It is incredibly simple. It's a luxury that we are able to afford thanks to capitalism. Private ownership helps as well since individuals are environmentalists, not the government.
And the prez has an executive agency called the EPA to help him. By trial ands error, the state agencies also have a role in environmental law. The EPA sets the standards and each state determines how it will achieve that standard. The state submits an environmental plan to EPA and when the EPA approves a state's enviro plan, it is difficult for the enviros to sue the state.
Of course all of this is subject to judicial review and the courts hand down decisions that have the force of law. For example: In 2007 SCOTUS ruled that CO2 was a pollutant and EPA should determine the risk that CO2 posed to the nation and if need be, EPA could regulate CO2 with the Clean Air Act, which means they needed nothing from Congress.
In the coming year there will be about 10-12-15 issues before the court that you will be hearing about and CO2 is one of those issues.
Another is the Toxic Substances Control Act which was originally enacted in the 70s but was updated by Congress in 2016. Obama got a little of that implemented but Trump never gets anything done so he is way behind on his rule making. Plus, he hired someone from the chemical industry to write the rules so the lawsuits have already started flying