Goodyear looks at the work of Brian Stone of the Urban Climate Lab at Georgia Tech, one of the country's leading researchers on the urban "heat island" effect — "the difference between the temperature of a major metro area and the surrounding countryside."

"Last year, he and his colleagues released an analysis of data [PDF] from the 50 largest cities in America. And it came as something of a surprise that Louisville, Ky. had the unhappy distinction of being on top."

"The average increase in the temperature difference between urban and rural environments in the Louisville area has been 1.67 degrees Fahrenheit every decade between 1961 and 2010," explains Goodyear. "That’s nearly double the rate of the next city on the list, Phoenix, which saw an average change of .96 degrees in the same period."

In addition to "the unfortunate meteorological conditions" of the Ohio River Valley, "another likely contributing factor is the lack of tree cover in Louisville," she notes.

“The tree canopy downtown is one of the sparsest of any city I have seen in the country,” Stone said. "The tree cover in Louisville’s larger metro area is around 30 percent, according to Stone’s research [PDF], with the urban core at just 10 percent. That compares to about 45 percent in the city of Atlanta."

"And that lack of greenery — unlike Ohio River Valley weather patterns or global warming — is something that Louisville’s municipal leaders could change."