Chicago is considered an Urban Heat Island (UHI) and suffers from extreme heat in the summer because of all the cement and glass surfaces reflecting solar energy instead of absorbing it.
According to an August 1, 2016 article in the journal Geographical, implementing green rooftops across the city of Chicago could drop the peak summer temperatures in the city by as many as 7 degrees Fahrenheit!
You can find more interesting environmental research like this in Greenr.
Washington County Cooperative Library Services Hillsboro, Oregon 97124 ● wccls.org