Climate Science Myths And Misconceptions – Post #6 On Carbon Dioxide As A Pollutant

I have posted a number of times with respect to whether atmospheric concentrations of CO2 are a pollutant; e.g. see

New Plans To Regulate CO2 As A Pollutant

I want to discuss this further in order to expose a misconception on this issue.  

Misconception #6:  Carbon Dioxide Is In The Same Group As The EPA Criteria Pollutants.

As I wrote in my post

Is CO2 a Pollutant?

A “pollutant” is defined as:

“a harmful chemical or waste material discharged into the water or atmosphere.”

To “pollute” is to:

“make unclean, impure, or corrupt; defile; contaminate; dirty.”

The American Meteorological Society’s Glossary lists the definition as:

air pollutionThe presence of substances in the atmosphere, particularly those that do not occur naturally. These substances are generally contaminants that substantially alter or degrade the quality of the atmosphere. The term is often used to identify undesirable substances produced by human activity, that is, anthropogenic air pollution. Air pollution usually designates the collection of substances that adversely affects human health, animals, and plants; deteriorates structures; interferes with commerce; or interferes with the enjoyment of life. Compare airborne particulates, designated pollutant, particulates, criteria pollutants.

The question is: How does atmospheric carbon dioxide fit into this definition? Carbon dioxide does occur naturally, of course, and is essential to life on Earth, as it is an essential chemical component in the photosynthesis process of plants. This is in contrast with other trace gases in the lower atmosphere such as carbon monoxide, ozone, and sulfur dioxide which have direct health and environmental effects on humans and vegetation. Indeed, when combustion is optimized, less carbon monoxide and more carbon dioxide are produced. There are no positive effects that I am aware of at any level of these pollutants in the lower atmosphere.

Thus, it is more informative to define anthropogenic inputs of carbon dioxide as a climate forcing, as was done in the 2005 National Research Council Report. This provides the recognition that carbon dioxide does not have direct health effects ….. but it does significantly affect our climate. Of course, carbon monoxide, ozone, and sulfur dioxide are also climate forcings. When these other atmospheric constituents are referred to in news articles and elsewhere, we would benefit by a distinction between an “air pollutant” and a “climate forcing” depending on the context.

The distinction between a pollutant and a human climate forcing is significant. The criteria pollutants of the Environmental Protection Agency are described in their text

“The Clean Air Act requires EPA to set National Ambient Air Quality Standards for six common air pollutants. These commonly found air pollutants (also known as “criteria pollutants”) are found all over the United States. They are particle pollution (often referred to as particulate matter), ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. These pollutants can harm your health and the environment, and cause property damage. Of the six pollutants, particle pollution and ground-level ozone are the most widespread health threats. EPA calls these pollutants “criteria” air pollutants because it regulates them by developing human health-based and/or environmentally-based criteria (science-based guidelines) for setting permissible levels. The set of limits based on human health is called primary standards. Another set of limits intended to prevent environmental and property damage is called secondary standards.


“Exposure to these pollutants is associated with numerous effects on human health, including increased respiratory symptoms, hospitalization for heart or lung diseases, and even premature death. “

The distinction between these criteria atmospheric pollutants and atmospheric carbon dioxide is that the criteria pollutants have NO positive benefits. In contrast, CO2 does have positive benefits to vegetation since plants use added CO2 to grow. While there can be undesirable effects (such as certain vegetation being better able to utilize added CO2) as well as climate effects, the fact that CO2 does have positive effects for some situations makes it different from (tropospheric] ozone, particulate matter, carbon monoxide, nitrogen oxides, sulfur dioxide and lead.


Human additions of carbon dioxide is NOT  in the same group as the EPA criteria pollutants. The criteria pollutants have NO positive benefits. Added CO2, while it may have negative climate effects, also has positive benefits [as do all of the climate forcings].

For the EPA to regulate CO2 as a pollutant would be a significant expansion of the definition of what is a pollutant.

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