News release

From: The Kids Research Institute Australia

Rising carbon dioxide levels are being detected within the human body, with new research warning a key blood marker for the gas could near its healthy limit within decades if current trends continue. The findings are especially relevant for children and adolescents, whose developing bodies will experience the longest cumulative exposure to rising atmospheric CO₂.

In a study published in Air Quality, Atmosphere and Health, researchers from The Kids Research Institute Australia, Curtin University and The Australian National University (ANU) analysed more than two decades of U.S. population data and found steady shifts in blood chemistry that closely track the rise in atmospheric CO₂.

Using data from the U.S. National Health and Nutrition Examination Survey (NHANES), the team examined blood results from around 7,000 people every two years between 1999 and 2020.

Average levels of serum bicarbonate – a marker closely linked to carbon dioxide in the body – have risen by approximately seven per cent since 1999. Over the same period, average calcium and phosphorus levels have declined.

These changes mirror the rise in atmospheric CO₂, which has increased from about 369 parts per million (ppm) in 2000 to more than 420 ppm today.

Author Associate Professor Alexander Larcombe said the findings suggest the human body may already be compensating for a changing atmosphere.

“What we’re seeing is a gradual shift in blood chemistry that mirrors the rise in atmospheric carbon dioxide which is driving climate change,” A/Prof Larcombe said.

Bicarbonate plays a central role in maintaining the body’s acid–base balance. When CO₂ levels rise, the body retains more bicarbonate to stabilise blood pH. Over time, however, sustained compensation may carry physiological consequences.

"If current trends continue, modelling indicates average bicarbonate levels could approach the upper limit of today’s accepted healthy range within 50 years," A/Prof Larcombe said

"Calcium and phosphorus levels could also reach the lower end of their healthy ranges later this century."

Humans evolved in an atmosphere containing roughly 280–300 ppm of CO₂. The average annual increase over the past decade has been about 2.6 ppm per year, with 2024 recording a 3.5 ppm rise.

Fellow Author Dr Phil Bierwirth, a retired environmental geoscientist who is affiliated with the ANU Emeritus Faculty, said while the study does not prove direct causation, the consistent, population-wide trends are difficult to ignore.

“I actually think that what we are seeing is because our bodies are not adapting,” Dr Bierwirth said.

“It appears we are adapted to a range of CO2 in the air that may now have been surpassed.

“The normal range maintains a delicate balance between how much CO2 is in the air, our blood pH, our breathing rate and bicarbonate levels in the blood.

“As CO2 in the air is now higher than humans have ever experienced, it appears to be building up in our bodies. Maybe we can never adapt such that it is vitally important to limit atmospheric levels of CO2.”

The researchers say the findings point to an emerging dimension of climate risk, one that extends beyond heatwaves, extreme weather and sea-level rise.

Rather than viewing rising CO₂ solely as an environmental issue, A/Prof Larcombe says it may also need to be considered a long-term public health variable requiring ongoing monitoring.

“We’re not saying people are suddenly going to become unwell when we cross a certain threshold,” he said.

“But this suggests there may be gradual physiological changes occurring at a population level, and that’s something we should be monitoring as part of future climate change policy.”

The study calls for atmospheric composition and population biomarkers to be tracked alongside traditional climate indicators to better understand how gradual environmental change may influence human biology over decades.

Reducing CO₂ emissions remains critical to limiting global warming. The researchers’ findings suggest emission reduction may also be important for safeguarding long-term human health, and that the potential physiological effects of rising CO₂ should form part of future climate policy discussions.

Click here to read the full paper in Air Quality, Atmosphere and Health

Associate Professor Larcombe is part of the Wal-yan Respiratory Research Centre, a partnership between The Kids Research Institute Australia, Perth Children’s Hospital and Perth Children’s Hospital Foundation.