Thousands of animal species threatened by climate change

The study was published today in BioScience.

“We’re at the start of an existential crisis for the Earth’s wild animals,” said Oregon State University’s William Ripple, who led the study. “Up till now, the primary cause of biodiversity loss has been the twin threats of overexploitation and habitat alteration, but as climate change intensifies, we expect it to become a third major threat to the Earth’s animals.”

Ripple, distinguished professor of ecology in the OSU College of Forestry, and collaborators in the U.S. and Mexico used publicly available biodiversity datasets to examine animal data for 70,814 species from 35 existing classes. They categorized the species by class and climate change risks as assessed by the International Union for Conservation of Nature.

The researchers found that at least one-quarter of the species in six different classes are threatened by climate change; these classes include arachnids and chilopodans (centipedes) as well as anthozoans and hydrozoans (marine invertebrates related to jellyfish and corals). Smaller percentages of other classes’ species are also directly at risk from a warming climate.

“We are particularly concerned about invertebrate animals in the ocean, which absorbs most of the heat from climate change,” Ripple said. “Those animals are increasingly vulnerable because of their limited ability to move and promptly evade adverse conditions.”

Sudden impacts on animal communities can take the form of mass mortality from extreme events like heat waves, wildfires, droughts and floods.

“The cascading effects of more and more mass mortality events will likely affect carbon cycle feedbacks and nutrient cycling,” Ripple said. “Those effects also likely will have an impact on species interactions such as predation, competition, pollination and parasitism, which are vital for ecosystem function.”

The 90% reduction in mollusk populations along Israel’s coastline because of escalating water temperatures shows how susceptible invertebrates are, he said. Other examples include the deaths of billions of intertidal invertebrates during the 2021 Pacific Northwest heat dome, and the catastrophic die-off of corals across 29% of the Great Barrier Reef following a severe 2016 marine heat wave.

Mass mortalities have not been limited to invertebrates, Ripple notes. In 2015 and 2016, about 4 million common murres off the west coast of North America starved to death via an altered food web caused by an extreme marine heat wave.

The same heat wave caused a 71% decline in Pacific cod because of an increase in metabolic demand and a reduced prey base, and marine heat waves have likely played a role in the deaths of approximately 7,000 humpback whales in the North Pacific.

Further cause for concern, the authors note, is the comparatively small amount of information that’s been gathered regarding climate change risk to wildlife. Most wildlife classes (66 of 101) have not yet had any species assessed by the IUCN, and the 70,814 species that have been assessed represent 5.5% of all described wildlife species alive today.

“Our analysis is meant to be a preliminary effort toward assessing climate risk to wildlife species,” Ripple said. “Understanding the risk is crucial for making informed policy decisions. We need a global database on mass mortality events due to climate change for animal species in all ecosystems, and an acceleration in assessing currently ignored species.”

The IUCN Red List of Threatened Species, he notes, has a bias toward vertebrates, which make up less than 6% of the Earth’s named animal species.

“There is also a need for more frequent climate risk assessments of all species and better consideration of adaptive capacity,” Ripple said. “We need the integration of biodiversity and climate change policy planning on a global scale.”

Roger Worthington, an attorney in Bend, Oregon, provided partial funding for this study, which also included Christopher Wolf and Jillian Gregg of Terrestrial Ecosystem Research Associates and Erik Torres-Romero of the Biotechnology Engineering-Polytechnic University of Puebla in Puebla, Mexico.