by Daniel Brouse

Preface

This summer, I began noticing a significant decline in both my overall sleep quality and, in particular, my REM (Rapid Eye Movement) sleep. After reviewing the data from my sleep tracker, I was able to link much of the disruption to elevated nighttime temperatures. Then, last night, another factor became impossible to ignore: severe thunderstorms, high winds, and frequent lightning repeatedly interrupted my sleep.

The connection became even more compelling when I realized my dog had been experiencing the same restless nights. Heat, noise, and rapidly changing weather were affecting both of us. That realization led me to a broader question: if these environmental changes are disrupting sleep in my own home, how many millions of others are experiencing the same effects?

I woke up inspired to explore the science behind these observations. This paper examines how climate change—through rising nighttime temperatures, increasing humidity, and more frequent extreme weather events—is affecting sleep quality, REM sleep, and ultimately human health and well-being.

Abstract

Climate change is increasingly recognized as a public health crisis extending far beyond heat-related mortality and cardiovascular disease. One of its lesser-known but rapidly emerging consequences is the degradation of human sleep, particularly Rapid Eye Movement (REM) sleep. REM sleep is essential for memory consolidation, emotional regulation, learning, creativity, and cognitive performance. A warming climate disrupts REM sleep through multiple interacting mechanisms including elevated nighttime temperatures, increased humidity, wildfire smoke, air pollution, psychological stress, and extreme weather disasters. These impacts are compounded by the increasing frequency, duration, and intensity of heatwaves and the accelerating rise in nighttime minimum temperatures. This review examines the physiological basis of REM sleep, the mechanisms through which climate change disrupts REM architecture, and the broader implications for human health and societal resilience.

Introduction

Sleep represents one of the body’s most critical restorative processes. Among its various stages, Rapid Eye Movement (REM) sleep plays a unique role in maintaining healthy brain function. During REM sleep, memories are consolidated, emotional experiences are processed, neural pathways are strengthened, and learning occurs.

Historically, sleep evolved under predictable environmental conditions characterized by cool nights and stable seasonal temperature cycles. Anthropogenic climate change is fundamentally altering these conditions. Rising greenhouse gas concentrations have increased average global temperatures while disproportionately elevating nighttime minimum temperatures. The resulting loss of nocturnal cooling increasingly prevents the human body from maintaining the thermal conditions necessary for uninterrupted REM sleep.

Climate change therefore represents not only an environmental crisis but also a growing neurological and public health challenge.

Normal REM Sleep

Healthy adults typically require approximately 90 to 120 minutes of REM sleep each night, representing roughly 20–25% of total sleep time. REM sleep supports numerous neurological functions, including:

Memory consolidation
Emotional regulation
Learning
Creativity
Cognitive flexibility
Neural development

REM sleep becomes progressively longer throughout the night, with the largest REM periods occurring during the final third of sleep immediately before awakening.

Age influences REM requirements:

Age Group	Approximate REM Sleep
Infants	Up to 50%
Children & Adolescents	20–25%
Adults	20–25%
Older Adults	15–20%

Because REM occurs predominantly during the second half of the night, disturbances during early morning hours disproportionately reduce total REM sleep.

Thermoregulation During REM Sleep

REM sleep differs fundamentally from every other sleep stage because the body’s normal temperature regulation is largely suspended.

During REM sleep:

sweating is greatly reduced
shivering ceases
metabolic heat production decreases
behavioral temperature regulation becomes impossible

This temporary loss of thermoregulation makes REM sleep particularly vulnerable to elevated ambient temperatures.

If body temperature rises excessively, the brain interprets overheating as an immediate survival threat. Rather than remaining in REM sleep, protective neural circuits trigger arousal, forcing the sleeper into lighter sleep stages or complete awakening.

Consequently, REM sleep becomes the first major casualty of excessive nighttime heat.

Heatwaves and REM Sleep

Heatwaves interfere with sleep architecture through several overlapping physiological mechanisms.

