Studies show CO2 concentrations that we are headed toward have a huge impact on cognitive functioning

In a landmark public health finding, a new study from the Harvard School of Public Health finds that carbon dioxide (CO2) has a direct and negative impact on human cognition and decision-making. These impacts have been observed at CO2 levels that most Americans — and their children — are routinely exposed to today inside classrooms, offices, homes, planes, and cars.

…the implications for climate policy are stark. We are at 400 parts per million (ppm) of CO2 today outdoors globally — and tens of ppm higher in many major cities. We are rising at a rate of 2+ ppm a year, a rate that is accelerating. Significantly, we do not know the threshold at which CO2 levels begin to measurably impact human cognition.

Vivian Loftness — University Professor and former Head of the School of Architecture — one of the world’s leading experts on “Health, Productivity, and the Quality of the Built Environment,” which is a graduate course she teaches, explained that CMU’s analysis showed that “humans are pretty good sensors of high CO2 levels.” Occupant perception of indoor air quality drops sharply as CO2 levels rise from 600 to 750 ppm.  She said first, the immediate public health message is to increase ventilation and the use of outside air in buildings. And second:

We have to do everything we can to keep outdoor CO2 levels below 600 ppm because something serious starts happening then.

Researchers at Climate Interactive put together a chart of where CO2 levels headed as we head into the crucial Paris climate talks in December.

Future CO2

The world had been on a path toward 900 ppm of CO2 in the air by 2100. Commitments made by major countries to cut or constrain CO2 emissions through 2030 — Intended Nationally Determined Contributions (INDCs) — would put us on a sharply lower trajectory. To avoid catastrophic impacts, however, we will need much stronger commitments post-2030.


On the immediate public health front, we need to start monitoring indoor CO2 more closely and keep inside levls as close as possible to levels outdoors through greater use of outside air. According to the building design experts I have interviewed, such as Dr. Loftness, that can be donewithout increases in building energy consumption using cost-effective strategies and technologies available today. Indeed, systematic green design will lower total energy consumption. I will examine these design strategies later in this series.

A new study from the Harvard T.H. Chan School of Public Health’s Center for Health and the Global Environment, SUNY Upstate Medical University and Syracuse University has found that improved indoor environmental quality doubled occupants’ cognitive function test scores.

Now, consider the fact that most of us spend about 90 percent of our time indoors and 90 percent of the costs associated with a building are due to the people inside it – and you can see why focusing on the air you breathe could turn your building into your business’ strongest human resource tool.

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Allen and his colleagues looked at the impact of carbon dioxide on cognitive function, independent of ventilation. Outdoor carbon dioxide concentrations are typically around 400 parts per million, but people routinely experience indoor carbon dioxide levels between 800 and 1,200 parts per million — and it’s not uncommon to see carbon dioxide as high as 1,500 parts per million or even up to 3,000 parts per million, Allen says.

“We found that when people were moved from an environment with low-carbon dioxide concentrations to a level of about 950 parts per million — a level we find in most indoor spaces — we saw a fifteen percent decrease in cognitive performance scores for the people in that space,” Allen says. “And when they moved to an environment with 1400 parts per million, we saw fifty percent lower cognitive performance scores when they were in that environment.”

That is very big impact, Allen says. “This is new for our field. We measure carbon dioxide all the time when we’re doing studies of buildings and health, because it’s a good indicator of how well the space is ventilated,” he explains. “But now we’re starting to see that maybe carbon dioxide isn’t just a useful proxy for ventilation and for other things that [might be] building up in our environment — it might actually be a direct pollutant, a primary pollutant.”

…John Mandyck, chief sustainability officer for the United Technologies Corporation (UTC), says the findings may revolutionize the way we think about buildings. UTC is the world’s largest provider of building technologies and the key underwriter of the study, though it was not involved in the data collection, analysis, interpretation, or drafting of the peer-reviewed paper.

“If you look at the true cost of operating a building, just one percent is energy,” Mandyck says. “Ninety percent of the true operating cost of a building is the salaries and the benefits of the people inside the building. [If] green buildings can improve thinking, can improve productivity, can improve health, [then] buildings become human resource tools. Buildings can become ways that we can find competitive advantages simply by optimizing the indoor environmental quality.”

