Urban trees are playing a major role in protecting cities from extreme heat, with a new global study showing they reduce nearly half of the urban heat island effect that makes cities hotter than surrounding rural areas.
Researchers analysed data from almost 9,000 cities worldwide, home to nearly 3.6 billion people, to understand how much hotter cities would become without trees.
Trees act like natural air conditioners
Cities are often 1°C to 3°C hotter than nearby countryside because materials such as asphalt, concrete, and brick absorb and slowly release heat. In some places, temperatures can rise by as much as 7°C, creating what scientists call the “urban heat island” effect.
Researchers found that trees help reduce this heat by providing shade and cooling the air through transpiration — a process where leaves release water vapour into the atmosphere.
The study found urban trees lower city air temperatures by around 0.5°C to 1.5°C in many areas, bringing meaningful relief during heat waves.
Poorer areas often have fewer trees
The research also highlighted growing inequality in urban greenery. Wealthier neighbourhoods and suburban regions generally have more trees and cooler temperatures, while poorer and densely populated areas remain significantly hotter.
In the United States, for example, lower-income neighbourhoods reportedly have 15 per cent fewer trees and are around 1.5°C warmer than affluent areas.
Experts warned that the people most vulnerable to extreme heat are often the ones with the least access to natural cooling.
Trees alone cannot solve climate crisis
While trees provide major environmental and health benefits, researchers stressed they are not enough on their own to combat rising global temperatures caused by climate change.
The study estimated that current urban tree cover may offset only around 10 per cent of projected future warming by mid-century. Even with aggressive tree planting, that figure may rise only to about 20 per cent.
Experts called for broader solutions including greener urban planning, reflective building materials, shaded streets, improved airflow, and urgent cuts in greenhouse gas emissions.