 United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued September 26, 2013             Decided April 11, 2014

                        No. 11-1423

COMMUNITIES FOR A BETTER ENVIRONMENT AND WILDEARTH
                     GUARDIANS,
                     PETITIONERS

                             v.

          ENVIRONMENTAL PROTECTION AGENCY,
                    RESPONDENT

                       SIERRA CLUB,
                       INTERVENOR


          On Petition for Review of a Rule of the
      United States Environmental Protection Agency


     Nicholas J. Lopez, Student Counsel, argued the cause for
petitioners and intervenor. On the briefs was Michael Ray
Harris. Kelly D. Davis, Kevin J. Lynch, and Shannon Love,
Student Counsel, entered appearances.

    Andrew J. Doyle, Attorney, U.S. Department of Justice,
argued the cause for respondent. With him on the brief was
David P.W. Orlin, Attorney, United States Environmental
Protection Agency.
                               2
   Before: BROWN and KAVANAUGH, Circuit Judges, and
WILLIAMS, Senior Circuit Judge.

    Opinion    for   the   Court    filed   by   Circuit   Judge
KAVANAUGH.

     KAVANAUGH, Circuit Judge: Carbon monoxide is an
odorless, colorless gas that can be produced by human
activity, mainly by operation of motor vehicles. Carbon
monoxide can cause adverse health effects, particularly for
people with pre-existing health problems.

    Under the Clean Air Act, EPA must establish primary
and secondary national air quality standards to regulate the
levels of six common air pollutants, including carbon
monoxide. The primary standards must be set at a level
“requisite to protect the public health,” which encompasses
human health. 42 U.S.C. § 7409(b)(1). The secondary
standards must be set at a level “requisite to protect the public
welfare,” which is defined in the statute to encompass the
welfare of animals, the environment, and climate, among
other things. Id. §§ 7409(b)(2), 7602(h). Once EPA
identifies the proper levels for the standards, States administer
programs for reduction in emissions of pollutants. See id.
§ 7410.

    The primary standards for carbon monoxide have
remained the same since 1971. There has not been a
secondary standard for carbon monoxide since EPA revoked a
secondary standard in 1985. In 2007, EPA began reviewing
whether to alter the current primary standards and whether to
adopt a secondary standard. In 2011, EPA decided to keep
things as they were: to retain the same primary standards and
to continue without a secondary standard. See Review of
                               3
National Ambient Air Quality Standards for Carbon
Monoxide, 76 Fed. Reg. 54,294 (Aug. 31, 2011).

    State and local governments and industry groups agreed
with EPA’s decision. But three non-profit environmental and
wildlife organizations – Communities for a Better
Environment, WildEarth Guardians, and Sierra Club – have
objected. Petitioners argue that EPA’s decisions concerning
both the primary and secondary standards for carbon
monoxide were arbitrary and capricious.

     We conclude that EPA acted reasonably in retaining the
same primary standards for carbon monoxide, and that
petitioners lack Article III standing to challenge EPA’s
decision not to set a secondary standard for carbon monoxide.

                               I

     Under Sections 108 and 109(b)(1) of the Clean Air Act,
EPA must set National Ambient Air Quality Standards,
commonly known as NAAQS, for six common air pollutants:
carbon monoxide, lead, nitrogen dioxide, ozone, particle
pollution, and sulfur dioxide. See 42 U.S.C. § 7408. For each
pollutant, EPA identifies primary ambient air quality
standards that are “requisite” to protect the public health. Id.
§ 7409(b)(1). Specifically, the EPA Administrator must
“identify the maximum airborne concentration of a pollutant
that the public health can tolerate, decrease the concentration
to provide an ‘adequate’ margin of safety, and set the standard
at that level.” Whitman v. American Trucking Associations,
Inc., 531 U.S. 457, 465 (2001). At least every five years,
EPA must reevaluate the standards and, if appropriate, revise
them. See 42 U.S.C. § 7409(d).

