Urban heat islands (UHIs) are urban or built-up areas that experience significantly higher temperatures than surrounding rural or suburban areas. This is a well-documented climatic phenomenon driven by human modifications to the landscape.

In the United States, daytime temperatures in urban areas are often about 1–7°F (roughly 0.5–4°C) higher than outlying areas, and nighttime temperatures about 2–5°F (1–3°C) higher.

Globally, average UHI intensities commonly range from about 1–6°C or more, varying by city density, climate, and measurement method (surface vs. air temperature).

Surface urban heat islands (measured via satellite) can be stronger than canopy (air) UHIs. Intensities are often greater at night and during calm, clear weather.

UHIs form due to the altered energy balance in cities:

• Materials and surfaces: Dark asphalt, concrete, and roofs absorb and store more solar radiation than natural vegetation or soil, then slowly release heat (especially at night).
• Reduced vegetation and water: Fewer trees, parks, and water bodies mean less shade, less evaporative cooling (transpiration and evaporation), and more heat retention.
• Urban geometry: Tall buildings and narrow streets create “urban canyons” that trap heat, reduce wind flow, and limit radiative cooling to the sky.
• Anthropogenic heat: Waste heat from vehicles, air conditioning, industry, buildings, and other human activities adds directly to the local temperature.
• Other factors: Higher air pollution can trap heat; dense development reduces overall cooling capacity.

Health and human well-being: Elevated temperatures increase risks of heat exhaustion, heatstroke, dehydration, and death—especially for the elderly, young children, outdoor workers, people with chronic illnesses, and those without access to cooling.

UHIs worsen air quality (e.g., by promoting ozone formation) and can amplify the effects of heatwaves. Studies link them to thousands of premature deaths annually in various regions.

Energy and economy: Higher temperatures drive up demand for air conditioning, increasing electricity use, costs, and associated emissions. This can strain power grids during peak periods.

Environment: Altered local climates affect precipitation patterns, water quality, and ecosystems.

UHIs interact with global climate change, making extreme heat more frequent and intense in cities.

Exposure has risen sharply with urbanization—one study found global urban extreme-heat exposure nearly doubled from 1983–2016, with urban warming contributing substantially beyond population growth alone.

Equity: Heat burdens often fall disproportionately on lower-income neighborhoods, which may have less green space, poorer housing insulation, and higher density of heat-absorbing surfaces.

Effective approaches include:

• Increasing tree canopy, parks, green roofs, and green walls for shade and evaporative cooling (can reduce local temperatures by 1–4°C or more in favorable conditions).
• Using cool (high-albedo/reflective) roofs, pavements, and materials that reflect more sunlight.
• Expanding blue infrastructure (ponds, fountains, permeable surfaces) and improving urban design for better airflow and shade.
• Reducing anthropogenic heat through energy efficiency and smarter building practices.
• Combining strategies (hybrid green-blue systems) often yields the best results.

Research continues to refine global datasets, modeling, and city-specific solutions.

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Researchers from ETH Zurich, Eawag (Swiss Federal Institute of Aquatic Science and Technology), and international partners have proposed a “Thermal Justice” framework as a fairer approach to urban heat adaptation.

As cities warm due to climate change and the urban heat island effect, standard advice (drink water, avoid peak-heat activity, stay cool indoors, check on vulnerable people) and measures like warnings or cooling centers save lives. However, these reveal inequalities: not everyone can stop work, afford air conditioning, access shaded paths, or live in night-safe housing.

Thermal Justice applies Environmental Justice principles specifically to heat.

Author Lucas Gobatti notes: “The question is not only whether a measure lowers temperatures, but whether people can actually sleep, work, move, care for others, and remain healthy during heat.”

Cooling solutions can shift risks elsewhere (“thermal displacement”). These become unjust when burdens fall on less powerful communities, ecosystems, or future generations.

Success should be judged not just by trees planted or centers opened, but by whether people and ecosystems can live safely without shifting heat risks elsewhere.

