Climate change is now causing more local extinction in temperate regions than the tropics, study shows

While many tropical species such as this Asian Tree Frog are threatened by climate change, species in temperate regions are affected by local extinction to an even greater degree, according to the new study. Credit: John Wiens

Imagine returning to a favorite hiking trail 15 years after your first visit and discovering that many of the plants and animals that once lived there are gone. While these species may still exist elsewhere, these disappearances—known as local extinctions—are among the clearest signs that climate change is already transforming ecosystems and threatening species across the globe.

University of Arizona researchers compared local extinctions from recent climate change among more than 5,100 plant and animal species from around the world, including hundreds of species of moths and beetles, hundreds of fish and birds, many mammals, frogs, salamanders and lizards, and almost 3,000 species of plants.

In the study published in Nature Climate Change , the researchers found that 49% of temperate species experienced local extinction at the hottest parts of their ranges, compared with only 33% of tropical species.

The research drew on repeated biodiversity surveys from nearly 40,000 sites worldwide, allowing the researchers to compare historical records with surveys conducted years or decades later, making it the largest analysis of climate-driven local extinctions conducted to date.

"For decades, scientists generally believed that temperate species were less vulnerable to climate change," said Gopal Murali, the lead author of the paper and a former postdoctoral scholar at the University of Arizona. "We were surprised by our results, which showed that was not the case."

A European fire salamander (Salamandra salamandra), one of the temperate species included in the study that has experienced climate-related local extinctions. Credit: John Wiens

Faster warming changed the pattern

These results were consistent across many different groups of organisms, including insects, vertebrates, plants, and marine and freshwater species.

"I actually published a study of 976 species in 2016 using the same type of data that showed the exact opposite pattern, with more local extinction among tropical species," said John Wiens, senior author of the paper and a professor in the University of Arizona Department of Ecology and Evolutionary Biology in the College of Science. "That's part of why we were so surprised."

To understand the unexpected pattern, the researchers analyzed multiple climate-related factors, including long-term warming trends, rainfall changes, drought conditions and heat waves across global sites. They also excluded sites that may have been affected by nonclimatic stressors, such as deforestation.

The researchers found one main explanation for the pattern: Temperate regions are warming faster than tropical regions.

"The world has changed since 2016," Wiens said. "There's been more heating in the temperate zone, especially at higher latitudes, and it's possible that the pattern has simply flipped in recent decades, and that helps explain the reversal in findings. For animals, we did not find that tropical extinctions were less common than we thought before. Instead, we found that temperate extinctions had outpaced tropical extinctions."

This dead alligator juniper (Juniperus deppeana) from near Bisbee, Arizona is one of the temperate species included in the study that has experienced climate-related local extinctions. Credit: John Wiens

Species are not simply moving

The researchers found that the maximum increase in temperature over a 25-year period was approximately 3.3 degrees Fahrenheit in tropical regions. In temperate regions, the maximum increase was about 6 degrees Fahrenheit (3.3°C)—nearly twice as much.

The team also examined how species responded to warming in each region. For decades, scientists believed that tropical species would be especially vulnerable to climate change because of their physiology. Because tropical species evolved under relatively stable temperatures year-round, they were thought to have less tolerance for temperature changes than temperate species, which experience greater seasonal temperature variation.

"While faster warming in temperate regions appears to be the primary driver of local extinctions, we also found that temperate species are at least as sensitive to rising temperatures as tropical species," Murali said.

The observed local extinctions do not necessarily mean that the entire species went extinct, but they do show that the populations cannot survive the changing environmental conditions. Similar losses across a species' range can lead to extinction of the whole species.

"People often think that a species will simply move into cooler areas as the climate warms, but we found that more than 70% of the species were not doing so," Wiens said. "Essentially, the life and death of the majority of species may be determined by these local extin…