    EPA must also promulgate secondary standards
“requisite to protect the public welfare from any known or
                               4
anticipated adverse effects” of those six pollutants in the
ambient air. Id. § 7409(b)(2) (emphasis added). An adverse
effect on public welfare includes adverse effects on “soils,
water, crops, vegetation, . . . animals, wildlife, weather,
visibility, and climate,” among other things. Id. § 7602(h).

     Since 1971, the primary standards for carbon monoxide
have remained at an eight-hour average of 9 parts per million
and a one-hour average of 35 parts per million, neither to be
exceeded more than once per year. See Review of National
Ambient Air Quality Standards for Carbon Monoxide, 76 Fed.
Reg. 54,294, 54,295 (Aug. 31, 2011). In 2007, EPA began its
five-year review of those standards, as required by statute. Id.
at 54,296. As part of that review, EPA prepared an Integrated
Science Assessment consolidating relevant data on carbon
monoxide’s effects. See id. In 2011, EPA determined that the
current levels of the primary standards provide an “adequate
margin of safety” under the statute. Id. at 54,308.

     As to the secondary standard, since 1985 EPA has found
that a secondary standard for carbon monoxide was not
needed to protect the public welfare. Id. at 54,296. EPA’s
five-year review of that standard focused on carbon
monoxide’s effect on climate, the only element of public
welfare known to be affected by carbon monoxide. Id. at
54,309. In 2011, EPA concluded that the connection between
carbon monoxide and climate change was tenuous. Id. at
54,308. As a result, EPA could not determine whether any
secondary standard would reduce climate change. Id. at
54,309-10.

     EPA published its conclusions as a Proposed Rule and
sought comments. During the notice-and-comment period,
petitioners argued that the primary standards were inadequate
to protect the public health and would cause adverse health
                               5
effects on some of their members. Petitioners also challenged
the lack of a secondary standard, contending that there was a
causal connection between carbon monoxide and climate
change and that EPA had to establish a secondary standard to
help reduce or prevent climate change. EPA disagreed,
incorporating the reasons given in the Proposed Rule into a
Final Rule. Id. at 54,297.

     Petitioners now seek review of EPA’s decision (i) to
retain the primary standards for carbon monoxide and (ii) to
continue without a secondary standard for carbon monoxide.

                               II

    Petitioners contend that EPA’s decision to retain the
same primary standards for carbon monoxide was arbitrary
and capricious.

     The arbitrary and capricious standard is deferential; it
requires that agency action simply be “reasonable and
reasonably explained.” National Telephone Cooperative
Association v. FCC, 563 F.3d 536, 540 (D.C. Cir. 2009). As a
general matter, we grant EPA significant deference in setting
the NAAQS. See Mississippi v. EPA, slip op. at 9-10 (D.C.
Cir. Dec. 11, 2013); Lead Industries Association, Inc. v. EPA,
647 F.2d 1130, 1146 (D.C. Cir. 1980) (“Congress has
entrusted the Agency with the responsibility for making these
scientific and other judgments, and we must respect both
Congress’ decision and the Agency’s ability to rely on the
expertise that it develops.”). We also “give an extreme degree
of deference to the agency when it is evaluating scientific data
within its technical expertise.” City of Waukesha v. EPA, 320
F.3d 228, 247 (D.C. Cir. 2003) (internal quotation marks
omitted). We “do not look at the decision as would a
scientist,” but only to ensure that EPA adheres to “certain
minimal standards of rationality.” National Environmental
                              6
Development Association’s Clean Air Project v. EPA, 686
F.3d 803, 810 (D.C. Cir. 2012) (internal quotation marks
omitted); see ATK Launch Systems, Inc. v. EPA, 669 F.3d
330, 336 (D.C. Cir. 2012); American Trucking Associations,
Inc. v. EPA, 283 F.3d 355, 374 (D.C. Cir. 2002); American
Petroleum Institute v. Costle, 665 F.2d 1176, 1185 (D.C. Cir.
1981); Ethyl Corp. v. EPA, 541 F.2d 1, 36-37 (D.C. Cir.
1976) (en banc).

