Cities need thermal justice. Here's what that really means

Cities are responding to extreme heat with more trees, cooling centres, housing retrofits and air conditioning. These measures are essential, but as investment accelerates, cities need to ask a more challenging question: does an intervention actually reduce heat risk, or merely displace it elsewhere?

The urgency is difficult to overstate. The World Health Organization reports that heat claimed more than 200,000 lives across the European Union and associated countries over the previous four years. Nearly all were preventable through measures that included urban shade, cooling centres, outreach to older people and protections for outdoor workers. The challenge is to ensure that these actions protect people fairly.

On the same hot day, heat may be a manageable inconvenience for someone with a cool home and flexible working hours, but constitute a health emergency for someone in poor housing or doing physical work outdoors. Heat risk is shaped by weather, but also by housing, labour, infrastructure and public space.

Heat policies are often evaluated by outputs: trees planted, cooling centres opened, homes retrofitted or temperature reductions. These indicators matter, but can conceal who benefits and who bears the costs.

Air conditioning can be lifesaving indoors, yet access depends on housing, income and a reliable electricity supply. Cooling demand also strains power systems during extreme heat. In 2024, more than 40 countries representing nearly 70% of global electricity demand reached new peak-demand records during heatwaves, while many others experienced major outages and rolling blackouts. The technology protects those who can afford and power it, while its waste heat is discharged outdoors and its energy burden is shared more widely.

Urban greening presents a different trade-off. Trees and parks can reduce heat exposure, yet new green amenities can contribute to rising property values and displacement pressures. An observational study of 28 European and North American cities found that earlier additions of public green space were associated with subsequent gentrification in 17 cities during at least one decade. In dry climates, vegetation may also require water and long-term maintenance that budgets do not adequately secure.

These are examples of thermal displacement: transferring heat-related risks across people, places, infrastructures, ecosystems or generations. This does not make air conditioning or greening undesirable; it means local cooling alone is an incomplete measure of success.

Interest in thermal justice is growing faster than conceptual clarity. In our assessment of the current use of the terms “thermal justice” and “heat justice”, annual records in scientific literature rose 6-fold in the past two years. Yet more than 85% used the term without defining it; among those records, 63% also failed to cite an existing definition.

In August, researchers from ETH Zurich, Swiss Federal Institute of Aquatic Science and Technology (Eawag), and other international institutions proposed a framework for addressing this gap.

Our research defines “Thermal Justice” as the application of Environmental Justice to heat. Its five dimensions translate into five practical questions for cities.

1. Distribution: Are thermal burdens and benefits shared fairly? Cities should examine where cooling is delivered, who can access it and who bears the costs. Are investments concentrated where exposure and vulnerability are greatest? Do tenants benefit from retrofits without unaffordable rent or energy bills? Equal provision does not necessarily produce equal protection.

2. Recognition: Why are people at risk? Heat risk reflects not only exposure, but also housing conditions, income, health, age, working conditions and access to cooling. Cities should, therefore, treat cooling as basic public infrastructure, much like sanitation or safe drinking water, and pair investment with measures that allow lower-income residents to remain and benefit. Vienna provides a promising example of how to do this: researchers found no systematic association between street greening and gentrification between 1991 and 2021, and identified extensive social housing, rent regulation and decentralized greening policies as important buffers against displacement.

3. Capabilities: Can people function safely? Evaluate outcomes at the scale of daily life, not only through average neighbourhood temperatures. Can outdoor workers take breaks? Can older residents reach cool spaces? Can tenants sleep safely at night? Can people continue to learn, travel and care for others during heat? Success means enabling people to perform these essential activities safely, not simply delivering a small average temperature reduction.

4. Participation: Who decides? Treat residents, workers and caregivers as decision-makers, not simply as groups experiencing vulnerability. Their knowledge can reveal barriers that technical indicators miss, such as opening hours that exclude shift workers or cooling centres that are inaccessible or unsafe. Participatory tools such as serious games can help residents, researchers and decision-makers explore trade-offs and decide how limited resources should be allocated.

5. Ecological justice: Who bears displaced risks? Assess energy, water, housing and maintenance consequences alongside local temperature reduction. Do benefits in one place depend on greater outdoor heat release, resource demand, ecological damage or future maintenance burdens elsewhere? Cities should combine efficient indoor cooling with passive building design, clean and resilient power, affordability support, appropriate vegetation and funded long-term maintenance.

The objective is not merely a cooler city. It is a city in which people can safely live, work and move during heat, while the systems and ecosystems on which cooling depends remain viable. Counts of trees, cooling centres and recorded temperature reductions show what was delivered. Thermal justice asks whether it worked, for whom, at whose expense and for how long.