Louisville is hot and getting hotter.

A report from a climate change nonprofit has ranked the city in the top 10 most intense "heat islands" and the most rapidly growing among U.S. cities, NPR's WFPL News reported.

 "The materials that make up cities like concrete and asphalt absorb a lot of heat and cities also have more cars and industry that generates heat," author Alyson Kenward said in the report published Wednesday by Climate Central.

"And urban areas tend to have fewer trees and less vegetation than rural areas and it's those things, the shade and the moisture that they provide that helps keep rural areas cooler."

According to the Climate Central report, Louisville's urban areas are an average of 4.8 degrees Fahrenheit warmer compared with rural areas in the last decade.

The city, which is ranked No. 5 for biggest difference between urban and rural areas, has higher temperatures at night as well, with night figures at 7 degrees warmer on average than rural areas for the same period.

Temperatures in the city at night have been rising an average of .61 degrees every decade since 1970, the researchers found.

At the highest, city temperatures are up to 20 degrees hotter than nearby rural areas, and each year sees 23 more days on average that are above 90 degrees.

Experts warn that hotter temperatures will mean more health problems for people that include heatstroke as well as respiratory irritation from increased ozone levels.  

"When cities become hotter, the ozone levels in cities tend to rise," said Howard Frumkin of the University of Washington's School of Public Health, as quoted by WFPL. "Ozone is toxic to our airways. Higher ozone results in irritation and inflammation of the airways and that translates into more respiratory symptoms, especially among people with asthma or bronchitis or other underlying conditions of the airways."

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