TL: When Congress passed the Environmental Protection Act, they claimed authority under the Commerce Clause, claiming to find that air pollution has a "substantial effect on interstate commerce".
Many of the enabling statutes upon which the EPA relies, (such as the ESA) cite treaties for their authority.
Congress can not do by treaty what it is not authorized to do absent the treaty. All the powers the federal government has are given to them by the States. Congress cannot negotiate with foreign governments to acquire power, because no foreign government has the authority to grant it any power. Only the States can do that.