Answer: Natural CO2 is not a pollutant. Anthropogenic CO2 is a pollutant.
Too difficult to understand?
Apparently it is for at least one member of the US Supreme Court: Samuel Alito.
According to Slate, here's what Alito said this past Saturday, at a keynote speech at the Claremont Institute’s 2017 annual dinner on Saturday night:
Now, what is a pollutant? A pollutant is a subject that is harmful to human beings or to animals or to plants. Carbon dioxide is not a pollutant. Carbon dioxide is not harmful to ordinary things, to human beings, or to animals, or to plants. It’s actually needed for plant growth. All of us are exhaling carbon dioxide right now. So, if it’s a pollutant, we’re all polluting. When Congress authorized the regulation of pollutants, what it had in mind were substances like sulfur dioxide, or particulate matter—basically, soot or smoke in the air. Congress was not thinking about carbon dioxide or other greenhouse gases.This is just dumb on a couple of levels.
First, as Mark Joseph Stern at Slate points out, EPA was the defendant in Mass v EPA 2007. The EPA didn't want to regulate CO2 -- Massachusetts sued them to force them to do so, under the Clean Air Act.
It's very strange that a Supreme Court Justice would not understand the basics of such a case that appeared before his court.
Morever: let's please start specifying clearly that anthropogenic CO2 is the pollutant, not all CO2, and certainly not the natural CO2 that existed in the atmosphere before the Industrial Revolution, about 280 ppm.
That's really all you have to say: anthropogenic CO2, from our burning of fossil fuels is a pollutant -- an unwanted substance with deleterious effects -- but natural CO2, existing before the Industrial Revolution, is not.
And no, Justice Alito, human breathing do not contribute to the CO2 problem. If it did, and likewise for the respiration of all other mammals, we'd be up to our necks in CO2 and probably would not exist by now.
Please, man, learn a little science.