Europe’s summer heatwave has exposed tens of millions of people to temperatures above 35°C, broken records and claimed hundreds of lives.
Early climate attribution studies suggest Europe’s event would have been “virtually impossible” just 50 years ago without human-caused climate change.
Meanwhile in South Asia, where temperatures have been edging past 45C, schools have been forced to close . As the planet continues to warm, severe heatwaves like this are expected to grow more frequent – and even more intense.
New Zealand, with its mild, maritime climate, might seem insulated from such extremes. But it, too, is expected to experience significantly warmer temperatures in future.
By the end of the century, in centres such as Auckland and Christchurch, peak summer temperatures in the hottest years could climb several degrees higher than they reach today.
Our new research explores what that could mean for human health – and how cooling in summer, rather than heating in winter, may place greater pressure on Aotearoa’s electricity system.
Modelling homes in a hotter future
New Zealand’s houses have traditionally been designed to keep people warm in winter. As temperatures rise, managing overheating will increasingly require either expensive retrofits or greater use of air conditioning, which has historically been uncommon.
That is already beginning to change. A recent survey found nearly three-quarters of households with heat pumps use them for cooling. But renters, families with children and Māori are all less likely to have access to, or use, space cooling, largely because of cost.
This reflects a wider problem of energy poverty in New Zealand. Many low-income and other marginalised households already limit – or go without – heating because they cannot afford it . Combined with poorly insulated homes, these compromises worsen health outcomes and increase healthcare costs.
To test how homes might respond to higher temperatures, we used a specific computer model that simulated how households use electricity under different conditions. It considered factors such as income, temperature and housing, and estimated when people would choose to use air conditioning.
We then modelled how rising temperatures over the rest of this century, under mid-range and high-end warming scenarios, could affect neighbourhoods across the socio-economic spectrum in Auckland and Christchurch. As well, we tested how greater access to heat pumps changed the results.
Our findings suggest climate change will have major consequences for both New Zealand’s health and electricity systems. In our highest warming scenario, summer electricity demand overtook winter demand and homes were more likely to overheat.
By 2100, this could mean thousands of additional heat-related deaths each year, with the greatest impacts falling on the most vulnerable communities. Under lower emissions scenarios and over shorter timeframes, the effects were much smaller.
We also found that coordinated policies could help reduce these impacts by improving access to cooling – but there was trade-off.
While greater use of heat pumps reduces overheating and saves lives, it further increases electricity demand.
In our highest-temperature scenario, annual cardiovascular deaths increased by between 1,264 and 2,390, depending on how many households had heat pumps.
Greater uptake of heat pumps also increased costs for electricity providers and consumers, with a combined average cost of around NZ$640,000 for each excess life saved.
Why adaptation should begin now
Without action, the burden of higher temperatures would not be shared equally. Lower-income households and older people would bear a disproportionate share of the health impacts.
Our modelling may also underestimate the scale of the risk. It does not account for the additional heat generated in urban areas, for instance, and may understate the intensity of future heatwaves.
In other words, these findings are unlikely to represent a worst-case scenario. Nonetheless, they clearly highlight a need for interventions spanning Aotearoa’s energy, health and infrastructure sectors.
So, what can be done? Our findings point to several priorities.
Space cooling should be recognised as a public health tool, with greater access to heat pumps helping save lives while also providing year-round heating and cooling benefits.
Support should be targeted towards lower-income and other at-risk communities, where access to cooling is often limited despite greater vulnerability to extreme heat. Building standards should also place greater emphasis on preventing overheating through passive cooling, reflecting a future where cooling becomes increasingly important.
At the same time, electricity generators, transmission companies and distributors will need to prepare for growing summer demand to ensure security of supply.
Most importantly, saving lives in the future means planning needs to begin now. While the effects of climate change are already being felt today, adapting homes, infrastructure and energy systems is likely to take decades.
