More than five million people will die from a frightening cause - breathing.
Do you sometimes find yourself losing focus on the job? Is your thinking a little fuzzy? It could be something in the air - and you and your co-workers may be the source.
We all know that excess carbon dioxide in the atmosphere is bad. It's a greenhouse gas that contributes to global warming, though it has no immediate harmful effects on people in concentrations that occur outdoors. Until recently, experts believed that indoor carbon dioxide - which is emitted, for example, when people exhale - also was harmless except at extremely high levels of 5000 parts per million (ppm) or more.
New research, however, has prompted scientists to rethink this assumption.
Two studies, one published in 2012 and another last year, suggest that indoor exposure to carbon dioxide can impair performance and decision-making. Although the research focused on workers, the findings pose troubling questions for people in many indoor environments, including schools even homes.
"We spend 90 per cent of our time indoors," says Joseph Allen, an assistant professor of exposure assessment science at the Harvard T.H. Chan School of Public Health, lead author of the most recent study. "To get a sense of this, multiply your age by 0.9. That's how many years you have spent indoors."
Until now, research used CO2 measurements as a rough indicator of overall ventilation in buildings. Low ventilation rates allow concentrations of many pollutants - including CO2 - to build up, which experts have blamed for illnesses. This new research, however, suggests that even carbon dioxide may be causing problems.
"Does this mean that kids in a crowded and poorly ventilated classroom have impaired decision-making? Does it mean that kids taking a high-stakes test might be impaired? We don't know," says Mark Mendell, one of the authors of the 2012 study, which was conducted by the Department of Energy's Lawrence Berkeley National Laboratory. "But the results for the first time raise this question."
The Berkeley Lab scientists decided to conduct their study after coming across two small Hungarian studies suggesting that indoor CO2 was harmful at levels lower than 5000 ppm.
We found astonishing, unbelievable effects with CO2 levels that were not that high.
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On nine scales of decision-making performance, participants in the Berkeley study showed significant reductions on six scales at CO2 levels of 1000 ppm and large reductions on seven at 2500 ppm. The most dramatic declines in performance, in which subjects were rated as "dysfunctional", were for taking initiative and thinking strategically.
The Berkeley researchers, initially sceptical of the Hungarian studies, were flabbergasted by their findings. "We found astonishing, unbelievable effects with CO2 levels that were not that high," Mendell says. "Our study suggested that even at 1000 ppm there were some adverse effects on decision-making, and 2500 produced 'dysfunctional' performance."
Outdoor concentrations of CO2 in the air are around 400 ppm. Building operators have long tried to keep levels below 1000 - as an indication of adequate general ventilation, not because they had concerns about CO2 itself. But concentrations often exceed that, especially in crowded rooms with poor ventilation, Mendell says. Indoor levels can reach several thousand parts per million, according to the Berkeley scientists, with concentrations in classrooms occasionally exceeding 3000 ppm.
Illnesses apparently related to tight, energy-efficient new buildings received increasing attention beginning in the 1970s, with the emergence of "sick building syndrome," a cluster of symptoms that include headaches, respiratory symptoms and difficulty concentrating. Experts identified indoor air pollutants as the likely source, but they didn't suspect that carbon dioxide was part of the problem.
The Harvard study, which involved researchers from SUNY Upstate Medical Centre and Syracuse University, confirmed the 2012 results.
Twenty-four participants - architects, designers, programmers, engineers, creative marketing professionals and managers - spent six full workdays in an environmentally controlled office space, blinded to test conditions. All were exposed to the same conditions which varied each day.
On average, cognitive scores were 61 per cent higher on days with low concentrations of pollutants, compared with the same participants' scores when they spent time in a low-ventilation environment with elevated levels of pollutants, and 101 per cent better on days with the most ventilation.