Medically reviewed by
Dacelin St Martin, MD
Triple board-certified in Sleep Medicine,
Internal Medicine, and Pediatrics.
Each passing day, the earth gets a tad hotter from global warming. A recent study suggests that while our bodies attempt to adjust to living in an increasingly warmer environment, getting a good shut-eye might become more challenging.
Global Warming and Sleep
Global warming is the warming of the earth’s climate due to burning fossil fuels, increasing the amount of heat-retaining greenhouse gases in the earth’s atmosphere, and making it a lot warmer than it should be.
Research indicates that the earth is warming at a rate of 0.2 degrees Celsius (0.36 degrees Fahrenheit) every decade.
It’s estimated that the earth’s average temperature has risen by around 1 degree Celsius (1.8 degrees Fahrenheit) since the pre-industrial ages.
A study conducted by sleep experts at the University of Copenhagen found that the earth’s rising temperature might cause people to lose sleep.
The research found that on warm nights, sleep decreases by an average of fourteen minutes. Also, the risk of getting less than seven hours of sleep grew as temperatures rose.
Furthermore, sleep experts predict that by the end of the 21st century, excessive temperatures caused by global warming may cause individuals to lose at least two weeks of sleep annually.
“It may be more gloomy for specific vulnerable populations, particularly seniors,” noted Kelton Minor, the study’s principal author.
“The projected sleep loss per degree of temperature rise was twice as great for the elderly compared to younger or middle-aged persons, three times greater for inhabitants of low-income nations compared to those of high-income countries, and significantly greater for females than males,” said Minor.
How Does Temperature Impact Sleep?
Typically, your body temperature drops in the evening as your body prepares to sleep.
Your circadian rhythm regulates this event alongside other sleep parameters and bodily functions.
At daybreak, your retina (the part of the eyes made up of specialized light-sensitive cells) detects light. It then signals the suprachiasmatic nucleus (the area of the brain that controls your circadian rhythm) to wake you up.
This string of events also increases the release of cortisol, an alerting hormone. It maintains your temperature at its typical awake level.
Typically, your body temperature varies between 97°F (36.1°C) to 99°F (37.2°C) throughout the day. However, the body temperature is higher during the day than at night.
Typically, when the sun sets, the light-induced signal from your retina to the SCN (suprachiasmatic nucleus) reduces, causing the production of melatonin, the hormone responsible for inducing sleep. This hormone secretion also causes your core temperature to decrease.
Your body temperature will keep declining when you sleep. It remains this way in the first two sleep cycle stages, characterized by non-rapid eye movement (NREM).
Your body temperature will eventually fall to its lowest point and stay there for the rest of the night. Typically, the body temperature dips by about 2 degrees Fahrenheit during sleep.
Your body temperature will slowly return to the average awake level just before you wake up, allowing you to wake up feeling refreshed and ready to go.
Hot weather can make it harder for your body to regulate its temperature while sleeping. If your bedroom is too warm, it can cause your body temperature to rise and keep you from getting quality sleep. The body is typically more sensitive to changes in environmental temperature during the first two stages of sleep.
So, changing your bedroom temperature when you are in the first two stages of sleep might cause you to wake up, interfering with your sleep cycle as you might not get the total sleep time you need.
Also, it can reduce the time you spend in the third (slow-wave sleep stage) and final stage of sleep (REM sleep). REM sleep and slow-wave sleep are vital to the proper functioning of your immune system and healing bodily processes. So, sleeping in a warm bedroom can ultimately harm your total well-being.
How To Optimize Your Sleep On Hot Nights
Keeping your body temperature at an ideal range while you sleep is critical to your health. Here are some tips on optimizing your sleep on hot nights. They include:
- Keep Sunlight Out of your Bedroom: Keeping the sun out of your bedroom is vital to keeping your bedroom cool. Dark-colored drapes or curtains help keep sunlight out from your bedroom and can help you keep your room warm during winter.
- Don’t Exercise Close to Bedtime: Mild exercise during the day can benefit your sleep. On the other hand, exercising too close to bedtime can cause your body temperature to rise, making it more difficult to sleep.
- Use the Right Mattress: Thick foam mattresses absorb and retain body heat, making you feel overheated. Additionally, bed sheets and pillow cases made from natural materials like linen can help to keep your bed cool.
- Optimize your Room Temperature with a Thermostat: Sleep experts believe that the ideal environmental temperature for sleep ranges between 60-67 degrees Fahrenheit (15.6-19.4 degrees Celsius). Keeping your room temperature in this range will help keep your body cool and improve sleep.
- Wear Comfortable Bedtime Clothes: Choose pajamas that are most comfortable for you. However, avoid heavy, insulating bedclothes that may raise your body temperature and disrupt sleep, particularly on hot evenings.
- Use an Air-Conditioner/Fan: An air conditioner or fan can help circulate air in your bedroom and keep you cool.
- Rising Temperatures Erode Human Sleep Globally: One Earth. https://www.cell.com/one-earth/fulltext/S2590-3322(22)00209-3.
- “Overview: Weather, Global Warming and Climate Change.” NASA, NASA, 14 Apr. 2022, https://climate.nasa.gov/resources/global-warming-vs-climate-change/.
- Harding, E., Franks, N., & Wisden, W. (2019). The Temperature Dependence of Sleep. Frontiers in Neuroscience, 13. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6491889/
- National Institute of Neurological Disorders and Stroke. Brain Basics: Understanding Sleep. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/understanding-Sleep
- Walker, H. K., Hall, W. D., & Hurst, J. W. (1990). Clinical Methods: The History, Physical, and Laboratory Examinations (3rd ed.). Boston: Butterworths. https://pubmed.ncbi.nlm.nih.gov/21250045/
- Okamoto-Mizuno, K., & Mizuno, K. (2012). Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology, 31(1), 14. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3427038/