The dangerous consequences of rising levels of carbon dioxide in the Earth's atmosphere are well-documented, from destructive weather events and deadly health effects, to its harmful impact on oceans, species migration, agriculture and national security.
But, until recently, no one thought carbon dioxide posed a danger indoors. It may be time to rethink that thesis.
New research suggests humans who breathe carbon dioxide in the workplace or other indoor settings (such as classrooms) have a much tougher time learning, performing simple and complex tasks, and making decisions. This is a disturbing finding that raises the specter of far-reaching consequences for those routinely exposed to poor air quality on the job, in schools, airplanes and in the home.
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This new study, combined with others in recent years looking at indoor CO2 consequences should give everyone who spends considerable time in poorly ventilated indoor spaces pause. With outdoor CO2 levels raising base levels of CO2 everywhere – including indoors – we may have a new CO2 threat looming that very few even recognize.
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Once considered a benign indoor air pollutant, CO2 can, as it turns out, significantly impair peoples' cognitive functioning. This presents an important new implication for climate policy, since the traditional way of fixing indoor pollution has been to increase ventilation from the outside.
If outside levels continue to increase as a result of global warming, it will become harder, if not impossible, to reduce indoor levels of carbon dioxide by pumping in air from the outside, according to the researchers.
"We can now add potential adverse effects on human cognitive function to a long list of public health reasons why we need to act on climate to prevent carbon dioxide concentrations from increasing,'' says Joseph Allen, assistant professor of exposure assessment science at the Harvard T.H. Chan School of Public Health and lead author of the study.
As carbon dioxide concentrations continue to climb outside, "this increases the potential for direct impacts on human cognitive function, and it also makes it more difficult for us to successfully ventilate our indoor environments to acceptable levels," he adds.
The study was published online in Environmental Health Perspectives, a journal of the National Institute of Environmental Health Sciences.
Indoor carbon dioxide concentrations are driven by a combination of outdoor CO2, indoor breathing – as people exhale CO2 through respiration - and the ventilation rate of the building. The amount of CO2 generated on the inside depends on the number of people in the space and the type of activities they perform. Ventilation depends on the amount of CO2 in the atmosphere.
Society, in its zeal to conserve energy in the 1970s, created airtight buildings with sealed windows that cut heating and air conditioning costs, but likely contribute to making people sick, and – according to the most recent findings – poorer job performance.
"We are now at 400 ppm [parts per million] outdoors, with levels rising more than 2 ppm a year, a rate of rise that is projected to increase unless we sharply and quickly cut CO2 emissions,'' the researchers wrote in an email response to questions about the study. "If emissions are not cut, we are on a path toward carbon dioxide levels in the atmosphere of 900 ppm or more."
This is important because the scientists found impairments in cognitive function test scores at CO2 concentrations in the 950-1,000 ppm range, and significantly worse performance when CO2 rose to 1500 and 2,500 ppm. The researchers stressed that carbon dioxide levels in indoor environments, especially schools, frequently rise above 1,000 ppm.
"And, because a threshold was not identified in either study, and the dose-response is roughly linear across the concentrations tested, it is possible that impacts on decision-making performance could happen at the lower range of predicted future outdoor CO2 concentrations," they added.
The researchers from Harvard T.H. Chan School of Public Health, SUNY Upstate Medical and Syracuse University found cognitive-function test scores among office workers doubled for those working in green buildings with enhanced ventilation when compared to results from those same people working in environments simulating conventional office buildings with higher levels of carbon dioxide and other pollutants. Carbon dioxide also had significant, independent effects on cognitive function scores.
The study supports an earlier 2012 study, also published in Environmental Health Perspectives, conducted by the U.S. Department of Energy's Lawrence Berkeley National Laboratory.
"The impacts of carbon dioxide on anthropogenic (human-caused) climate change are well understood, but our findings on carbon dioxide, and those from [the] previous study...are upending previous notions that carbon dioxide concentrations are benign at levels we typically encounter indoors," says Allen.
