Once upon a time, environmentalists concentrated on real pollutants, i.e., stuff that should not be in the environment because it makes you sick. The only solution was more government control and higher taxes.
Then, the Soviet Union fell and took the Iron Curtain with it. Suddenly it became obvious to everyone that the worst environmental hell holes on Earth were all located in countries with the most government control.
Meanwhile, as free market economies became more wealthy they cleaned up their envirnoments. A simple combination of private property ownership and basic Maslow's hierarchy of needs. Once you no longer have to worry every day about feeding and housing your family you can start to look at cleaning up your property.
So what were environmentalists to do? Focus on carbon dioxide, something that affluent capitalist countries produce more of per capita than poor socialist countries, simply by virtue of the fact that they produce and consume more energy while producing more wealth for all of their citizens.
So what if carbon dioxide is a natural trace gas that is essential to the existence of all life on Earth? So what if the only observed effect that the production of carbon dioxide has is that it makes plants healthier and the world greener?
"It causes the world to get colder ... I mean it causes the world to get warmer ... I mean it changes the climate somehow dammit!" The only solution is more government control and higher taxes.
According to legislation, there are ONLY 5 criteria pollutants; NOx, SOx, VOC, CO and PM10.
All others were created by the DC bureaucracy and never...I repeat...never agreed to by congress.