Robert Brown|Scientists looked at nearly every known amphibian type. They're not doing great.

When JJ Apodaca was starting graduate school for biology in 2004,Robert Brown a first-of-its-kind study had just been released assessing the status of the world's least understood vertebrates. The first Global Amphibian Assessment, which looked at more than 5,700 species of frogs, toads, salamanders, newts and other amphibians became "pretty much the guiding light of my career," said Apodaca, who now heads the nonprofit group Amphibian and Reptile Conservancy.

Nineteen years later, a second global assessment of the world's amphibians has been completed.

"It's a gut punch," said Apodaca, who was not involved in the study but has reviewed its findings. "Here we are 19 years later with things not only not improved but getting worse."

The assessment, published in the journal Nature, Wednesday, looked at two decades worth of data from more than 1,000 scientists across the world. It assessed the status of nearly for nearly every known amphibian on the planet, "Ninety-four percent," said Jennifer Luedtke, one of the lead authors on the study. Though, she noted, an average of 155 new amphibians are discovered each year.

Discovered or not, the study found that the status of amphibians globally is "deteriorating rapidly," earning them the unenviable title of being the planet's most threatened class of vertebrates.

Forty-one percent of the assessed amphibians are threatened with extinction in the immediate and long-term, Luedtke said. "Which is a greater percentage than threatened mammals, reptiles and birds."

Habitat loss from agriculture, logging and human other encroachment, was the biggest driver of the deterioration. As was the case in 2004. Diseases like the infectious chytrid fungus were a major threat as well.

But the scientists were struck by how fast climate change is emerging as one of the biggest threats to amphibians globally. Between 2004 and 2022, the time surveyed in the new assessment, climate change effects were responsible for 39% of species moving closer to extinction, Luedtke said. "And that's compared to just one percent in the two decades prior."

As global temperatures have warmed, driven by the burning of fossil fuels, the length and frequency of droughts is increasing. Seasons are shifting. Precipitation patterns are changing. Extreme weather events like hurricanes, heatwaves and wildfires are becoming more common.

And amphibians are particularly vulnerable to changes in their environment. Many rely on water to reproduce. They're cold-blooded and, thus, susceptible to small changes in temperature.

"They don't have any protection in their skin," said Patricia Burrowes, a professor of biology at the University of Puerto Rico. "They don't have feathers, they don't have hair, they don't have scales."

Scientists have documented many species moving to new places, retreating to higher ground, as temperatures have shifted. Burrowes studied the forest coqui, Eleutherodactylus portoricensis, a small, endangered yellow or tan frog, native to the mountains of Puerto Rico. It had been observed moving to higher elevations while some similar Puerto Rican frog species were not. Burrowes and a graduate student found that the specific, already endangered, forest coquis that were moving were more sensitive to small shifts in temperature.

"Patterns aren't predictable anymore," Burrowes said.

Salamanders and newts were found to be the most at risk, according to the new assessment. The highest concentration of salamander diversity in the world is in the southeastern U.S. — the Southern Appalachia — where Apodaca, the executive director of the Amphibian and Reptile Conservancy, works and lives.

"This isn't just a problem of things going extinct in the Global South and Australia and Central America and places like that," he said. "This is the story of things declining and being endangered right here in our own backyard, so it's our responsibility, our duty to save these things."