Urban planners and public health officials are grappling with the
best way to approach this complicated issue. But there’s one solution we
can implement now with a big impact: plant more trees. Trees and other
vegetation naturally cool the air around them by shading surfaces and
releasing water vapor. And while the effects are local—most of the
improvement is within 100 meters—they can still be meaningful, reducing
temperatures by up to 2°C.
The Nature Conservancy has carried out a study of 245 cities
around the world that stand to benefit from tree-planting initiatives,
assessing their efficiency and return on investment. Compared to other
ways to cool outdoor air temperatures, such as white roofs, trees
deliver similar benefits per dollar spent. Urban trees can also reduce fine particulate matter air pollution, a problem that contributes to 5 percent of all deaths worldwide each year.
Given that the most significant effects of
trees are highly localized, we found that densely populated megacities
in Pakistan, India, and other parts of South and Southeast Asia would
benefit most. Yet this also means that within cities there are will be
individual neighborhoods that could benefit, depending on their density
and existing level of vegetation. This is an advantage both for
efficiency and from a social equity standpoint, as planting can be
targeted directly to those neighborhoods with greatest need.
also offer a huge range of other benefits. In addition to the cooling
and air quality benefits, trees provide habitat for wildlife, reduce
storm-water runoff, and sequester carbon from the atmosphere, which
helps to mitigate climate change. There is also a growing body of research showing that exposure to trees and other vegetation has a positive effect on mental health, especially for children.