Empirically grounded projections of shifts in 24-hour movement behaviours under climate change–driven warming

Abstract Introduction Climate change is expected to alter daily patterns of sleep, sedentary behaviour and physical activity, yet empirically grounded projections across the full 24-hour movement spectrum are lacking. This study estimated how projected future warming may alter 24-hour movement behaviour patterns in adults. Methods A Monte Carlo simulation framework estimated temperature-dependent distributions of daily movement behaviour duration using data from 368 adults in the Annual Rhythms in Adults (ARIA) study in Adelaide, Australia. A total of 85,182 valid person-days were linked to daily temperature data to determine empirical temperature-behaviour relationships. The resulting distributions were used to simulate behaviour under five Intergovernmental Panel on Climate Change warming scenarios (+1.5°C to +4.4°C above pre-industrial levels) across a full calendar year relative to current-climate conditions (+0.99°C above pre-industrial levels). Results Simulations projected small but consistent behavioural shifts with warming. Annual median increased for MVPA (+49min to +4h 22min per person) and LPA (+3h to +13h 1min per person), while sleep declined (–5h 29min to –23h 19min per person). Physical activity gains were concentrated in cooler months, whereas sleep losses persisted year-round. Changes in sedentary behaviour were minimal and inconsistent. Discussion Rising temperatures may modestly increase year-long physical activity but reduce sleep duration, in a temperate-zone Mediterranean climate geography producing meaningful cumulative health implications. However, these might be confounded by the effect of other meteorological changes such as rainfall and humidity, which warrant further investigation.