Louisville residents are well acquainted with the challenges caused by urban heat, such as higher utility bills and serious health problems that disproportionately affect residents with pre-existing health conditions.

The new study also involves Brian Stone, a professor and director of the Urban Climate Lab at Georgia Institute of Technology, whose previous work identified Louisville as having one of the fastest-growing urban heat islands in the nation.

An urban heat island exists when the built environment – buildings, sidewalks and paved roads – absorbs more heat than natural surfaces such as grass, trees and exposed soil, causing higher air temperatures. Those heat-absorbent surfaces also retain that heat during nighttime hours.

“Louisville has been at the forefront of studying urban heat for years, thanks to foundational work like ,” Stone said. “However, the climate continues to change and the city continues to grow. This new project provides an unprecedented, highly detailed look at current temperatures and the specific cooling power of different types of vegetation in 2025. It’s about giving Louisville the most up-to-date, actionable science to make truly impactful decisions, which is especially relevant as residents are facing extreme heat right now.”

The project will use advanced climate models to generate highly detailed, hourly temperature maps for June, July and August 2025. These maps will cover the entire Jefferson County area – nearly 398 square miles – at a remarkable resolution of 100 meters, offering an unparalleled view of where heat is most intense across Louisville’s urban core. Sensors installed by the Envirome Institute around Louisville will provide data to help enrich the model. The project, supported by the James Graham Brown Foundation, begins in July and is expected to be completed within three months.

Beyond traditional temperature readings, the study will also measure factors that provide a more complete picture of actual heat stress experienced by individuals.

A key focus of this research involves an in-depth analysis of how various tree canopies reduce temperatures. Researchers will investigate which areas benefit most from new tree plantings and how different tree species — and whether they are coniferous or deciduous — impact cooling differently.

Precise insights gained from the new project also will enhance and expedite the Envirome Institute’s research into health benefits of additional greenness, including the and the in downtown Louisville.

“At the Envirome Institute, our mission is to understand how the environment shapes our health. This new analysis comes at a time when we are all facing tremendous heat burden,” said Aruni Bhatnagar, executive director of the . “By precisely mapping urban temperatures and land cover like trees and other vegetation, we’re not just gathering data; we’re creating a powerful new tool. This research will allow us to strategically use urban greening as a direct intervention to improve public health in our downtown core and across every neighborhood in Louisville.”

The project will also analyze heat-related mortality at the neighborhood level in order to highlight areas where residents are most vulnerable to heat-related illnesses and where targeted interventions are most urgently needed to improve public health outcomes. This insight will help guide tree planting initiatives by and other partners, ensuring that efforts maximize cooling benefits.

“TreesLouisville has been working tirelessly to expand our urban canopy, utilizing data from previous assessments to guide our strategic planting,” said Cindi Sullivan, executive director of TreesLouisville. “This new study will provide us with an even sharper focus, pinpointing exactly where our efforts will have the greatest impact and helping us choose the right trees for the right places to achieve significant temperature reductions for our community. This is particularly urgent as we continue to push towards our city’s goal of every neighborhood having at least 30% canopy cover.”

Article is co-authored by Ted Smith.

“These past two years have simply flown by,” Schatzel said, expressing her appreciation to the UofL community and the city of Louisville as she begins her third year as president.

Schatzel then highlighted a series of accomplishments from 2024 and the collective effort that made them possible:

