Document ID: ./input/supremecourt_opinions/opinions/06pdf/05-1120.pdf
Page Number: 64

Cite as:  549 U. S. ____ (2007) 

11 

SCALIA, J., dissenting 

Evidently, the Court defers only to those reasonable inter-
pretations that it favors. 

B 
Using (as we ought to) EPA’s interpretation of the defi-
nition of “air pollutant,” we must next determine whether
greenhouse  gases  are  “agent[s]”  of  “air  pollution.”    If  so, 
the statute would authorize regulation; if not, EPA would 
lack authority.

Unlike  “air  pollutants,”  the  term  “air  pollution”  is  not
itself defined by the CAA; thus, once again we must accept
EPA’s interpretation of that ambiguous term, provided its
interpretation  is  a  “permissible  construction  of  the  stat-
ute.”  Chevron, 467 U. S., at 843.  In this case, the petition
for  rulemaking  asked  EPA  for  “regulation  of  [greenhouse 
gas]  emissions  from  motor  vehicles  to  reduce  the  risk  of
global  climate  change.”  68  Fed.  Reg.  52925.  Thus,  in 
deciding whether it had authority to regulate, EPA had to 
determine whether the concentration of greenhouse gases 
assertedly  responsible  for  “global  climate  change”  quali-
fies as “air pollution.”  EPA began with the commonsense 
observation  that  the  “[p]roblems  associated  with  atmos-
pheric  concentrations  of  CO2,”  id.,  at  52927,  bear  little 
resemblance  to  what  would  naturally  be  termed  “air 
pollution”: 

“EPA’s  prior  use  of  the  CAA’s  general  regulatory 
provisions  provides  an  important  context.    Since  the 
inception of the Act, EPA has used these provisions to
address air pollution problems that occur primarily at 
ground level or near the surface of the earth.  For ex-
ample,  national  ambient  air  quality  standards 
(NAAQS)  established under  CAA  section  109  address 
concentrations  of  substances  in  the  ambient  air  and 
the related public health and welfare problems.  This 
has meant setting NAAQS for concentrations of ozone, 
carbon  monoxide,  particulate  matter  and  other  sub-