Symptoms of a Warming World

Climate change is a global phenomenon, but its impacts are highly differentiated and highly local. The impact of extreme heat varies, sometimes, from city block to city block. Just read health studies about extreme heat in New York that were based on temperature measures taken at the airport: “But nobody lives at the airport,” Just says. Most heat maps available were painted in strokes far too broad to illuminate the impacts of severe temperatures on human bodies.

“It struck me that we’ve been underestimating how unequal climate-related exposures are,” says Just. “Each of us experiences heat in the places where we live, which makes it hard to imagine what it feels like across town. But heat varies much more than we recognize, and we’ve been underestimating how bad it is.”

Take Providence. “We assume that whatever weather you see when you pull out your phone is accurate, and applies to everyone in the area,” Just says. But in the summer, the temperature can vary considerably between neighborhoods, with areas like those around Brown, with tall trees and shady, narrow streets, tending to be cooler than parts of the city, like Pavilion Avenue, where the heat lingers on the asphalt. These ‘heat islands’ are disproportionately home to communities of color. But this uneven impact is not reflected in the meteorological data.

A shortcut is being used in research, Just says: to assign everybody to the closest meteorological station. “What we’re missing is more fine-grained, high-resolution information about the quality of the air we breathe, and the temperatures of our neighborhoods,” he says. “When you assume that everyone in the area is experiencing the same thing, you underestimate the health impacts, because you’re flattening out the extremes.”

Just knew there must be a way of building high-resolution heat maps that could assign temperatures down to the city block. The creative solutions he found demanded painstaking work—an effort that exemplifies the urgent research that new scholars of public health are conducting at Brown, building on the School of Public Health's long-standing expertise in environmental epidemiology by unpacking how climate change is impacting human health. 

And so Just returned to Brown. Now Nazareth-Ferguson Family University Associate Professor of Public Health and associate professor of environment and society, Just is one of several scientists who has joined Brown as part of a significant strategic investment on the part of the School of Public Health to uncover the ways our changing climate is impacting population health, and to develop tools for building better, more equitable futures. 

“Health is one of the most pressing and fundamental ways that we’re going to experience the impacts of climate change,” says infectious disease scholar Rachel Baker, who is John and Elizabeth Irving Family Assistant Professor of Climate Health and assistant professor of epidemiology and of environment and society at Brown. 

In addition to increasing extreme heat, climate change also threatens water and food supplies, supercharging the threat of malnutrition and water-borne diseases like cholera, cryptosporidiosis and harmful algal blooms. Severe weather events impact vector-borne ecology, boosting diseases like malaria, dengue fever and West Nile virus. Extreme weather events disrupt health infrastructure, especially in low-income countries, while causing injury and exacerbating mental health problems. 

“Climate change is the ultimate threat multiplier,” says Dr. Ashish K. Jha, dean of the School of Public Health. “It takes all the threats to human health and makes them more complicated, harder or worse.”

And the burden is not carried equally. All of these health hazards disproportionately impact vulnerable communities—which, in the U.S., often means low-income groups and communities of color. Black households are more likely to live in areas at risk of climate-triggered health threats—near coastal sites menaced by sea level rise, in areas of high air pollution and in heat islands. 

Vulnerable communities are also burdened with higher rates of the medical conditions exacerbated by climate change, including physical disabilities, asthma and heart disease. On the whole, communities of color generally have worse access to high-quality health care. And they are more likely to lack the financial resources to help them bounce back from climate-related crises.

Researchers across the Brown campus are working to figure out where climate threats are, and how to deliver solutions on behalf of communities, with a strong focus on equitable and just outcomes, says Kim Cobb, director of the Institute at Brown for Environment and Society (IBES), a frequent partner of the School of Public Health. 

In 2023, Brown launched Equitable Climate Futures, a three-year research program focused on furthering climate solutions, driven by a partnership between the School of Public Health, IBES, the School of Engineering and the Watson Institute for International and Public Affairs. It’s an example of how Brown is leveraging its existing cross-campus expertise in climate research, at the same time it’s making strategic new investments to deepen the bench. 

“Taking climate action is the single biggest opportunity of this century to improve health outcomes and well-being,” says Cobb.

Ten years ago, Just was working on an air pollution study in Mexico City. He and his colleagues were hoping to uncover the impact of poor air quality on children in the world’s fifth-largest metropolis. They had access to high-quality mortality data that was broken down by locations across the city. But modeling air pollution exposure in a similarly fine-grained way was made difficult, as the city  had relatively few air quality monitors. 

From his time studying environmental science as an undergraduate at Brown, Just had been interested in using satellites to collect environmental data. He knew satellite imagery was updated daily, making it an extremely valuable data source. Perhaps, he thought, he could use the images to build maps of how air pollution travels around a city. But it hadn’t been done before: Integrating geospatial data from satellites into an epidemiological model was new. 

Motor engines, factories and—particularly in the Global South—home cooks burning biomass for cooking fuel, all pump out particulate matter. These particles, which are smaller than the width of a human hair, burrow deep into the lungs and then cross over into the bloodstream. They cause systemic inflammation and are linked to numerous health problems, including cardiovascular disease. Invisible to the naked eye, the particles nevertheless scatter light, and, in large enough quantities, they form a haze that can be seen from space. “From the satellite data we can infer that, if there’s lots of light scattering, then there must be lots of particles in that air column,” says Just.

