Endangered Species Law & Policy

On August 25, 2026, the United States Court of Appeals for the D.C. Circuit issued a notable Endangered Species Act (ESA) decision in Center for Biological Diversity v. EPA, No. 25-1005. The Center for Biological Diversity (CBD) had filed a petition for review challenging a final rule published by the Environmental Protection Agency (EPA), which retained the existing national ambient air quality standard for nitrogen oxides and particulate matter and revised the standard for sulfur oxides. CBD argued that EPA violated the ESA by concluding that the challenged air quality rule would have no effect on listed species or critical habitat because neither the retained nitrogen oxide and particulate matter standards nor the more stringent sulfur oxide standard would result in any changes to air quality that could affect listed species. In upholding EPA’s “no effect” determination, the D.C. Circuit made a number of noteworthy statements regarding consultation under section 7(a)(2) of the ESA.

Section 7(a)(2) requires federal agencies to consult with the U.S. Fish & Wildlife Service and the National Marine Fisheries Service to “insure that any action authorized, funded, or carried out by such agency . . . is not likely to jeopardize the continued existence of any endangered species or threatened species or result in the destruction or adverse modification” of designated critical habitat. Before proceeding with an “action,” a federal agency must make a threshold determination whether the “action” may affect listed species or designated critical habitat.  If the agency determines the action will have “no effect” then the agency has no further obligations under section 7(a)(2). 

In October 2024, EPA prepared a memorandum concluding that the rule at issue would have no effect on listed species or designated critical habitat because retaining the existing air quality standard for nitrogen oxides and particulate matter and revising the standard for sulfur oxides would not result in any changes to air quality that could affect listed species or critical habitat. CBD argued EPA arbitrarily disregarded evidence of cumulative and ongoing ecological effects of nitrogen oxides, sulfur oxides, and particulate matter on listed species and designated critical habitat.

When it turned to the merits of the case, the D.C. Circuit cited its own prior precedent for the proposition that review of EPA’s decision is “highly deferential, and presumes agency action to be valid.” This signals that while reviewing courts will not necessarily defer to agency legal interpretations following the 2024 Supreme Court decision in Loper Bright Enterprises v. Raimondo, they continue to defer to agency factual determinations, perhaps especially in highly technical subjects like air quality.

Turning to the substantive disagreement, the principal dispute between EPA and CBD related to EPA’s “effects analysis,” which is at the heart of the consultation process. The ESA requires a federal agency to analyze the “effects of the action.” The D.C. Circuit held that for a consequence to be an “effect of the action,” it must be the but-for cause of the action. In other words, the federal action must be the actual, factual cause of effects on listed species and designated critical habitat.

When analyzing the “effects of the action” an agency also must identify the “environmental baseline.” CBD argued that past harms from emissions of nitrogen oxides, sulfur oxides, and particulate matter that cause ongoing effects are effects of the action. The D.C. Circuit disagreed, explaining that “[b]ecause any ongoing and accumulating harms would occur even if EPA had promulgated no rule at all, such harms cannot be considered ‘effects of’ EPA’s rule.” The decision highlights that when conducting “effects analysis,” federal agencies are obligated to differentiate between the effects of the action and the environmental baseline.