Louisville And Climate Change

Climate Change

More pollen.

More mold.

More mosquitoes, and more of them carrying deadly diseases.

More water main breaks, and more treatment to keep our water tasting good.

Warmer and wetter.

That is what is happening to Louisville (and all of Kentucky) or likely to happen as climate change becomes obvious and palpable, according to climate experts and ecologists.

“The uncertainty is not that that the temperature of the planet is going to increase. The uncertainty is the magnitude of the effect because we don’t have much documented evidence in terms of what happens when the planet gets really warm,” said Omar Attum, an associate professor of biology at Indiana University Southeast where he teaches ecology.

Evidence is mounting, though, for the impact locally.

2018 broke the rainfall record for the Louisville area, besting the record set in 2011.

“Kentucky’s climate is changing. Although the average temperature did not change much during the 20th century, most of the Commonwealth has warmed in the last 20 years,” according to a 2016 bulletin from the U.S. Department of Environmental Protection. It said the changing climate is likely to cut crop yields and threaten some aquatic ecosystems. “Average annual rainfall is increasing, and a rising percentage of that rain is falling on the four wettest days of the year,” it said. “Floods may be more frequent, and droughts may be longer, which would increase the difficulty of meeting the competing demands for water in the Ohio, Tennessee and Cumberland Rives.”

A study by the Georgia Institute of Technology in 2012 found that Louisville was “the fastest warming urban heat island in the United States.” Louisville is in the Ohio River Valley, which traps heat and pollutants. Asphalt coverage has increased as development has accelerated, and the tree canopy has diminished. All of this has contributed to the warming, which the researchers discovered was “more than double of the warming rate of the planet as a whole.”

Insects, oh my

Longer summers and more precipitation will also potentially affect even those not vulnerable to direct heat. Consider allergies and diseases transmitted by mosquitoes and ticks.

“I think more of the insects like mosquitoes and ticks become more prevalent,” Attum said.

The Ohio River Valley is in the natural range of mosquitoes in the genus Culex, which includes the Northern House Mosquito. Among diseases that it is known to transmit are St. Louis encephalitis, Western equine encephalitis and heartworm in dogs. In 1999, West Nile Virus entered the United States and was able to spread because Culex species already here were able to act as vectors.

All of those diseases are on the radar of the Louisville Metro Department of Public Health & Wellness, which has operated a mosquito control program since the 1950s. The agency traps mosquitoes to identify vector species and tests for pathogens they could be carrying. There is also a program for treating places such as catch basins where mosquitoes could breed in the standing water.

One possible consequence of climate change on mosquito populations is that not only could the number of mosquitoes already here increase, but new species, carrying more diseases, would be able to survive thanks to warmer winters.

Among its other tasks, the federal Centers for Disease Control and Prevention monitors the presence of disease transmitting insects. Historically a tropical and subtropical species, Aedes aegypti has the potential to increase its range in North American as winters warm. This is the mosquito that spreads yellow fever, dengue fever, Zika and chikungunya.

The CDC has published a map on its website showing the potential range of Aedes mosquitos and Kentucky is in the “very likely” portion of the map.

Health department environmental scientist Patrick Rich said that the Aedes is indeed here already, but in small numbers. The agency is on the lookout for changes in the insect and pathogen populations. Among the tick-borne diseases the agency monitors are Spotted Fever and Lyme.

Source: U.S. Global Climate Change Research Program (2009)
Source: U.S. Global Climate Change Research Program (2009)


Anyone with allergies knows that the Ohio Valley has always ranked among the worst places in the nation.

The good news is that climate related changes to local plants do not seem to be having an impact for people already allergic to tree, grass and weed pollens, according to Dr. James Sublett, a Louisville allergist. “Each year is a little different, earlier, later and peaks may vary.”

But, he also cited a study that found “stressed” plants may produce more pollen.

What concerns Sublett more is the potential for mold growth as related to warmer winters.

“The Ohio Valley is already bad for mold. Contrary to common belief, most mold exposure occurs outdoors, especially with activities like raking leaves, mowing grass, mulching, etc. and on athletic fields for soccer, baseball, field hockey, etc. We see mold activity year round except during freezing weather, so milder winters could certainly increase mold spore counts and more exposure.”

More water, much more water

The EPA’s prediction for Kentucky is dire:

“Although rainfall during spring is likely to increase during the next 40 to 50 years, the total amount of water running off into rivers or recharging ground water each year is likely to decline 2.5% to 5%, as increased evaporation offsets the greater rainfall. Droughts are likely to be more severe, because periods without rain will be longer and very hot days will be more frequent.”

2018 broke the rainfall record for the Louisville area — 68.05 inches — and we had record rainfall in the months of February and September.

“August and September are traditionally dry months for us,” said Sheryl Lauder, spokesperson for the Metropolitan Sewer District. “But this was the fifth wettest August and the wettest September on record with 10.9 inches, which is completely unheard of.”

It wasn’t just last year. According to records kept by the National Weather Service, eight of the 10 wettest years on record have occurred since 1990. Five of the 10 since 2002.

Following the catastrophic flooding of 1997, MSD built basins, many of which are underground, able to capture a billion gallons of storm run-off. When the rain stops, this excess water is gradually returned to the drainage and treatment system. These basins have been effective at preventing flooding in many areas that were under water in that flood nearly a quarter century ago. Nonetheless, MSD continues to expand its capacity, anticipating flooding brought by climate change.

Brian Bingham, MSD’s chief of operations, said a consultant’s study concluded: “We are definitely seeing more frequent, larger storm events. They’re more intense, and they’re happening more often.”

