Overview
- Climate Central published its high-resolution attribution analysis on July 15, 2026, reporting that people lost about 56 hours of sleep per year to high nighttime temperatures between 2020 and 2025 and that roughly six of those hours are attributable to human-caused warming.
- The team applied a published sleep–temperature relationship to ERA5 climate reanalysis and compared observed nights with a counterfactual no‑human‑warming scenario so that the difference estimates the climate‑attributed portion of lost sleep.
- City results vary widely with Mediterranean cities losing tens of hours per year (Barcelona about 39, Valencia up to 42) while some Middle East cities and tropical coasts report more than 90 hours lost annually.
- The burden falls hardest on older adults, children, women, pregnant people and lower‑income households where air conditioning is limited, and the study notes that cooling by air conditioners raises energy demand and can worsen urban heat islands.
- Researchers warn repeated warm nights reduce deep and REM sleep, raising short‑ and long‑term health risks such as impaired cognition, immune and cardiovascular problems, and they say rising nocturnal temperatures magnified by cities will make adaptation and rapid emissions cuts urgent.