Health & Beauty
Mortality & urban tree shade
New study finds that protecting mature trees could help save lives.
20 August 2026
When temperatures rise, public advice is familiar: drink water, avoid strenuous activity during the hottest hours, keep homes cool and check on older or isolated people.
These recommendations are reflected in the latest heat-health guidance from the WHO Regional Office for Europe.
Authorities can reinforce them through clear warnings, accessible cooling spaces and protection for outdoor and overheated indoor workers.
Such actions save lives – yet they also reveal a basic inequality: not everyone can decide when to stop working, afford air conditioning, reach a shaded route or live in a home that remains safe at night.
Researchers from ETH Zurich, the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and international partner institutions address this problem in a Comment in Nature Climate Change. They define ‘Thermal Justice’ as an application of Environmental Justice to heat.
‘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.’
LUCAS GOBATTI
Lead author and Environmental Engineering researcher
The framework brings together five dimensions: the fair distribution of thermal burdens and benefits; recognition of structurally produced vulnerabilities; participation in decision-making; the capability of people and communities to function safely and the protection of ecosystems and future generations.
The framework also draws attention to thermal displacement: cooling one person or place can transfer heat-related risks elsewhere.
Air conditioning protects people indoors but releases waste heat outside, increases electricity demand and excludes those who cannot afford it.
Urban greening can provide shade while raising rents and pushing residents towards hotter neighbourhoods.
Cooling that depends on intensive irrigation, fragile energy systems or neglected maintenance may solve an immediate problem while also creating future vulnerability. These shifts become unjust when the burdens fall on communities, ecosystems or generations with less power to avoid them.
A thermally just heat response must, therefore, combine emergency protection with structural change.
During heatwaves, cities should prioritise exposed and isolated residents, accessible public cooling, worker protection, shaded routes to essential services and affordable indoor cooling.
Between heatwaves, they should retrofit poorly protected housing, expand durable green and blue infrastructure, match vegetation to water availability and prevent cooling investments from displacing the people they were intended to protect.
Ultimately, success should be measured not only by warnings issued, cooling centres opened or trees planted, but by whether human and ecological life can continue safely without shifting heat risk elsewhere.
New study finds that protecting mature trees could help save lives.
Urban canals can cut temperatures by more than 2°C during heatwaves.
Harvesting rainwater from rooftops could help cities stay cool and cut the number of heatwave days.
