Trees for life: Making our cities greener can 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 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 93 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, according to the team behind The Lancet report. 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.

The infographic above shows how temperatures rise in line with the density of urban development. 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. In turn, this creates the conditions for cities to become even hotter, posing an even greater threat to public health.

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.

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. It details some startling risks and opportunities arising from the relationship between urban development and nature.

Firstly, the report finds that 44% of global GDP is at risk of disruption from nature loss. Reversing the decline of nature presents a $583 billion investment opportunity in nature-based solutions and preserving undeveloped land. The outcome of such investments is the potential creation of 59 million jobs by 2030 and a total return on investment of $1.5 trillion.

A number of the investment areas detailed in the chart above could have a significant impact in reducing the health impacts of UHIs. Land-sparing initiatives that avoid urban sprawl and the creation of more heat-absorbing infrastructure will help to keep temperatures down while protecting nature and biodiversity.

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.

As efforts to bring more tree cover to urban areas gather pace, it will be important to ensure all citizens enjoy the benefits equally. Research into previous urban greening initiatives, published in nature.com, has found some projects have led to the gentrification of districts, with rents and property prices soaring.

This in turn can exclude people from historically marginalized backgrounds, particularly in terms of race and income. The report finds that despite the best of intentions; “interventions become embedded in processes that contribute to the displacement of the very residents urban greening was often meant to benefit”.

The World Economic Forum’s UpLink initiative is working with innovators and corporate partners around the world on nature-based solutions to the climate crisis. The 1t.org initiative, meanwhile, has a target of planting a trillion trees by 2030. This project is mainly focused on forest restoration but UpLink is also working with partners on projects to scale up tree cover in cities.

Urban Ecologist Mariellé Anzelone is on a mission to convince people in New York that preserving and increasing the city’s natural green cover will bring environmental benefits and help residents to live healthier lives. Her #popupforest initiative is engaging citizens and schools with the aim of seeing more trees planted in the city, greening the streets and bringing biodiversity back into areas that have been nature-free zones for decades. You can watch Anzelone’s story in this video.

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.