Warming Signs: How Diminished Snow Cover Puts Species in Peril
he wolverine is highly adapted to life in a snowy world. It has thick fur and snowshoe-like feet, and it dens high in the mountains as a way to avoid predators that aren’t as nimble in deep snow and to provide its kits with insulation from the bitter high-elevation cold.
lynx have snowshoe-like feet that give them
a competitive edge in catching prey on thick snow.
STANISLAV DUBEN
a competitive edge in catching prey on thick snow.
STANISLAV DUBEN
But as snow cover in western North America diminishes — across much of the Rocky Mountain West there are up to two fewer weeks of snow cover than a half-century ago, a trend that’s expected to worsen — the wolverine is finding it tough sledding.
The wolverine raises kits in the spring, into May. With spring arriving markedly earlier, the animals may not be able to find new den sites because the snow that once lasted until later in the season has already melted. And because a great deal of the reduction in snowpack is taking place at lower elevations, it could mean that the best snowy habitat will be widely separated and will prevent wolverines from traveling from mountain range to mountain range. Some worry the animal may simply abandon the Northern Rockies, its last stronghold in the Lower 48 states.
“This is an animal that operates in a very specific habitat,” said Jeff Copeland, a retired U.S. Forest Service wolverine biologist and board member of the Wolverine Foundation. “Wolverines don’t reproduce in the absence of snow. We will be able to maintain them in the snowiest habitats, but we will probably lose them in some places.”
Wolverines are just one of the species facing the impacts of reduced snow cover in many parts of the globe. The cryosphere — those places where water on the planet is in solid form — is rapidly shrinking and otherwise changing. Many plants, animals and other species have adapted to living in, under, or on top of a white blanket of snow and ice. They have also adjusted to the rhythm of snow, ice, and thaw, and as snow cover diminishes and changes because of warming, these organisms are having to adapt to a new, very different reality.
Much of the western United States experienced sharp declines in April snowpack (shown in red) from 1955 to 2016
The impacts of diminishing snow cover on ecosystems, animals, and plants can be highly disruptive. Root systems lose the insulation of snow that protects trees from extreme cold. Animals, such as the lynx, that are adapted to snowy regions have a harder time pursuing prey. Creatures whose coats or coloration turn white in winter are more exposed to predators. Fires become more common in higher or more northerly regions, and diminished snowmelt reduces flow into streams and rivers, harming aquatic life.
“Snow is the king when it comes to effects on ecosystems,” said Daniel Fagre, a geologist with the U.S. Geological Survey (USGS) in Glacier National Park. “The effects of disappearing glaciers are pretty tiny. But snow is so dominant because it holds a huge amount of moisture for a large part of the year as a natural reservoir system. And it releases all that collected moisture slowly as it warms, so plants — and irrigators — can use it. If we lose that, it will cause fundamental changes not only to ecosystems, but to how people use water in the West.”
Snow cover in the Northern Hemisphere has been diminishing since the era of satellite monitoring began in the 1960s. The snow in the Alps has been particularly hard-hit, disappearing faster than other parts of the world. The European mountain range has warmed 3.6 degrees Fahrenheit over the last century, twice the rate of warming in other parts of the world. And a recent paper found that if little to nothing is done to slow climate change, the Alps could lose 70 percent of their snow cover by 2100.
A number of researchers are looking at the cascade of effects of a dwindling snowpack, which will be widespread since nearly a quarter of the planet is covered with seasonal snow. And because the earth is warming, the precipitation that used to fall as snow now comes as wet snow or rain, precipitation types that course through the system faster than the many feet of snow that were held high in the mountains in below-zero temperatures much longer into the spring and summer. In fact, warming wintertime minimum temperatures in the West’s mountain valleys are one of the region’s strongest signals of climate change.
Snowshoe hares have been shifting their range north at the rate of more than five miles a decade in response to declining snow cover. MARIO TAMA
The ecosystem changes from reduced snow cover are legion. One of the most important stems from the fact that snow cover plays an essential role in regulating the earth’s climate. White snow reflects as much as 90 percent of solar radiation back into space, while darker-colored plants and soil reflect just 10 percent to 30 percent of the sunlight, and so the ground absorbs much more of the sun’s energy. That causes a positive feedback — the warmer earth melts more snow, which exposes more ground, which absorbs more warmth. This feedback contributes to the rise in global temperatures.