• Historic Records: UofL had a record enrollment of 24,123 students, representing 117 Kentucky counties, 54 states and U.S. territories and 90 countries. The university also celebrated historic highs in fall-to-fall retention and fall-to-spring persistence all pointing to a soon-to-be-realized 70% six-year graduation rate.
• Redefining Student Success: Schatzel highlighted the university’s commitment to access, noting increased enrollment for Pell-eligible, first-generation and underserved students for the past three years, as well as a 10% increase in military-connected student enrollment. The president credited these achievements to innovative best practices such as strengthened support services, expanded transfer pathways (including the new partnership with KCTCS), the 15 to Finish program, enhanced bordering states benefit programs, the Cardinal Commitment grant and the Comeback Cards program. Schatzel also mentioned UofL’s significant jump in U.S. News & World Report rankings and recognition as a top 100 public university. “These incredible – yes, historic – results were achieved via implementing and investing in numerous innovative best practices,” she said.
• Research & Innovation: UofL had several significant achievements in research in 2024, most notably the internationally recognized Green Heart project. Schatzel also celebrated the launch of the  Louisville Clinical and Translational Research Center made possible by the single largest investment in clinical research in the university’s history –$24 million to train clinical researchers. Other research highlights included record research expenditures of $188.4 million, nearly $67 million from the National Institutes of Health, a $6.75 million grant from the Humana Foundation for health equity research and the ongoing research computing initiative.
• Athletic Momentum: Schatzel celebrated the achievements of UofL’s athletic programs, from national runners-up in volleyball to a Sun Bowl championship in football and the revival of the men’s basketball program.
• Legislative Partnership:  UofL received unprecedented support during the 2024 legislative session, securing over half a billion dollars in support for the university. This included $260 million for a simulation center and collaboration hub, over $90 million for physical plant renovations and continued progress on the new engineering building.
• Community Engagement: Schatzel reaffirmed UofL’s commitment to Louisville and Kentucky, highlighting the expansion of University Hospital, the establishment of a rural cancer center in Bullitt County, the opening of a School of Dentistry practice at the Goodwill Opportunity Center in west Louisville, and the launch of an immigration law clinic by the Brandeis School of Law. “Our community impact is strong, and it is growing even stronger,” she said.

Schatzel also recognized outstanding individuals within the UofL community, including Fulbright Scholars, 2024 Trustees Award winner Jennifer Brueckner-Collins and 2024 George J. Howe Distinguished Staff Award recipient Angela Taylor. She emphasized the university’s commitment to its employees, highlighting investments in compensation studies and market adjustments.

Looking ahead to 2025, Schatzel outlined several key priorities including:

• Beginning a five-year strategic plan for 2026-2030;
• Finalizing the university leadership team;
• Launching the Inclusive Excellence Strategic Plan and the submission for reaffirmation of the Community Engaged University designation; and
• Developing Belknap Campus with a recent acquisition of the Cardinal Center property by the UofL Foundation, with initial plans to create green space and then determine the best permanent use.

Schatzel concluded her address with a message of momentum and pride.

“I am so proud of all that is happening right now at the University of Louisville,” she said. “I think you’ll agree that there has been no better time to be a Cardinal.”

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Air pollution, a warm bedroom and high levels of carbon dioxide and ambient noise all may adversely affect our ability to get a good night’s sleep, suggests a study from researchers with the Perelman School of Medicine at the University of Pennsylvania and the University of Louisville’s Christina Lee Brown Envirome Institute (CLBEI).

The study, published April 18 in Sleep Health, is one of the first to measure multiple environmental variables in the bedroom and analyze their associations with sleep efficiency—the time spent sleeping relative to the time available for sleep. The analysis found that in a group of 62 participants tracked for two weeks with activity monitors and sleep logs, higher bedroom levels of air pollution ( or PM_2.5), carbon dioxide, noise and temperature were all linked independently to lower sleep efficiency.

The study was a collaboration between Penn Medicine and UofL’s CLBEI which is led by Aruni Bhatnagar. The researchers recruited participants from the CLBEI’s National Institutes of Health-funded Green Heart Project that investigates the effects of planting 8,000 mature trees on the cardiovascular health of Louisville residents.

“These findings highlight the importance of the bedroom environment for high-quality sleep,” said study lead author Mathias Basner, professor and director of the division of Sleep and Chronobiology in the department of Psychiatry at Penn Medicine.

The researchers suggest that more research is needed now on interventions that could improve sleep efficiency by reducing exposures to these sleep-disrupting factors.

“This could be as simple as leaving a bedroom door open to lower carbon dioxide levels, and using triple-pane windows to reduce noise,” Bhatnagar said. “We also applied for (future) funding that will allow us to investigate whether planting trees can improve sleep and cardiovascular health through improving health behaviors and the bedroom environment.”

