Increasing Levels of CO2 May Directly Harm Human Thinking

With the advance of the 21^st century, an increase in the concentrations of atmospheric carbon dioxide (CO₂) will lead to a rise in the urban and indoor levels of the gas. This might considerably impair the complex strategic thinking and basic decision-making ability of humans, reports a new study led by CU Boulder.

At the end of the 21^st century, people could be exposed to nearly 1400 parts per million indoor CO₂ levels, which is greater than three times the current outdoor levels and much more than the levels ever experienced by humans.

It’s amazing how high CO₂ levels get in enclosed spaces. It affects everybody—from little kids packed into classrooms to scientists, business people and decision makers to regular folks in their houses and apartments.

Kris Karnauskas, CIRES Fellow and Associate Professor, CU Boulder

Karnauskas is the lead author of the new study reported recently in the GeoHealth journal from the American Geophysical Union (AGU).

Study coauthor Shelly Miller, who is a professor in CU Boulder’s school of engineering, said that “building ventilation typically modulates CO₂ levels in buildings, but there are situations when there are too many people and not enough fresh air to dilute the CO₂.” She added that CO₂ can also get accumulated in poorly ventilated spaces over extended periods, for example, while sleeping in bedrooms overnight.

In simple terms, when air containing high levels of CO₂ is breathed in by humans, the blood CO₂ levels increase, causing a reduction in the amount of oxygen that reaches the brain. Earlier research works have demonstrated that this can cause increased sleepiness and anxiety, and eventually affect cognitive function.

This feeling is familiar to all: when people sit for a very long period in a crowded, stuffy conference room or lecture hall, many tend to feel dull or drowsy. According to the authors, CO₂ concentrations are higher indoors than outdoors.

CO₂ concentrations outdoors in urban areas is higher compared to pristine locations. In buildings, the CO₂ concentrations are due to the gas that is otherwise in equilibrium with the outdoors, as well as the CO₂ produced by the occupants of the building as they exhale.

Since the Industrial Revolution, there has been a steady increase in the atmospheric CO₂ levels, which reached a 414 ppm peak in 2019, at NOAA’s Mauna Loa Observatory in Hawaii.

Under current conditions where people on Earth do not mitigate greenhouse gas emissions, the Intergovernmental Panel on Climate Change has estimated that outdoor CO₂ levels could increase to 930 ppm by 2100. Moreover, urban areas often have nearly 100 ppm CO₂ higher than this level.

Karnauskas and his team devised a detailed approach that takes estimated future outdoor CO₂ concentrations and the effect of localized urban emissions into account—a model of the relationship between outdoor and indoor CO₂ levels and the effect on human cognition. They discovered that even if the outdoor CO₂ concentrations increase to 930 ppm, that would cause an increase in the indoor concentrations to a hazardous level of 1400 ppm.

At this level, some studies have demonstrated compelling evidence for significant cognitive impairment. Though the literature contains some conflicting findings and much more research is needed, it appears that high level cognitive domains like decision-making and planning are especially susceptible to increasing CO₂ concentrations.

Anna Schapiro, Assistant Professor of Psychology, University of Pennsylvania

Schapiro is another co-author of the study.

How will CO₂ Affect Human Thinking?

The researchers found that CO₂ concentrations of 1400 ppm may reduce the basic decision-making ability of humans by 25%, and complex strategic thinking by nearly 50%.

The cognitive impacts of increasing CO₂ levels symbolize a so-called “direct” effect of the gas concentration, quite similar to ocean acidification. In both cases, higher CO₂ itself—not the ensuing warming it brings—is what causes harm.

According to the researchers, although there could be several means to adapt to higher indoor CO₂ levels, the ideal way to prevent levels from reaching hazardous levels is to bring down fossil fuel emissions. For this, globally adopted mitigation approaches would be required, for example, those set proposed by the Paris Agreement of the United Nations Framework Convention on Climate Change.

Karnauskas and his colleagues believe the study outcomes will lead to further studies on the “hidden” effects of climate change, for instance, that on cognition.

This is a complex problem, and our study is at the beginning. It’s not just a matter of predicting global (outdoor) CO₂ levels. It’s going from the global background emissions, to concentrations in the urban environment, to the indoor concentrations, and finally the resulting human impact. We need even broader, interdisciplinary teams of researchers to explore this: investigating each step in our own silos will not be enough.

Kris Karnauskas, CIRES Fellow and Associate Professor, CU Boulder