Urban Trees: An Underused Tool for Keeping People Cool

On a hot summer afternoon, the difference between one city block and the next can feel like a different world. On one street, the sun beats down from above while the pavement radiates heat from below. Just around the corner, on a sidewalk shaded by trees, the air seems noticeably cooler. The actual temperature change may only be a few degrees. But for people waiting for a bus or walking home from work, that difference matters a lot.

As cities get hotter, block-by-block temperature differences are becoming more consequential. In the world’s largest capital cities, the number of extremely hot days each year has risen by 25% since the 1990s. Longer, more intense heat waves are increasing health risks, straining energy systems, and disproportionately affecting lower-income neighborhoods that tend to have fewer trees. City leaders are searching for solutions that are effective, affordable and scalable.

Trees are one of the most practical tools cities have to combat heat. Offering both shade and “evaporative cooling” — trees’ version of air conditioning — they provide relief to people outdoors while helping lower surrounding temperatures. A 2023 modeling study found that almost 40% of the 6,700 deaths attributable to urban heat in Europe in 2015 could have been prevented if cities increased tree cover to 30% of their land area. In U.S. cities, urban trees reduce electricity use by nearly 39 million megawatt-hours per year, saving billions of dollars in cooling costs.

Our analysis of more than 60 cities worldwide reveals a clear gap: Large areas of plantable land — especially along streets — are underutilized, presenting a clear opportunity for expanding urban tree cover. Within most cities, local neighborhoods already demonstrate what’s possible, with high levels of tree cover delivering measurable cooling benefits. Extending that level of canopy more broadly could meaningfully reduce heat exposure citywide.

Of course trees alone won’t solve the problem of urban heat. But they’re an accessible and practical solution that can meaningfully ease its burden for residents.