As tropical and hot nights — when the overnight temperature does not fall below 20°C —  become more frequent worldwide, people’s sleep is paying the price.Globally, the average person lost nearly 56 hours of sleep — equivalent to nearly seven nights’ worth of sleep — per year due to high temperatures during the 2020-2025 period, according to a new study by Climate Central.Across nearly every city out of over 1,300 analysed, the amount of temperature-related sleep loss linked to climate change has at least doubled since the early 1970s. The highest level of sleep loss was in the Middle East and Southeast Asia, where people lost an average of between 55 and 91 hours per year. In the early 1970s, people living in an average city of 500,000 residents lost about 46 hours of sleep per year due to night-time heat; by the 2020s, that rose to about 50 hours. Between 2020 and 2025, that number rose to 56, and climate change accounts for a larger share of that burden, the analysis found.Where in Europe are people losing the most sleep? While extremely warm nights are affecting all cities across the world, the burden is not the same for everyone, and big differences can be seen across continents and within them. In Europe, the highest sleep losses were seen in the south. People in Naples, Italy,  lost 51 hours every year due to heat over the last five years. In Greece’s capital, Athens, the loss was 45 hours annually, 42 for Valencia in Spain, and 40 in Lisbon, Portugal, and in the French city of Marseille. However, even in the northernmost countries, while to a lesser extent, people are also suffering from sleep loss due to heat. People in Edinburgh, Scotland, lost 21 hours, while Stockholm and Helsinki lost 20 hours each. The lowest impact was in Oslo, at 18 hours. The importance of a good night’s sleep Sleep plays a major role in the correct functioning of the body during the day.Night-time is when the body is supposed to recover, but when temperatures fail to cool, this recovery does not happen and the body remains under strain.Poor sleep has been linked to impacts on mood, cognitive performance, productivity, and cardiovascular and immune health, the authors noted. While many factors influence sleep, night-time heat is becoming an increasingly important environmental risk as temperatures rise globally and as more people move to urban heat islands, which further amplify heat at night.Because sleep loss can accumulate over repeated nights, even modest reductions can become harmful over the course of a hot season. A recent study found that warmer nights affect sleep more than twice as much in adults over 65 as in middle-aged adults, and nearly three times as much in lower-middle-income countries as in high-income countries.Women and people already living in hotter climates were also more affected — a gap likely to widen as temperatures continue to rise.