About the study

In addition to work and family obligations that , a quickly changing environment due to growing urbanization and climate change seems to have made it harder to get a good night’s sleep. Sleep that is of inadequate duration, or inadequate efficiency due to frequent disruption (“tossing and turning”), affects work productivity and quality of life. It also has been linked to a higher risk of chronic diseases including heart disease, type 2 diabetes, depression and dementia.

This research is among a limited number of studies that looked at associations between multiple objectively measured factors in the sleep environment—such as noise and temperature—and objectively measured sleep.

For each of the environmental variables measured, the researchers compared sleep efficiency during exposures to the highest 20 percent of levels versus lowest 20 percent of levels. Through this analysis, they found that high noise was associated with a 4.7 percent decline in sleep efficiency compared to low noise, high carbon dioxide with a 4.0 percent decline compared to low levels, high temperature with a 3.4 percent decline compared to low temperature, and high PM_2.5 with a 3.2 percent decline compared to low PM_2.5. Two other sleep environment variables, relative humidity and barometric pressure, appeared to have no significant association with sleep efficiency among the participants.

Interestingly, only bedroom humidity was associated with sleep outcomes assessed with questionnaires, such that higher humidity was associated with lower self-reported sleep quality and more daytime sleepiness. This suggests that studies based on questionnaires may miss important associations readily detected by objective measures of sleep. This is not surprising as humans are unconscious and unaware of themselves and their surroundings during large portions of their sleep period.

Also, most study participants rated humidity, temperature and noise levels in the bedroom as “just right” regardless of the actual exposure levels.

“We seem to habituate subjectively to our bedroom environment, and feel there is no need to improve it, when in fact our sleep may be disturbed night after night as evidenced by the objective measures of sleep we used in our study,” said Basner.

The Envirome Institute has secured a 30-year lease with Louisville Metro Government to use Founders Square as an outdoor laboratory to research innovative ideas in urban greening. Patrick Piuma, director of the Envirome Institute’s Urban Design Studio, will oversee a project to intensely plant Founders Square with native plant and tree species while creating an accessible, inviting and functional public space for anyone to enjoy. The project at Founders Square will build on the Envirome Institute’s groundbreaking work with the , which is examining the scientific link between nature and human health.

“The Trager Micro-Forest Project is a transformative project connecting people with nature, starting in the heart of our city,” said Michael Trager-Kusman. “The members of our family are honored to support learning about the impact of scientifically planned and planted green spaces in the city we love.”

The project will provide an opportunity for UofL researchers in multiple disciplines to work with members of the community and other organizations to track and measure changes in human health and well-being and to study the project’s impact of biodiversity, micro-climates, economic development and public safety. The learning from this project can be used to inform the way city planners integrate nature into urban environments everywhere.

“This is an exceptional project for UofL’s Envirome Institute at the New Vision of Health Campus, and we are delighted to have the Trager family’s generous support as we embark on new fields of inquiry into the impact of the built environment on human health,” said Lori Stewart Gonzalez, interim president of UofL.

“The Envirome Institute is committed to the health and vitality of downtown Louisville, which is why we’re establishing our New Vision of Health Campus downtown at Fifth Street and Muhammad Ali Boulevard,” said Aruni Bhatnagar, director of the Christina Lee Brown Envirome Institute. “The Trager Micro-Forest Project is not simply a beautification project. It is a scientific project, which will be the first of its kind in our region of the country.”

“The Trager Micro-Forest Project and the Envirome Institute’s New Vision of Health campus are catalysts for positive momentum during this pivotal time for downtown Louisville. These initiatives complement our commitment to a sustainable future, a commitment that requires vision and action. We expect these initiatives will spur additional economic development in the area while adding well-planned and maintained green spaces that make our downtown area more attractive for those who live, work and visit there. Thank you to the Trager family for their support of the Envirome Institute’s innovative and forward-thinking project,” said Mayor Greg Fischer.

In the past, Louisville’s downtown was a vibrant hub of activity, from shopping and industry to entertainment and culture. The Trager Micro-Forest Project is intended to excite and engage the community while changing perceptions of downtown and promoting a greener and healthier city.

