Document ID: ./input/supremecourt_opinions/opinions/21pdf/20-1530_n758.pdf
Page Number: 15.0

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

9 

Opinion of the Court 

toward their own applicable emissions caps. 

EPA explained that taking any of these steps would im-
plement  a  sector-wide  shift  in  electricity  production  from 
coal to natural gas and renewables.  Id., at 64731.  Given 
the integrated nature of the power grid, “adding electricity
to the grid from one generator will result in the instantane-
ous reduction in generation from other generators,” and “re-
ductions  in  generation  from  one  generator  lead  to  the  in-
stantaneous  increase  in  generation”  by  others. 
Id.,  at 
64769.  So coal plants, whether by reducing their own pro-
duction,  subsidizing  an  increase  in  production  by  cleaner 
sources, or both, would cause a shift toward wind, solar, and 
natural gas.

Having decided that the “best system of emission reduc-
tion . . . adequately demonstrated” was one that would re-
duce  carbon  pollution  mostly  by  moving  production  to
cleaner sources, EPA then set about determining “the de-
gree of emission limitation achievable through the applica-
tion” of that system.  42 U. S. C. §7411(a)(1).  The Agency
recognized that—given the nature of generation shifting—
it could choose from “a wide range of potential stringencies 
for  the  BSER.”  80  Fed.  Reg.  64730.  Put  differently,  in
translating the BSER into an operational emissions limit, 
EPA could choose whether to require anything from a little 
generation shifting to a great deal.  The Agency settled on
what it regarded as a “reasonable” amount of shift, which it
based on modeling of how much more electricity both natu-
ral gas and renewable sources could supply without causing 
undue cost increases or reducing the overall power supply. 
Id.,  at  64797–64811.    Based  on  these  changes,  EPA  pro-
jected that by 2030, it would be feasible to have coal provide 
27%  of  national  electricity  generation,  down  from  38%  in 
2014.  Id., at 64665, 64694; see Dept. of Energy, U. S. En-
ergy  Information  Admin.,  Monthly  Energy  Review  (May
2015),  Electricity  Net  Generation:  Electric  Power  Sector, 
p. 106 (Table 7.2b).