From severe weather to warming oceans, most people are aware of the many adverse environmental effects of climate change. But along with these concerns, climate change impacts human health in a myriad of ways, Nelson Institute professor Dr. Jonathon Patz said.

Patz has been studying climate change and its effects on human health for over a quarter century. When Patz first started working in environmental epidemiology, the study of environmental determinants of health, he realized climate change poses a unique challenge to human health.

“There are so many pathways through which climate change affects our health that I view this as the largest environmental challenge of our time,” Patz said.

Patz and colleagues at the University of Hawaiʻi at Mānoa recently published a study in which they conducted a systematic review and found 70,000 scientific papers and 3,000 case examples of climate change affecting human health. These results indicated 58% of human infectious diseases are aggravated by climate change and that there are 1,006 distinct pathways where climate threats lead to pathogenic disease.

According to another paper Patz published in 2001, waterborne disease is strongly associated with heavy rainfall, which is becoming more extreme due to climate change. In 1993, Milwaukee experienced the heaviest month of rainfall in a 50-year period. The U.S’s largest waterborne disease outbreak ever recorded followed this heavy rainfall. An outbreak of cryptosporidiosis, a parasite that causes vomiting, diarrhea and fever, infected over 403,000 people and killed 54.

“The most important health prevention to do in this case is to go to the source and recognize that energy policy, transportation policy and basically getting to a low carbon economy is in fact a central public health policy,” Patz said, “It needs to happen at that level rather than on an individual disease basis. We need a multi-pronged approach to prevention.”

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Extreme heat is one of many ways climate change affects human health in Wisconsin and beyond. Climate and health program manager at the Wisconsin Department of Health Maggie Thelen said Wisconsin is becoming warmer and wetter. During heat waves when the temperature doesn’t drop enough at night, people’s bodies don’t have enough time to cool down and they can’t regulate their body temperature, Thelen said.

In Wisconsin, extreme heat kills more people than any other weather event combined, UW hospital ICU nurse Alex Dudek said. Extreme heat often worsens air quality, which can lead to more hospitalizations for respiratory issues. Additionally, when combined with COVID-19 infection, air pollution can lead to more patient deaths, Dudek said.

Interim chair of the Department of Medical History and Bioethics Richard Keller studies the social determinants of vulnerability during the 2003 heatwave that swept through western Europe, focusing specifically on France. During the August 2003 heatwave, 15,000 people died from heat related illness in two weeks, making the heatwave one of the most devastating weather disasters in modern French history, Keller said.

According to Keller, this heatwave was a real wake up call for the scientific community and for society in general.

“This was a moment when it came home to the northern hemisphere, and to Europe in particular … that this is real and that it kills people,” Keller said.

In 2003, most deaths occurred in the elderly population because aging reduces people’s ability to regulate body temperature. According to the American Journal of Physiology, elderly people are more at risk for hypothermia — a dangerously low body temperature — and hyperthermia — a dangerously high body temperature.

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According to Patz, with higher temperatures and changes in precipitation comes disease ridden mosquitoes. Tiger mosquitoes carry Zika virus and dengue fever, which is a leading cause of death in some Asian and Latin American countries.

Since 2004, tiger mosquitoes have lived in France, Keller said. In summer of 2022 over 40 people living in France contracted dengue. While people in places like the U.S. and France normally contract dengue abroad in tropical areas, the French cases occurred in people who did not have a travel history, meaning mosquitos are transmitting dengue locally.

“[Tiger mosquitos’] range is moving further and further north each year as a function of climate change,” Keller said. “So we will very soon be seeing this species of mosquito in a state like Wisconsin.”

It was in 2011 that UW school of nursing clinical instructor and PhD candidate Jessica LeClair first saw the effects of climate change in Madison communities, particularly through the effects of heavier rainfall and flooding. When she was working as a public health nurse in a north Madison neighborhood, a school principal told her more kids were coming to school with asthma and respiratory issues.

Upon further investigation LeClair learned the neighborhood flooded in 2008. By 2011, landlords had boarded up the basements of the houses, causing toxic mold to grow and seep through vents. LeClair said the toxic mold then made the families very sick.

Between families fearing eviction, a shortage of funding and policy issues LeClair struggled to find a solution. This experience led LeClair to pursue a masters in public health to better understand the connections between climate, health and equity.

“I took that knowledge back to our local health department and tried to convince them that as a nurse, all public health nurses should be addressing this,” LeClair said. “We’re embedded in the communities. We’re addressing health inequities in communities already. Climate change amplifies these health inequities so much.”

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When it comes to those whose health will be most affected by climate change, LeClair said communities who live in poverty, experience systemic racism and experience other inequities will also be experiencing the brunt of the health effects caused by climate change.

So while extreme heat affects all Wisconsin residents, it has a disproportionate impact on farmers, construction workers and other people who work outside, Dudek said.

“The health disparities are pretty extreme, so that’s another one of my goals,” Dudek said. “Trying to address the health concerns of climate change in a way that is equitable and puts people who are most affected by it first.”