In the last decade, report after report has warned that the Arctic is heating up faster than ever, cities are scorching, the Amazon is blazing, boreal forests are shrinking and the oceans are simmering — all because of human-caused climate change (How do we know? Here’s an evidence-based tool that tells us how much our emissions contribute to each of these). As ecosystems morph on a heating planet, the biodiversity they harbor — the fish, the birds, the mammals and billions of invertebrates — also faces the wrath of climate change. But where does climate change rank among the host of threats wildlife face today?

A new first-of-its-kind analysis of more than 70,000 wild animal species found that climate change is now a serious threat to Earth’s wildlife, after habitat loss and overexploitation. Climate change threatens nearly 5% of these species, with ocean invertebrates imperiled the most, according to the study, published in the journal BioScience.

“Our goal was to shine a spotlight on the growing, often underappreciated role of climate change in the global biodiversity crisis,” study lead author William Ripple from Oregon State University told Mongabay by email. “We’re seeing clear signs that climate change is no longer a distant threat; it’s already disrupting wild animal populations around the globe.” Ripple is also the director of the Alliance of World Scientists.

The researchers looked at more than 70,000 species of wild animals assessed by the IUCN Red List of Threatened Species — a catalog of conservation status and extinction risk for global species — and identified more than 3,500 of these species, or about 5%, as facing climate change-related threats. These include threats from storms, floods, droughts and temperature extremes — all of which affect a species’ survival. The analysis excluded species that were either extinct or about which we don’t know much (i.e., data deficient).

The study found that marine invertebrates, such as mollusks, sea stars, corals and horseshoe crabs, are increasingly being impacted by climate change, partly because the Earth’s oceans absorb nearly 90% of the excess heat trapped in the atmosphere due to global warming. In the past, overharvesting and pollution posed the biggest threats to them, but climate change is poised to take that place.

“Marine invertebrates are especially vulnerable because many of them are stationary or slow moving, so they can’t readily escape rising temperatures,” Ripple said. “Many of them build shells or reefs from calcium carbonate, which is sensitive to changes in ocean chemistry.”

Ocean acidification, where the sea water turns acidic due to absorbing excess carbon dioxide from the atmosphere, wreaks havoc on shell-building marine invertebrates by dissolving their shells or slowing their growth.

Still, we know very little about the many marine invertebrates living in the depths of the world’s oceans — and the crisis may be far larger for them. According to the Marine Invertebrates Red List Authority, only 15% of the IUCN assessed species are marine, and only 20% of those are invertebrates.

“It’s like flying blind, we know these species are crucial, but we’ve barely begun to track how badly they’re being hit by warming oceans,” Ripple said.

The study shows that climate change is hitting small, lesser-known species as well as larger ones in the spotlight.

“When we think of climate-threatened wildlife, larger animals often come to mind like sea turtles, polar bears, and penguins. This study highlights that many of the world’s smallest creatures are being hard-hit by climate change — invertebrates like bees, spiders, and corals,” Shaye Wolf, climate science director at the Center for Biological Diversity who was not involved in the study, told Mongabay by email.

“That’s disastrous because [the world’s small creatures] form the foundation of ecosystems, providing food, habitat and essential services like pollination,” she said.

Mass mortalities ring ‘alarm bells’

The analysis provides evidence for climate change’s devastating impacts on wildlife that’s already in the record. Extreme heat, marine heat waves, rising sea levels and disrupted food webs, all caused by climate change, have resulted in mass wildlife mortalities around the globe in the last two decades.

In the last 15 years, Israel’s mollusk populations have plummeted by 90% due to rising sea temperatures; the 2021 marine heat wave in the Pacific Northwest killed more than a billion sea animals; more than 10 billion snow crabs (Chionoecetes opilio) have disappeared due to starvation — that’s more crabs than humans on Earth — in the Bering Sea between 2018 and 2021; and nearly 7,000 humpback whales (Megaptera novaeangliae) have succumbed to marine heat waves in the northern Pacific Ocean between 2013 and 2021.

