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Building ventilation standards use indoor carbon dioxide (CO2) levels as a proxy for air quality, acknowledging that at typical indoor levels, CO2 itself is not a pollutant. By 2100, outdoor CO2 levels may reach 900 ppm. With current ventilation standards, that would nearly double the levels of chronic, indoor CO2 exposure, raising concerns for its potential effect on occupants. In the last 15 years, an effort to gain this understanding, particularly regarding cognitive performance, has been made by 11 studies. They focused on the effect of elevated CO2 while minimizing exposure to other indoor pollutants. Five of the studies found an effect of CO2 exposure on performance and six studies did not. Four studies found an effect on cognitive performance under 2000 ppm exposure. But three of these four studies used the same proprietary, closed-source tool to measure cognitive performance. Physiological effects – like blood pressure, heart rate changes – were found only at exposures over 2500 ppm and were not always associated with cognitive decrements. These discrepancies could have been due to differences in measures used and individual differences in response to CO2. Future works should adopt a more in-depth and holistic approach.