Rising night-time temperatures, driven by climate change, are quietly eroding sleep quality worldwide, with the average person now losing nearly 56 hours of rest per year, according to a new analysis by Climate Central. The study, covering over 1,300 cities, reveals that the burden is particularly acute in southern Europe, where cities like Naples, Athens, and Valencia are seeing significant sleep deficits.
Globally, the average person lost almost seven full nights’ worth of sleep annually between 2020 and 2025 due to heat. In the early 1970s, residents of a typical city of 500,000 lost about 46 hours per year; by the 2020s, that figure rose to 50, and it has now climbed to 56. Climate change accounts for an increasing share of this loss, the researchers note.
Southern Europe Bears the Brunt
Within Europe, the highest sleep losses are concentrated in the Mediterranean. In Naples, Italy, people lose 51 hours of sleep each year. Athens, Greece, follows with 45 hours, Valencia, Spain, with 42, and both Lisbon, Portugal, and Marseille, France, with 40 hours annually. These figures reflect the growing frequency of tropical nights—when overnight temperatures fail to drop below 20°C—which prevent the body from cooling down and recovering.
Even northern European cities are not immune, though the impact is smaller. Edinburgh, Scotland, records 21 hours of lost sleep per year, while Stockholm and Helsinki each lose 20 hours. Oslo sees the lowest impact at 18 hours. The disparity underscores how latitude and urban heat island effects amplify the problem in warmer regions.
The study highlights that sleep loss is not just a comfort issue. Poor sleep impairs mood, cognitive performance, productivity, and cardiovascular and immune health. As night-time heat accumulates over consecutive nights, even modest reductions can become harmful over a hot season. A recent study found that adults over 65 are affected more than twice as much as middle-aged adults, and lower-middle-income countries nearly three times as much as high-income ones.
Europe’s vulnerability is compounded by its aging population and the prevalence of poorly insulated buildings in many southern cities. The findings come as the continent faces increasingly frequent heatwaves, with France activating an unprecedented heatwave emergency plan and Germany bracing for temperatures up to 38°C. The WHO has warned that Europe is unprepared for deadly heatwaves, and this study adds a new dimension to the public health challenge.
While many factors influence sleep, night-time heat is becoming an increasingly important environmental risk. As more people move to urban heat islands, which amplify heat at night, the problem is likely to worsen. The analysis calls for better urban planning, green spaces, and cooling strategies to mitigate the impact on sleep and overall health.
