By Stephen Beech
More than 3,500 animal species are threatened by climate change, warns a new report.
Global warming now ranks alongside overexploitation and habitat alteration as the greatest threats to wildlife, say scientists.
Study leader Professor William Ripple said: "We're at the start of an existential crisis for the Earth's wild animals.
"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, of Oregon State University's College of Forestry, along with colleagues in the United States and Mexico, used publicly available biodiversity data to examine animal figures for 70,814 species from 35 existing classes.
They categorised the species by class and climate change risks as assessed by the International Union for Conservation of Nature (IUCN).
The findings, published in the journal BioScience, suggest that at least a quarter of the species in six different classes are threatened by climate change.
The classes at risk include arachnids and 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.
Ripple said: "We are particularly concerned about invertebrate animals in the ocean, which absorb most of the heat from climate change.
"Those animals are increasingly vulnerable because of their limited ability to move and promptly evade adverse conditions."
The research team say sudden impacts on animal communities can take the form of mass mortality from extreme events such as heatwaves, wildfires, droughts and floods.
Ripple said: "The cascading effects of more and more mass mortality events will likely affect carbon cycle feedbacks and nutrient cycling.
"Those effects also likely will have an impact on species interactions such as predation, competition, pollination and parasitism, which are vital for ecosystem function."
He says a 90% reduction in mollusk populations along Israel's coastline because of escalating water temperatures shows how susceptible invertebrates are.
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 heatwave.
Ripple pointed out that mass mortalities have not been limited to invertebrates, as, in 2015 and 2016, around four million common murres off the west coast of North America starved to death as a result of an altered food web caused by an extreme marine heatwave.
The same heatwave caused a 71% decline in Pacific cod because of an increase in metabolic demand and a reduced prey base, and marine heatwaves have likely played a role in the deaths of around 7,000 humpback whales in the North Pacific.
The research team say that further cause for concern 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 just 5.5% of all described wildlife species alive today.
Ripple said, "Our analysis is meant to be a preliminary effort toward assessing climate risk to wildlife species.
"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."
He noted that the IUCN Red List of Threatened Species has a bias toward vertebrates, which make up less than 6% of the Earth's named animal species.
Ripple added: "There is also a need for more frequent climate risk assessments of all species and better consideration of adaptive capacity.
"We need the integration of biodiversity and climate change policy planning on a global scale."
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