Heat now, deaths later: projecting Australia’s rising heatwave mortality - Lethal Heating Editor BDA

Key Points

Climate change has already increased some historic heatwave death tolls by around 20%.[1] Urban residents face higher heatwave mortality risk due to the urban heat island and social vulnerability factors.[2] A Heatwave Vulnerability Index can predict relative mortality risk at suburb scale.[3] Australia’s existing public health data show rising hospitalisations and heat-related impacts that vary by state and age group.[4] Policy responses must combine mitigation, urban planning, and health-system preparedness to limit future deaths.[5] Targeted action for low-income, elderly and health-compromised populations is essential to reduce projected mortality burdens.[6]

Australia’s exposure to deadly heat is increasing.

Recent studies show this is already translating into excess deaths during extreme events.

Researchers estimate that human-induced climate change raised mortality in major historical Australian heatwaves by around twenty per cent for some events.^[1]

City residents, especially those with low incomes or pre-existing health conditions, carry a larger share of the risk because of the urban heat island and uneven access to cooling and health services.^[2]

New tools such as a Heatwave Vulnerability Index can map neighbourhood-level risk and predict where mortality rises are most likely to occur.^[3]

National health data already record increases in heat-related hospital encounters and a growing burden on emergency services during prolonged hot spells.^[4]

If emissions continue on current trajectories, public health modelling indicates substantially higher mortality burdens in coming decades without stronger adaptation and mitigation.

This article reviews the evidence, explains the mechanisms linking heat to death, and sets out where policy and health systems must focus to lower future mortality.

Why heat kills

Extreme heat increases cardiovascular and respiratory stress and worsens chronic conditions that lead to hospitalisation and death.

Heat also disrupts medication efficacy and can cause dehydration and heat stroke especially among older adults and those with underlying illnesses.

Socioeconomic factors amplify physiological risks because poor housing, lack of cooling and social isolation reduce the chance of timely help.

Urban design matters because surfaces that store heat turn cities into heat islands that raise overnight temperatures and reduce recovery time between hot days.

What recent analyses show

A study led by Australian universities analysed a major Victorian heatwave and concluded excess deaths during the event were increased by about twenty per cent by human-caused climate change for that episode.^[1]

That same body of work and linked analyses found that heatwave mortality is concentrated in cities and suburbs where vulnerability factors cluster together, such as low income and limited health access.^[2]

Researchers have validated a Heatwave Vulnerability Index against Australian mortality records and found it predicts relative increases in deaths across more than two thousand suburbs.^[3]

National surveillance from the Australian Institute of Health and Welfare shows clear seasonality in heat-related injuries and increasing contact with health services during extreme heat years.^[4]

How projections are made

Projections combine observed relationships between temperature and mortality with climate model scenarios that estimate future temperature extremes.

Researchers calibrate models using historic events where mortality data are available to quantify how much human-caused warming shifted the probability or intensity of those events.

Indexes that combine social, demographic and built-environment variables allow researchers to map how exposure plus vulnerability translates into probable deaths at local scales.

Who is at greatest risk

Older Australians and people with cardiovascular disease, diabetes or chronic respiratory conditions face the highest individual risk during heatwaves.

People living alone, those on low incomes and communities with poor access to health and cooling infrastructure are also disproportionately affected.^[3]

Indigenous communities, many of whom already experience higher burdens of chronic disease and housing insecurity, are vulnerable in specific regions and deserve focused intervention planning.

Urban heat and inequality

Heat is not uniform within cities and suburbs with more sealed surfaces, less vegetation and older housing stock retain and re-emit heat at night.

These microclimates make recovery between hot days harder and increase cumulative physiological strain that leads to greater mortality risk.

Mapping tools show that the highest vulnerability scores align with low income and health disadvantage in Australia’s capital cities.^[3]

Health system and policy implications

Health systems must plan for surges in emergency presentations and supply appropriate workforce and cooling capacity during forecast heatwaves.

Public health messaging, community cooling centres and targeted welfare checks for isolated older people reduce near-term mortality risks.

Longer term, urban greening, heat-resilient building codes and reduced greenhouse emissions are necessary to reduce both exposure and the underlying climate driver of more intense heatwaves.^[5]

What adaptation looks like in practice

Successful adaptation blends immediate measures such as heat-health alerts and mobile cooling with structural changes such as increased tree canopy and cooler paving materials.

Investment in social housing upgrades to provide effective passive cooling and access to power for air conditioning is a high return intervention for heat-vulnerable households.

Integrating heat vulnerability mapping into local planning allows authorities to prioritise interventions where mortality reductions will be largest.^[3]

Limits and uncertainties

Projections are sensitive to the emission pathway assumed and to how well future social and health services evolve to protect vulnerable groups.

Local adaptation can substantially reduce mortality compared with an unadapted baseline but cannot remove all risks if global warming continues unabated.

Data gaps remain for some population groups and places which means monitoring and improved health surveillance are essential to refine projections over time.

Conclusions

Empirical studies now link human-induced warming to measurable increases in heatwave deaths for specific Australian events and show the burden is unevenly distributed.

Combining mitigation of emissions with targeted local adaptation and stronger health-system preparedness offers the best route to reduce projected mortality.

Policymakers should use validated vulnerability indices and public health data to allocate cooling, medical and social supports to the highest risk suburbs first.^[3]

Failure to act on both climate emissions and local adaptation will leave larger future cohorts of Australians exposed to preventable heat-related deaths.

References

1. Heatwave mortality studies reveal climate change impacts and risk for cities — University of Queensland, 18 February 2025
2. Heatwave fatalities in Australia: a new analysis — Risk Frontiers
3. Evaluating the association between heatwave vulnerability index and related deaths in Australia — HeatHealth (peer-reviewed article PDF)
4. Extreme heat — Australian Institute of Health and Welfare
5. Climate Council report on extreme heat impacts and solutions (PDF)
6. Vulnerability to extreme heat — The Australia Institute (PDF, Nov 2024)
7. Heat health — Victorian Department of Health
8. Feature — Heat health risk — Australian Climate Service / ACS

Back to top