Initial work on the Trager Micro-Forest Project is already underway. Researchers are analyzing current park usage and taking air and surface temperature measurements in Founders Square and surrounding properties, and they have completed an inventory of the existing trees. This past summer, they used ground-penetrating radar to peer beneath the surface of Founders Square to identify any possible underground obstacles. Community members will be invited to participate in activities on site and provide input into the project over the next few months, with plantings to follow.

In the first study, UofL researchers Aruni Bhatnagar, professor of medicine and director of the Envirome Institute, Ray Yeager and Daniel Riggs, with Carver Coleman and Arden Pope of Brigham Young University and others, analyzed retrospective data from more than 5.5 million cancer patients and survivors from 2003 to 2016. They found that cancer patients in greener counties lived longer than those in counties with less greenness. The protective effects of greenness against cancer mortality were seen with both males and females and individuals of all ages, but were more pronounced at urban locations. Individuals with cancers that were highly survivable – such as breast, prostate and skin cancer – benefitted more from greenness than those with cancers with low survival rates such as brain, esophageal, liver, lung and pancreatic cancer.   

The study, “,” published in the journal Environment International, evaluated associations between greenness and fine particulate matter in the air on causes of death in a large group of cancer patients and survivors in the United States.

“This is the largest study of the relationship between greenness and cancer mortality, and it provides clear evidence that living in green areas is beneficial to cancer patients,” said Bhatnagar “However, we do not yet understand why greenness protects against cancer mortality. Much more remains to be done to see whether greenness benefits cancer patients by lowering mental stress and anxiety or by reducing the levels of air pollutants or whether some other mechanisms are at play.”

The study also found that cardiopulmonary disease, but not cancer, was associated with higher levels of fine particulate air pollution. Mortality from cardiopulmonary causes – stroke, heart attack or COPD – was not affected by county greenness, except in rural locations.  

Greenness and depression

A second study, led by Kandi Walker and Joy Hart, professors in the UofL Department of Communication, Bhatnagar and other researchers in the Envirome Institute, found that people’s satisfaction with levels of greenness in their neighborhood was associated with lower levels of self-reported depressive symptoms.  

The researchers surveyed participants about their perceptions of greenness in their neighborhoods and their mental health symptoms and found that those who were more satisfied with the greenness surrounding their homes also reported lower depression symptoms on a health survey, the Patient Health Questionnaire-9.

The 44.5% of survey participants who reported they were satisfied with the level of greenness in their neighborhood collectively scored better on the health questionnaire for depression.

“Given the pervasiveness of depression in the U.S. population, any changes that can reduce depression are essential, particularly those that can affect a large number of people,” Hart said. “The findings of this study suggest that greening interventions that focus on greenness satisfaction may be a strategy to reduce depression in urban populations.”

The study, “,” was published in July in the journal Population Medicine.

South Louisville study participants needed

Participants in the greening satisfaction study were part of the Health, Environment and Action in Louisville (HEAL) study of the Great Heart Project, which is an ongoing assessment of the effects of neighborhood greenness on individual health. Additional participants are needed for the HEAL Study by the end of September. More information is available on the website.

“Together, these studies add weight to the importance of trees, shrubs and other vegetation in urban areas in benefitting and nurturing human health. Accumulation of such evidence strengthens the case that increasing greenness in urban locations can decrease the high rates of non-communicable diseases in cities,” Bhatnagar said. “And since greenness improves health in general, it may also be effective against infectious disease.”

The research, led by Aruni Bhatnagar, professor of medicine and director of the UofL Christina Lee Brown Envirome Institute, was published ahead of print in the .

Previous studies have shown that proximity to green space — trees and other vegetation — can lower blood pressure levels and the risk of heart disease. A number of environmental factors may come into play, including increased opportunity for outdoor exercise, reduced mental stress and socioeconomic status. However, the relationship between vascular (blood vessel) health, green space and air pollution has not been fully explored.

In this , researchers looked at the arterial stiffness of adult volunteers with co-occurring conditions such as obesity, high blood pressure, diabetes and high cholesterol, that put the volunteers in the moderate-to-severe risk category for heart disease.

“Although we have known for a long time that exposure to air pollution has adverse effects on our blood vessels, this study shows that those who live in greener neighborhoods may be less affected,” Bhatnagar said. “Therefore, one way of preventing the harmful health effects of air pollution may be to make neighborhoods more green.”

