According to a study published this month in the One Earth, warming nighttime temperatures harm sleep around the world throughout the year, particularly for the elderly, women and people who live in already hot climates. Researchers expect that, by 2099, people will lose an average of 50 to 58 hours of sleep per year – equal to two weeks of sleep time – if greenhouse gasses are not stabilized by the end of the century.
“Analysis reveals that elevated ambient temperatures may already be impairing human sleep globally,” the recent study said.
To conduct the study, scientists used 7 million sleep tracking data records from wristbands across 68 countries and linked that data to global weather and climate measurements. They found that ambient temperatures are rising worldwide, especially at night, and that increased temperatures were correlated with delayed onset of sleep, “increasing the probability of insufficient sleep.”
For adults over age 18, the Mayo Clinic recommends at least 7 hours of sleep per 24 hours. Problems associated with a lack of sleep include: weight gain, diabetes, high blood pressure, heart disease, stroke, and depression. As people age, they can have more difficulty getting the correct amount of sleep, said the clinic.
“A healthy amount of sleep is vital for ‘brain plasticity,’ or the brain’s ability to adapt to input,” according to Johns Hopkins Medicine. “If we sleep too little, we become unable to process what we’ve learned during the day and we have more trouble remembering it in the future. Researchers also believe that sleep may promote the removal of waste products from brain cells – something that seems to occur less efficiently when the brain is awake.”
In addition to the recent study, the National Oceanic and Atmospheric Administration found that the global surface temperature this April was higher than the 20th Century average and tied for the fifth highest April record in 143 years. Each of the 10 warmest April readings have been recorded since 2010, the administration said.
Data from the study in One Earth indicate that sleep declines by more than 14 minutes on “very warm nights over 86 degrees Fahrenheit.
Overall, nighttime minimum temperatures greater than 77 degrees increase the probability of getting less than 7 hours of sleep compared to the study baseline.
Regarding why warmer temperatures impact sleep, researchers hypothesized that “indoor environments may retain heat gained during the day or that daytime heat may impart physiological demands that extend into the sleep period.
Women may be more vulnerable to temperature-related sleep difficulty because their core body temperatures decrease earlier in the evening compared with males and because they are shown to “have greater subcutaneous fat thickness, which might impair nocturnal heat loss.”
Additionally, they found that humans adapt better to cooler temperatures than warmer temperatures.
“In real-world settings, humans appear to be better at adapting their surroundings to obtain sufficient sleep under cooler outside conditions, whereas sleep loss increases with rising ambient temperatures,” according to the study.
Following this pattern, researchers predict that “barring further adaptation and mitigation, with people living in hotter climates expected to lose considerably more hours of sleep per year by 2099,” which may “continue to exacerbate global environmental inequalities.”
For example, access to air conditioning may buffer the impact of high temperatures on sleep, but those who cannot afford it will not benefit from it. Cooling technology itself may also have an adverse impact on the environment, according to Time.
“Moreover, continued urbanization is expected to further amplify ambient heat exposure,” said the study. “Heat-resilient planning, environmental design, and biopsychosocial interventions may be needed to equitably protect the world’s urban population centers and vulnerable communities from differential exposure to magnified nighttime temperatures.”
As climate change is projected to continue causing an increase in nighttime temperatures “beyond the recent historical record,” researchers recommend “addressing the nocturnal impact of rising ambient temperatures on human sleep may be an efficient early intervention to reduce downstream adverse behavioral and developmental impacts linked to insufficient sleep.”
They also said further study is needed regarding temperatures and sleep, especially since the recent study had little coverage for large parts of Africa, Central America, South America, and the Middle East.