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Symptoms of high levels of CO2 include drowsiness, physical irritability, difficulty concentrating, fatigue and nausea. Study leader Joseph Allen, director of the Healthy Buildings Program at the Harvard School of Public Health, wrote, “We found statistically significant declines in cognitive function scores when CO2 concentrations were increased to levels that are common in indoor spaces (approximately 950 parts per million).”

Another study, conducted in 2011 by researchers at Lawrence Berkeley National Laboratory at the University of California, put a price tag on the effects of indoor air quality: by increasing ventilation rates in U.S. offices, thereby reducing illness-related absence and decreased output, businesses could enjoy economic benefits from $13 billion to $38 billion.

Numerous studies, including ones from NASA, have also shown that fresh green plants and potted flowers such as Gerbera daisies and chrysanthemums have a marked impact on air quality by absorbing as much as a quarter of the CO2.

Healthy air can have a critical impact on your response times dealing with crucial tasks such as crisis response and strategizing, said the authors of the Harvard study. So by optimizing your workspace, you can make a big difference in how much you accomplish – and give yourself lasting health benefits that go far beyond the bottom line.

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At a Glance

  • Office workers scored higher on performance measures when working in “green” environments with low indoor pollutants and low carbon dioxide levels.
  • The findings suggest that improving indoor air quality in office environments may increase the performance of office workers.
Effects of Acute Exposures to Carbon Dioxide Upon Cognitive Functions“What we found were quite shocking results,” Allen said. “We saw a doubling of cognitive performance scores in the environments that started with a green building, and we enhanced the outdoor ventilation rate.”

In the study, which was conducted in Syracuse at the university’s Center of Excellence in Environmental and Energy Systems, 24 professionals spent 6 full work days in a controlled office experimental setting where they performed their regular jobs. The space was equipped with Internet, printing facilities, phones — all the usual office stuff.

The big difference, though, was that at 3 pm each day, the subjects were given a 1.5 hour test called the Strategic Management Simulation, which tests “higher-order decision making.” Thus, for instance, respondents might have to figure out how to handle a tough problem — “handling a township in the role of a mayor or emergency coordinator” is one example provided in the study.

Unbeknownst to the participants, however, researchers manipulated the indoor environmental conditions in which they were working. Sometimes, levels of volatile organic compounds — including formaldehyde, benzaldehyde, and acetaldehyde — were higher or lower (green building designs aim to lessen the presence of these compounds). And sometimes, there was greater or lesser ventilation of the workspace with outdoor air. Indoor carbon dioxide levels were also varied, from 550 parts per million, to 945 parts per million, to as high as 1,400 parts per million.

The goal was to simulate conditions of a “conventional” building, versus a green building and, with the 550 parts per million carbon dioxide case, a “Green Building +” condition. And the study found a large effect of these indoor conditions on test performance. “Cognitive function scores were higher in Green building conditions compared to the Conventional building condition for all nine functional domains,” the researchers wrote, including crisis response, information usage, and strategy.

Carbon dioxide levels, in particular, seemed to have a major effect. “Cognitive function scores were 15% lower for the moderate CO2 day (~945 ppm) and 50% lower on the day with CO2 concentrations around 1400 ppm than on the two Green+ days,” the researchers wrote.

In a statistical sense, the study reported a quite strong link between the two variables under examination — office air quality and cognitive performance. The researchers claimed that they could explain 81 percent of the variability in the study subjects’ cognitive test scores based on the variations in the office’s indoor conditions, leaving only a quite small 19 percent attributable to other factors not controlled in the study, such as “diet, previous night sleep quality, and mood.”

The carbon dioxide part of the story is particularly striking, as there has in the past been little worry about this molecule in the air we breathe. The researchers note, however, that their work is consistent with a prior 2012 study, also published in Environmental Health Perspectives, which found that “statistically significant decrements” occurred in performance on decision-making tasks as carbon dioxide concentrations indoors increased from 600 to 1000 parts per million.

“Carbon dioxide at the concentrations we typically find indoors was long thought to be benign,” says Allen. “But our understanding of this is changing. We’re starting to see that carbon dioxide has direct effects.”