Projected heatwave-related excess mortality under climate change scenarios across 2288 communities in Australia: a nationwide ecological projection modelling study

Background

Climate change is intensifying the frequency, duration, and severity of heatwaves globally, posing a growing threat to human health. However, few fine-scale projections of heatwave-related excess mortality account for spatial disparities and adaptive capacity. We aimed to estimate future heatwave-related excess mortality across statistical area level 2 (SA2) communities in Australia under multiple climate scenarios.

Methods

In this modelling study, we projected excess mortality rates across 2288 SA2 communities in Australia for the period 2020–2100 under four shared socioeconomic pathways (SSPs) representing alternative trajectories of adaptation (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5). Daily all-cause mortality data from Jan 1, 2009, to Dec 31, 2019, were obtained from the Australian Coordinating Registry and the Australian Bureau of Statistics. We estimated historical exposure–response relationships using a two-stage distributed lag non-linear model with multivariate meta-regression. Future daily temperatures were obtained from bias-corrected, downscaled projections based on Coupled Model Intercomparison Project Phase 6 (a global climate model intercomparison project) and combined with mortality data and SSP-specific population forecasts to estimate annual excess deaths and excess mortality rates. We assessed median percentage changes in annual excess mortality rates for 2050–59 and 2090–99 using the 2020–29 period as a reference. Two adaptation scenarios were considered: no adaptation and full adaptation. Uncertainty was quantified through Monte Carlo simulations.

Findings

Heatwave-related excess mortality was projected to increase substantially across Australia under all SSP scenarios. We estimated that, in 2100, without adaptation, annual excess deaths would reach approximately 5820 under SSP5-8.5 (a scenario of a fossil fuel-intensive future with little mitigation) and the cumulative total of heatwave days across all communities would be 174 079. Heatwave-related excess mortality rates were projected to be highest in Northern Territory during 2090–99, at 33·9 deaths per 100 000 population (95% empirical CI 13·9–55·0), followed by Queensland, at 18·4 deaths per 100 000 population (7·6–29·8), and New South Wales, at 12·8 deaths per 100 000 population (5·3–20·7); projected percentage changes in excess mortality rate relative to 2020–29 ranged from 356% (in West Coast, South Australia) to 4412% (in Thamarrurr, Northern Territory). Although full adaptation substantially reduced the projected mortality burdens, considerable residual risks remained. Spatial disparities in excess mortality rates persisted across states, socioeconomic strata, and urban–rural classifications, although absolute differences were modest.

Interpretation

This study provides a comprehensive assessment of future heatwave-related excess mortality across Australia under multiple climate change and adaptation scenarios. These high-resolution projections underscore the urgent need for integrated mitigation and locally tailored adaptation strategies to address climate-related health inequities.