(CN) - There is no proof that stricter air-quality standards for carbon-monoxide levels would alleviate the effects of global warming or improve public health, the D.C. Circuit ruled.
Under the Clean Air Act, the Environmental Protection Agency must establish primary and secondary national air-quality standards by setting limits on air pollutants, including carbon monoxide.
The primary standards for carbon monoxide have not changed since 1971, and the agency has not set a secondary standard since 1985.
After reviewing these standards in 2011, the agency decided to keep the status quo.
The Sierra Club and two other wildlife organizations then challenged the agency's decision as arbitrary and capricious, citing studies linking the presence of carbon monoxide in the air with a higher number of hospital admissions.
They also claimed that the failure to set a secondary standard will worsen global warming, and displace migratory birds.
But the D.C. Circuit said Friday the EPA's decision to keep the same primary standards was reasonable.
"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," Judge Brett Kavanaugh wrote for a three-judge panel (italics in original). "As EPA reasonably explained, the modeling programs used in the epidemiological studies did not rule out the possibility that another pollutant was causing the adverse health effects observed in the studies."
While the Clean Air Scientific Advisory Committee supported a lower carbon-monoxide standard, its recommendation to the EPA also permitted the option of keeping the standard as is.
The agency had no obligation to consider carbon-monoxide-poisoning studies in its decision because these scientific studies "were not focused on the effects of carbon monoxide exposure at the levels permitted by the primary standards," the 11-page opinion states.
The wildlife organizations also do not have standing to challenge the EPA's decision not to adopt a secondary standard, the court found.
"Petitioners have not presented a 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," Kavanaugh wrote. "Moreover, citing and analyzing many scientific studies, EPA explained that carbon monoxide's effects on climate change involve 'significant uncertainties.'"
The judge concluded: "For the reasons identified by EPA, petitioners' theory of causation is simply a bridge too far given the current record."
Read the Top 8
Sign up for the Top 8, a roundup of the day's top stories delivered directly to your inbox Monday through Friday.