Climate change is the largest threat to U.S. endangered species

For the first time, scientists have shown that global warming has overtaken every other human-caused pressure on wildlife protected by the Endangered Species Act.

Drawing on a new analysis of 2,766 at-risk plants and animals across the United States and its territories, researchers report that 91 percent of federally listed species are now harmed by symptoms of climate change including rising temperatures, shifting rainfall, and other climate-linked disruptions.

“With the addition of comprehensive climate sensitivity data, climate change is just as prevalent a stressor to ESA-listed species as land and sea use change; this trend likely applies more broadly as well,” the authors wrote.

Climate threats to endangered species

The study, led by Defenders of Wildlife scientist Talia E. Niederman, set out to determine how the five dominant drivers of biodiversity loss – climate change, land and sea use change, pollution, invasive species and overexploitation – interact across taxonomic groups.

Previous national syntheses relied heavily on the threats listed in original ESA documents or in the global IUCN Red List, both of which can lag behind current knowledge. To correct that shortfall, the team merged those data with a suite of recent climate-sensitivity assessments that evaluate species’ exposure, sensitivity, and adaptive capacity to warming.

Incorporating this third layer revealed thousands of cases in which climate stress had gone unreported, vaulting global warming to the top of the threat ledger.

The researchers caution that historical listing decisions and many IUCN accounts vastly underrepresent the number of species affected by climate change and urge agencies to explicitly include climate sensitivity in ESA listing decisions and management plans.

Cascading risks for endangered species

Although climate change now dominates, it is rarely acting alone. Over 86 percent of the species in the data set face two or more of the five drivers at once, creating dangerous feedbacks that can accelerate decline.

Corals and other cnidarians are hit by an average of almost five threats each, while bivalves and amphibians typically contend with more than three. Habitat conversion remains the number-one menace to freshwater organisms, whereas marine species suffer most from overexploitation.

Overall, land and sea use change still endangers 82 percent of U.S. imperiled species, and invasive species trouble more than half. Pollution and direct exploitation each jeopardize roughly a third, but their true influence may be larger because both pressures are chronically under-documented.

How the numbers stack up

Among terrestrial vertebrates, 75 percent of birds, 92 percent of mammals and 83 percent of reptiles are already affected by a warmer, less predictable climate. Freshwater groups are equally vulnerable: 88 percent of assessed fish and 75 percent of amphibians show high sensitivity to temperature or hydrological shifts.

Even plant taxa, sometimes assumed to be more buffered, reveal striking exposure, with nearly 78 percent of flowering plants and over 90 percent of conifers triggered under at least one climate-sensitivity metric.

By contrast, initial ESA listings cited climate threats for fewer than half of these groups, and the IUCN captured only about a quarter, largely because many U.S. species have never been reassessed under the Red List’s newer climate criteria.

Urgent need for updated assessments

The authors highlight glaring information gaps: echinoderms, corals, and mollusks suffer from outdated or missing IUCN evaluations, while federal five-year reviews – required under the ESA – often arrive late or omit emerging climate data.

Without current assessments, managers can underestimate extinction risk and fail to deploy adaptive conservation tools such as assisted migration, habitat corridors or proactive fire management.

Expanding rapid, standardized climate-vulnerability screenings, they argue, would give agencies a clearer map of where limited resources can do the most good.

Policy pathways to prevention

Even under today’s daunting statistics, the team stresses that decisive action can still prevent losses. They recommend targeting the full suite of human pressures at once – curbing greenhouse-gas emissions while also restoring degraded habitats, controlling invasive species, reducing pollution and enforcing sustainable harvests.

Doing so, they contend, will yield co-benefits for people, from safeguarding fisheries and water supplies to buffering communities from extreme weather.

“We need no further research to know that biodiversity is facing multiple persistent threats. Addressing the five drivers of biodiversity loss promptly across all affected taxa will be critical to preventing further extinction,” the researchers concluded.

How climate affects endangered species

The findings arrive as the United States prepares its first National Nature Assessment, a report intended to guide conservation investment through the mid-century.

By demonstrating that climate change has already become the most pervasive danger for endangered species, the new study provides a sobering benchmark – and a potent call to integrate climate adaptation into every level of species recovery planning.

Whether policymakers heed that call may determine how many of today’s imperiled species can still be saved for future generations.

The study is published in the journal Earth System Dynamics.

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