Using study participants’ residential addresses and data from the U.S. Geological Survey and local Environmental Protection Agency monitoring stations, the research team analyzed environmental factors where the volunteers lived, including:

• Vegetation index, including the amount of and variation in greenness levels within 200-meter and one-kilometer (0.62 miles) radii around each volunteer’s home.
• Particulate matter, tiny toxic particles invisible to the naked eye, in the air.
• Levels of ozone, a colorless, toxic gas and significant air pollutant.

At times when the particulate matter and ozone levels were high, participants had higher levels of arterial stiffness, however, those who lived in areas with more flora had better blood vessel function. Trees and other greenery offset vascular dysfunction that air pollution causes, the researchers explained.

In previous work, the researchers found that individuals who live in areas with a large amount of greenness show lower exposure to volatile chemicals and have greater household income. In the current study, they explored the relationships between greenery, air pollution and arterial stiffness and found a similar correlation between the U.S. Geological Survey’s normalized difference vegetation index and average household income. Even when adjusting for self-reported lifestyle habits such as exercise and smoking — 70% of the volunteers were nonsmokers — the researchers found that “the effects of green spaces on hemodynamic function are largely independent of median household income, physical activity levels and tobacco use.”

“These findings indicate that living in green areas may be conducive for vascular health and that the [favorable] effects of greenness may be attributable, in part, to attenuated exposure to air pollutants such as [particulate matter] and ozone,” said Daniel Riggs, UofL biostatistician and the study’s first author.

This research was conducted in conjunction with the Green Heart Project, a first-of-its-kind study of the effects of plants on human health, led by researchers at the .

The Nature Conservancy is overseeing the planting of approximately 8,000 trees and shrubs in the designated neighborhoods. Researchers with the University of Louisville’s Christina Lee Brown Envirome Institute will compare data about the health of people living in the neighborhoods and air pollution levels collected before the plantings with data collected two years after the vegetation is planted. The results will provide insight into how the additional vegetation affects the health of people in the community.

“Our primary objective is to understand how increasing greenness affects the risk of heart disease within the community,” said Aruni Bhatnagar, PhD, director of the at the University of Louisville, who oversees the project. “Heart disease remains the leading cause of death throughout the world. We can treat heart disease with stents and statins, but we cannot prevent the disease. If we can show that putting in more trees will lower the incidence of the disease, even by a fraction of what it is, that would be a major achievement.”

The Nature Conservancy is planting the trees and shrubs in designated residents’ yards at no charge to property owners.

“We’re excited to enter the next phase of the Green Heart project,” said David Phemister, state director for in Kentucky. “Tree plantings at this scale require strong partnerships and deep engagement with the community. Green Heart is not just a science experiment – it is a deep investment to bring more nature to neighborhoods in the heart of Louisville.”

The residents’ health is being assessed by UofL researchers through the Health, Environment and Action in Louisville (HEAL) Study. The HEAL researchers obtained health information from approximately 700 participating residents of the Taylor-Berry, Jacobs, Hazelwood, Oakdale, Wilder Park and Beechmont neighborhoods before the planting began. They collected information such as blood pressure, cholesterol, heart health and other health indicators. The same participants will be evaluated again in two years to determine if these health indicators have changed.

“We wanted Louisville to become maybe one of the first cities in the country that makes its decisions through the lens of all forms of health,” said Christina Lee Brown, benefactor of the Envirome Institute. “That is the Envirome’s objective. This project is a magnificent example of healing our community from the roots up.”

In addition to the Envirome Institute and The Nature Conservancy, the project is funded by the National Institutes of Health and is supported by partnerships with Metro Louisville, Louisville Grows, Washington University in St. Louis, Hyphae Design Laboratory and the United States Forest Service. The total cost of the five-year project is more than $15 million.

A UofL video about this project is available on .

Today, UofL announced a five-year, $3 million grant from the National Institutes of Health to help fund the Green Heart project. The university also announced a $2 million grant from The Nature Conservancy to support the endeavor.

The Green Heart study will look at the connections between a green environment and human health. The institute will study air quality, innovative landscape design, the qualities of a friendly, healthy neighborhood and human health.

