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

IntroductionClimate 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. MethodsA 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{degrees}C to +4.4{degrees}C above pre-industrial levels) across a full calendar year relative to current-climate conditions (+0.99{degrees}C above pre-industrial levels). ResultsSimulations 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. DiscussionRising 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.