The scientists tested workers' decision-making performance under different environmental conditions. They looked at the outdoor air ventilation rate, as well as whether carbon-based chemicals such as acetone and formaldehyde -- commonly referred to as VOCs -- that evaporate at room temperature were present.
Twenty-four participants — architects, designers, programmers, engineers, creative marketing professionals and managers — spent six full workdays, from 9 a.m. to 5 p.m., in an environmentally controlled office space, blinded to test conditions, and each was exposed to the same conditions, although the conditions varied each day.
On different days, they were exposed to indoor air quality conditions representative of conventional office buildings in the United States, with a high concentration of VOCs — similar to what many workers encounter — as well as to "green" office space conditions, with a low concentration of chemicals.
Additionally, the scientists added exposures simulating a green building with a high outdoor air ventilation rate, which they called "green+." Finally, they carried out a set of experiments that specifically looked at the independent effects of artificially elevated carbon dioxide levels independent of ventilation.
The participants underwent cognitive testing at each level of exposure using a tool known as the Strategic Management Simulation, a technology used to evaluate decision-making and productivity. "Participants are immersed in real-world scenarios and their responses to the information and challenges presented are captured," says Usha Satish, a professor of psychiatry and behavioral sciences at SUNY Upstate Medical University and a co-author of the study.
Test subjects use a computer interface to make decisions about situations that match real-world, day-to-day challenges, from relatively simple tasks to highly complex thought and action. The scores can predict real-world success as measured by income, job level, promotions and level in organizations, revealing abilities needed both for routine daily activities as well as higher level decisions people make at home and work, according to the researchers.
On average, cognitive scores were 61 percent higher during the green building days and 101 percent higher on the green+ building days than on the conventional building day, according to the study. Participants scored higher on the green+ days than the green day in 8 of 9 test areas, resulting in a 25 percent increase in scores on average when outdoor air ventilation rates were increased.
For 7 of the 9 areas of productive decision-making, the average scores decreased at each higher level of carbon dioxide. Cognitive function scores were 15 percent lower for the moderate CO2 day — about 945 parts per million, or ppm, and 50 percent lower on the day with CO2 concentrations around 1,400 ppm than on the two green+ days, according to the study.
The researchers designed the study to represent typical conditions observed in many buildings, and did not include extreme exposures or choose uncommon VOC sources.
"Parents and workers should take this very seriously," says Vivian Loftness, a professor of architecture at Carnegie Mellon University, and environmental design expert. "CO2 has been used as an indicator of serious changes in our outdoor (climate change) and indoor (poor ventilation) environments, but has not been considered a toxin for humans until this time."
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If carbon dioxide is both an indicator and a toxin, she said society must find immediate ways to increase outside air ventilation rates in occupied spaces "to keep indoor CO2 levels below 600 ppm, and make sure that the breathing air gets to each occupant," as well as take action to "stop the increase in outdoor CO2 to keep it below 600 ppm."
Historically, "carbon dioxide levels in the atmosphere were in a fairly narrow range of 180 to 280 ppm," says Joseph Romm, founding editor of Climate Progress and author of the book Climate Change: What Everyone Needs to Know. "Also, during that time, most people spent most of their time outdoors or in enclosures that were not tightly sealed."
Today, however in " the places where most people work and live, CO2 concentrations are considerably higher than outdoors," he added.
Reducing the indoor levels of carbon dioxide is achievable "by [adding] trees and greenspace, the great consumers of CO2, and massive energy conservation — insulation, shade, daylight, natural ventilation to minimize power plant demands," Loftness says.
Dr. Jennifer Lowry, chief of the toxicology section of Children's Mercy Hospital in Kansas City, Missouri, and chairwoman of the American Academy of Pediatrics Council on Environmental Health, agreed, adding: "This study shows the effects of climate change on a much smaller scale."
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Study author Allen says that actions taken now could "enhance indoor environmental quality and benefit human health, well-being and productivity," adding: "This is all within reach."
Otherwise, as the scientists wrote in their opinion piece: "From a global climate change perspective, these findings...suggest that the increased levels of CO2 that humans could be routinely exposed to by century's end could have impacts on decision-making performance and consequent effects on productivity for everyone on the planet."
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