Based on an analysis of 1,338 cities around the world, the group found that the amount of temperature-related sleep loss linked to climate change had at least doubled since the early 1970s, severely straining people\u2019s health.<\/p>\n
The analysis showed that over five years through 2025, the average person globally lost nearly 56 hours of sleep per year because of high temperatures. More than 10% of that sleep loss was attributed to climate change, primarily caused by burning fossil fuels like coal, oil, and gas, and cutting down forests, the group said.<\/p>\n
\u201cThis analysis reveals how climate change is translating into measurable hours of lost sleep for people around the world,\u201d said Kristina Dahl, Climate Central\u2019s vice president for science. \u201c(The) impacts of fossil fuel-driven warming extend beyond extreme weather to undermine one of the most fundamental requirements for human health.\u201d<\/p>\n
The group estimated sleep loss due to higher nighttime temperatures based on a model published in 2022 by Denmark-based scientist Kelton Minor. He quantified the relationship between nighttime temperatures and sleep loss worldwide by tracking the sleep data of over 47,000 people across 68 countries who wore fitness wristbands, and matched the data to local weather records.<\/p>\n
He found that, once the outdoor nighttime temperature rises above 10 degrees Celsius, sleep duration begins to decline sharply. When it exceeds 25 C, the share of people sleeping less than seven hours a night \u2014 and therefore considered sleep-deprived \u2014 increases by 3.5%. He also estimated the number of minutes of sleep lost across different groups, including by age, gender and the income level of the countries they lived in.\u00a0<\/p>\n
Climate Central combined these findings with its own estimates of what temperatures would have been in a world without climate change, and calculated the amount of sleep lost in each of the 1,338 cities.\u00a0<\/p>\n
Dahl cautioned, however, that sleep loss is caused by a mix of factors not covered in the study, which looked just at temperature changes\u2019 impact on sleep.<\/p>\n
\u201cAside from temperature, there are many things that can affect sleep duration and quality, including work schedules, stress, health, caffeine, light, noise, bedroom conditions, and humidity,\u201d the scientist said. \u201cOur study didn\u2019t look at any of those factors, but as many of us have experienced, they can be very important as well.\u201d<\/p>\n
Sleep and health<\/p>\n
Sleeplessness can cause a variety of health issues, including poor concentration, lower productivity, weaker immune systems, depression and anger.<\/p>\n
A chronic sleep shortage raises the risk of diabetes, high blood pressure and severe brain and heart conditions such as strokes and heart attacks, experts say.<\/p>\n
In addition, sleep deprivation is a major cause of traffic accidents. The U.S. National Highway Traffic Safety Administration estimates 91,000 crashes reported to police in 2017 involved drowsy drivers. These crashes led to nearly 800 deaths and an estimated 50,000 people injured, though experts agree that the figures underestimate the impact of drowsy driving.\u00a0<\/p>\n
Japan\u2019s National Police Agency statistics show that December sees the highest number of traffic accidents in Japan due to worsening road conditions and shorter daylight hours. But experts say drivers fatigued by extreme summer heat tend to cause serious crashes resulting in deaths or severe injuries, as such incidents often involve motorists drifting out of their lanes, colliding head-on with oncoming vehicles or crashing into utility poles.\u00a0<\/p>\n
<\/p>\n <\/a><\/p>\n \n A chronic sleep shortage raises the risk of diabetes, high blood pressure and severe brain and heart conditions, experts say. The effects of climate-attributed sleep loss are not evenly distributed.\u00a0<\/p>\n The Climate Central study showed sleep loss affects vulnerable demographics such as infants, older adults and pregnant women more severely. Tropical cities in lower-income countries are hit harder, too.<\/p>\n For example, cities in Saudi Arabia, Oman, and the United Arab Emirates lost between 55 and 87 hours of sleep per year due to higher nighttime temperatures, with 12 to 16 of these lost hours due to climate change.\u00a0<\/p>\n People in southern India and several countries in Southeast Asia lost 78 to 91 hours of sleep annually due to higher nighttime temperatures, including about eight to nine hours due to climate change, the study found.<\/p>\n Impact on Japan<\/p>\n The research covers 36 municipalities in Japan with populations of half a million or more. It showed people in Japanese cities lost 34 hours to 50 hours per year from 2020 to 2025, and 9% to 14% of that was attributable to climate change.<\/p>\n Tomohiko Ihara, associate professor of environmental social systems at the University of Tokyo, has also tracked the impact of rising temperatures on sleep quality and health. In a study published in 2022<\/a>, his team asked a total of 1,284 people in Nagoya to answer a questionnaire on the duration and quality of their sleep. Based on their responses and the city\u2019s lowest daily temperatures, he found that people\u2019s health started to worsen when outside air temperatures rose above 24.8 C. Furthermore, 40% of people were shown to have sleep problems once the lowest daily temperature rose to 30 C.<\/p>\n He also measured the collective health damage for Nagoya\u2019s population by using a universal health metric called DALY (disability-adjusted life years).<\/p>\n Ihara based his calculations on the premise that, unlike heatstroke, sleep disorders during the summer do not directly cause deaths. However, by using DALY, he was able to quantify the health losses caused by sleep disorders, which are much more common than heatstroke.<\/p>\n The researchers concluded that the health burden of sleep loss due to summer heat was comparable in scale to deaths and hospitalizations from heatstroke.<\/p>\n \u201cEven if you don\u2019t die directly from sleep loss, sleep disturbances (caused by hot summer nights) are in fact a big social loss,\u201d he said.<\/p>\n Setting your AC just right<\/p>\n So what should you do?<\/p>\n![\"A](\"https:\/\/cdnx.premiumread.com\/?url=https:\/\/www.japantimes.co.jp\/japantimes\/uploads\/images\/2026\/07\/19\/552136.jpg&q=100&f=webp&t=1.53\" "\\"A")
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