Apart from being clear from the individual statutory provisions, that’s the premise of the statute as a whole. The whole idea was that the EPA could limit emissions to the point that existing point sources could go out and buy equipment to meet the emissions criteria. The statute thus talks about BACT versus RACT and LEAR and whatnot. (I took a bunch of classes in environmental law in law school.)
If you read “system” to be a nonce word that can refer to any possible measure, then the statute makes no sense. The EPA could just pick an arbitrary emissions limit, and demand industry-level restructuring to hit that limit. That’s exactly what Congress was trying to avoid by imposing that requirement.
The statute as a whole clearly delineates between when it means to limit authority to technological systems of control. Elsewhere in different provisions, Congress declined to give the EPA broad authority as it does in 111, using phrasing like
"reflect the greatest degree of emission reduction achievable through the application of technology."
"best available retrofit technology"
"best available control technology"
"maximum achievable control technology"
Congress clearly was conscious of the difference between technological systems and more general ones, and it declined to limit the EPA's authority here to technological systems.
But the fact that those other things are all emissions control technologies strongly suggests that “system of emissions reduction” is referring to a some kind of emissions control technology, not a wholesale change in the operation of the industry.
If a statute addressed SVN, git, Mercurial, and CVS, and then had a catch all referring to “system for version control,” how would you read the meaning of the latter term?
Look at it this way. Wouldn’t it be odd for Congress to go to all the trouble of enumerating all these levels of emissions control technologies that apply in different situations (new sources versus old sources) and then have this catch-all provision that gives the EPA sweeping powers far beyond unrelated to emissions control technologies?
So the Majority asserts. The law, however, specifies nothing of the sort and intentionally uses broad phrasing.
The plain meaning of "system of emissions reduction" is "a set of measures that work together to reduce emissions" (as the EPA itself points out). And this is consistent with usage elsewhere in the Clean Air Act: in it, Congress refers to a cap-and-trade setup as an "emission allocation and transfer system." Systems clearly can be things that aren't just control technology.
The Majority is inventing an arbitrary and unsupported narrow definition of system for ideological reasons.