     In this case, petitioners raise a number of distinct
arguments in support of their claim that EPA’s decision not to
alter the primary standards for carbon monoxide was arbitrary
and capricious. We here address the weightiest of those
arguments.

     First, petitioners contend that EPA acted unreasonably in
light of various epidemiological studies on the effects of
carbon monoxide. Epidemiological studies identify the
presence of a pollutant in a local area and monitor the number
of hospital admissions, physician visits, and emergency room
visits over a certain time period. A statistically significant
correlation between the presence of the pollutant in the
ambient air and the number of hospital admissions may
suggest that the pollutant caused the onset of sickness in the
population.       See National Environmental Development
Association’s Clean Air Project, 686 F.3d at 807. Petitioners
argue that the relevant epidemiological studies on carbon
monoxide show that the current primary standards for carbon
monoxide allow emissions at levels that cause adverse health
effects. However, EPA concluded that the studies show only
that carbon monoxide emissions at the levels of the primary
standards correlate with adverse health effects, not that
emissions at those levels cause those health effects. See 76
Fed. Reg. at 54,299, 54,304-05.           As EPA reasonably
explained, the modeling programs used in the epidemiological
                              7
studies did not rule out the possibility that another pollutant
was causing the adverse health effects observed in the studies.
See 76 Fed. Reg. at 54,305; Response to Comments 33.

     Petitioners counter that EPA relied on similar
epidemiological data in setting the standards for two other
pollutants, nitrogen dioxide and sulfur dioxide. But in those
cases, as EPA reasonably explained, toxicology and clinical
studies produced similar results and thus buttressed the
epidemiological studies.       See National Environmental
Development Association’s Clean Air Project, 686 F.3d at
811-12; Primary National Ambient Air Quality Standard for
Nitrogen Dioxide, 74 Fed. Reg. 34,404, 34,409 (July 15,
2009). With carbon monoxide, by contrast, no toxicology or
clinical studies show that carbon monoxide emissions at the
levels of the primary standards caused adverse health effects.
See 76 Fed. Reg. at 54,305 & n.26.

     Second, petitioners argue that EPA did not include
several kinds of studies in its Integrated Science Assessment,
including scientific review studies and carbon monoxide
poisoning studies. As EPA pointed out, however, the
scientific review studies only summarize the results of other
studies and provide no new information. See Response to
Comments 9 n.3. And EPA reasonably explained that the
carbon monoxide poisoning studies were not focused on the
effects of carbon monoxide exposure at the levels permitted
by the primary standards, and thus were not helpful for
determining what physical effects are caused by emissions of
carbon monoxide at the levels of the primary NAAQS. See
Integrated Science Assessment 1-7; Response to Comments
8-10.

    Third, petitioners assert that EPA accepted the findings of
an outdated human clinical trial, the Allred study of 1989, to
                              8
the exclusion of other relevant studies. EPA acknowledges
that it relied heavily on the Allred study in the carbon
monoxide rulemaking. See 76 Fed. Reg. at 54,300. But
according to EPA, it did so because human clinical trials like
the Allred study remained “the most compelling evidence of
CO-induced effects on the cardiovascular system.” Id.
Subsequent studies reinforce the findings of the Allred study.
See id. at 54,300 & n.11. In short, EPA reasonably explained
why it relied on the Allred study.

    Fourth, petitioners say that EPA mischaracterized and
ignored the advice of its Clean Air Scientific Advisory
Committee. Under the Clean Air Act, the Clean Air Scientific
Advisory Committee acts as an “independent scientific review
committee” and advises EPA during the NAAQS rulemaking.
42 U.S.C. § 7409(d)(2)(A); see American Trucking
Associations, 283 F.3d at 358. The Advisory Committee’s
“pertinent findings, recommendations, and comments” must
be “set forth” or summarized by EPA in the Final Rule. 42
U.S.C. § 7607(d)(3). EPA must also explain any reasons for
“important” departures from the Advisory Committee’s
recommendations. Id.

