Document ID: ./input/supremecourt_opinions/opinions/06pdf/05-1120.pdf
Page Number: 61.0

8 

MASSACHUSETTS v. EPA 

SCALIA, J., dissenting 

GHGs. 

“Reducing the wide range of uncertainty inherent in 
current model predictions will require major advances 
in understanding and modeling of the factors that de-
termine  atmospheric  concentrations  of  greenhouse 
gases  and  aerosols,  and  the  processes  that  determine 
the  sensitivity  of  the  climate  system.”  68  Fed.  Reg.
52930. 

I simply cannot conceive of what else the Court would like
EPA to say. 

II 

A 

Even  before  reaching  its  discussion  of  the  word  “judg-
ment,” the Court makes another significant error when it
concludes that “§202(a)(1) of the Clean Air Act authorizes 
EPA to regulate greenhouse gas emissions from new motor 
vehicles  in  the  event  that  it  forms  a  ‘judgment’  that  such
emissions contribute to climate change.”  Ante, at 25 (em-
phasis added).  For such authorization, the Court relies on 
what  it  calls  “the  Clean  Air  Act’s  capacious  definition  of 
‘air pollutant.’ ”  Ante, at 30. 

“Air pollutant” is defined by the Act as “any air pollution 
agent or combination of such agents, including any physi-
cal,  chemical,  . . .  substance  or  matter  which  is  emitted 
into  or  otherwise  enters  the  ambient  air.”  42  U. S. C. 
§7602(g).  The  Court  is  correct  that  “[c]arbon  dioxide, 
methane,  nitrous  oxide,  and  hydrofluorocarbons,”  ante,  at 
26,  fit  within  the  second  half  of  that  definition:  They  are
“physical, chemical, . . . substance[s] or matter which [are]
emitted into or otherwise ente[r] the ambient air.”  But the 
Court mistakenly believes this to be the end of the analy-
sis.  In order to be an “air pollutant” under the Act’s defi-
nition,  the  “substance  or  matter  [being]  emitted  into  . . . 
the ambient air” must also meet the first half of the defini-
tion—namely, it must be an “air pollution agent or combi-