Summer peaks, overheating, and excess deaths by 2100? The energy and health system impacts of space cooling in a changing climate

Climate change is increasing global temperatures, with implications for indoor overheating, cooling energy demand, and public health. This study uses a validated agent-based model of residential energy use to assess the impacts of climate change on residential space cooling in Aotearoa New Zealand, modelling eight representative neighbourhoods across the socioeconomic spectrum in Auckland and Christchurch, the two largest cities. In the highest-temperature scenario (SSP5-8.5 in 2081-2100), space cooling could shift the national electricity system from winter to summer peaks, while lower-temperature scenarios (SSP2-4.5 and/or shorter time horizons) do not switch overall peak demand seasonality. Without adequate adaptation, indoor overheating could increase annual cardiovascular mortality by up to 6.4% in the highest-temperature scenario, which would disproportionately affect low-income and other vulnerable populations. These effects are lesser, but still present, in SSP2-4.5 and shorter time horizons. Increased heat pump adoption mitigates health impacts but increases electricity demand and infrastructure costs, with an average 610,000 NZD of additional costs per excess life saved. These findings highlight the need for integrated energy and health policy responses, including equitable access to cooling, building design reforms, and proactive infrastructure planning, and the need to address both energy justice and system resilience to minimise harms across society.