Carbon dioxide in homes, offices, and classrooms could cut our capacity for complex, strategic thinking by 50% within 80 years, scientists warn

• By the end of the century, indoor carbon dioxide levels could climb so high that they cut human performance on complex cognitive tasks by 50%, according to scientists' calculations.
• A growing body of research indicates that high levels of carbon dioxide impair human cognition.
• Curbing carbon emissions from fossil fuels could help prevent these negative effects.
• Visit Business Insider's homepage for more stories.

The world's carbon-dioxide problem doesn't just affect the atmosphere - the gas is starting to fill our homes, schools, and offices, too.

Indoor levels of the gas are projected to climb so high, in fact, that they could cut people's ability to do complex cognitive tasks in half by the end of the century.

That prediction comes from three scientists from the University of Colorado Boulder and the University of Pennsylvania, who presented their findings last week at the annual meeting of the American Geophysical Union. The study is still under peer review but available online in the repository Earth ArXiv.

The findings show that, if global carbon dioxide (CO2) emissions continue to rise on their current trajectory, the concentration of CO2 in the air could more than double by 2100. Based on measurements of how humans function in spaces with that much CO2, the scientists warn, we could find ourselves scoring 50% lower on measures of complex thought by the end of the century.

That includes the ability to plan strategies, respond to a crisis, make decisions, and use new information to achieve a goal.

Brain function drops as carbon-dioxide levels rise

Beyond being to blame for Earth's climbing temperature, carbon dioxide also has direct impacts on the human brain.

That's bad news for office workers and schoolchildren. Americans spend about 90% of their lives indoors, where carbon-dioxide levels can build up quickly as we inhale oxygen and exhale CO2.

Researchers behind a 2015 Harvard paper had 24 people spend six full work days in a lab-controlled office space with varying levels of carbon dioxide. Each afternoon, the participants took part in a computer simulation in which they responded to an evolving real-world scenario, like managing a town as its mayor.

The software tracked the participants' cognitive ability as they went through the simulation. The results showed that as CO2 levels increased, participants consistently struggled with strategy, information use, and crisis response.

That backed up the findings of a similar study, which put 22 people in an office-like setting with different levels of carbon dioxide in the air and evaluated their performance on a set of tasks. As CO2 levels rose, participants showed significant decreases in decision-making ability.

Similar results have been found in schools. A 2015 study found that, across 140 fifth-grade classrooms in the southwestern US, poor ventilation and high CO2 levels were strongly correlated with lower math scores for students. An earlier study of 434 classrooms in Washington and Idaho found a similar relationship between CO2 levels and rates of student absence.

What's more, a 2018 study in China found that chronic exposure to some types of air pollution (apart from CO2) were linked to detrimental cognitive effects that got worse as participants grew older.

Scientists aren't yet sure what CO2 does in the brain that impairs cognitive functioning, but preliminary research suggests that breathing in too much of the gas can prevent your brain from using oxygen efficiently.

"It always comes down to the ability to get oxygen to the brain," Kris Karnauskas, a climate scientist and lead author on the new research, told Business Insider. "Hopefully this [study] will spur more investigation into the physiology of it."

Complex cognitive performance could drop 50% by 2100

Karnauskas said that when he came across the results of the 2015 Harvard study, he immediately thought about the 36.2 billion tons of carbon dioxide humans pumped into the atmosphere in 2017.

"When you talk about droughts in the Southwest or wildfires or how El Niño is going to change in the future - there's a lot of complicated dynamics between a molecule of CO2 going in the atmosphere and that outcome," he said. "This is just as simple as here we are, we're breathing CO2, and this is how people respond to it."

So Karnauskas worked with a mechanical engineer and a cognitive neuroscientist to make back-of-the-envelope calculations based on the Harvard findings and projections about rising carbon-dioxide emissions.

They created a model of a classroom full of elementary school children, with the appropriate breathing rates and room ventilation. (Karnauskas said the results would be similar for any group of people.) Then they looked at what would happen in two potential emissions scenarios projected by the Intergovernmental Panel on Climate Change (IPCC).

The results showed that in a business-as-usual scenario, in which carbon emissions continue to rise, humans would score 50% lower on measures of complex cognitive ability by 2100. For more basic cognitive measures, performance would drop about 25%.

Karnauskas emphasized, however, that these are rough calculations "to give an indication of the scale of the problem."

"As we continue to increase the outdoor carbon dioxide, we're going to keep on going along here and lower our ability to solve problems," he said. "Climate change is a problem, so it's a nasty feedback [loop] in a way."

'There's no way to solve this except to keep the CO2 low'

The US' National Institute for Occupational Safety and Health Administration considers 5,000 parts per million (ppm) to be the highest acceptable level of CO2 for a workplace.

But many studies linking increased CO2 to decreased cognitive function, including the Harvard study, used much smaller concentrations - between 1,000 and 2,500 ppm. Scientists think those levels are already common in many schools and office spaces today.

In a 2002 study, researchers tested the air in 120 Texas classrooms, and found CO2 levels above 1,000 ppm in 88% of them. In 21% of the classrooms, the concentration exceeded 3,000 ppm. In England, a 2012 study found that some primary-school classrooms had concentrations as high as 5,000 ppm.

As carbon dioxide levels rise, better ventilation won't be enough to protect us from its effects.

"There's no way to solve this except for keep the CO2 low," Karnauskas said. "You can try to increase ventilation, but you're only going to be ventilating higher-CO2 air, because it's going up outside."

A well-ventilated room starts with the same CO2 concentration as the air outside. Today, the atmospheric carbon-dioxide concentration is about 407 ppm. With people inside, a room's CO2 levels can jump to 1,000 ppm in a matter of minutes.

In the business-as-usual projection, the atmosphere would have a CO2 concentration of 930 ppm by 2100. So indoors, human breathing would take it higher from there.

But there is still time to prevent the drastic drop in human brain function that Karnauskas and his colleagues project. They also charted a more optimistic scenario outlined by the IPCC, one in which governments enact policies to severely cut carbon emissions, such as transitioning to renewable energy, sucking carbon out of the air, and expanding forests.

In that optimistic scenario, humans would retain most of their cognitive ability, both basic and complex.

"This is a whole new thing to, unfortunately, worry about, and it's a very different outcome whether we emit a lot or a little," Karnauskas said.