A new study by The Nature Conservancy based in California says that planting and cultivating nature (i.e. trees) in our urban centers would do exactly what you would hope they would do—make our lives better.
We are at the beginning of the urban century. One of the preeminent tasks of cities will be making themselves vibrant, healthy, attractive places to live. This report has focused on just one small part of this task: the quest to make urban air healthier. Cities continue to strive to reduce concentrations of particulate matter and other atmospheric pollutants. And they are beginning to plan for the increased frequency and intensity of heat waves that climate change will likely bring. Succeeding against these twin challenges—air pollution and excess heat— will require an array of approaches. In this report, The Nature Conservancy – in coordination with C40 Cities Climate Leadership Group – has tried to understand whether nature can play a role in helping to solve these twin challenges.
The answer appears to be a qualified “yes.” Street trees can be a part of a cost-effective portfolio of interventions aimed at controlling particulate matter pollution and mitigating high temperatures in cities. While trees cannot and should not replace other strategies to make air healthier, trees can be used in conjunction with these other strategies to help clean and cool the air. Moreover, trees provide a multitude of other benefits beyond healthier air. In the right spot, trees can both help make our air healthier and our cities more verdant and livable.
As more and more people live in cities, we need to come up with more and more solutions for the environmental stresses that urban living causes. The good news is that even the wealthy haven’t figured out how to immunize themselves from urban pollution and so this is something that we can all get behind, regardless of our economic status.
According to the UN World Health Organization (WHO), about 90% of the global population living in cities in 2014 was exposed to particulate matter that exceeded the WHO air quality guidelines.
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As everyone within an urban area breathes the same air, the pollution does not discriminate - both rich and poor are exposed to the dangers. But, it adds, people living near the source or busy roads are more exposed and more affected.
The study looks into ways and projects the economic benefits of planting trees and gardens in targeted, cost-effective ways.
"We also looked at how much more trees could help if we planted more trees. We found that there was a lot more scope there. All of the cities we looked at, if all the people in them spent an extra US $4 a year on planting trees, you could save between 11,000 and 36,000 lives each year. This is mostly as a result of having cleaner air.
"As well as the avoided mortality, there is even more avoided hospitalisation, and it will benefit tens of millions of folks.
But street trees alone provide benefits and along with cleaner energy and transportation we must figure out ways to combat rising temperatures and the unhealthy atmosphere in the environments we have created.
The current stock of street trees in our studied cities is already delivering real benefits. We estimate that trees are currently providing on average 1.3 million (Low scenario to High scenario range: 0.0 to 6.1) people at least a 10 µg/m³ reduction in PM2.5, 10.2 million (1.0 to 15.4) people at least a 5 µg/m³ reduction, and 52.1 million (23.8 to 63.1) people at least a 1 µg/m³ reduction. Similarly, trees are already providing 68.3 million people with a roughly 0.5 to 2.0° C (0.9 to 3.6° F) reduction in summer maximum air temperatures. As discussed in detail in the report, this magnitude of impact on PM and temperature has real health benefits for those affected.
These numbers are just for the current stock of street trees. As we show in the report, many cities are struggling to maintain their current stock of street trees, and our results emphasize the importance of investments to maintain this stock. However, in many cities there also exist substantial additional opportunities for adding tree cover to further mitigate air pollution and summer heat. In this study, we assessed the impact of such largescale but feasible tree cover increases, measuring their return on investment (ROI) in terms of PM2.5 reduction or temperature mitigation delivered to people per dollar spent.
Also, who doesn’t like having some trees around?