New review details the direct human health risks of increased atmospheric carbon dioxide exposure

August 13, 2019

A recent review out of the University of Wisconsin—Madison suggests that the increasing elevations in carbon dioxide may pose direct risks for human health. Led by an interdisciplinary team of researchers, including Nelson Institute affiliate and Wisconsin School of Business Lecturer Michael Hernke, the review titled, “Direct human health risks of increased atmospheric carbon dioxide,” compiles the latest research on the health risks associated with increasing atmospheric levels of carbon dioxide, including inflammation, reduction of high-level cognitive abilities, and more.

The paper, which synthesizes carbon dioxide related information from a range of fields including physiology, immunology, and building engineering, not only summarizes the factors increasing human exposure to carbon dioxide, but also presents preliminary evidence that indoor, and possibly future outdoor, exposure to carbon dioxide could have adverse health effects.

“Concentrations of carbon dioxide are currently sixty-four percent higher than the level of carbon dioxide our species evolved at,” said Hernke, who also shared that the atmosphere now contains carbon dioxide levels of around 410 parts per million (ppm), which is the highest it has been in human history, with some estimates suggesting carbon dioxide levels haven’t persisted at these levels in the past 15 to 25 million years.

Hernke’s hope is that by bringing more attention to the rise in carbon dioxide as well as its health effects, the issue can be further studied and addressed before “colossal failure.”  In fact, the idea to compile the growing evidence surrounding environmentally relevant elevations in carbon dioxide exposure and health began a few years ago when Hernke began to consider the implications of carbon flux and how the increasing atmospheric carbon dioxide might be impacting public health. Soon after, Hernke formed a team who shared his interest in this area, including student, Tyler Jacobson, who was looking for a way to connect his research in medicine with his interests in business operations and sustainability. Jacobson, a Wisconsin School of Business alumnus who is set to begin medical school in the fall, worked with Hernke to set up meetings with University of Wisconsin-Madison pulmonology research scientist, Rudolf Braun, during which the group reviewed and discussed peer-reviewed articles that related to carbon dioxide exposure. Over time, the team began to notice that a common theme among the papers was the mention of a correlation between indoor and outdoor carbon dioxide exposure and a range of physical and psychological effects.

In fact, the amount of research backing this notion was so strong, that the team decided to reach out to Keith Meyer, MD, a University of Wisconsin Hospital and Clinic pulmonary & critical care specialist, to get his expert opinion on the review. Meyer, who has served as the Director of the University of Wisconsin Adult Cystic Fibrosis Center, as the Medical Director of the UW Lung Transplant Program, and as the Director of the UW Interstitial Lung Disease Program, was happy to review the material and lend a hand in developing this paper. Additionally, the team received assistance and support from Northwestern University Assistant Professor of Preventive Medicine, William Funk, and student researcher and UW-Madison alumnus Jasdeep Kler, who is now at the University of Michigan School of Public Health.

“This is a hard thing to study and translate to what is really going on in humans, so it was satisfying to have pulmonologists and a molecular epidemiologist in the room agreeing that there might be something here,” said Hernke. “What a great thing it is to be at a great university and a part of the interdisciplinary Nelson Institute where we can get out of our silos and work together.”

Together, the team examined approximately 130 studies, developing a multifaceted review that includes a range of findings, including that adverse health outcomes associated with acute carbon dioxide exposure can begin when the level is above 1,000 parts per million (ppm) for more than a few hours. Additionally, the review suggests that behavioral changes and physiological stress related to carbon dioxide exposure have been associated with prolonged exposure at levels between 700 and 3,000 ppm. While these levels may seem high when compared to the average 410 ppm present in the atmosphere, several studies throughout the review suggested that the “average indoor carbon dioxide concentrations in offices, schools, and homes typically range from 600-1,000 ppm, but can exceed 2,000 ppm with increased room occupancies and reduced building ventilation rates.” This is of particular concern, as these elevated levels are likely to become more common as a result of increased anthropogenic carbon dioxide emissions, increased time spent in air-conditioned indoor spaces, and increased adoption of energy efficient building designs, including increasingly airtight office spaces and homes,  which make it more difficult for indoor-sourced air pollutants to escape through cracks and leaks. Air-conditioning in hot and humid climates could also increase indoor concentrations of carbon dioxide if the outdoor air exchange rates are reduced to lower the cooling demands of buildings.

Hernke shared that while these levels impact everyone, it is likely that these increasing risk factors will be particularly concerning for the most vulnerable populations, including infants, those with pulmonary or neurodegenerative diseases, and the elderly population. It will also present challenges to those living in densely populated urban areas as well as those in tropical climates, who may be subjected to elevated levels of exposure. 

While this paper was a review of the current literature on the topic, and not a new study, Hernke and the team hope that this will serve as a catalyst for more studies on this topic. He also hopes that this study will showcase the true human impact of increased carbon dioxide levels and climate change.

“If you want to know why this is important, just hold your breath for a bit,” said Hernke. “It doesn’t take long for carbon dioxide to build up. This truly isn’t a political paper. This is hard science and we’ve been careful with it. After all, we all breathe air.”

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