James Smith
BISBEE, Arizona. – Dusty boots and heaving lungs, Dr. John Wiens searched the rocks of a desolate Arizona mountain for the last survivors of a 3-million-year-old population of lizards – and then spoke the words that confirmed his life’s work and broke his heart.
“They’re not there,” he said. “It appears the species is extinct.”
Chance Horner/CBS News
The loss of plant and animal species on Earth is happening at a speed never seen in the history of humanity, according to the United Nations. That includes the likely extinction of the lizards Wiens studied for 10 years — the population of spiny yarrow lizards found in the Mule Mountains of southern Arizona.
“There are many species on Earth, and we are going to lose many of them because of climate change,” said Weins, an evolutionary biologist at the University of Arizona. “It’s catastrophic.”
Riding the elevator to extinction
Over the past 3 million years – a million years longer than humans have existed – the spiny yarrow lizards in Mules have adapted to live in cold mountainous climates called sky islands.
Because the desert floor below is so hot, the lizards were essentially marooned at higher elevations, as if on an island, and isolated from other Yarrow populations in southern Arizona and northern Mexico.
These lizards were also easy to find in the wild, unlike many other species. They used to sun themselves on large rocky outcrops. This behavior allowed Wiens and his colleagues to regularly count their population to see how they were affected by the warming climate.
In 2014, the team was unable to find any lizards below 5,700 feet. Up to that altitude the temperature in the mountains had become very hot. In 2021-22, they returned to Mules to count lizards in the same location. They are gone.
“They are dying at lower altitudes,” he said.
At this point, lizards could only be found living much higher, at 7,000 feet, a colder altitude. In a scientific environment paperWiens and his colleagues calculated the lizards’ death rate, concluding that it is among the fastest rates ever recorded.
But since Mules’ highest peak is 7,700 feet, Yarrow’s spiny lizards were quickly running out of altitude with colder air. Based on the calculated rate of decline, and with nowhere else to go, Wiens projected that lizards would go extinct here by 2025 — a phenomenon scientists call riding the “elevator to extinction.”
In March of this year, a research trip to the mountains with CBS News proved his hypothesis correct, a year ahead of schedule. Wiens was unable to find any more lizards, although it would take several trips before he reached a conclusion.
“It appears that the species is extinct, this distinct lineage that has been separated for about 3 million years,” he said. “This is what the future will be like. This is climate-related extinction.”
According to Krista Kemppinen, a senior scientist at the Center for Biological Diversity who was not involved in Wiens’ research, the implications are dire for other species in the Sonoran Desert where the mules are located, as they may already be at the upper limit of how much heat they can tolerate.
“The region is really like a ticking time bomb when it comes to climate change,” she said.
Humans “bear some responsibility for this”
According to an exhaustive 2019 UN report report1 million plant and animal species are threatened with extinction around the globe.
Wiens concluded that the number is likely much higher in a more recent study. to look for article, he published in Biology of Global Change. He estimates that 3 to 6 million species will be threatened with extinction in the next 50 years, heavily driven by climate change, which will make the climate too hot for many species to survive.
“As human beings in the developed world, we all have some responsibility for this,” Wiens said.
Although the distinctive 3-million-year-old population of the Yarrow lizard species is considered extinct in the Mule Mountains, its distant relatives still exist in other mountainous locations in Arizona and Mexico—although many are also in decline.
Still, across the country, 1,700 plants and animals are listed as threatened or endangered under the Endangered Species Actwhich provides resources to help protect species and their habitat.
The law is widely seen as an environmental success story. Some prominent species on the list include:
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O California condorthe largest flying bird in the US, with about 90 adults remaining in the wild.
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The iconic Florida Pantherleaving around 200 animals.
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The huge North Atlantic right whale, which runs along the Atlantic Ocean; all that remains are 250 individuals.
Still, the Endangered Species Act covers only a fraction of the species at riskin part because the process of listing a species can be long, bureaucratic and political.
“It can take an average of 12 years, when legally it should only take two,” Kemppinen said.
There is not enough time for the spiny lizards of the Mule Mountains.
