On a hot summer’s day, a team led by Argonne National Laboratory scientists launched weather balloons from four Chicago locations, hoping they’d make it up to 12 miles above the city. The goal is to track how hot air rises over the city so it’s possible to better predict how climate change-driven heat will affect different neighborhoods in the future.
Scott Collis, an atmospheric scientist at Argonne National Laboratory in Lemont, says he thinks the information collected will prove to be “a groundbreaking, world-first dataset” for scientists and policymakers.
Scientists haven’t had a substantial, vertical profile of Chicago’s atmosphere. The closest sites collecting similar data via weather balloons are in downstate Lincoln and Davenport, Iowa. There’s no data on how Chicago’s atmosphere responds to its massive cityscape and proximity to Lake Michigan.
The research in Chicago is part of a federal study led by the U.S. Department of Energy’s Community Research on Climate and Urban Science program examining how the topography of neighborhoods — the size of buildings, the amount of paved surfaces and the density of the tree canopy — can affect how hot it feels on the ground. This is the urban heat island effect.
To do that, scientists need to better understand how high the heat captured in the ground rises into the atmosphere and what it does when it gets there.
“How temperatures change with height, how that cooling effect of the lake breeze moves across [Chicago] is intrinsically linked not just to the temperatures at the surface but the temperatures above us as well,” Collis says. “That’s why it’s really vital that we measure how the temperature changes with height.”
The weather balloons were launched from lakefront and points on the West and South sides.
Juanpablo Ramirez Franco/WBEZ
During the two-week study period, student-volunteers scattered across the city to collect temperature readings at ground level while scientists installed five long-term weather sensors.
The centerpiece was the more than 40 weather balloons launched from four sites: Humboldt Park, the Shedd Aquarium, Greater Grand Crossing and West Woodlawn. Every five feet or so, a radio transmitter attached by a string recorded measurements including temperature, moisture, air pressure and the location of the balloon.
The scientists hope the data will provide insights into how to build a more climate-resilient city as extreme heat increasingly becomes the norm. Consider that the European Union’s Copernicus Climate Change Service documented the hottest day on Earth in recorded history happened just this summer — on July 22.
Max Grover, an Argonne atmospheric data scientist, says it will be months before the collected data will be fully analyzed.
But scientists already know the uneven distribution of heat across Chicago tends to be felt disproportionately in under-resourced communities due largely to the city’s history of racial segregation and redlining.
A recent Columbia University analysis found that more than 80% of historically redlined areas — areas where discriminatory lending practices hindered urban renewal — are more likely to suffer extreme summer temperatures than non-redlined areas. That’s translated into fewer trees and more impervious surfaces, like asphalt and concrete — a recipe for locking heat into the ground.
Trees and tree canopies are among the most effective strategies to mitigate urban heat islands. They absorb the sun’s rays, provide shade and release vapor from their leaves in the evening, which cools the surrounding environment.
Ralph Cintron, a Latin American studies processor at the University of Illinois Chicago, says that, even within Humboldt Park, there’s a massive development gap between the east side of the neighborhood and the west.
“There’s a big difference in terms of gentrification, in terms of property values, in terms of ethnicities,” Cintron says, and there also are major differences in tree coverage that contribute to hotter conditions on the heavily paved west side of the neighborhood.
Humboldt Park and West Woodlawn are among Chicago neighborhoods that lack a significant tree canopy, according to a Morton Arboretum report.
Scientists are counting on the recently collected data to strengthen their modeling capacity — not just to better understand the urban heat islands throughout the city, but also the effects of the lake breeze and how the towering buildings downtown interact with it to shape Chicago’s climate.
“The climate simulations we’ve got right now, they just don’t cut it.” Collis says. “So we’re busy making the next generation of climate simulations that will allow communities to make data-driven decisions.”