But humans only breathe at the bottom of the air column. To model the quality of the air that actually gets into people’s lungs, Just had to combine NASA’s satellite imagery with data from monitors on the ground, which are very expensive, and therefore unevenly distributed. He also used physics-based models that use information about emissions and weather patterns to reconstruct the journeys that pollution particles make around a city. Feeding all of that data into a machine-learning model, Just and his team could estimate different air pollution exposures down to a range of one square kilometer over a period of ten years—a much higher resolution than was previously possible. 

“I realized that the same method and approaches that I was using for air pollution, could also be applied to reconstructing temperature and humidity,” he says, an area where there was also a dearth of fine-grained monitoring data. 

Just’s fine-grained model was successful. Applying it across thirteen Northeastern states and combining it with U.S. census data, he and his colleagues found that minoritized groups tended to experience hotter summers than white people. This is a finding that will help to support community resilience investment, such as tree canopy cover and increasing access to air conditioning, in the areas with the greatest need. 

Policies that help to mitigate the health impacts of climate change and air pollution are essential. But figuring out whether they actually improve air quality or positively influence health outcomes can be a daunting challenge. 

“Let’s say you want to evaluate the health effects of a regulation designed to incentivize renewable energy production,” says Corwin Zigler, professor of biostatistics. “In the background, there might be other regional policies going on that may impact the same thing simultaneously. So it’s very difficult to know the impact of this policy when there are overlapping policies.”

Zigler, who recently joined the School of Public Health from the University of Texas at Austin, has developed new statistical tools that attempt to unpack the impacts of policies in an area where causation is notoriously complicated. These tools attempt to settle questions that have long perplexed researchers: What, exactly, are the effects of climate policies on air pollution? And what are the climate impacts of policies that are focused on pollution reduction?

For example, Zigler was able to discover that, in 2014, U.S. wind power dramatically improved the quality of the air and led to health benefits—a gain that he calculates saved $2 billion. Around 30 percent of those benefits, he found, accrued to low-income groups and to communities of color. His work demonstrates that improving air quality and mitigating climate change can be two sides of the same coin. “It can go both ways,” says Zigler. “An energy policy relating to carbon emissions can have a large and immediate health impact due to changes in pollution. And on the other hand, pollution policies can have long-term climate benefits.”

Extreme heat, and other dramatic weather events, are perhaps the most obvious symptoms of our warming world. But climate change is also causing an increase in disease risk. 

The reasons behind the increase in zoonotic diseases—outbreaks of which have tripled since 1980—are complex. With increasing global travel, diseases are spreading beyond their usual borders. But climate change is likely also a culprit. Vector-borne illnesses like malaria and dengue fever are increasing in range as previously safe areas are now warm enough to harbor disease-carrying mosquitoes. And respiratory viruses, like influenza, are set to pose a year-round threat as warmer temperatures make them less seasonal. 

In 2012, Rachel Baker, who has a background in math, physics, environmental studies and ecology, was completing her Ph.D. at Princeton University. She was working with climate scientists to build models to understand how the Earth is warming. At the same time, Baker was collaborating with researchers modeling disease outbreaks. Her innovative work brought the two fields together in a new way—enabling her to model the impact of a warming world on disease threats. 

“We were founding this new area,” says Baker, who has a joint appointment between the Department for Epidemiology in the School of Public Health and the Institute at Brown for Environment and Society. “We were trying to understand how climate change could impact outbreaks of infectious disease.”

At Brown, Baker studies how climate impacts diseases from COVID-19 and HIV to dengue fever and chickenpox. She builds models to understand how a warming world will shape their dynamics. 

Think of influenza. In the tropics, flu poses a year-round problem. But go further north or south, and outbreaks tend to spike in the colder months. This will likely change as the world warms. “The short version is, we’re going to see more year-round causes of the disease in the temperate regions,” says Baker—who uses data about historical influenza outbreaks to model the climate’s impact on influenza up to one hundred years into the future.

Baker says there are two theories about why this would be. The first is human behavior. In cold weather, people tend to huddle together inside, “where they’re more likely to cough and sneeze at each other,” says Baker, increasing transmission. People huddle together a little less as winters get warmer. Conversely, as summers get hotter, people will increasingly retreat indoors to air-conditioned rooms—making flu more of a year-round problem. 

The second idea is that the influenza virus may survive for longer in warmer climates. “Human behavior matters, but also, the climate’s direct effect on virus survival matters,” says Baker, who is currently working on a project in which she has placed the flu virus in a climate-controlled box to study how temperature affects its viability. 

Professors Just, Zigler and Baker are each developing creative modeling strategies for understanding the impact of climate on health. But just as the School of Public Health is investing in the future, they, like many other Brown scientists who study the diverse impacts of our changing climate, are focused on finding solutions, too.

Just regularly consults with colleagues at Brown’s School of Engineering, considering how to ensure we are better able to withstand extreme heat. And Baker’s models of the future seasonality of infectious diseases will help health care providers prepare for a more chaotic world. “Mitigation is often focused, appropriately, on greenhouse gas reductions,” says Just. “But we should also be thinking about how we make our communities more resilient.” 

For Just, decarbonization presents an opportunity to build more heat-resilient communities. Take nursing homes. “So many nursing homes in our region are in older buildings which may not have ventilation and cooling,” he says. “When we decarbonize the buildings, we need to be weatherizing them, too.” 

It’s a way of thinking that pairs the global with the grassroots. And thanks to the partnership between the School of Public Health and IBES, this approach is flourishing at Brown. “These collaborations are so powerful,” Just says, “as a way to bring environmental science and public health together.”