Cities would be really cold with more trees around

The effects can be felt most strongly in our cities, which are on average 1.5°C warmer than surrounding areas due to so-called Urban Heat Islands (UHIs). This happens when building materials (concrete, asphalt, metals) and machinery (cars, trucks, air-conditioners) absorb and generate heat, turning city blocks into baking ovens.

The heat is just one way that cities can become unhealthy places to live; UHI accounts for 4.3% of premature deaths in cities during the summer months. Outdoor air pollution kills more than 4 million people a year. Noise causes the loss of more than 1.8 million healthy life years in Europe. Depending on where you live, you may be surrounded by shades of gray or stuck in a food desert. For many people, health, location and financial pressures make moving out of town a highly desirable option when it comes to raising children or settling down.

It’s a shame because cities aren’t just spectacular centers of human activity; They also provide an incredibly efficient way of living. Studies have shown that people who live in cities have a lower carbon footprint than those in suburbs and rural areas. Urban residents walk more, cycle more and use public transport more than their suburban and rural counterparts. They also live in smaller homes with fewer furnishings. Encouraging denser living can be an important part of the race to net zero carbon emissions. But if we’re going to persuade people to live in them, we must first make cities more livable.

Lots of solutions exist, but we have one powerful tool that can help cool cities, reduce pollution, and improve our mental and physical health: trees.

A new study published in The Lancet suggests that increasing tree cover to 30% of a city can reduce premature deaths in cities by almost 40%, through a combination of shading and lowering temperatures. By reducing, evaporating water and removing heat sources such as concrete and asphalt.

Satellite data have shown that 30% tree coverage is a viable target in the 93 cities studied, but the average in Europe is still only 14.9%.

Despite its relative simplicity, there are real obstacles to urban forestry. Part of it comes down to competing urban interests, says Marc Nieuwenhuizen, co-author of the study and director of urban planning, environment and health at the Barcelona Institute for Global Health. Cities have historically prioritized space for vehicles. Wide roads and car parks can be reduced to make way for foliage, but as the fight over cycle lanes and low-traffic neighborhoods in the UK has shown, this fight is politically charged.

There is also an expense. New trees require maintenance after purchase and planting. Like people, they too can find it difficult to survive in an urban environment. In Lisbon, landscape architect Ana Luisa Soares estimates that each new tree costs the city €2,000 ($2,180).

There are other ways to cool down the city—through reflective roofs or white-over-white paint. But… they don’t provide the full package of benefits that trees do.

In a 2011 study, Soares estimated the cost of maintaining the trees at $1.9 million per year. Profit came in at $8.4 million. Nieuwenhuijsen ran through a list of proven benefits: Not only are streets more aesthetically pleasing when they’re adorned with trees, but there are proven benefits for mental health. Urban green spaces are also associated with a lower prevalence of diabetes, heart problems, better birth outcomes and better cognitive functioning. Plus, trees are handy carbon stores that can help prevent flash flooding – another climate risk.

The important thing would be to ensure that there is an even distribution of trees across the city. A large forested park will not have the same beneficial effects as several tree-lined streets. Wealthier areas already tend to be greener than poorer ones, so there’s also a social justice element to making sure everyone has equal access to nature.

Cecil Konijndijk, Professor of Urban Forestry at the University of British Columbia, suggests a 3-30-300 rule: Everyone should be able to see 3 trees from their window, live in a neighborhood with 30% tree cover and be within 300 m Must be at a distance of a green space But there is still a lot of work to be done. For example in Barcelona, ​​only 5% of people live somewhere that meets that standard.

Making our cities more livable and sustainable will involve a lot of tough decisions about more than just plant life. But given that trees can take decades to grow, we must plant now.

Lara Williams is a Bloomberg Opinion columnist covering climate change.