Is carbon dioxide a pollutant?

On 9th January 2025, nine people were hospitalised due to carbon monoxide poisoning in Hobart, Australia. Authorities say the incident was caused by inadequate ventilation of petrol fumes while cutting concrete.

And in November 2024, three people were hospitalised with carbon monoxide poisoning at an automotive workshop in Hobart. The workshop had a “low air exchange” and could not remove all fumes that would build up. The fumes could travel through an open door into the student lounge, and then an office area.

Carbon monoxide (CO) is a colorless, odorless gas. It results from incomplete oxidation of carbon in combustion processes. And Carbon dioxide (CO2) is also a colorless, odorless product of carbon combustion. It is a part of the air we breathe and the earth’s vegetation depends on it.

In the 1980s I worked for the State Pollution Control Commission in NSW, Australia – a state environmental regulatory authority. The air pollutants that we used to monitor included, carbon monoxide, sulfur dioxide, ozone, hydrocarbons, oxides of nitrogen, and suspended particulate matter.

So, carbon monoxide is definitely an air pollutant – too much acts like poison. But the view that CO2 is a pollutant is a recent phenomenon – it was not a pollutant in the 1980s.

Indoor air quality

Carbon dioxide (CO2) monitoring is used to check the safety of indoor air. It indicates if additional ventilation is required to reduce the concentration of air pollutants. Generally, levels below 1000 ppm are considered acceptable for most indoor spaces, while consistently exceeding this threshold indicates inadequate ventilation.

In Australia, outdoor CO2 levels are around 420ppm (0.04% CO2 in air by volume). Higher concentrations of CO2 can be found indoors if there is insufficient ventilation (mixing with outside air). These can impact human health:
– > 1,000 ppm (0.1%), drowsiness.
– >2,000 ppm (0.2%), headaches, fatigue, stagnant, stuffiness, poor concentration, loss of focus, increased heart rate, nausea.
– > 50,000 (5%), toxicity due to oxygen deprivation.

In indoor settings, a CO2 concentration of up to 1,000 ppm is considered acceptable. And the American Conference of Governmental Industrial Hygienists (ACGIH) recommends an 8-hour time-weighted average Threshold Limit Value (TLV) of 5,000 ppm.

Fire suppression

CO2 is used to extinguish fires by displacing oxygen and suppressing combustion. The range of CO2 concentrations needed to extinguish various fuel fires is between 34% and 72% by volume. At this level, oxygen is reduced to below 15%, which is insufficient to support most fires. It’s important to note that these high concentrations of CO2 pose significant risks to human health. At concentrations between 17% and 30%, CO2 can rapidly cause unconsciousness, coma, and death. Therefore, to prevent asphyxiation, areas protected by CO2 fire suppression systems must be immediately evacuated when the system is activated.

When CO2 became a pollutant

In the 1990s I worked for the Electricity Commission of NSW (renamed Pacific Power in 1995), in Australia – a state-owned electricity power generator. I was in the Environmental Services Branch, which managed environmental management systems, licencing, compliance, and monitoring. During this period, we trained staff of coal-burning power plants on the enhanced greenhouse effect. But we didn’t realize that this would grow to be a major environmental issue in the 21st century.

In 2009, the US Environmental Protection Agency declared that CO2 was a pollutant that endangered public health or welfare. The endangerment finding was documented in; “Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act,” Final Rule, 74 FR 66496 (December 15, 2009). This finding under former President Barack Obama, is the foundation, for every climate regulation, policy, and rule that has been adopted in the United States since then.

When I helped my son to buy a car in France recently, one of the main specifications advertised was the rate of emissions of CO2! Such regulations are being used in many countries to replace internal combustion engines in vehicles with electric engines. They are electric vehicle (EV) mandates and part of the push for net-zero human carbon emissions, which threatens people’s freedom, economy and way of life.

The new administration

The new Trump administration has issued many Executive Orders to reverse the climate change initiatives of the Biden administration. For example,
– withdrawing the US from the Paris climate agreement.
– Requiring an assessment of the legality and continuing applicability of the greenhouse gas endangerment finding. If the facts do not justify the endangerment determination they can start the process to rescind it.
– repealing multiple Biden orders regarding climate change, including guidelines for implementing climate-related provisions of the Inflation Reduction Act of 2022.

It remains to be seen how quickly Trump’s orders will take effect, as many will require the agencies to issue corresponding rules and may face legal challenges.

What does the data say?

The concentrations of CO2 measured in the atmosphere of the northern and southern hemisphere is graphed below. At Mauna Loa in Hawaii (altitude of 3400m above sea level), the CO2 increased from 315 ppm to 425 ppm in 65 years (1960 to 2025). That is a mean increase of 1.7 ppm per year. At Cape Grim in Australia (altitude of 94m above sea level) the CO2 increased from 330 ppm to 420 ppm in 50 years (1975 to 2025). That is a mean increase of 1.8 ppm per year.

Note that any measurements of CO2 that are assigned to older dates than these were not made in real-time. These means that they are probably unreliable as they depend on the assumption that the sample has been isolated and preserved for a long period of time or it is a proxy measurement (of another parameter) that makes assumptions that cannot be tested.

The real-time data show that the concentration of the CO2 in the atmosphere has no direct impact on human health or welfare– the levels are well below 1000ppm, which is safe.

But has there been any indirect impact? During the past 65 years, the earth’s population has increased from 3 billion to 8 billion, which is a growth of 5 billion people! So, humanity has flourished. Overall, there is increased life expectancy and declining infant mortality rate. So there is no obvious negative indirect impacts associated with the increasing concentration of CO2 in the atmosphere. And any impact via the enhanced Greenhouse effect is negligible.

Conclusion

There could be a debate soon in the US as to whether CO2 is a pollutant (like in 2009) or not (like in the 1980s).

But according to the real-time CO2 data measured in the atmosphere and the flourishing of humanity, it is not a pollutant.

Written, January 2025