Greener cities can protect millions from extreme urban heat and cut early deaths by a third

For billions of people around the world, the health hazards of city living are a daily reality.One of the biggest threats is stifling temperatures, which can be a summer phenomenon or a year-round problem, depending on location.High city temperatures are not just a matter of discomfort. Every year, thousands of premature deaths are attributed to excessive urban heat.A new study, published in The Lancet medical journal has estimated that more than a third of these premature deaths could be prevented by planting more trees in cities.The researchers identified 6,700 premature deaths in some 93 European cities that could be attributed to excess summer heat. They then modelled the impact of increasing city tree cover to 30%.The results showed that this level of tree cover across those European cities would prevent 2,644 premature deaths – more than a third of the total.Creating more shade in cities by planting more trees would reduce the mean temperature by 0.4C, The Lancet reported. This would limit the health threats posed by a phenomenon known as the urban heat island effect.Urban heat islands (UHIs) occur when the surfaces of buildings, roads and pavements absorb heat from the sun, pushing up the temperature in cities and other built-up areas.Scientists at the Berkeley National Laboratory say a hot and sunny afternoon can increase the temperature in urban areas by 1-3°C, compared with the air in nearby rural areas.Japan’s capital city, Tokyo, provides a good example of how urban development can send temperatures soaring. The UHI effect in Tokyo has seen the average temperature climb by 3°C over the last 100 years.When cities like Tokyo get warmer, the use of air conditioning increases, pushing up energy use and carbon emissions.Greening our cities with trees and bringing nature back into urban environments can help overcome some of the greatest challenges facing the world’s growing urban populations, says the World Economic Forum.In 2022, the World Economic Forum published a report looking into the benefits that could be created by changing the relationship between nature and our cities.The BiodiverCities by 2030 report calls on city leaders and populations to play a crucial role in reversing nature loss.The report finds that 44% of global GDP is at risk of disruption from nature loss. Reversing the decline of nature presents a $583bn investment opportunity in nature-based solutions and preserving undeveloped land.The outcome of such investments is the potential creation of 59mn jobs by 2030 and a total return on investment of $1.5tn.Turning the roofs and surfaces of buildings into urban gardens will provide new wildlife habitats in the hearts of our cities. Green roofs absorb much less heat than concrete surfaces, creating the opportunity to bring down temperatures in urban environments.Both real-world experience and scientific research have demonstrated the benefits that urban trees bring. If we act purposefully and significantly increase the number of trees in our cities, we could reduce urban temperatures by up to 2.9°C and protect thousands of people from the life-threatening impact of extreme urban heat.