I could be totally wrong, but my impression is that at the time of the EPA’s creation, the model of pollution that it was designed to prevent was based on more or less directly harmful contamination: litter, mercury, smog, that kind of thing.
I don’t think (and again, this is only an impression) that they saw the EPA as addressing global CO2 emissions.
Your impression is certainly consistent with the major environmental legislation that gave the EPA its teeth: we have a Clean Air Act and we have a Clear Water Act. We do not have a Carbon-free Act from the same time period empowering the EPA to significantly reduce greenhouse gas emissions.
I don’t think (and again, this is only an impression) that they saw the EPA as addressing global CO2 emissions.