     In this case, as EPA explained: “Although CASAC [the
Clean Air Scientific Advisory Committee] expressed a
preference for a lower standard, CASAC also indicated that
the current evidence provides support for retaining the current
suite of standards and CASAC’s recommendations appear to
recognize that their preference for a lower standard was
contingent on a judgment as to the weight to be placed on the
epidemiological evidence.” 76 Fed. Reg. at 54,304. By its
terms, as EPA noted, the Advisory Committee’s report
expressly supported either of two options: “retaining or
revising the current 8-hr standard.” Letter from Dr. Joseph
Brain, Chair, Clean Air Scientific Advisory Committee
                              9
Carbon Monoxide Review Panel, & Dr. Jonathan Samet,
Chair, Clean Air Scientific Advisory Committee, to EPA
Administrator Lisa P. Jackson 12 (June 8, 2010). Because the
Advisory Committee’s recommendation permitted the option
of retaining the current primary standards, it cannot be said
that EPA departed from the Committee’s recommendations in
this case.

     In sum, we have considered all of petitioners’ challenges
to EPA’s decision to retain the extant primary standards. We
find none of petitioners’ arguments persuasive.

                             III

    Petitioners also challenge EPA’s decision not to set a
secondary standard for carbon monoxide in order to protect
the public welfare. The “public welfare” encompasses the
welfare of animals, the environment, and climate, among
other things.

     EPA initially responds that petitioners lack standing to
make this argument. To establish standing, a party must
demonstrate an injury-in-fact that was caused by the
defendant and that may be redressed by the court. To support
their standing, petitioners rely on Massachusetts v. EPA, 549
U.S. 497 (2007), which held that States have standing to
complain about the effects of global warming caused by
EPA’s allegedly illegal under-regulation of certain
greenhouse gas emissions. But even assuming for the sake of
argument that Massachusetts v. EPA grants standing for
plaintiffs other than States, petitioners here have failed to
establish the causation element of standing. Petitioners claim
that EPA’s decision not to set a secondary standard for carbon
monoxide will worsen global warming and in turn displace
birds that one of petitioners’ members observes for
recreational purposes. But petitioners have not presented a
                             10
sufficient showing that carbon monoxide emissions in the
United States – at the level allowed by EPA – will worsen
global warming as compared to what would happen if EPA
set the secondary standards in accordance with the law as
petitioners see it. Moreover, citing and analyzing many
scientific studies, EPA explained that carbon monoxide’s
effects on climate change involve “significant uncertainties.”
Review of National Ambient Air Quality Standards for
Carbon Monoxide, 76 Fed. Reg. 54,294, 54,310 (Aug. 31,
2011). EPA’s Clean Air Scientific Advisory Committee
likewise agreed that the “current high level of uncertainty
does not favor the development of a secondary standard.”
Letter from Dr. Joseph Brain, Chair, Clean Air Scientific
Advisory Committee Carbon Monoxide Review Panel, & Dr.
Jonathan Samet, Chair, Clean Air Scientific Advisory
Committee, to EPA Administrator Lisa P. Jackson 9 (Jan. 20,
2010). EPA ultimately determined, therefore, that it was “not
possible to anticipate how any secondary standard that would
limit ambient CO concentrations in the United States would in
turn affect climate and thus any associated welfare effects.”
76 Fed. Reg. at 54,310.

     For the reasons identified by EPA, petitioners’ theory of
causation is simply a bridge too far given the current record.
Petitioners have not presented a sufficient showing that
carbon monoxide at the level permitted by EPA would worsen
global warming as compared to what would happen if EPA
set the secondary standard in accordance with the law as
petitioners see it. See Sierra Club v. EPA, 292 F.3d 895, 898
(D.C. Cir. 2002). Therefore, petitioners do not have standing
to advance this claim in this case.
                             11
                            ***

     We have considered all of petitioners’ arguments. We
deny the petition for review of the primary standards and
dismiss the petition for review of the secondary standard for
lack of standing.

                                                 So ordered.