Failure of Core Body Cooling

Normal sleep requires a gradual decline in core body temperature.

When nighttime temperatures remain elevated:

heat dissipation slows
skin temperature remains elevated
the brain struggles to initiate deeper sleep stages
REM duration decreases

Without adequate cooling, REM episodes become shorter and increasingly fragmented.

Activation of Stress Responses

Persistent heat activates multiple stress systems including:

sympathetic nervous system activation
elevated cortisol
increased heart rate
heightened neuronal arousal

Instead of transitioning smoothly into REM sleep, individuals remain trapped in lighter sleep characterized by repeated awakenings.

Sleep Fragmentation

Because REM sleep predominates during the second half of the night, rising early morning temperatures have an especially damaging effect.

Even brief awakenings interrupt REM cycles.

Repeated fragmentation produces:

reduced REM duration
impaired emotional regulation
slower reaction times
diminished concentration
poorer memory formation

Research increasingly shows that elevated nighttime temperatures reduce both REM sleep and slow-wave (deep) sleep, leaving individuals less physically and mentally restored upon waking.

Climate Change Has Intensified Heatwaves

Anthropogenic climate change has dramatically altered the characteristics of extreme heat events.

Increased Frequency

Heatwaves that historically occurred approximately once every decade now occur several times more frequently under approximately 1.2–1.4°C of global warming.

Across the United States, the annual number of extreme heat events has increased substantially since the mid-20th century.

Greater Intensity

Modern heatwaves are significantly hotter.

Globally, heat extremes that historically occurred once every ten years are now approximately 1.2°C (2.2°F) warmer than they would have been without human-caused climate change.

Some regional heatwaves have been intensified by 2–3.5°C due to anthropogenic greenhouse gas emissions.

Longer Duration

Heatwaves now persist for longer periods.

Persistent atmospheric blocking patterns, commonly known as heat domes, allow hot air masses to remain stationary for days or even weeks.

In the United States, the heatwave season has expanded by more than 40 days compared with the mid-twentieth century.

Rising Nighttime Temperatures

Perhaps the most important climate-related threat to REM sleep is the rapid rise in nighttime minimum temperatures.

Across much of the United States:

overnight temperatures are increasing nearly twice as fast as daytime highs
nighttime minimum temperatures have increased approximately 1.4°F per century
daytime maximum temperatures have increased roughly 0.7°F per century

Climate Central reports that average summer nighttime temperatures across the contiguous United States have risen approximately 2.5°F since 1970.

This phenomenon is known as asymmetric warming.

Why Nights Are Warming Faster

Several physical mechanisms contribute to accelerated nighttime warming.

Greenhouse Blanket Effect

Greenhouse gases continuously absorb and re-radiate outgoing infrared radiation.

During daylight hours, incoming solar radiation dominates Earth’s energy balance.

At night, however, greenhouse gases slow radiative cooling by trapping heat near the surface, preventing the Earth from shedding accumulated daytime energy.

Increased Humidity

A warmer atmosphere holds more water vapor.

Water vapor is itself a powerful greenhouse gas.

Higher humidity:

traps additional infrared radiation
slows nighttime cooling
prevents sweat evaporation
keeps body temperature elevated

This directly interferes with the physiological cooling required for REM sleep.

Increased Cloud Cover

Clouds act differently during day and night.

During daytime they reflect some incoming sunlight.

At night they behave like insulating blankets, absorbing outgoing infrared radiation and re-emitting heat back toward the surface.

The result is warmer nights.

Urban Heat Islands

Concrete, asphalt, brick, and other urban materials absorb enormous amounts of solar energy during daylight.

After sunset they slowly release stored heat.

Urban environments therefore remain significantly warmer than surrounding rural areas throughout the night, reducing opportunities for nocturnal cooling.

Wildfire Smoke and REM Sleep

Climate change has substantially increased wildfire frequency and burned area across many regions.

Wildfire smoke contains extremely high concentrations of fine particulate matter (PM₂.₅).

