High carbon dioxide levels in your car might be harming you
Part one of two - the case for circulating fresh air and cracking a window
~6 minute read~
You are driving on a freezing night in your cozy car, windows up, heat on, and belly full of turkey. Your eyes start to glaze over, and you catch yourself feeling sleepy at the wheel. It must be the tryptophan in the turkey, or the insufficient sleep last night. You turn the radio up and sing along for a couple lines, but your singing voice is terrible. The other passengers ask you to stop. You slap your face, but still you are tired, and your face stings. Before pulling over to the side of the road you roll all the windows down. A blast of cold, well-oxygenated, low-carbon dioxide air refreshes you. But the other passengers implore you to roll up the windows. You recall that carbon dioxide levels can soar when three people are in a car with the heat on and air recirculation mode on. So you keep a window barely cracked and switch the heat setting to bring in fresh air. Awake, alert, and singing defiantly under your breath (your voice is actually great and underappreciated), you drive on and make it home safely.
Carbon dioxide levels in cars, buildings, and other enclosed situations can rise quite rapidly. Higher CO2 levels are associated with problems like drowsiness, reduced cognitive abilities, dizziness, and even shortness of breath. Along a continuum of high to low, additional effects of increasing CO2 range between headaches, dizziness, restlessness, a tingling or pins or needles feeling, difficulty breathing, sweating, tiredness, increased heart rate, elevated blood pressure, and at extremely high levels coma, asphyxia, and convulsions.
Distracted driving and fatigue are among the top causes of car accidents. The invisibly high concentration of carbon dioxide in cars is undoubtedly contributing. We all know about dangerous drivers not getting enough sleep, drinking alcohol, texting, or having poor quality sleep from conditions like obstructive sleep apnea. But I propose that another major yet fixable problem is the poor ventilation in our cars. Realizing this, and then cracking a window or turning off the air recirculation option, might save lives and limbs and prevent accidents.
Quick example of CO2 levels in my car
I previously wrote a long post about the importance of good ventilation, and how to use a CO2 monitor as a good proxy for measuring it. CO2 levels in the atmosphere are now 425 parts per million (ppm). Before the Industrial Revolution 280 ppm was the norm. Scientists are speculating whether humans are already experiencing cognitive effects from this rise in CO2, but more about that later. Suffice it to say that most experts agree that a good level is close to outdoor levels of 425 ppm. Buildings (and cars!) should aim for no more than 700-800 ppm.
Here are some examples of CO2 levels in my car.
552 ppm CO2 while driving at 70 mph is not bad. Windows are actually closed, but car vents are open and not on recirculation mode. The fast speed forces a lot of fresh air into the car through the vents and small crevices, and CO2 escapes. No significant adverse cognitive effects expected at this level.
1301 ppm CO2 while still driving at 70 mph is not good. Windows are still closed, but now I’ve set the heating vent mode to recirculate. It took just 5 minutes for the CO2 level to almost triple. Drowsiness and adverse effects on cognitive functions have been shown to occur at this level.
1542 ppm CO2 while driving at 25 mph is even worse. Windows still closed, vent still on recirculate, but now slower driving forces even less air exchange.
The evidence for higher CO2 levels affecting our brains
There is still some debate as to what level of CO2 we need to worry about, but I’m going to cite a few references that I think are relevant and authoritative. Otherwise you might think I’m being alarmist. The Atlantic had a good article about this, too.
A 2016 study by researchers at Harvard and Syracuse University found that human cognitive function declined by about 15% when indoor CO₂ reached 945 ppm, and plummeted by 50% when indoor CO₂ reached 1,400 ppm.
A review of 10 well-designed studies published since 2012 found that on moderate tests of cognition, higher CO2 levels showed mixed results. But substantial evidence supported the fact that human performance can decline with challenging problems at moderate concentrations.
Pilot performance on flight simulators starts to fall at 1,200 ppm.
The Wisconsin Department of Health Services (I know, sounds random), broke it down by CO2 levels and symptoms expected
400 ppm: average outdoor air level.
400–1,000 ppm: typical level 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 could also 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.
GPT-4 came up with similar ranges after scouring the entire world of online literature, but AI information must always be taken with a skeptical grain of salt:
Low Levels (Normal indoor levels, around 400 ppm):
• Minimal physiological effects.
