Measuring the CO2 concentrations of air trapped at different depths of Antarctic ice has uncovered a cycle of CO2 levels, which predates the human species, that rises and lowers in co-ordination with glacial cycles, with CO2 levels at their lowest during ice ages and at their highest in interglacial periods. Modern records escape this cycle, and CO2 concentrations have increased by nearly 50% in the past 200 years. This strongly correlates with the increased volume of fossil fuels being burned since the first industrial revolution.

This 50% increase, which is predicted to continue growing, has a significant impact on health, both indirectly and directly. The impacts most visible to us are not often the direct impacts, but rather the indirect impact of the warming caused by increased atmospheric CO2. However, concerns are growing around the direct impact of high CO2 concentrations on health, most notably on cognition.

Concerns that high CO2  can impact cognitive function first arose in those working in enclosed spaces, such as submarines and aeroplanes. Initial studies revealed that operating in high-CO2 can impair vision and a reduce the ability to manoeuvre an aircraft. More recently, interest has shifted towards highly populated indoor spaces like school buildings, particularly older buildings re-fit with modern insulation that results in poor ventilation. These studies show a large decline in decision making ability and complex strategizing at CO2 concentrations that are only double current atmospheric levels.

Unfortunately, there is little experimental data to explain this phenomenon. It has been suggested that cognitive decline may be indirectly caused by increased drowsiness or anxiety associated with high CO2, but Karnauskas believes that it is more likely that cognitive impairment, drowsiness, and anxiety are all a result of the same biological effect of high CO2.

Increased CO2 prevents efficient gas transfer in the lungs, in turn increasing the CO2 concentration of the blood, which can lower the pH of blood causing symptoms associated impaired cognitive ability, including confusion and sleepiness. Further to this, CO2 can diffuse across the blood brain barrier impeding oxygen transfer to the brain. These observations offer an insight into the effect of CO2 physiologically but are far from the full picture and require much more research to uncover the full mechanism linking CO2 and impaired cognitive function. Although little is known, the observation of CO2’s impairment of cognitive function is enough to justify treating increasing CO2 seriously.

The Intergovernmental Panel on Climate Change determined four possible representative concentration pathways (RCPs) that characterize the possibilities for how CO2 concentrations will change until the year 2100. They predict that if we do not act to reduce fossil fuel emissions, CO2 concentrations will double by 2100. This level of CO2 was found to be harmful to cognition in the aforementioned studies of decision making and complex strategizing at different indoor CO2 concentrations.

If outdoor CO2 concentrations reach harmful levels, indoor levels will be even more harmful. This is particularly concerning because, as Karnauskas demonstrates, CO2 concentrations in classrooms in urban areas are already at risk of reaching harmful CO2 levels. However, we cannot account for unforeseen physiological adaptation to long-term exposure to increased CO2 concentrations.

Nevertheless, increasing CO2 concentrations are increasingly concerning, particularly in populated indoor spaces, and have been shown to negatively impact aspects of cognitive function. Since indoor CO2 concentrations are largely dictated by the outdoor concentration, the best way to keep CO2 concentrations below a harmful level is by stemming the rise in atmospheric CO2, which is best tackled by reducing fossil fuel emissions.

Sources:

1. Kristopher B. Karnauskas et al. Fossil Fuel Combustion Is Driving Indoor CO2 Toward Levels Harmful to Human Cognition. GeoHealth.2020: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GH000237

2. Photo by Marcin Jozwiak from Unsplash: https://unsplash.com/photos/uKvPDQop-JA/info