These microscopic particles affect REM sleep through multiple biological pathways.

Neuroinflammation

PM₂.₅ particles can enter the brain through the olfactory system.

Inflammation develops within regions involved in sleep regulation, impairing normal REM transitions.

Suppression of REM Sleep

Experimental studies have demonstrated that inhalation of biomass smoke suppresses paradoxical sleep—the scientific term for REM sleep—while simultaneously increasing nighttime heart rate and blood pressure.

Airway Irritation

Smoke exposure increases:

coughing
airway inflammation
respiratory resistance

These physiological disturbances repeatedly awaken sleepers from deeper sleep stages, fragmenting REM sleep.

Climate Anxiety and REM Sleep

Climate change also affects REM sleep psychologically.

Increasing exposure to floods, hurricanes, wildfires, droughts, and heatwaves elevates rates of:

anxiety
depression
post-traumatic stress disorder (PTSD)
chronic stress

Elevated cortisol levels associated with these conditions interfere with normal REM initiation.

In addition, growing concern about future climate risks—often termed eco-anxiety—can produce intrusive thoughts, nightmares, insomnia, and repeated nighttime awakenings.

Instead of facilitating healthy emotional processing, REM sleep becomes increasingly disrupted by persistent activation of the brain’s threat-detection networks.

Humidity and REM Sleep

Humidity represents another important but often overlooked consequence of climate change.

Successful REM sleep requires efficient evaporative cooling.

When humidity is high:

sweat evaporates poorly
body temperature remains elevated
heat loss slows
REM episodes become abbreviated

Rather than entering long uninterrupted REM periods near morning, sleepers cycle repeatedly through brief periods of lighter sleep.

Public Health Implications

Declining REM sleep carries consequences extending well beyond daytime fatigue.

Chronic REM deprivation has been associated with:

impaired memory
reduced learning capacity
diminished decision-making
slower reaction times
depression
anxiety disorders
impaired emotional regulation
weakened immune function
increased cardiovascular risk
reduced workplace productivity
higher accident rates

Because climate change affects millions of people simultaneously, widespread reductions in REM sleep may have substantial economic and societal consequences.

Sleep loss may become an increasingly important—but largely invisible—component of climate-related disease burden.

Mitigation and Adaptation

Although climate change is driving long-term warming trends, several measures can help preserve REM sleep.

Recommended strategies include:

Maintaining bedroom temperatures between 65–68°F (18–20°C).
Using blackout curtains to reduce daytime solar heating.
Increasing nighttime ventilation and airflow.
Limiting indoor heat accumulation during daytime.
Using air conditioning or evaporative cooling where available.
Reducing exposure to wildfire smoke through high-efficiency filtration.
Maintaining consistent sleep schedules.
Addressing climate-related psychological stress through appropriate mental health interventions.

Ultimately, however, adaptation alone cannot eliminate the problem. Long-term protection of human sleep requires reducing greenhouse gas emissions and slowing global warming.

Conclusion

Climate change is reshaping one of humanity’s most fundamental biological processes: sleep. Rising nighttime temperatures, prolonged heatwaves, increasing humidity, worsening wildfire smoke, deteriorating air quality, and climate-related psychological stress all converge on the same vulnerable target—REM sleep.

Unlike many climate impacts that unfold gradually over decades, sleep disruption is immediate, measurable, and experienced nightly by millions of people. Because REM sleep underpins memory, emotional regulation, learning, cognitive performance, and neurological health, its progressive loss represents a significant but underappreciated consequence of anthropogenic climate change.

As the planet continues to warm, protecting REM sleep will require both personal adaptation and systemic climate mitigation. Ensuring cooler nights, cleaner air, and a more stable climate is not merely a matter of comfort—it is essential for preserving the restorative sleep upon which human health, resilience, and cognitive function depend.

Climate Change and REM Sleep: How a Warming Planet is Disrupting the Brain’s Most Restorative Sleep Stage