Rising carbon dioxide levels trap heat, causing warming, intensifying storms, increasing sea levels, acidifying oceans, inflicting all around death and destruction. Not just outside, but your body, your physiology is marked too. The changing chemistry of the atmosphere could potentially trigger chemical changes in our blood, according to a study published in the journal Air Quality, Atmosphere and Health.
As of September 15, 2026, carbon dioxide level is at 425.53 ppm; the safe level is at 350 ppm. Parts per million (ppm) expresses the concentration of a substance in a mixture.
Atmospheric carbon dioxide has risen about 12 per cent since the turn of the century, and the researchers wanted to know whether this might be impacting people’s physiology.
Researchers used the National Health and Nutrition Examination Survey (NHANES) survey for their study. The NHANES measures the health and nutrition of adults and children in the United States.
Using the NHANES that samples roughly 7,000 people every two years, the researchers looked at 1999–2020 and found three things moving consistently: bicarbonate rose, while calcium and phosphorus fell. All three population averages remain inside the accepted healthy range.
“This is a trend that parallels rising carbon dioxide, not proof that carbon dioxide caused it” the lead author Alexander Larcombe tells Hot Rock. He is an associate professor and head of Respiratory Environmental Health, The Kids Research Institute, Curtin University, Australia.
The study unveils a correlation between rising carbon dioxide levels and changing blood chemistry; it’s not an exercise in finding cause-and-effect relationship.
What the researchers found is that average blood bicarbonate levels rose by about 7 per cent in the 21 years from 1999 to 2020. By a similar proportion, CO2 levels too rose in the same period.
The three markers—bicarbonate, calcium and phosphorus—play important roles in blood chemistry. Larcombe explains the mechanism of how CO2 affects blood: CO2 dissolves in blood and forms carbonic acid; the kidneys compensate by excreting acid and generating extra bicarbonate, which is why bicarbonate is the marker we can measure. Bone is the longer-term buffer—it stores CO2 as carbonate, with calcium and phosphate drawn out of the blood into bone alongside it.
Larcombe says all three markers moved in the direction you would predict if people were carrying a slightly higher CO2 load.
“If the bicarbonate trend simply continues, the population average reaches the top of the accepted healthy range in around 50 years,” he says. He adds that whether that matters, nobody can currently say. That’s because there is no health-based standard anywhere in the world for continuous, lifelong CO2 exposure. “Every guideline we have was written for temporary exposure in people who then return to normal air.”
Whether this is cause for worry—not as of now.
As Larcombe says bicarbonate, calcium and phosphate are all on a routine blood panel. “I would discourage anyone from looking for this in their results,” he says. The study points out population shifts of a few percentage points, smaller than the normal variation between two tests on the same person on two different days.
The bottom-line: “There's no individual signal to find. If you want to act on CO2, buy a cheap indoor monitor: a stuffy bedroom often sits at 1,000–2,000 ppm, which dwarfs anything happening outdoors,” says Larcombe.
The research broadens the ramifications of CO2 loading in the atmosphere. Rising CO2 levels are seen as a climate problem rather than something that affects body directly. The researchers say that their results don’t establish that it does but they emphasise that the question needs investigating.
Larcombe says, “Specifically, track these blood markers deliberately over time and revisit ventilation standards, since indoor air is likely very important in this context.”
There's a small literature on direct CO2 effects: short-term studies say moderately enhanced levels of CO2 consistently show effects like headache, tiredness and declines in concentration.
“What is missing was anyone looking for it in humans at real-world concentrations over decades,” says Larcombe.
To find it out, they exposed mice to 890 ppm of CO2 from before conception through early life. Their tests showed altered lung structure and function, altered growth and hyperactive behaviours. Then there was analysis of NHANES data to ask whether anything comparable is detectable in people.
“I'd rather this be read as a case for looking than a case for worry. Nothing here means anyone's blood chemistry is unhealthy today,” Larcombe says.
The changes in blood chemistry could be due to one or more of the trends: people spending more time indoors, rising obesity and kidney disease, dietary changes, changes in laboratory methods.
“But CO2 is the one variable that has changed for everyone on the planet at once, with no unexposed control group anywhere, which is exactly the kind of exposure epidemiology is worst at detecting. Better to watch carefully than look away,” Larcombe says.
(This edition of Hot Rock was emailed to subscribers on Septemeber 19, 2026)
