Increasing atmospheric concentrations of carbon dioxide (CO2) not only adds to change in earth’s climate, but also poses a significant threat to our cognitive competences, according to a new study at University of Colorado, Boulder.

Prior to the Industrial Revolution, global average concentration of CO2 was about 280 ppm, but the most recent measurement at NOAA’s Mauna Loa Observatory in Hawaii in 2019 shows the atmospheric CO2 levels have plateaued at 414 ppm. Also the anthropogenic greenhouse gas emissions, if not mitigated, could put the outdoor CO2 levels at 930 ppm with 100 ppm higher in the urban areas by 2100.

Breathing in an area where concentrations of CO2 are high could cause the CO2 levels in our blood to rise. This reduces the amount of oxygen that reaches the brain, which in turn increases sleepiness, anxiety, and undermines cognitive function. If you have ever been to lecture hall or conference room jammed with people, you get the feeling.

CO2 concentrations are generally higher in indoors than outdoors. The reason being both the CO2 that is otherwise in equilibrium with the outdoors, and the CO2 that apartment inhabitants generate as they exhale. Also the level of outdoor CO2 in metropolis is much higher compared to cleaner locations like the countryside or rural areas.

“It’s amazing how high CO2 levels get in enclosed spaces,” explained Kris Karnauskas, associate professor and lead author of the study. “It affects everybody — from little kids packed into classrooms to scientists, business people and decision makers to regular folks in their houses and apartments.”

“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 CO2said co-author Shelly Mille. “CO2 can also build up in poorly ventilated spaces over longer periods of time, such as overnight while sleeping in bedrooms.”

For the study, Karnauskas and his team formulated a holistic approach that assesses predicted future outdoor concentrations of carbon dioxide and the impact of localized urban emissions, a model which studies the relationship between indoor and outdoor CO2 concentration and how it impacts human cognitive faculties. They found that if the outdoor concentrations of the gas reach 990 ppm, it would push the indoor concentration at 1400, the effect of which can be detrimental.

Evidence of people exhibiting substantial deficits in cognitive function after a sustained exposure to this level of CO2 has been demonstrated in some studies. Although the studies yield some conflicting results, most researchers seem to agree that elevated CO2 concentrations can cause disruption in high level cognitive domains like decision-making and planning. In fact, at 1400, our ability to make decision plummet by 25 percent and strategic thinking by 50 percent, the researchers found.

The effect that elevated CO2 has on the cognitive function is much like what triggers ocean acidification. Both are a “direct” effect of the gas’ concentration, and it’s the elevated CO2 that induces harm not the warming it causes.

Cutting emissions is the most effective means to stop CO2 from reaching harmful concentrations, but this would require globally adopted mitigation strategies like the ones put forth by the Paris Agreement of the United Nations Framework Convention on Climate Change, the researchers say.

“This is a complex problem, and our study is at the beginning. It’s not just a matter of predicting global (outdoor) CO2 levels,”Karnauskas explained. “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.”

The study has been published in the AGU journal GeoHealth.