A sweeping new analysis of more than 5,100 species found that temperate regions are losing local populations to climate change at a faster rate than the tropics — a finding that caught even the researchers off guard.
The conventional wisdom held that tropical species faced the steepest climb as global temperatures rose. A major new study suggests that assumption is no longer accurate — and may not have been for years.
Researchers at the University of Arizona analyzed local extinction patterns across more than 5,100 plant and animal species worldwide, drawing on biodiversity surveys from nearly 40,000 sites. The results, published June 18 in Nature Climate Change, reveal that 49% of temperate species had disappeared from the hottest parts of their ranges, compared with just 33% of tropical species — flipping what scientists long thought they knew about climate vulnerability.
A Reversal That Surprised Even the Scientists Behind It
Senior author John Wiens, a professor in the University of Arizona’s Department of Ecology and Evolutionary Biology in the College of Science, knows this terrain well.
“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,” Wiens said in a news release. “That’s part of why we were so surprised.”
Lead author Gopal Murali, a former postdoctoral scholar at the university, echoed that sentiment.
“For decades, scientists generally believed that temperate species were less vulnerable to climate change,” Murali said in the news release. “We were surprised by our results, which showed that was not the case.”
The findings held across a wide range of organisms — insects, birds, fish, mammals, amphibians, reptiles and nearly 3,000 plant species — as well as across marine and freshwater environments, making this the most comprehensive analysis of climate-driven local extinctions conducted to date.
Why Temperate Zones Are Now Warming Faster
The team examined long-term temperature trends, rainfall shifts, drought patterns and heat wave frequency across global sites, also filtering out locations affected by non-climate factors like deforestation. One explanation emerged as primary: temperate regions are simply heating up more rapidly than the tropics.
Over a recent 25-year period, maximum temperature increases reached roughly 3.3 degrees Fahrenheit in tropical regions. In temperate zones, that figure climbed to about 6 degrees Fahrenheit — nearly double.
Wiens put it plainly.
“The world has changed since 2016,” he 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.”
The team also challenged an older assumption about physiology. Tropical species were historically thought to be more temperature-sensitive because they evolved in stable, warm climates. But Murali said the data told a more nuanced story: “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.”
Why Moving to Cooler Ground Isn’t a Simple Fix
One might assume that as temperatures climb, wildlife simply shifts toward cooler territory. The data puncture that idea.
“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 added. “Essentially, the life and death of the majority of species may be determined by these local extinctions and whether local populations can survive in place or not.”
For many animals, migration is blocked by highways, urban development and fragmented habitats. Aquatic species are typically confined to specific lakes or river systems. Mountain-dwelling species can climb higher as warmth creeps upward, but eventually they run out of mountain. Near Tucson, Ariz., the dead trunks of trees that once lined the lower slopes of Mount Lemmon now serve as quiet markers of this process already underway.
The study also found that temperate extinctions aren’t confined to the warmest corners of a species’ range — they’re occurring broadly throughout species’ territories. That shifts the calculus for conservation, according to Wiens.
“In the past, we have been laser-focused on the warmest areas,” Wiens said. “But it turns out that nowhere is really safe for populations of many temperate species.”
Why It Matters for Students and Future Conservationists
For students studying biology, environmental science, ecology or policy, this research underscores a critical point: the biodiversity crisis tied to climate change is not a future problem. Murali emphasized that directly.
“People often think climate change is something that will affect species in the future,” he said. “But for both tropical and temperate species, we’re already seeing the effects. The patterns we documented show that biodiversity is already changing in ways we are still working to understand.”
Across all species in the dataset, 45% had already vanished from the warmest part of their former range. For insects, terrestrial vertebrates and marine species, that figure exceeded 50%.
The implications extend to conservation strategy. Protecting only tropical biodiversity hotspots — long the dominant paradigm — may leave temperate ecosystems dangerously underprioritized. The study does not argue that tropical species are safe; rather, it calls for a broader, more geographically inclusive approach to protecting life on Earth as warming accelerates.
Source: University of Arizona