New Zealand's housing stock, designed primarily for winter warmth, is dangerously unprepared for the escalating heatwaves driven by climate change, according to new research from the University of Otago and others. The study, published in the journal Climate Risk Management, models the impact of rising temperatures on homes in Auckland and Christchurch, projecting that by 2100, under a high-emissions scenario, summer electricity demand could overtake winter demand, leading to thousands of excess heat-related deaths annually.
Europe and South Asia Heatwaves as Warning
The research comes as Europe suffers a severe summer heatwave, with temperatures exceeding 35°C affecting tens of millions, breaking records, and causing hundreds of deaths. Early climate attribution studies indicate that such an event would have been “virtually impossible” 50 years ago without human-caused climate change. In South Asia, temperatures have surpassed 45°C, forcing school closures. While New Zealand's maritime climate has historically provided a buffer, the study warns that peak summer temperatures in cities like Auckland and Christchurch could climb several degrees higher by century's end.
Modelling Homes in a Hotter Future
Lead author Dr. Kimberley O'Sullivan explained that the team used a computer model simulating household electricity use under different income, temperature, and housing scenarios. The model estimated when households would opt for air conditioning, examining mid-range and high-end warming pathways. “We found that in our highest warming scenario, summer electricity demand overtook winter demand, and homes were more likely to overheat,” O'Sullivan said. “By 2100, this could mean thousands of additional heat-related deaths each year, with the greatest impacts falling on the most vulnerable communities.”
The study highlights that nearly three-quarters of households with heat pumps already use them for cooling, but renters, families with children, and Māori are less likely to have access due to cost. This reflects a wider energy poverty issue, where low-income households often forgo heating or cooling, worsening health outcomes and increasing healthcare costs.
Trade-offs Between Cooling and Energy Demand
The research found that coordinated policies to improve cooling access could reduce health impacts, but at a cost. Greater heat pump use reduces overheating and saves lives but increases electricity demand. Under the highest-temperature scenario, annual cardiovascular deaths increased by between 1,264 and 2,390, depending on heat pump uptake. The combined average cost of greater heat pump use was around NZ$640,000 per excess life saved, including costs for electricity providers and consumers.
Urgent Need for Adaptation
Without action, lower-income households and older people would bear a disproportionate health burden. The modelling may underestimate risks, as it does not account for urban heat island effects or the intensity of future heatwaves. The authors call for interventions across energy, health, and infrastructure sectors. “Space cooling should be recognised as a public health tool, with greater access to heat pumps helping save lives,” O'Sullivan said. Building standards should emphasise passive cooling, and electricity providers must prepare for growing summer demand.
“Most importantly, saving lives in the future means planning needs to begin now,” O'Sullivan added. “While climate change effects are already felt, adapting homes, infrastructure, and energy systems will take decades.”
