Louisville, Fastest-Warming City in U.S., Reaches for the Brakes

Researchers at the Georgia Institute of Technology found that since the 1960s, urban Louisville, Ky., saw its temperature rise above that of its surroundings at a rate greater than any other city in the country and more than double the warming rate of the planet as a whole.

This trend puts Louisville on track to receive another unwanted crown:  most heat-related excess deaths in the United States.  A 2012 report from the Natural Resources Defense Council found that years of rising temperatures due to climate change will lead to an additional 18,988 deaths by the end of the century.

The reports made national news at the time, but the headlines were unwanted attention and a serious headache for Maria Koetter, the city's newly minted sustainability director.  "If we can't get it under control, we're going to be jeopardizing the quality of life for the people in our city," she said.

Hired in 2012 as a fulfillment of Mayor Greg Fischer's campaign promise, Koetter was tasked with implementing the city's sustainability plan.  The heat island findings soon dominated her radar.

The concept of a heat island is neither new nor unique to Louisville.  Urban areas around the world accumulate more heat than their rural surroundings as vegetation yields to sunlight-absorbing pavement and heat-trapping pollution.

However, Louisville faces some unique challenges.  Located in the Ohio River Valley, the geography acts as a basin for urban and industrial pollution, trapping it over the city.  The region is notorious for air quality problems, and urban emissions can drive up local temperatures.

Another issue is the city's tree canopy.  Advocates have long lamented the lack of shade in the metropolitan region, a problem that goes beyond aesthetics; moisture transportation from trees and other vegetation plays an important role in regulating air temperatures.

Over time, foliage diminished as concrete and asphalt crept over the land.  "We have a lot of impervious surface downtown," Koetter said.  "We've got these five- and six-lane streets that hold a lot of heat."

As the climate warms, these problems are poised to get worse.  Though the global average temperature may only rise by 2 to 3 degrees Celsius, urban temperatures could rise by 10 C or more.

Louisville, Fastest-Warming City in U.S., Reaches for the Brakes