• Cognitive performance typically unaffected.
Moderate Levels (Up to 1,000 ppm):
• Increased respiratory rate and discomfort in some individuals.
• Cognitive performance may decline slightly, affecting decision making and attention.
High Levels (1,000 to 5,000 ppm):
• Headaches, dizziness, and shortness of breath.
• Cognitive functions such as decision-making and problem-solving may be noticeably impaired.
Very High Levels (Above 5,000 ppm):
• Significant discomfort, headaches, and dizziness.
• Concentration and cognitive abilities further decline.
• Increased heart rate and potential for more severe health effects with prolonged exposure.
Here are the results of a trial published in 2012 in the journal Environmental Health Perspectives:
Relative to 600 ppm, at 1,000 ppm CO2, moderate and statistically significant decrements occurred in six of nine scales of decision-making performance. At 2,500 ppm, large and statistically significant reductions occurred in seven scales of decision-making performance.
A study published in 2020 in the journal GeoHealth (coauthored by a researcher in my backyard at the University of Pennsylvania) concluded:
At 1400 ppm CO2 concentrations may cut our basic decision-making ability by 25%, and complex strategic thinking by around 50%, the authors found.
A comprehensive review of 99 “peer-reviewed articles pertaining to original research or review of experimental or human studies” over the past 68 years, found:
Physiological changes occur at CO2 exposures levels between 500 and 5000 ppm. Effects on cognitive performance begin at 1000 ppm during short-term exposure. Comorbid indoor pollutants may be involved in building-related symptoms.
How to improve the CO2 levels in our cars
Don’t use recirculate mode all the time.
The only time I put my car vents on recirculate is if the outside world is full of smelly exhaust, such as in high traffic situations, tunnels, and driving behind an old car. Auto experts rarely concede the problems with recirculation mode, but instead tout usefulness in terms of better air conditioning performance and reducing exposure to pollution. I have read other sources citing up to an 80% reduction in pollutants entering the car when recirculation mode is on. Recirculate is not all bad, and there are tradeoffs.
But in lower traffic areas it makes sense to ventilate at will. In smelly, high exhaust situations, or indeed during times of wildfires, recirculation mode is a better option in my opinion. Yet we should realize the tradeoff in terms of higher CO2 levels building up quickly.
Implications for life outside our cars
What are high CO2 levels doing collectively to our cognitive capacities and attention spans at work, home, and in other buildings full of people? Can you imagine a company intentionally improving ventilation, installing windows and then opening them, if only to increase worker productivity? I’m glad a few corporate strategists read this newsletter - this idea is on the house if you haven’t yet heard of it. There are zero windows that open in my office. We have decent ventilation from air exchanges only through the heating/cooling system. And in terms of our home environments, better ventilation may help our cognitive abilities, and have us folding laundry into intricate origami structures with our newfound, better oxygenated smarts.
My next post will be an extrapolation of these troubling effects of rising CO2 levels upon the health of human brains on planet Earth, now and over the next 80 years. There are overlooked implications for the future of the planet, and I would say it’s shocking, and worth staying tuned, focused, and attentive… preferably in a low CO2 environment while you read on. The United Nations Climate Change Conference (COP28) kicks off today in Dubai. They have invited me to speak with the world’s leaders, so I need to finish this next post ASAP ;)
Carbon dioxide levels increase rapidly in cars with windows closed, recirculate mode on, higher number of passengers, and slower driving speeds. Numerous studies have found varying degrees of evidence, but overall provide significant proof that cognition and attention suffer. CO2 levels improve rapidly with cracking windows, turning off recirculate mode, and stuffing a thousand green plants in the car. Being aware of the soporific effects of carbon dioxide is an important safety variable that most people don’t think about.
Consider forwarding this post to anyone you know who might be prone to getting sleepy while driving. This might be everyone you know, so feel free to be somewhat judicious. Or not.
I think a simple fix like cracking a window or reducing time spent in recirculation mode might save lives and limbs on the hazardous roads as we balance the tradeoffs with AC efficiency and ambient pollution entering the car.
Until part two, take good care, and so many thanks to the folks who upgraded their memberships over the weekend. 💪