“The Green Heart project is the epitome of collaboration,” said UofL President Neeli Bendapudi, PhD. “Dr. Aruni Bhatnagar and his team are bringing together people from not only all of the university, but throughout Louisville and beyond to create a new paradigm for population research that truly has international implications.

“His creative thinking is leading to innovative public-private partnerships that eventually will lead to healthier communities.”

“People appreciate trees and they’re good and they’re aesthetically pleasing, but whether they actually have specific quantifiable health-promoting effects by removing pollutants from air has never been rigorously tested,” said Bhatnagar, director of the Envirome Institute and the Smith and Lucille Gibson Chair in Medicine. “Through the Green Heart project, we are changing that.”

More than half the world’s population resides in urban areas, which have higher than average levels of air pollution. Air pollution is a significant contributor to cardiovascular disease and is linked to 7 million premature deaths worldwide annually, 200,000 in the United States alone.

Bhatnagar and his team will include 16 low-vegetation neighborhood clusters in Louisville to examine the impact of urban greenery on their health. The researchers are recruiting 700 community participants within these 16 clusters for the study. The team will examine blood, urine and hair samples to assess cardiovascular health.

In eight of the clusters, the team and their partners will plant as many as 8,000 native trees of all sizes. Additionally, they will plant shrubbery and grasses to further optimize the ability to filter pollutants from the air.

Two years later, the researchers again will collect samples from the volunteers and analyze the differences. They also will compare the results to those from the participants in the eight neighborhood clusters that did not live in the areas that had the plantings.

“We believe that the greening of the neighborhoods will positively impact not only the air quality, but also the health of the people who live in those areas,” Bhatnagar said. “If we are correct, we may be able to create new strategies for the prevention of cardiovascular disease.

“The results of this project also will provide new insights into the effects of urban vegetation on community environment. These findings will be relevant to the development of new public health polices and the optimization of ongoing planting efforts in cities around the world to enhance public health.

The Green Heart Project is a collaborative initiative of the University of Louisville with Washington University in St. Louis; Cornell University, The Nature Conservancy, Hyphae Design Laboratory, the United States Forest Service and other partners. The grant from the National Institutes supports health evaluation of community participants, whereas the greening efforts are supported by the grant from The Nature Conservancy.

Check out highlights from today’s announcement: 

Aruni Bhatnagar, PhD, director of the at UofL, will discuss the research, the , at the next Beer with a Scientist event on March 14.

“No one knows whether and to what extent trees and neighborhood greenery affect human health and why,” Bhatnagar said. “This work will tell us how to design a neighborhood that supports human health and whether an increase in the urban greenspaces and vegetation could enhance physical and mental health by decreasing the levels of ambient air pollution.”

The Green Heart Project is a collaboration of UofL, The Nature Conservancy, Hyphae Design Laboratory, the Institute for Healthy Air Water and Soil, the U.S. Forest Service and the City of Louisville. The goal of the project is to assess how residential greenness and neighborhood greenspaces affect the health of our communities by decreasing the levels of pollution and promoting physical activity and social cohesion.

The talk begins at 8 p.m. on Wednesday, March 14, at Against the Grain Brewery, 401 E. Main St. in Louisville. A 30-minute presentation will be followed by an informal Q&A session.

Admission is free. Purchase of beer, other beverages or menu items is not required but is encouraged.

At the next Beer with a Scientist, April 18, Deborah Yoder-Himes, PhD, will discuss super bacteria, antibiotic resistance and why everything is labeled “anti-bacterial.”

UofL Physiology Professor Alex Carll says the goal is to, “reduce air pollution levels and therefore, ideally, see improved health.”

UofL, The Nature Conservancy, Hyphae Design Laboratory and the Institute for Healthy Air Water and Soil are collaborating on the Green Heart Project. They planted more than 100 trees in St. Mary Margaret’s front lawn with the idea that the trees could filter out heavy traffic pollutants such as nitrogen dioxide and nitric oxide. Previous research has connected high levels of pollution to the risk of cardiovascular and respiratory illnesses. 

UofL is monitoring the air as well as the health of both students and staff with preliminary results showing improvements in all areas. 

Learn more: