Document ID: ./input/supremecourt_opinions/opinions/21pdf/20-1530_n758.pdf
Page Number: 35.0

Cite as:  597 U. S. ____ (2022) 

29 

Opinion of the Court 

points out that the Act elsewhere uses the word “system” or 
“similar words” to describe cap-and-trade schemes or other 
sector-wide mechanisms for reducing pollution.  Ibid.  The 
Acid Rain program set out in Title IV of the Act establishes 
a  cap-and-trade  scheme  for  reducing  sulfur  dioxide  emis-
sions, which the statute refers to as an “emission allocation 
and transfer system.”  §7651(b) (emphasis added).  And Sec-
tion 110 of the NAAQS program specifies that “marketable
permits” and “auctions of emissions rights” qualify as “con-
trol measures, means, or techniques” that States may adopt 
in  their  state  implementation  plans  in  order  “to  meet  the
applicable requirements of ” a NAAQS.  §7410(a)(2)(A).  If 
the  word  “system”  or  similar  words  like  “technique”  or
“means”  can  encompass  cap-and-trade,  the  Government 
maintains, why not in Section 111? 

But just because a cap-and-trade “system” can be used to
reduce emissions does not mean that it is the kind of “sys-
tem of emission reduction” referred to in Section 111.  In-
deed,  the  Government’s  examples  demonstrate  why  it  is 
not. 

First, unlike Section 111, the Acid Rain and NAAQS pro-
grams contemplate trading systems as a means of comply-
ing with an already established emissions limit, set either 
directly  by  Congress  (as  with  Acid  Rain,  see  42  U. S. C. 
§7651c) or by reference to the safe concentration of the pol-
lutant in the ambient air (as with the NAAQS).  In Section 
111,  by  contrast,  it  is  EPA’s  job  to  come  up  with  the  cap 
itself: the “numerical limit on emissions” that States must 
apply to each source.  80 Fed. Reg. 64768.  We doubt that 
Congress directed the Agency to set an emissions cap at the 
level  “which  reflects  the  degree  of  emission  limitation 
achievable through the application of [a cap-and-trade] sys-
tem,” §7411(a)(1), for that degree is indeterminate.  It is one 
thing  for  Congress  to  authorize  regulated  sources  to  use 
trading to comply with a preset cap, or a cap that must be
based  on  some  scientific,  objective  criterion,  such  as  the