Visitors to the Santa Catalina Mountains just outside Tucson, Arizona encounter a very disturbing sight: patches of dead alligator junipers scattered across hillsides at the base of the range. Wildfires did not destroy these trees — climate change did.
The trees can’t survive where it’s hot, so many have moved to higher elevations, where it is cooler. But if the heat keeps rising, they will die there too, and eventually cease to exist entirely.
“They can’t cope with the conditions,” says John J. Wiens, professor of ecology and evolutionary biology at the University of Arizona. “They simply can’t change fast enough.”
What is far worse, however, is that this is no isolated example.
The plight of the alligator juniper is but one obvious piece of a frightening pattern of local extinction currently underway “everywhere, all over the planet,” Wiens says, “It is happening among birds, plants, animals, in the ocean and in the freshwater environment.”
Climate change could doom numerous species irreversibly, including those that people depend on for resources and food. “If it’s happening a little now, it will happen a lot in the future,” Wiens says. “We have a moral imperative to be sure that the future does not play out.”
The trend is especially troubling in tropical and subtropical environments––lowland places like the rainforest, where climate-threatened species have nowhere else to go. “For plants and animals that can’t move, they’re dead,” Wiens says.
Wiens recently examined the fate of hundreds of plant and animal species around the world, concluding that local extinctions already have occurred in nearly half of the 976 species he studied. His research, published today in PLOS Biology, found that 450 plant and animal species have disappeared locally, a result he finds especially striking, since mean temperatures have increased less than 1 degree Celsius since the pre-industrial era.
“Local extinctions are already widespread,” he says. “The results suggest that even modest changes in climate are enough to drive local populations in many species to extinction. They also suggest that local populations in many species cannot shift their climatic niches rapidly enough to prevent extinction. We know the climate is going to change even more, which bodes really badly for overall survival.”
Camilo Mora, assistant professor of geography at the University of Hawaii at Mānoa, who has studied the impact of climate change on plant growth, describes Wiens’ work as an important new piece of evidence of “the massive destruction of nature” caused by human-induced warming.
“The fingerprint of climate change on nature is demonstrated yet again,” says Mora, who was not involved in Wiens’ study. “This is not rocket science. Whenever you heat up a place, species are forced to deal with it. Climate change, compounded by other stressors, appears to be too much for species to take. Clearly, we are making it hard for species to endure us.”
Jeremy Kerr, a professor of biology at the University of Ottawa who has studied the effects of climate change on bumblebees, called these growing extinctions “dangerous [because] we rely on a lot of these species for ecosystem services we can’t really do without, like pollination.”
“Some of the species that are disappearing serve critical functions,” he adds. “We all know about monarch butterflies, one of the most beautiful animals in the world. Climate change… is contributing to their decline. Other animals that are even more important for practical reasons are bumblebees, and we now know that climate change is part of the reason for their decline also. These losses chip away at the planet’s life support systems, which we need.”
David Inouye, a professor emeritus of biology at the University of Maryland who studies the impact of climate change on the environment, agrees.
“Scientists have predicted for a while now that we are entering the sixth major mass extinction event in the history of life on the planet,” he says. “Evidence for this is now accumulating…this study provides insights into the range shifts that can already be documented in both plants and animals in response to the changing climate, and how the dynamics of range shifts can lead to local, and eventually, global extinctions.”
In fact, Inouye says, he has seen similar trends in his own research. “In my work in the Rocky Mountains, we have observed several species of animals, from moose to mosquitoes, moving up in altitude, and plants disappearing from the lower part of their former ranges,” he says. “Bumblebees are also moving up in altitude. If plants and pollinators don’t move at the same rates, historic interactions will be disrupted, potentially leading to more examples of local extinctions.”
Even those species that try to move upward may not be able to do so, according to the new study. Human factors, such as agriculture, roads, and increasing urbanization may impede their ability to relocate by leaving them no other live-able habitats, the study says.
Moreover, “many species are already confined to islands, peninsulas and mountaintops where dispersal to higher latitudes or elevations may not be possible,” the study says, adding: “Even if dispersal is unimpeded by human or natural barriers, it may simply occur too slowly to allow species to remain within their climatic niche.”
If the heat doesn’t kill directly, it can encourage potentially dangerous interactions, Wiens says. Certain plants may become vulnerable to beetle attacks, for example, and amphibians are prone to the deadly chytrid fungus, whose growth is stimulated by heat.
“In Arizona, we no longer have any natural Tarahumara frog populations because of the fungus,” Wiens says. “Climate is the basic cause, but the proximate cause may be something else.’’
For his study, Wiens conducted a meta-analysis of dozens of existing studies demonstrating how species have shifted their geographic ranges over time in response to global warming. Using these “range-shift” studies, he found that local extinctions have occurred in the warmest parts of the ranges for nearly half of the plant and animal species studied.
His research also found that local extinctions varied by region, and were more than twice as likely to occur among tropical species compared to those in more temperate locations. This latter is important because most plant and animal species live in the tropics.
“If species live in a preserve in the topics, or in a place that has been deforested, it’s not really possible for them to move,” Wiens says. “They may be able to move up a mountain in Arizona, but that’s not going to work in a rainforest.”
“We are locked into a climate pattern, and things don’t seem to be able to adapt,” added Wiens. “This is only going to get worse if the climate warms further.”
Mora, of the University of Hawaii, agrees. “When places start failing to meet basic human needs for water… We will also very likely start seeing people moving as well,” he says. “Our planet is increasingly becoming unsuitable for many species, potentially even us.”
Marlene Cimons writes for Nexus Media, a syndicated newswire covering climate, energy, policy, art and culture.