Colombia planted 880,000 trees across the streets of one city to tackle rising temperatures, and the plantation delivered localised cooling of up to 5°C in shaded areas
Why Medellín needed a solution to rising temperatures What the Green Corridors project involved How trees naturally cool urban environments Benefits extended far beyond temperature
Why Medellín needed a solution to rising temperatures What the Green Corridors project involved How trees naturally cool urban environments Benefits extended far beyond temperature reduction Separating fact from the viral 10°C claim A model for cities adapting to climate change As heatwaves become more frequent and intense, cities around the world are searching for ways to stay cooler without relying solely on energy-intensive air conditioning. Medellín, Colombia, has emerged as one of the world's most celebrated examples of nature-based urban cooling. Through its Green Corridors programme, the city planted around 880,000 trees and more than 2.5 million shrubs and other plants along roads, parks, rivers and public spaces. The large-scale greening effort transformed concrete-heavy streets into shaded corridors, helping lower temperatures, improve air quality and restore biodiversity. Studies found the project delivered localised cooling of up to 5°C in shaded areas, demonstrating how urban forests can become a powerful tool for adapting to climate change.Medellín lies in the Aburrá Valley, where surrounding mountains restrict airflow and allow heat to accumulate. Decades of rapid urban growth replaced vegetation with roads, buildings and paved surfaces that absorb and retain solar heat, creating a pronounced urban heat island effect.
As temperatures climbed, residents experienced hotter streets, reduced outdoor comfort and greater exposure to heat-related health risks.To address these challenges, the city launched the Green Corridors (Corredores Verdes) initiative in 2016. Instead of focusing only on engineered cooling systems, planners invested in expanding urban vegetation. The aim was to naturally cool public spaces while making the city healthier, greener and more resilient to future climate change.The initiative created a network of green corridors stretching across roads, pedestrian walkways, riversides, parks and transport routes. Approximately 880,000 trees were planted alongside more than 2.5 million shrubs, palms and ground-cover plants, carefully selected for Medellín's tropical climate and their ability to provide shade.Rather than concentrating greenery in a few parks, planners distributed vegetation throughout the city so residents could experience cooler conditions in everyday public spaces. The project also included ongoing maintenance, irrigation and pruning to ensure the plants remained healthy and continued providing environmental benefits.Trees reduce heat through a combination of shading and evapotranspiration. Their canopies block direct sunlight from reaching roads, pavements and buildings, limiting the amount of heat absorbed by urban surfaces. At the same time, trees release water vapour through their leaves, cooling the surrounding air in much the same way perspiration cools the human body.Scientific assessments found Medellín's Green Corridors reduced average city temperatures by around 2°C, while some heavily shaded locations recorded localised cooling of up to 5°C.
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