Document ID: ./input/supremecourt_opinions/opinions/06pdf/05-1120.pdf
Page Number: 27

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

21 

Opinion of the Court 

that any realistic possibility exists that the relief petition-
ers seek would mitigate global climate change and remedy 
their  injuries.  That  is  especially  so  because  predicted
increases  in  greenhouse  gas  emissions  from  developing 
nations,  particularly  China  and  India,  are  likely  to  offset 
any marginal domestic decrease. 

But EPA overstates its case.  Its argument rests on the 
erroneous  assumption  that  a  small  incremental  step, 
because it is incremental, can never be attacked in a fed-
eral  judicial  forum.  Yet  accepting  that  premise  would
doom most challenges to regulatory action.  Agencies, like 
legislatures, do not generally resolve massive problems in
one  fell  regulatory  swoop.    See  Williamson  v.  Lee  Optical 
of  Okla.,  Inc.,  348  U. S.  483,  489  (1955)  (“[A]  reform  may 
take  one  step  at  a  time,  addressing  itself  to  the  phase  of
the  problem  which  seems  most  acute  to  the  legislative
mind”).  They  instead  whittle  away  at  them  over  time, 
refining their preferred approach as circumstances change
and as they develop a more-nuanced understanding of how 
best to proceed.  Cf. SEC v. Chenery Corp., 332 U. S. 194, 
202 (1947) (“Some principles must await their own devel-
opment, while others must be adjusted to meet particular, 
unforeseeable  situations”).    That  a  first  step  might  be 
tentative does not by itself support the notion that federal 
courts  lack  jurisdiction  to  determine  whether  that  step 
conforms to law. 

And reducing domestic automobile emissions is hardly a 
tentative  step.  Even  leaving  aside  the  other  greenhouse 
gases,  the  United  States  transportation  sector  emits  an 
enormous  quantity  of  carbon  dioxide  into  the  atmos-
phere—according  to  the  MacCracken  affidavit,  more  than 
1.7 billion metric tons in 1999 alone.  ¶30, Stdg. App. 219. 
That  accounts  for  more  than  6%  of  worldwide  carbon 
dioxide emissions.  Id., at 232 (Oppenheimer Decl. ¶3); see
also  MacCracken  Decl.  ¶31,  at  220.    To  put  this  in  per-
spective:  Considering  just  emissions  from  the  transporta-