Document ID: ./input/supremecourt_opinions/opinions/06pdf/05-1120.pdf
Page Number: 5

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

5 

Syllabus 

otherwise-unambiguous  statute,  EPA  identifies  nothing  suggesting
that  Congress  meant  to  curtail  EPA’s  power  to  treat  greenhouse 
gases as air pollutants.  The Court has no difficulty reconciling Con-
gress’  various  efforts  to  promote  interagency  collaboration  and  re-
search  to  better  understand  climate  change  with  the  agency’s  pre-
existing  mandate  to  regulate  “any  air  pollutant”  that  may  endanger 
the public welfare.  FDA v. Brown & Williamson Tobacco Corp., 529 
U. S. 120, 133, distinguished.  Also unpersuasive is EPA’s argument
that  its  regulation  of  motor-vehicle  carbon  dioxide  emissions  would 
require it to tighten mileage standards, a job (according to EPA) that
Congress  has  assigned  to  the  Department  of  Transportation.    The 
fact  that  DOT’s  mandate  to  promote  energy  efficiency  by  setting
mileage  standards  may  overlap  with  EPA’s  environmental  responsi-
bilities in no way licenses EPA to shirk its duty to protect the public
“health” and “welfare,” §7521(a)(1).  Pp. 25–30.

4. EPA’s alternative basis for its decision—that even if it has statu-
tory authority to regulate greenhouse gases, it would be unwise to do 
so at this time—rests on reasoning  divorced from the statutory text. 
While  the  statute  conditions  EPA  action  on  its  formation  of  a  “judg-
ment,”  that  judgment  must  relate  to  whether  an  air  pollutant
“cause[s],  or  contribute[s]  to,  air  pollution  which  may  reasonably  be 
anticipated to endanger public health or welfare.”  §7601(a)(1). Under 
the Act’s clear terms, EPA can avoid promulgating regulations only if 
it  determines  that  greenhouse  gases  do  not  contribute  to  climate
change  or  if  it  provides  some  reasonable  explanation  as  to  why  it
cannot  or  will  not  exercise  its  discretion  to  determine  whether  they 
do.  It has refused to do so, offering instead a laundry list of reasons 
not  to  regulate,  including  the  existence  of  voluntary  Executive 
Branch  programs  providing  a  response  to  global  warming  and  im-
pairment  of  the  President’s  ability  to  negotiate  with  developing  na-
tions to reduce emissions.  These policy judgments have nothing to do 
with whether greenhouse gas emissions contribute to climate change 
and do not amount to a reasoned justification for declining to form a
scientific  judgment.    Nor  can  EPA  avoid  its  statutory  obligation  by
noting  the  uncertainty  surrounding  various  features  of  climate 
change and concluding that it would therefore be better not to regu-
late  at  this  time.    If  the  scientific  uncertainty  is  so  profound  that  it 
precludes  EPA  from  making  a  reasoned  judgment,  it  must  say  so. 
The statutory question is whether sufficient information exists for it
to  make  an  endangerment  finding.    Instead,  EPA  rejected  the  rule-
making  petition  based  on  impermissible  considerations.    Its  action 
was  therefore  “arbitrary,  capricious,  or  otherwise  not  in  accordance
with law,” §7607(d)(9).  On remand,  EPA must ground its reasons for 
action or inaction in the statute.  Pp. 30–32.