The current level of carbon dioxide in the Earth’s atmosphere is about 440 parts per million (ppm). The CO2 levels are officially measured at three “pristine” sites: Mauna Loa, HI; Barrow, AK; and Grimes Point, Tasmania. However, levels encountered in some of our day-to-day experiences are higher. OSHA set the acceptable level of CO2 in the workplace to 1000 parts per million. However, this is often exceeded in some office buildings, schools, and homes.

Each and every one of us exhales CO2 at a level of about 40000 ppm. It follows that in some poorly ventilated enclosures that levels of CO2 are above 1000 ppm. Some office meeting rooms are at 1900 ppm or more. Airliners in flight have levels around 1400 ppm. Cars with recirculated air can reach a level that is 4 times the acceptable level.

Effects of CO2 in the air:

• <150 ppm: all vegetation dies
• 400 ppm: background (normal) outdoor air level
• 400-1,000 ppm: typical levels found in occupied spaces with good air exchange
• 1,000-2,000 ppm: level associated with complaints of drowsiness and poor air
• 2,000-5,000 ppm: level associated with headaches, sleepiness, and stagnant, stale, stuffy air; poor concentration, loss of attention, increased heart rate and slight nausea may also be present
• >5,000 ppm: This indicates unusual air conditions where high levels of other gases also could be present. Toxicity or oxygen deprivation could occur. This is the permissible exposure limit for daily workplace exposures.
• >40,000 ppm: This level is immediately harmful due to oxygen deprivation.

This would explain why some people nod off during meetings and in class. The dangers of high levels in unventilated cars are obvious. The efforts to make office buildings and homes more energy efficient have made them more airtight. This has caused the CO2 levels to increase within. The new LEED standards include air quality standards to mitigate the effects of high CO2 levels. One double-blind study shows that high CO2 levels also have a profound effect on our cognitive ability (Allen et al. 2015). The study found that the decision-making performance of working professionals became impaired at high CO2 levels. Averaged across all metrics, performance was reduced by 15% at 945 ppm and 50% at 1400 ppm compared to the 550 ppm control. The annual increase in carbon dioxide levels is about 2 ppm. At that rate, it would take over four centuries to double the current concentration. However, in reality, vegetation would increase and absorb more carbon. So, another way to mitigate CO2 levels is to introduce more plants inside office buildings, homes, and schools.
References:
Allen, J.G., MacNaughton, P., Satish, U., Santanam, S., Vallarino, J., Spengler, J.D., Environmental Health Perspectives 124, 805 (2015).