A comprehensive new research study reveals that urban forests are offsetting approximately half of the temperature increases caused by concrete and buildings in metropolitan areas worldwide, yet the communities most in need of cooling relief aren’t receiving adequate benefits.
Published Wednesday in Nature Communications, the research shows that tree coverage provides an average temperature reduction of 0.27 degrees Fahrenheit (0.15 degrees Celsius) across global urban areas through shade provision and water vapor release.
Cities would experience an additional 0.56 degrees Fahrenheit (0.31 degrees Celsius) of warming without existing tree coverage due to urban heat islands, where dark surfaces and pavement trap thermal energy. This warming process operates independently from greenhouse gas-driven climate change.
The research team analyzed temperature data from nearly 9,000 major cities worldwide, examining areas equivalent to roughly 150 city blocks each. This detailed approach enabled scientists to measure localized cooling impacts, ensuring that parks in one neighborhood weren’t incorrectly credited with cooling distant urban areas.
While 185 million residents across 31 major metropolitan areas currently experience at least 0.5 degrees Fahrenheit of tree-based cooling, lead researcher Rob McDonald from the Nature Conservancy noted that economically disadvantaged and hotter urban centers receive insufficient protection from dangerous heat levels that can cause brain dysfunction, organ failure, and cardiac stress.
The research methodology combined weather station readings, satellite imagery, and computational modeling to quantify tree-based cooling effects, measuring temperature differences between city centers and surrounding rural regions.
Twenty cities housing at least 3 million people each provide residents with less than one-tenth of a degree of tree-based cooling. Four metropolitan areas—Dakar, Senegal; Jeddah, Saudi Arabia; Kuwait City; and Amman, Jordan—have such limited tree coverage that their combined 15 million inhabitants receive virtually no natural cooling benefits.
Cities achieving cooling effects of at least 0.45 degrees Fahrenheit show stark economic disparities. Nearly 40% of wealthy nations’ cities reach this cooling threshold, compared to fewer than 9% of cities in the world’s poorest countries.
Berlin leads the list of most effectively cooled cities, joined by Atlanta, Moscow, Washington, Seattle, and Sydney, all featuring extensive tree coverage. Atlanta maintains tree canopy over 64% of its land area, McDonald reported. Wealthier North American communities benefit from larger property sizes, individual ownership patterns, and residents with greater political influence, all contributing to expanded tree growth and coverage, according to Chris Greene from the University of Dalhousie in Canada, who wasn’t involved in the research.
“There’s this inequality,” McDonald explained. “When you look at cities globally, there are many, many cities, especially in developing countries, that have very low tree cover, and so I think the air temperature cooling number was a little less than we expected.”
Thomas Crowther, an ecological researcher at King Abdullah University of Science and Technology in Saudi Arabia, emphasized that incremental improvements matter significantly. His regional cities receive minimal tree-based cooling, often due to water scarcity constraints.
“As up to 75% of the human population shifts towards living in urban environments, these buffering effects of urban vegetation are going to be vital,” Crowther stated. “But we have to overturn the devastating inequities in the distribution of urban trees, so that their benefits can be experienced by the low- and middle-income communities that are often most vulnerable to the effects of extreme temperatures.”
Study authors emphasized that municipalities, particularly those in hotter and economically challenged areas, should prioritize expanding tree coverage. However, constraints including water availability, suitable land, appropriate species selection, and intensifying climate change limit potential future urban heat reduction to approximately 20%, McDonald noted.
“Trees won’t save us from climate change,” McDonald cautioned. “The climate scenarios are showing a much warmer world and there’s only so much of that that tree cover can help with.”
Tree planting offers additional environmental benefits beyond temperature reduction. Crowther and Jean-Francois Bastin proposed in a 2019 Science journal study that planting one trillion additional trees—supplementing Earth’s existing 3 trillion trees—could capture significant carbon dioxide.
“Planting trees does help fight climate change in multiple ways, but this strategy is not nearly enough to slow climate change to a significant degree,” said University of Michigan environment dean Jonathan Overpeck, who wasn’t involved in the current research. “Only by transitioning away from fossil fuels in favor of renewable energy and battery storage can we hope to halt the climate change that is wreaking havoc around the planet.”
