A community-gardening and forestry organization called Louisville Grows has planted city-hardy tree species on private land, churchyards, roadways, and curb strips to help the city cool its heat island. Photograph by Mark Peterson / Redux

We already know that climate change is no longer something to be concerned about for the future, but rather a very present danger. There are ways they can adapt, and part of that involves becoming more sustainable, as some are already doing. But one thing we hadn’t learned much about until now is the impact of increasing heat on the urban environment. Madeline Ostrander writes:

Katy Schneider, the former deputy mayor of Louisville, Kentucky, lives near Eastern Parkway, which forms one strand of her city’s necklace of green. Spending time on the leafy boulevard can make Louisville seem deceptively lush and shady, even when midsummer heat bakes the downtown. But about five years ago, Schneider was surprised to learn that the city had a shortage of trees. In the spring of 2011, students at the University of Louisville surveyed the local canopy and found that it had about thirteen per cent fewer trees than the average for metropolitan areas in the region.

Although Schneider was “not the original tree hugger,” she told me, she was concerned enough to help persuade the mayor to form a tree commission, which she co-chaired. In early 2012, she met Brian Stone, a professor of city and regional planning at the Georgia Institute of Technology, and discovered an even more troubling fact. Stone had analyzed five decades of temperature data from fifty cities around the United States. He found that the majority were getting hotter than the rural areas around them, and the change was most profound in Louisville—an increase of about 1.7 degrees every decade since 1960. The city had quietly become the country’s worst example of what meteorologists call the urban heat-island effect, in which dark, paved surfaces absorb solar radiation, raising the temperature of the air around them. As Louisville’s trees died from age, neglect, drought, and a pest called the emerald ash borer—and more bare, black asphalt and concrete lay exposed to the sun—the crisis was getting worse.

Schneider and her fellow-tree commissioners were tasked with drafting a preservation ordinance, but she initially had a hard time persuading people that greenery was an urgent matter. “We basically needed a wake-up call,” Schneider said. Stone’s research sounded the alarm. On the Sunday after the 2012 Kentucky Derby, held at the city’s famed Churchill Downs racetrack, the Louisville Courier-Journal ran a front-page story on local heat-island woes. Seven weeks later, as if on cue, one of the most intense heat waves since the Dust Bowl era arrived in the Plains, Midwest, and mid-Atlantic. From late June through much of July, Louisville’s temperatures blazed into the high nineties and hundreds. Libraries filled with patrons seeking air-conditioning. Churchill Downs cancelled one race of its Spring Meet and moved others to cooler evening times. Around town, leaves on the trees curled and browned. City officials gave out hundreds of fans to seniors, hoping to prevent episodes of heat stroke and other medical emergencies.

Louisville has since been coming to grips with its heat problems. Last year, the city released a study of its tree canopy, which showed that fifty-four thousand trees were being lost every year. It also commissioned Stone to map out its urban heat island in fine detail. He and his collaborators assembled one of the most sophisticated models of local heat ever created for an American city, using satellite and meteorological data to help them estimate the risk of death by heat throughout the city. (They used as a case study the heat wave of 2012, which killed an estimated eighty-six people.) How many lives could be spared, the researchers then asked, if the city planted more trees and grass, replaced dark asphalt and concrete with light-colored and reflective roofs and pavement, and cut back on the excess heat seeping out of buildings and the tailpipes of cars and buses? Neighborhood by neighborhood, they produced precise recommendations—how many trees and white roofs, how much less pavement and more grass might make a difference to the health of the people living there. “What we’re proposing is rather extraordinary,” Stone said. “We’re suggesting that cities can change their own weather if they want to.”

Read the rest of the article at The New Yorker.