A court decision on endangered species holds lessons for us all

In the wake of a 2024 US Supreme Court decision called Loper Bright (603 US 369), many commentators predicted that the deregulatory mood of the current federal government would unravel numerous environmental protections. That decision struck down the Court's 1984 Chevron deference doctrine (467 US 837), which instructed judges to defer to federal agency interpretation and technical expertise when a statute is ambiguous or vague. Because statutes are often ambiguous or simply too general to address the specifics of complex environmental problems, the 1984 Chevron deference was invoked in 18,000 subsequent court decisions, according to one prominent estimate. The new Loper Bright standard replaced the Chevron deference with a non-deferential standard—encouraging judges to interpret statutes themselves (as they are trained to do), rather than adopt an agency's interpretation thereof.

After Loper Bright, legal scholars expressed concerns about a coming wave of unpredictable, chaotic, and inconsistent decisions across federal courts. With authority returned to the courts under a non-deferential standard, decisions would no longer be as predictable: some judges might persist in deferring to the agency, while other judges might strike out on their own—even if facing similar fact patterns. Likewise, chaos might ensue as judges without training in technical environmental issues hand down decisions guided too much by the influence of their individual preferences. While not immune to political or other pressures, US federal agencies are often constrained by having more individuals involved in decision-making and by legally binding duties to seek public input. To me, it's unclear whether judges are as constrained by either factor. Now that data are beginning to accumulate about the effect of Loper Bright on environmental policy, I offer one example of a federal court case for those of us conducting policy-relevant research.

On August 5, 2025, a federal district court judge—in the case Center for Biological Diversity et al. v. US Fish & Wildlife Service et al. (CV 24-86-M-DWM), Ninth circuit, District Court of Montana—invoked Loper Bright when explaining why he would disregard a 2014 policy promulgated by the US Fish and Wildlife Service (FWS) interpreting a provision of the Endangered Species Act (ESA). At issue was FWS’ interpretation of the term “range” to solely refer to currently occupied range, and Judge Molloy looked to both Congressional intent and the plain language of the ESA, determining that “range” should include historical range. He thus ordered the FWS to reverse course and consider the historical range of gray wolves in the northern Rocky Mountains.

If the above case (hereafter CBD) withstands appeal, it could ripple to other endangered species whose current ranges differ substantially from their historical ranges. Beyond endangered species, CBD might be instructive for cases involving other environmental agencies, because it also addressed the science used in agency decisions.

The ESA requires agencies to make determinations “based solely on the best scientific and commercial data available” (“best available science” or BAS). One of the factors requiring use of BAS is the adequacy of existing regulatory mechanisms. Adequate existing regulatory mechanisms must be present and sufficient to ensure that the species in question is not likely to be in danger of extinction now or in the foreseeable future. Judge Molloy therefore had to weigh the scientific evidence for the effectiveness of state regulation of wolf-killing by the BAS standard. Many environmental laws have BAS standards applied to regulatory mechanisms or policy interventions. Therefore, ecologists and environmental scientists who investigate the functional effectiveness and side-effects of government actions are well positioned to inform public policy debates.

Loper Bright did not remove all judicial deference to environmental agencies. In general, judges will defer to the agency in its field of expertise—though this is not an absolute deference. To illustrate this with CBD, Judge Molloy weighed the scientific evidence presented by both plaintiffs and defendants. He deferred to the FWS on one scientific subject (effective population size), but not on several others (population estimation dispersal and connectivity, genetic health, and human-caused mortality). Because court scrutiny of scientific questions is likely to take each piece of evidence independently as in the above example, I expect to see more split decisions on science.

Two colleagues shared with me their frustration or disappointment that the CBD court did not distinguish the best evidence from less reliable evidence. In public policy debates, contested evidence provides scientists an opportunity to help the public and policy experts sharpen their skills in discerning BAS. I also expect fewer wins on the science for the current US administration, given how many federal agency scientists have been dismissed or gagged. Given the loss of judicial deference to agency interpretations of statute following Loper Bright, will courts scrutinize the scientific evidence underpinning agency policies more frequently? Will we see more debates between environmental scientists play out in legal briefs and courtrooms? Obviously, I have more questions than answers. Expect a reenergized dialogue between science and policy following Loper Bright.