The Not-So-Emerald City? Seattle struggles to increase tree canopy cover to improve equity, health and climate-change resilience

Seattle’s status as “The Emerald City” may be under threat. Washington state’s biggest metropolis earned the nickname for its lush greenery. But now that’s decreasing, despite almost two decades’ efforts to expand the urban forest.

In 2007, officials began pushing for 30 percent canopy cover within 30 years. But Seattle recently lost 255 acres of greenery, an area half the size of Monaco, according to its Tree Canopy Assessment. The setback — a 0.5 percent drop from 28.6 percent coverage — may seem small across five years. Yet its knock-on effects could be big, scientists warn.

“Trees are critical climate infrastructure, helping to mitigate extreme heat,” the assessment notes. “Our urban forest supports health, provides habitat, sequesters carbon, absorbs pollution and manages stormwater.” It also helps residents “adapt to a changing climate, protecting us from extreme heat.”

That need is becoming more urgent. A 27-day “heat dome” spiked Seattle’s temperatures to a record 108 F in 2021, contributing to 159 deaths across the state. Now a new study estimates this unprecedented event was 34 percent larger and lasted 59 percent longer than it would have without human-caused climate change. It also helped ignite wildfires along the Pacific Coast, accounting for roughly a third of 18.5 million acres charred in North America that year.

Some experts worry that Washington faces another dangerous summer, due to drought caused by low snowpack and dry forecasts. That’s extra concerning for the 54 percent of Seattleites who live in “heat islands,” urbanized areas where temperatures run up to 8.2 F higher than in more natural landscapes, reports the research nonprofit Climate Central.

Compounding the crisis, these islands disproportionally occur in neighborhoods impacted by racial and economic injustices. A 2021 study revealed that more melanated homes suffer disproportionate heat exposure, says co-author Glenn Sheriff, an Arizona State University associate politics professor. “The average person of color is wealthier than the average person below the poverty line,” he notes. Nonetheless, they face the same environmental risks when the mercury rises. “This suggests it’s not just real estate markets causing the unequal distribution of exposure,” Sheriff says.

Whatever the root cause, Seattle wants to stop this inequity as it expands its urban forest. And President Biden’s Inflation Reduction Act has awarded $12.9 million to reach both these goals.

“Growing canopy cover takes time,” says Mayor Bruce Harrell, “but our urgency and action today reflect a healthier, greener Emerald City tomorrow.”