The pace of the human-caused climate change we see today is more rapid than anything humans – or the animals we share the biosphere with – have ever experienced. A 2016 study suggested the Earth’s global temperature has increased by about 4°C over the past 10,000 years as the planet emerged from the most recent ice age. This major warming cycle transformed ecosystems and caused the extinction of species like woolly mammoths and saber-toothed cats. By comparison, the warming trend of the past 150 years is unfolding 20 times faster. Some models predict that warming could intensify to about 50 times faster than the post-ice-age rate over the next 80 years. Such a rapid rise in temperature has and will continue to tax the ability of animals, plants, and humans to adapt. Let’s look at some of the forces at play when animals find themselves in an era of rapid climate change.
Melting Ice & Shriveling Snowpack
The polar bear is probably the most well-known animal directly affected by climate change. This apex carnivore depends on the very sea ice that is rapidly dwindling. Polar bears rely on Arctic sea ice to hunt their primary prey – seals – which they ambush on the ice floes. Less ice means fewer opportunities for a meal and less food for their young. The prevalence of open water in the Arctic Ocean reduces hunting grounds for polar bears, but it may expand the range of another mighty predator, the orca. More killer whales in Arctic waters will likely have ripple effects down the food chain.
Melting ice and famished polar bears in the Arctic may be an especially potent sign of a warming planet, but current climate change is impacting animals all across the globe. Moose in the Midwestern region of the United States are becoming infected with brain worms and liver flukes brought northward by expanding white-tailed deer, who are unaffected carriers of these parasites. It is also causing ramped-up tick infestations thanks to milder winters—a problem that’s also been killing moose calves in New England.
Up in the mountains of western North America, little rabbit relatives known as pikas are another creature in the crosshairs of climate change. Adapted to the snowy high country, pikas may soon run out of habitat in many mountain ranges. Warmer temperatures will stress their bodies in summer and as the snowpack that helps insulate pikas from subzero temperatures in winter diminishes, some will freeze. As they search for a rangeland that is just right for their evolutionary skills, they will crowd each other out. Evidence suggests these effects have already fragmented and reduced pika geography in places such as California’s Sierra Nevada. Decreasing mountain snowpack may also shrivel the range of one of North America’s rarest and least-understood carnivores, the wolverine, which relies on deep snowdrifts lasting late into spring and early summer to rear its young.
Warming Water, Warming Land
In the Gulf of Maine, warming ocean temperatures are forcing Atlantic herring and hake—the main summer food of puffins—into northern and deeper waters. That reduces the availability of the seabirds’ mainstay prey during the critical nesting season. Puffins appear to be seeking out alternative menus, but not always successfully. Scientists have seen puffins bringing butterfish to their chicks, which can’t easily swallow their larger bodies.
A new study by the University of Washington and the NOAA Northwest Fisheries Science Center suggests the acidification of our oceans from anthropogenic emissions of carbon dioxide may hamper salmons’ sense of smell, which rely on olfaction to find food and navigate to spawning waters. If they can’t return to their spawning grounds – often hundreds of miles through inland waterways – they can’t maintain their population levels, and they face the possibility of extinction. In some reptiles, ambient temperature determines the sex of developing eggs, which means a warming climate may cause population imbalances. Higher temperatures, for example, may skew sea-turtle populations to a female-heavy state.
Shifting Weather Patterns
Like many creatures, sea turtles face multiple challenges from a changing climate. Rising sea levels and potentially more frequent, intense hurricanes resulting from warming temperatures may eliminate turtle nesting beaches. At one point in time, the loss of a nesting beach might not have been so devastating to a sea turtle that could simply seek out another sandy seashore elsewhere. These days, though, many potential nesting sites have been lost to human development.
Along with stronger storms, warming temperatures are likely fueling bigger, fiercer, and more numerous wildfires in many parts of the world, including the American West. Fire is a natural element of global ecosystems, but enhanced frequency and intensity may threaten even the most fire-adapted species. This additional threat is more damaging where an animal population is perilously low to begin with, or can’t move elsewhere because of human development or other habitat loss. For instance, a 2017 wildfire in Arizona roared through the only remaining stronghold for the endangered Mount Graham red squirrel, only 35 of which were estimated to survive the burn. (The squirrels are showing some encouraging signs of a rebound, thankfully).
Evolutionary Response to Climate Change
It’s important to emphasize that animals have dealt with climate fluctuations – sometimes extreme – throughout life’s history on Earth. Climate and its shifts across time is one of the great driving forces of evolution. But by altering food availability and habitats, allowing the spread of predators, competitors, and pathogens, and otherwise upending ecosystems, climate change is also a major cause of extinction. Over the long term, many animal species can adapt to a changing climate, often by evolving into new species better configured for the new environment. But evolution takes time. In the short-term, populations decline, geographic ranges contract, and creatures unable to adjust quickly enough go extinct. The faster climate change happens, the less time animals have to adapt, which is why the current rate of global warming is so threatening to wildlife numbers.
When it comes to a rapidly changing climate, the threats to animals stack up. Besides transforming ecosystems and altering the nature of disturbances such as storms and wildfires, climate change acts in concert with the spread of invasive species and diseases, the reduction of habitat due to development and resource extraction, and pollutants caused by human activity. Because many of the sources of stress on animal populations come from human activity, there’s a lot we can do about it.
It’s also important to remember that humans are animals, too, and the same threats faced by wildlife also threaten us. As we depend on animals for our own existence, we would benefit from including their well-being in our efforts to be better stewards of the planet.
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