Document ID: ./input/supremecourt_opinions/opinions/06pdf/05-1120.pdf
Page Number: 31

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

25 

Opinion of the Court 

ties,  including  a  public  explanation.”    Id.,  at  4;  see  also  5 
U. S. C.  §555(e).    They  moreover  arise  out  of  denials  of 
petitions  for  rulemaking  which  (at  least  in  the  circum-
stances  here)  the  affected  party  had  an  undoubted  proce-
dural right to file in the first instance.  Refusals to prom-
ulgate rules are thus susceptible to judicial review, though
such  review  is  “extremely  limited”  and  “highly  deferen-
tial.”  National  Customs  Brokers  &  Forwarders  Assn  of 
America,  Inc.  v.  United  States,  883  F.  2d  93,  96  (CADC 
1989).

EPA concluded in its denial of the petition for rulemak-
ing  that  it  lacked  authority  under  42  U. S. C.  §7521(a)(1) 
to  regulate  new  vehicle  emissions  because  carbon  dioxide 
is not an “air pollutant” as that term is defined in §7602. 
In  the  alternative,  it  concluded  that  even  if  it  possessed
authority,  it  would  decline  to  do  so  because  regulation 
would  conflict  with  other  administration  priorities.    As 
discussed  earlier,  the  Clean  Air  Act  expressly  permits 
review of such an action.  §7607(b)(1).  We therefore “may
reverse  any  such  action  found  to  be  . . .  arbitrary,  capri-
cious,  an  abuse  of  discretion,  or  otherwise  not  in  accor-
dance with law.”  §7607(d)(9). 

VI 
On the merits, the first question is whether §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.  We  have  little  trouble  concluding  that  it 
does.  In relevant part, §202(a)(1) provides that EPA “shall
by  regulation  prescribe  . . .  standards  applicable  to  the 
emission  of  any  air  pollutant  from  any  class  or  classes  of
new motor vehicles or new motor vehicle engines, which in 
[the Administrator’s] judgment cause, or contribute to, air
pollution  which  may  reasonably  be  anticipated  to  endan-
ger  public  health  or  welfare.”    42  U. S. C.  §7521(a)(1).