Current projects such as the Waterway Protection Tunnel near the intersection of Lexington Road and Grinstead Drive and the Shawnee Park Basin will help maintain the capacity of MSD to deal with projected volumes of water.

“The largest piece of this project is under the newly-paved parking lots at Churchill Downs,” said Sheryl Lauder of MSD.

Of additional importance, to help with urban heat island concern, is that MSD is planting trees there, as it is at other project sites. In the case of Churchill Downs, more than 900 trees will become part of the Louisville landmark’s landscape and the city’s tree canopy.

Drinking water

Kelley Dearing-Smith is vice president of communications and marketing for the Louisville Water Co. She, like Lauder, cited last year as being the wettest on record for the city, which, for water supplies, means something different.

“We have an abundant supply. About 75 billion gallons of Ohio River water flow by us each day. On average, we are pulling about 120 million gallons [16/100ths of a percent] and turning it into drinking water. So, it’s not volume that creates issues for us, but extreme weather conditions.”

Dearin-Smith said that for instance, “brutal cold” and drought cause water mains to break.

Prolonged heat causes algae to bloom in the river, giving water a musty taste that adds to treatment costs. These greater costs for more electricity and more chemicals translate into increases in customers’ monthly water bills.

Fewer trees

Concern about the inadequate tree canopy was one of the key components cited in the 2012 Georgia Tech study about Louisville’s rising temperature. After that study was released, the city hired an urban forester, and created TreesLousiville, a private nonprofit dedicated to planting more trees.

Both have a daunting task.

A 2015 study by the Davey Resource Group and paid for in part by MSD, found that not only was a lack of tree cover a problem, but the existing canopy was under assault on multiple fronts. Windstorms and ice storms, as well as age, have taken a toll on mature trees. The emerald ash borer is steadily destroying the populations of all ash species in the area. The result of these multiple stresses is that Louisville is losing an average of some 54,000 trees (820 acres of canopy) every year.

Furthermore, an Environmental Protection Agency study cited climate change as a threat to other forest species common in Louisville’s parks and neighborhoods, including maples, birches and beeches. (By the way, the loss of maple trees will result in a significant loss of fall color, since it is mostly maples that provide the bright splashes of red in the autumn color palette.)

All of these trees need cold winters. But, a look at the Plant Hardiness Zone Map published by the U.S. Department of Agriculture, shows that Louisville has moved into a warmer zone in the last few decades.

Hardiness zones help gardeners and farmers determine which plants are likely to grow in a particular region, which is based on the annual minimum winter temperature divided into 10-degree Fahrenheit zones.

In 1990, Jefferson County was in Zone 6a. Today, it is split between Zones 6b and 7a.

In short, Louisville’s hardiness zone now favors plants that used to be more characteristic of regions farther south.

Then, there is the direct effect on human health.

Hot, hot, hot

The same EPA study that identified tree species at risk also reported the health risks of heat:

High air temperatures can cause heat stroke and dehydration and affect people’s cardiovascular and nervous systems. Certain people are especially vulnerable, including children, the elderly, the sick and the poor. Higher temperatures can also increase the formation of ground-level ozone, a key component of smog. Ozone has a variety of health effects, aggravates lung diseases such as asthma and increases the risk of premature death from heart or lung disease. The EPA and the Kentucky Department for Environmental Protection have been working to reduce ozone concentrations. As the climate changes, continued progress toward clean air will require even more reductions in the air pollutants that contribute to ozone.

The number of people who could be affected was cited in the earlier Georgia Tech urban heat island study. It predicted that Louisville would earn the dubious distinction of having “the most heat-related excess deaths on the United States.” That number is 18,988 additional deaths by the end of the century.

Climate vs. weather

If the planet is warming, what about this year’s round of record breaking low temperatures in January, when a polar vortex descended on a large portion of the central United States?

While politicians from the right and fossil fuel lobbies have tried to create uncertainty about climate science and research, Attum offered this perspective on the overall issue of climate change and its consequences.

“You are talking about the difference between climate and weather,” said Attum.

“What [people] don’t realize is that climate is cumulative. It’s the overall environmental conditions. ... So if you look at the overall mean average per month ... you’ll see that temperature is rising. And while highs are not getting much higher, the number of days with high temperatures is increasing and lows are getting higher.”

Attum further explained that while air temperatures fluctuate (what we experience day to day as weather), it’s the rising temperature of ocean waters that provides “irrefutable evidence” that the planet’s climate is warming. It takes about four times more energy to raise the temperature of water than of air. Once that water is warmed, it cannot cool unless the air temperature gets cooler.

An article on the website of the National Oceanic and Atmospheric Administration, entitled “Climate Change: Ocean Heat Content,” notes that since the oceans cover 70% of the Earth’s surface, they can absorb a lot of heat, “This tremendous ability to store and release heat over long periods of time gives the ocean a central role in stabilizing Earth’s climate system.”

But that has changed.

The article further states: “Increasing concentrations of greenhouse gases are preventing heat radiated from Earth’s surface from escaping into space as freely as it used to; most of the excess heat is being stored in the upper ocean. As a result, upper ocean heat content has increased significantly over the past two decades.”

So the patterns of the planet-wide flow of energy has been disrupted, which has multiple effects on weather patterns. Warmer oceans mean more moisture evaporates into the atmosphere to fall as more rain. There is also more heat energy to be taken up by tropical storm systems; therefore hurricanes and cyclones are more powerful. And weather pattern shifts can also result in cold air usually concentrated in the Arctic being shifted farther south, resulting in the extreme cold the American Midwest experienced this January. •

Susan Reigler is a former member of the biology department at Indiana University Southeast and received an MA in zoology from Oxford University. Her current independent research involves environmental influences on polymorphism in moths.