Scientists find long-term shift in human blood chemistry tied to rising CO2
Australian researchers analyzing two decades of US health data found persistent changes in blood chemistry that track rising atmospheric CO2, a trend they say could be particularly significant for children and teenagers.
Researchers from The Kids Research Institute Australia, Curtin University and The Australian National University published a study in Air Quality, Atmosphere and Health examining more than 20 years of US population health data. The team drew on blood test results from roughly 7,000 people collected every two years between 1999 and 2020 through the US National Health and Nutrition Examination Survey (NHANES).
A gradual chemical shift
The analysis found that average serum bicarbonate levels have risen by about 7 percent since 1999. Bicarbonate is closely linked to the amount of carbon dioxide carried in the blood. Over the same period, average calcium and phosphorus levels declined. These shifts occurred as atmospheric CO2 rose from about 369 parts per million in 2000 to more than 420 ppm today.
Associate Professor Alexander Larcombe said the pattern suggests the human body may already be adjusting to changes in atmospheric composition. Bicarbonate plays a key role in maintaining the body's acid-base balance — as CO2 levels rise, the body retains more bicarbonate to keep blood pH stable.
Possible long-term effects
Modeling by the researchers indicates that if current trends continue, average bicarbonate levels could approach the upper end of today's healthy range within about 50 years, while calcium and phosphorus levels could drop toward the lower end of their healthy ranges later this century.
Humans evolved under atmospheric CO2 concentrations of roughly 280 to 300 ppm. Over the past decade, CO2 has risen by an average of about 2.6 ppm annually, with 2024 alone seeing an increase of 3.5 ppm.
Co-author Dr Phil Bierwirth, a retired environmental geoscientist, noted that the study does not prove direct causation, but said the consistency of the trend across a large population is notable. He suggested the changes may reflect the body's inability to adapt to CO2 levels beyond what humans historically experienced.
The researchers stressed there is no evidence of sudden illness tied to any specific threshold, but said the findings point to gradual physiological changes at a population level that should be tracked alongside atmospheric CO2 as part of future climate and public health policy.
