Experts have issued a stark warning that the intense heatwaves experienced across Australia this summer, including record-breaking temperatures, can severely disrupt sleep and place significant strain on cardiovascular systems, kidneys, and mental health. This comes as data reveals one of the hottest summers since measurements began, with minimal relief during the night.
Record-Breaking Summer Temperatures
Australia's summer has been marked by extreme heat, with over 60 weather stations recording their highest-ever daily maximum temperatures during a January heatwave. Notably, it wasn't just the days that were scorching; the country also endured its fifth-warmest summertime night temperatures on record. Analysis of Bureau of Meteorology data shows at least nine stations recorded consecutive days, primarily from 28 to 30 January, where minimum temperatures remained in the 30s or high 20s Celsius throughout the night.
Health Impacts of Prolonged Heat
High night-time temperatures are particularly concerning as they prolong pressure on the body's systems. Disturbed sleep hampers recovery from daytime heat, exacerbating risks for cardiovascular disease, kidney conditions, and mental health issues. Dr Aaron Bach from Griffith University explains that heat events often worsen chronic conditions, stating, "The vast majority of people that are turning up to hospitals, and that are vulnerable to heat events, are really turning up with other chronic conditions that get worse during these heat events."
This is especially alarming for older Australians and those with comorbidities, such as the estimated 4.5 million Australians living with cardiovascular disease, who may lack access to cooling measures like fans or air conditioning.
Climate Change and Increasing Risks
Heatwaves are the deadliest climate hazard, with more than half of fatalities occurring in the most disadvantaged areas. Climate change is driving an increase in the frequency and intensity of both maximum and minimum temperatures. A recent CSIRO report found that "very high night-time temperatures" now occur five times more often than between 1960 and 1988. For instance, on 27 January, some stations recorded minimum temperatures 10°C above the monthly average.
Assessing Heat Stress and Vulnerability
Dr Bach emphasises that both intensity and duration of heatwaves are critical, as prolonged exposure without recovery opportunities heightens medical risks. "That's where overnight temperatures come into play," he says. "Because without the opportunity to recover throughout the hot days, that duration becomes more problematic even at lower intensities."
However, raw temperature data alone may not capture full risks, as factors like activity level, clothing, environment, and physiology compound effects. Prof Ollie Jay from the University of Sydney, along with Dr Federico Tartarini, developed the HeatWatch app to calculate a risk score from 1 to 6 based on these variables. Their modelling for Adelaide, which experienced its hottest night on record, showed elevated risk for profiles including outdoor workers and an 82-year-old with cardiovascular disease, with severe or extreme risk during parts of the day and high risk overnight.
Prof Jay notes that older individuals are more vulnerable due to reduced sweating capacity, leading to higher core temperatures under the same conditions. Longer heatwaves increase exposure opportunities, as people may need to venture outside over multiple days, especially if they lack air conditioning.
Broader Implications and Future Concerns
The combination of extreme daytime and night-time heat underscores the urgent need for public health strategies to protect vulnerable populations. As climate change continues to intensify heatwaves, understanding and mitigating these health risks becomes increasingly vital for communities across Australia and globally.
