April 29, 2026, 3:02 pm | Read time: 5 minutes
More CO₂ in the atmosphere is primarily known as a climate issue. However, Australian scientists asked a different question: Does the increase in carbon dioxide also leave measurable traces in human blood? Their research findings indicate that a critical blood value for the gas could reach its critical threshold within a few decades if current trends continue.
When the Air Becomes Thinner to Breathe
According to the report “State of the Global Climate 2025,” the CO₂ content in the air is at its highest level in two million years.1 Humans originally evolved in an atmosphere with a CO₂ content of about 280 to 300 parts per million (ppm). However, scientists from Curtin University and the Australian National University point out that the average annual increase over the last decade was about 2.6 ppm per year, with an increase of 3.5 ppm recorded for 2024. But what impact does it have on human health when the air we breathe changes?
As Carbon Dioxide Rises in Blood, So Does Bicarbonate
The authors’ basic idea is: If people inhale slightly more carbon dioxide over the years, it could show up in blood values. Carbon dioxide is converted in the body into bicarbonate, which plays a significant role in stabilizing the acid-base balance. As carbon dioxide rises in the blood, so does bicarbonate.
So far, there is little data on how lifelong exposure to increased CO₂ could affect humans. The authors wanted to examine whether long-term trends could already be identified in large population data.
Analysis of Population Data
The study’s data comes from NHANES, a large, representative health and nutrition study in the U.S. Since 1999, ongoing interviews, physical examinations, and laboratory analyses have been conducted.2
For this analysis, the authors used NHANES data from 1999 to 2020. These included datasets from 7,000 individuals across the entire age range from birth to over 80 years. For each survey cycle (every two years), serum values for bicarbonate, calcium, and phosphorus were taken and averaged for each survey period.
The authors compared these averages with atmospheric CO₂ measurements from the Mauna Loa Observatory in Hawaii. Based on this, they calculated temporal trends and estimated when the observed trends could mathematically reach the currently accepted limits of healthy blood ranges.
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Blood Values Could Become Critical in a Few Decades
Average bicarbonate values increased by about seven percent during the study period. At the same time, average calcium values decreased by two percent and phosphorus values by seven percent. Calcium and phosphorus are also involved in the acid-base balance, buffering acids.
According to the authors, these changes paralleled the increase in atmospheric CO₂ over the same period. They cite a healthy bicarbonate upper limit for venous blood of up to 30 milliequivalents per liter (mEq/L). Assuming a linear trend and an annual increase of about 0.34 percent, this value would be reached mathematically in 2076. For phosphorus, the lower limits would be reached in 2085, and for calcium in 2099.
Co-author Dr. Phil Bierwirth, a retired environmental geoscientist, emphasizes in a press release: “I truly believe that what we are observing is due to our bodies not adapting. It seems we are adapted to a certain CO₂ level in the air, which may now be exceeded.” He adds, “The normal range maintains a delicate balance between the CO₂ concentration in the air, our blood pH, our breathing rate, and the bicarbonate level in the blood.”3
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What This Could Mean for Health
Initially, author and associate professor Alexander Larcombe reassures: “We are not saying that people will suddenly become ill when we exceed a certain threshold.” However, “This suggests that there could be gradual physiological changes at the population level, and we should keep this in mind in future climate policy.”
If the observed trends are indeed related to a long-term increase in CO₂ exposure, the health consequences could be far-reaching. More carbon dioxide and bicarbonate in the body could long-term affect processes important for acid-base balance, kidneys, blood vessels, the nervous system, and protein function. The authors discuss, among other things, an increase in oxidative stress, i.e., cell-damaging chemical reactions, disruptions in protein folding in cells, possible tissue calcifications, as well as cognitive impairments and anxiety reactions.
Decreasing calcium and phosphorus values are also relevant because both substances are indispensable for bones, muscles, nerves, heart rhythm, energy production, and oxygen transport. Too low values can, among other things, promote muscle cramps, fatigue, heart rhythm disturbances, and disruptions of important cell functions.
However, it is important to note: This NHANES analysis did not examine the increase in specific disease patterns but describes blood trends that the authors believe could be of health concern.
Study Assessment and Conclusion
The study is an important warning signal that climate change could affect human health more extensively than previously known. Nevertheless, the authors emphasize that these are estimates. The observational study design only provides indications and cannot prove causality between rising CO₂ and changing blood values. Other influences could also play a role, such as changes in diet, medication use, or indoor air.
Still, the study is relevant because it addresses a topic that has been little studied so far. The findings are particularly relevant for children and adolescents, as their still-developing bodies will be exposed to the rising CO₂ levels the longest.
Dr. Bierwirth warns: “Since the CO₂ level in the air is now higher than humans have ever experienced, it seems to be accumulating in our bodies. We may never adapt in such a way that it is crucial to limit the CO₂ level in the atmosphere.”