; doi: 10.3390/ijerph16020270