A new study published in the Lancet, a peer-reviewed public health journal, finds that doubling the average amount of tree cover in European cities from 15 to 30 percent could reduce urban temperatures by 0.4 degrees Celsius (0.7 degrees Fahrenheit). It may not sound like much, but this small temperature change could cut heat-related deaths by more than a third.
Modeling cities that are 30 percent shaded by trees isn’t random; it’s an actual target that many European cities are working towards, and that some, like Oslo, have already achieved.
The study's findings are based on a new model of 93 European cities, home to about 57 million people. An international team of researchers found that more trees could significantly mitigate the “urban heat island effect,” in which unshaded city blocks can get up to 22 degrees F hotter than rural areas. The findings indicate that approximately 2,600 deaths could have been prevented by greater tree cover.
Trees have other powerful benefits too, including better mental health and cognitive function. Greenery can also reclaim urban space from cars, creating room for recreation and more sustainable forms of transportation.
“If asphalt is an indicator for having more cars, generally, trees are an indicator for having a more livable area,” Mark Nieuwenhuijsen, a research professor at the Barcelona Institute for Global Health and a coauthor of the study, told Time.
As summer heat waves get more extreme, several European cities have already set goals to plant more trees over the next several years: Paris and Milan, for example, both of which currently have less than 10 percent tree cover.
U.S. cities are also recognizing the need for trees - particularly as research piles up showing how racist housing and city planning policies have deprived Black, brown, and low-income neighborhoods of trees, putting their residents at elevated risk of heat-related health problems.