By Laura Paddison, CNN
(CNN) — As humans burn fossil fuels and pump carbon dioxide into the atmosphere, we are heating up the planet. But there is another alarming impact of this climate pollution: it may be changing the chemistry of our blood.
When respiratory physiologist Alex Larcombe was approached by a colleague a few years ago suggesting he look at the impacts of increasing carbon dioxide levels on the human body, he was skeptical. “I thought: ‘This sounds weird’,” said Larcombe, who is head of respiratory environmental health at The Kids Research Institute Australia.
But he decided to start digging anyway, and what he found is deeply concerning.
Larcombe and his colleague Philip Bierwith, emeritus research associate at Australian National University, analyzed more than two decades of US health data and discovered shifts in people’s blood chemistry that appear to mirror the rise of atmospheric carbon dioxide.
The scientists used the US National Health and Nutrition Examination Survey, which collected a slew of health information from roughly 7,000 Americans every two years between 1999 and 2020. It’s “the most comprehensive (dataset) by far in terms of blood chemistry,” Larcombe said.
They were looking for markers in the blood that are intricately linked with how much carbon dioxide people breathe in.
Humans evolved in an atmosphere where carbon dioxide remained fairly steady, at around 300 parts per million, or ppm. But burning fossil fuels has caused levels soar to more than 420 ppm today — higher than any point in human history.
As atmospheric carbon dioxide increases, humans have no option but to breathe in more of it, which increases blood acidity. The body has ways to buffer this, including the kidneys producing and retaining more bicarbonate, which plays a key role in controlling blood acidity.
Average blood bicarbonate levels have increased by 7% since 1999, closely tracking the rise of in atmospheric carbon dioxide over the same period, according to the study, published last month in the journal Air Quality, Atmosphere and Health.
If these trends continue, bicarbonate in human blood could “reach unhealthy levels” within the next 50 years, the study concluded.
The scientists also looked at levels of calcium and phosphorus. One of the ways the body deals with blood being a little acidic is for bones to absorb some of the excess carbon dioxide and lock it away as calcium carbonate and calcium phosphate. The kidneys can also become less efficient at holding onto calcium.
Over time, circulating levels of both can drift downward, which is what the research found. Blood calcium levels decreased by 2% and phosphorus levels by around 7% over the same period.
If these drops continue, calcium and phosphorus levels could fall below healthy levels by the end of the century. These are “permanent and growing changes in human blood chemistry,” the study notes.
While the evidence suggests a link between rising carbon dioxide and shifts in blood chemistry, the authors caution more work is needed to confirm it.
The study did not take into account other potential influencing factors including people’s diets, medications, kidney function, rates of obesity or the amount of time people spend indoors, where CO2 levels tend to be higher.
“We can’t say for certain that these changes that we’re seeing are 100% due to climate change,” Larcombe said. But if the findings hold up, he added, it’s more evidence that we need to view rising carbon dioxide pollution not just as an environmental problem but also a long-term public health issue.
The big question is exactly how humans will be affected by blood chemistry changes. It turns out this isn’t easy to answer, not least because there is so little research in this area.
Some studies suggest our bodies will be able to handle increases in carbon dioxide without negative impacts, even under worst-case global warming scenarios, by breathing more and increasing bicarbonate production.
But Larcombe said this argument doesn’t consider the longer-term implications of exposures over a person’s lifetime. There’s a growing body of research on animals which points to measurable impacts, including neural damage and changes in heart rate, the study notes.
In humans, shorter-term exposure to carbon dioxide concentrations typically found indoors has been linked to reduced cognitive and decision-making abilities.
“There’s just these extra little bits of evidence piling up and piling up that show that there is potentially something going on here,” Larcombe said. He is particularly concerned about potential impacts on children, who will experience the longest cumulative exposure.
Kristie Ebi, a professor of global health at the University of Washington who was not involved in the study, said “this issue is raised every few years, so is not new,” but there has been limited follow up from previous studies. She said the human studies the report cites suggest that even at higher levels of carbon dioxide than currently projected, there would not be “overt health impacts,” although, she added, “that would not rule out consequences for particularly vulnerable groups.”
“It’s still very early days,” Larcombe said, and much more research is needed, but as humans continue to ratchet up carbon dioxide levels, it’s increasingly important to understand the health impacts.
The message of this study is “not that we’re all going to die and it’s catastrophically bad,” Larcombe said, it’s “there’s something going on, and we want to explore it more.”
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