Document ID: ./input/supremecourt_opinions/opinions/06pdf/05-1120.pdf
Page Number: 35

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

29 

Opinion of the Court 

tion of greenhouse gases from new motor vehicles.  Even if 
it had, Congress could not have acted against a regulatory 
“backdrop”  of disclaimers of  regulatory  authority.   Prior  to 
the  order  that  provoked  this  litigation,  EPA  had  never 
disavowed the authority to regulate greenhouse gases, and
in 1998 it in fact affirmed that it had such authority.  See 
App. 54 (Cannon memorandum).  There is no reason, much 
less a compelling reason, to accept EPA’s invitation to read
ambiguity into a clear statute. 

EPA  finally  argues  that  it  cannot  regulate  carbon  diox-
ide emissions from motor vehicles because doing so would 
require it to tighten mileage standards, a job (according to 
EPA)  that  Congress  has  assigned  to  DOT.    See  68  Fed. 
Reg.  52929.  But  that  DOT  sets  mileage  standards  in  no
way  licenses  EPA  to  shirk  its  environmental responsibili-
ties.  EPA  has  been  charged  with  protecting  the  public’s
“health” and “welfare,” 42 U. S. C. §7521(a)(1), a statutory 
obligation  wholly  independent  of  DOT’s  mandate  to  pro-
mote  energy  efficiency.  See  Energy  Policy  and  Conserva-
tion Act, §2(5), 89 Stat. 874, 42 U. S. C. §6201(5).  The two 
obligations  may  overlap,  but  there  is  no  reason  to  think 
the two agencies cannot both administer their obligations
and yet avoid inconsistency. 

While the Congresses that drafted §202(a)(1) might not 
have  appreciated  the  possibility  that  burning  fossil  fuels
could  lead  to  global  warming,  they  did  understand  that 
without regulatory flexibility, changing circumstances and 
scientific  developments  would  soon  render  the  Clean  Air 
Act obsolete.  The broad language of §202(a)(1) reflects an 
intentional  effort  to  confer  the  flexibility  necessary  to 
forestall  such  obsolescence.  See  Pennsylvania  Dept.  of 
Corrections  v.  Yeskey,  524  U. S.  206,  212  (1998)  (“[T]he
fact  that  a  statute  can  be  applied  in  situations  not  ex-
pressly  anticipated  by  Congress  does  not  demonstrate
ambiguity.    It  demonstrates  breadth”  (internal  quotation 
marks omitted)).  Because greenhouse gases fit well within