The concepts have also been turned into an open collaborative board game, “Thermal Justice: a serious game,” which explores trade-offs in protecting a city from heat with limited energy, water, space, and money.

It is being presented at Zurich’s Scientifica science festival.

The framework aims to make urban heat adaptation both effective and equitable amid rising temperatures and more frequent extremes.

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Thermal justice in urban climate change adaptation

Thermal justice in urban climate change adaptation is a framework that applies principles of environmental justice specifically to extreme heat risks in cities.

It was formalized in a Comment published in Nature Climate Change on 19 August 2026 by Lucas Gobatti (lead author, affiliated with Eawag and ETH Zurich) and co-authors including P.M. Bach, A. Mazzone, G. Falchetta, M. Santamouris, M. Maurer, and J.P. Leitão.

Extreme heat events are increasing due to climate change and the urban heat island effect, requiring urgent adaptation for both humans and ecosystems to function safely.

Standard responses (warnings, cooling centers, individual advice to stay hydrated and avoid peak heat) save lives but often overlook or worsen inequalities: not everyone can afford air conditioning, access shaded routes, stop outdoor work, or live in adequately insulated housing that stays cool at night.

Thermal justice asks not only whether a measure lowers temperatures, but whether people can actually sleep, work, move, care for others, and remain healthy during heat—without shifting burdens onto others, ecosystems, or future generations.

It integrates five dimensions drawn from environmental justice theory:

• Fair distribution of thermal burdens and benefits (who bears the heat and who gains cooling).
• Recognition of structurally produced vulnerabilities (e.g., those arising from poverty, informal housing, outdoor labor, age, or historical planning decisions).
• Participation in decision-making (who has a voice in how cities adapt).
• Capabilities of people and communities to function safely under heat.
• Ecological justice (protection of ecosystems and future generations).

Cooling one person, building, or neighborhood can transfer heat-related risks elsewhere. Examples include:

• Air conditioning that protects indoor occupants but releases waste heat outdoors, raises electricity demand, and excludes those who cannot afford it.
• Urban greening that provides shade and cooling but can increase property values and rents, displacing lower-income residents to hotter areas (“green gentrification”).
• Solutions dependent on intensive irrigation, fragile energy grids, or poor maintenance that create new long-term vulnerabilities.

These become unjust when the costs fall on communities, non-human life, or generations with less power to avoid them.

A thermally just approach combines emergency protection with structural change:

• During heatwaves: Prioritize exposed and isolated residents, ensure accessible public cooling spaces, protect outdoor and indoor workers, create shaded routes to essential services, and expand affordable indoor cooling options.
• Between heatwaves: Retrofit poorly protected housing, expand durable green and blue infrastructure matched to local water availability, and design cooling investments to avoid displacing the people they are meant to help.

Success should be measured not merely by the number of trees planted, warnings issued, or cooling centers opened, but by whether human and ecological life can continue safely without shifting heat risks elsewhere.

The authors have also developed an open collaborative board game (“Thermal Justice: a serious game”) that simulates these trade-offs, requiring players to protect a city from heat stress while managing limited energy, water, space, and financial resources. It highlights who benefits and who bears the costs of different adaptation choices.

This framework builds on broader literature on urban thermal inequity, heat justice, and climate justice, emphasizing that equitable adaptation is essential to avoid locking in or amplifying existing social and spatial inequalities as cities grow hotter.

Published:  Nature Climate Change (2026)

DOI: 10.1038/s41558-026-02727-5

Provided: ETH Zurich 

Authors: Lucas Gobatti (lead author, affiliated with Eawag and ETH Zurich) and co-authors including P.M. Bach, A. Mazzone, G. Falchetta, M. Santamouris, M. Maurer, and J.P. Leitão.

Extreme heat events are increasing, and urban adaptation is urgently needed for humans and non-humans to function safely under heat. Here we present a thermal justice framework and highlight how its use facilitates equitable adaptation and minimizes heat-risk displacement.