Document ID: ./input/supremecourt_opinions/opinions/06pdf/05-1120.pdf
Page Number: 38

32 

MASSACHUSETTS v. EPA 

Opinion of the Court 

gases  because  of  some  residual  uncertainty—which,  con-
trary  to  JUSTICE  SCALIA’s  apparent  belief,  post,  at  5–8,  is 
in fact all that it said, see 68 Fed. Reg. 52929 (“We do not 
believe . . . that it would be either effective or appropriate
for EPA to establish [greenhouse gas] standards for motor 
vehicles  at  this  time”  (emphasis  added))—is  irrelevant. 
The  statutory  question  is  whether  sufficient  information 
exists to make an endangerment finding.

In  short,  EPA  has  offered  no  reasoned  explanation  for 
its  refusal  to  decide  whether  greenhouse  gases  cause  or
contribute  to  climate  change.    Its  action  was  therefore 
“arbitrary,  capricious,  . . .  or  otherwise  not  in  accordance 
with law.” 42 U. S. C. §7607(d)(9)(A).  We need not and do 
not  reach  the  question  whether  on  remand  EPA  must 
make  an  endangerment  finding,  or  whether  policy  con-
cerns can inform EPA’s actions in the event that it makes 
such  a  finding.  Cf.  Chevron  U. S. A.  Inc.  v.  Natural  Re-
sources  Defense  Council,  Inc.,  467  U. S.  837,  843–844 
(1984).  We  hold  only  that  EPA  must  ground  its  reasons 
for action or inaction in the statute. 

VIII 
The  judgment  of  the  Court  of  Appeals  is  reversed,  and
the  case  is  remanded  for  further  proceedings  consistent
with this opinion. 

It is so ordered.