How Urban Trees Can Save Lives

The analysis found that investing just US$4 per resident in each of these cities in tree planting efforts could improve the health of millions of people, and that trees are as cost-effective as many other common solutions.

Most of the cooling and filtering effects created by trees are fairly localized, so densely populated cities—as well as those with higher overall pollution levels—tend to see the highest overall return on investment (ROI) from tree plantings.

The localized nature of trees’ effects, however, means that particular neighborhoods in virtually any city could benefit from plantings. City planners can even target plantings to protect areas with especially vulnerable populations—such as near schools and hospitals—or use trees as a screen against PM coming from highways and industrial areas.

While trees alone can’t solve the entirety of cities’ air and heat problems, they are a critical piece of the puzzle. The report shows that even a conservative global investment in urban trees can save tens of thousands of lives.

Case Study of High City-Wide ROI: Jakarta, Indonesia

With 28 million people living in the greater metro area, Jakarta is the largest city in the world without a metro system—and also home to some of the world’s worst traffic jams. The resulting emissions from vehicles, along with smoke from the burning of forests and agricultural land, contribute to dangerous levels of PM—not just for Jakarta but much of the surrounding region, too.

While the Indonesian government has taken steps in recent years to control pollution and prevent illegal burnings, Jakarta would still see a high ROI from tree plantings compared to other global cities, especially for PM reduction. An annual investment equivalent to US$4 per person could bring significant temperature and PM-level reductions for nearly 4 million people in the city.

Case Study of High Neighborhood-Level ROI: Atlanta, Georgia (USA)

Atlanta already has some of the densest canopy cover of any North American city—so, unsurprisingly, it shows a relatively low overall ROI from new tree plantings compared to other global cities. But the study shows that particular high-density neighborhoods within Atlanta—such as downtown neighborhoods along the Interstate 85 corridor—could benefit greatly from increased tree plantings, especially for heat mitigation. As Atlanta’s already-warm summer temperatures climb in the future, ensuring that all neighborhoods are protected from excessive heat will be even more important.