On land, the Bramble Cay melomys (Melomys rubicola), a rodent native to a tiny Pacific island, became the first recorded mammal to go extinct due to climate change. Storm surges and rising sea levels depleted leafy plants on the island, starving most of the rats to extinction and washing the surviving ones out to sea. Meanwhile, heat waves are decimating bumblebees in North America and Europe, with more than 60 species declared locally extinct.

“These mass mortality events show that ecosystems can unravel quickly when exposed to climate stress,” Ripple said. “The world’s animals are already sounding the alarm bells. Climate change isn’t just a future threat, it’s happening now, and it’s deadly.”

This sudden collapse of wildlife populations could have a domino effect on the entire ecosystem as food webs get perturbed, ecosystem services such as pollination and nutrient recycling decline and human well-being is impacted.

“This study rings alarm bells about the increase in mass die-offs of ocean wildlife, especially from heat waves. The climate crisis is making it harder for animals from whales to sea stars to survive and produce the next generation,” Wolf said.

A need to monitor mass die-offs to understand climate change

As human-caused climate change progresses, the world enters uncharted territory, and it is crucial to understand how wildlife responds to unprecedented environmental changes. A recent study found that climate change is now the leading threat to 2,766 species in the U.S., listed under the Endangered Species Act. Cataloging how climate change impacts wildlife can build a knowledge base that helps scientists understand the cause-and-effect relationship and enables policymakers to develop conservation plans for species at risk of extinction.

One way to catalog these events, the researchers recommend, is to build a global database of mass mortality events in wild animals caused by climate change, similar to the T-MEDNet initiative in the Mediterranean Sea, which monitors mass die-offs. It would record the type of event, the species affected and the severity of such events, helping scientists track when and where these mortality events occur, which species are involved and under what conditions.

“That kind of information is essential for early warning systems, risk modeling, and conservation planning,” Ripple said. “Right now, we’re reacting after the fact. With a global mortality database, we could start getting ahead of the curve.” He added that the database would help prioritize which species and ecosystems are in greatest need of protection and restoration.

Given that only about 5.5% of all species on the planet are assessed by the IUCN Red List, the researchers emphasize that their analysis is likely a vast underestimate of the actual impacts of climate change. In addition to quickly assessing the threats to other ignored species, especially invertebrates, the authors recommend stronger integration between biodiversity policy and climate action.

“Policymakers need to listen to scientists and act on the evidence, even when it’s politically difficult,” Ripple said, adding that the public can help by supporting science, speaking up for endangered species and demanding climate accountability from their leaders. “Biodiversity and climate policy need to walk hand in hand. We can’t solve one without tackling the other.”

But the first step in saving the world’s wild animals from the catastrophic impacts of climate change is to reduce our greenhouse gas emissions. Last year, carbon dioxide emissions hit a new record high of around 41.6 billion metric tons.

“Fossil fuels are the main driver of the climate crisis,” Wolf said. “Rapidly phasing out fossil fuels is essential if we’re going to prevent mass extinctions of animals and plants and maintain healthy wildlife populations and ecosystems with all the benefits they provide.”

“Without deep and rapid emissions cuts, the future of much of Earth’s biodiversity is bleak,” Ripple said.

Banner image: A Schrenck’s bumblebee (Bombus schrencki) in Estonia. In recent years, heatwaves in North America and Europe have decimated bumblebee populations, with more than 60 species declared locally extinct. Image by Ivar Leidus via Wikimedia Commons (CC BY-SA 4.0).

Citations:

Ripple, J., Wolf, C., Gregg, W., & Torres-Romero, E. J. (2025). Climate change threats to Earth’s wild animals. BioScience. doi:10.1093/biosci/biaf059

Niederman, T. E., Aronson, J. N., Gainsbury, A. M., Nunes, L. A., & Dreiss, L. M. (2025). US Imperiled species and the five drivers of biodiversity loss. BioScience. doi:10.1093/biosci/biaf019

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