Climate Change May Be as Hard on Lizards as on Polar Bears

A female chuckwallaCameron Barrow

Desert ecologist Cameron Barrows is a sand country cowboy. His white-brown beard and wide cotton hat deflect the brutal sun as he leads volunteers—citizen scientists—through Joshua Tree National Park. They weave past smooth orange boulders and the menacing white spines of cholla cacti, on the lookout for lizards and tortoises.

Barrows’ band is sweeping 27 sites in California’s High Desert in an effort to understand how climate change impacts the populations of local reptiles, including western whiptails, desert iguanas, and chuckwallas, which are foot-long, vegetarian lizards. Long droughts—like California's current five-year episode—have been hard on creatures in the park, especially at the hottest low-elevation sites. When healthy, chuckwallas are especially “rotund,” like “a lizard that could be mistaken for Shrek,” Barrows says. But now, “they’re just not plump, chubby chuckwallas anymore.”

You’d think desert creatures would love climate change. They already thrive in the hottest, driest places on earth. But Barrows sees their numbers “dwindling,” an observation that reflects a larger trend: From Southern Africa to the Southwestern U.S., arid environments are becoming even less hospitable, and their denizens—animals as well as plants—seem to be struggling to keep up.

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A growing body of research suggests many desert species are already pushed to their physiological limits. In California’s Mojave and Sonoran deserts, tortoises and chuckwallas are already losing habitat, which could constrict by up to 88 percent if temperatures rise by two degrees. Joshua Tree National Park could lose up to 90 percent of its eponymous trees if already-sweltering July temperatures rise by another three degrees. From Arizona to Australia, hotter, longer, and more frequent heat waves could cause massive die-offs for desert birds like hummingbirds and thornbills. And in the hot, sandy soils of South Africa and Namibia, dwarf succulents may disappear by 2069.

“Life is always living on the edge in these places,” says plant scientist Andrew Young, the lead researcher on the dwarf succulent study. “Any shift could have really serious consequences, but we’re only starting to understand it now.”

A male chuckwalla (Cameron Barrow)

Young and his colleagues work in a dry region of southwestern Africa that is basically plant-lover heaven. It's called the “Succulent Karoo,” and boasts more than 5,000 plant species, including a third of all succulents. If you’ve got a split rock plant or coral aloe growing at home, chances are you’re tending a Karoo native. Out there, dwarf succulents called Conophytum or “cone plants” are resilient as they come. On first inspection, they look more like pebbles than living things. “They’re wonderful,” Young says, laughing. “Some are tiny, just a few millimeters across. Others are much bigger. There’s huge variation, and huge variability.”

Since these mini succulents are so diverse, and tough as rocks (literally), scientists expected them to thrive even as temperatures rise. But when Young mapped the distributions of 159 species across 3,000 desert sites, he found that many grow on specific types of rock, like quartz, or live in narrow temperature bands. If climate patterns change as global models predict, so will these microhabitats, and the dwarf succulents will have nowhere to go. Fifty to 100 percent of their habitat could disappear in the next 50 years.

A Joshua tree in Joshua Tree National Park in Southern California (Lucy Nicholson / Reuters)

Cacti and succulents as far away as Texas and Mexico could face similar risks, Young worries, because they’ve adapted to extreme environments in many of the same ways. “Most people thought these were some of the best-adapted [plants] around,” he says. “So then, what are the implications for everything else?”

In California’s Joshua Tree National Park, Barrows says many critters will have to migrate to cooler, higher-elevations sites to survive, likely by the end of the decade. That could be too much to ask of slow-moving species, like some lizards, tortoises, and the Joshua trees themselves. And even quick and ubiquitous species like the side-blotched lizard may suffer. These animals are short-lived, and when a generation only lasts 14 months, a multi-year drought can be devastating. “They’re so common in most places, no one pays them much heed,” Barrows says. But “the population crashes very quickly.”

Today, side-blotched lizards are almost gone from low elevation sites in Joshua Tree, but at higher, cooler, and wetter elevations, their numbers are actually increasing, Barrows says. If populations may keep moving upward as temperatures rise, eventually there will be nowhere left to run.

A baby tortoise (Cameron Barrow)

That forecast may seem bleak, but by tracking the effects of climate change now, and its predicted impacts in the future, Barrows hopes to find oases in the desert. On his excursions into the park, he records the age and location of each reptile he finds, and plots his sightings on a series of maps. By comparing the maps over time, he can see patterns of change across the landscape, and pockets of relative stability. Those pockets are key to sustained conservation in the park, because they are the places where species will hold out, “even if climate change gets really bad,” Barrows says.  

Rather than hot, dry wastes—immune to the effects of climate—deserts, as scientists like Barrows see them, are a canary in the coal mine. They’re “our first glimpse into how severe climate change might get,” Barrows says. By watching how they change, and how they don’t, perhaps we can better prepare for an uncertain future.