Document ID: ./input/supremecourt_opinions/opinions/06pdf/05-1120.pdf
Page Number: 15.0

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

9 

Opinion of the Court 

jurisdiction  over  an  “industry  constituting  a  significant
portion of the American economy,” ibid. 

EPA reasoned that climate change had its own “political
history”:  Congress  designed  the  original  Clean  Air  Act  to 
address  local  air  pollutants  rather  than  a  substance  that 
“is  fairly  consistent  in  its  concentration  throughout  the 
world’s  atmosphere,”  68  Fed.  Reg.  52927  (emphasis
added); declined in 1990 to enact proposed amendments to 
force  EPA  to  set  carbon  dioxide  emission  standards  for 
motor  vehicles,  ibid.  (citing  H. R.  5966,  101st  Cong.,  2d
Sess.  (1990));  and  addressed  global  climate  change  in
other  legislation,  68  Fed.  Reg.  52927.    Because  of  this 
political  history,  and  because  imposing  emission  limita-
tions  on  greenhouse  gases  would  have  even  greater  eco-
nomic and political repercussions than regulating tobacco, 
EPA was persuaded that it lacked the power to do so.  Id., 
at 52928.  In essence, EPA concluded that climate change
was  so  important  that  unless  Congress  spoke  with  exact-
ing  specificity,  it  could  not  have  meant  the  agency  to
address it. 

Having  reached  that  conclusion,  EPA  believed  it  fol-
lowed  that  greenhouse  gases  cannot  be  “air  pollutants” 
within the meaning of the Act.  See ibid. (“It follows from
this  conclusion,  that  [greenhouse  gases],  as  such,  are  not 
air  pollutants  under  the  [Clean  Air  Act’s]  regulatory  pro-
visions  . . .”).    The  agency  bolstered  this  conclusion  by
explaining that if carbon dioxide were an air pollutant, the
only feasible method of reducing tailpipe emissions would 
be  to  improve  fuel  economy.  But  because  Congress  has
already  created  detailed  mandatory  fuel  economy  stan-
dards  subject  to  Department  of  Transportation  (DOT)
administration, the agency concluded that EPA regulation
would either conflict with those standards or be superflu-
ous.  Id., at 52929. 

Even  assuming  that  it  had  authority  over  greenhouse
gases, EPA explained in detail why it would refuse to exer-