Snow is also an effective insulator that keeps everything from tree roots to soil life to wildlife such as the wolverine warm in the coldest winters. When the ground is bare in cold weather, tree roots can be killed. Researchers also suspect it could affect the interaction between plant roots and the dense community of microbes the live around them and perform vital ecosystem functions such as filtering clean water for the trees — and human communities.
Snow, ice, and water have very different properties, and a variation in state changes can have very different ecological effects. As temperatures rise and snow thaws and freezes more often, for example, this forms a crusty barrier that hinders the ability of bison, elk, deer, and other browsers to forage.
Some predators suffer, too. Lynx, with their snowshoe-like feet, are built for walking on a blanket of snow. With more ice or bare ground, they lose their evolutionary advantage over coyotes and other predators and find themselves in greater competition for prey.
Researchers in Wisconsin have found that snowshoe hare are shifting their range north at the rate of more than five miles a decade, in sync with the receding snow line, presumably to maintain their camouflage advantage. Other researchers have found that many snowshoe hare populations have not been able to adapt to the ground becoming snow-free earlier, while the animals are still in their white phase.
White hares lose all camouflage against a brown background, researchers say, and there is a mortality cost — a seven percent drop in their weekly survival rate. “Mismatch costs are severe enough to cause hare populations to steeply decline in the future unless they can adapt to the change,” said Marketa Zimova, a PhD candidate at the University of Montana who worked on the project.
There is a glimmer of good news in the fate of the hare. Some individuals molt at different times, and natural selection should favor those that turn brown earlier in the year, although there might not be enough time for evolutionary processes to adjust. Researchers say it’s important to maintain habitat connectivity to keep large populations — and their sizable gene pool — intact.
At least 14 species worldwide, from weasels in Siberia to arctic foxes in Sweden, could be affected by camouflage mismatch from disappearing snow, according to researchers.
Reduced snow cover is impacting the Hudsonian godwit, a migratory bird that flies from South America to Canada in the spring. While overall the planet is warming, the route the birds follow through Nebraska, South Dakota, and Manitoba is generally cooling. When the birds cross the plains, the cooler air is telling them to slow down. So instead of arriving in early May, as was their custom, they arrive in late May and lay their eggs. Their babies are born in mid to late June.
The rub is that early June temperatures are warming very rapidly, and so the snow melts in a matter of a few days. “After the snow melts, it starts to get hot right away,” Senner said. “It can go from 3 feet of snow to completely snow-free within four days.” Pack ice in the Hudson Bay and Arctic Ocean is also melting earlier, which contributes to regional warming. That prompts insects to hatch earlier than usual.
“The baby godwits are out of phase with the peak insect abundance,” Senner says, hatching too late to take advantage of the fly larvae and caterpillars. As a consequence, the babies are starving to death. Just 3 percent of the chicks in the Manitoba population survive, while 25 to 30 percent of the Alaska population of Hudsonian godwits make it to adulthood. “The survival rate is not sustainable,” Senner says of the Canadian godwit. It is one of the fastest-declining species of shorebird in North America.
Alpine regions in the Rockies are also seeing fundamental changes because of less snow. Trees that used to have snow around them all year now experience long periods of bare ground when their seeds can germinate and establish, and in many places trees are crowding alpine meadows. Another feedback is that less snow is windblown because large numbers of trees act as a snow fence and block the wind, and so snow builds up and, when it melts, fosters more tree growth. More trees in alpine meadows means less grass and forage for browsing animals.
“And because you now have continuous fuel with all of these trees increasing biomass, you can now carry fires into the alpine area, where they weren’t able to go because it was too dispersed,” said Fagre. “We’ve had several tree line fires that, anecdotally, have not occurred in the past.”
Declining snowpack is also contributing to more forest fires at lower elevations, and more intense fires. Forests retain snow on the ground for a much shorter period than they used to and get rain instead, which disappears much faster, especially with warmer temperatures. Fires now occur much later in the year and earlier in the spring. The devastating fires around Fort McMurray, Alberta in May 2016 — which swept across 1.5 million acres and forced the evacuation of 90,000 people — were largely due to very early spring snowmelt, according to David Robinson, director of the Global Snow Lab at Rutgers University, which studies snow cover. Temperatures then rose into the 80s and 90s that spring, helping the fires burn into July.
“There’s a very strong connection between the early loss of snow and fires,” Robinson said. Some experts predict we are heading for year-round fire seasons in many colder regions.
The lack of lingering moisture from snow, combined with warmer temperatures, also contributes to disease and pest outbreaks because water stress reduces a forest’s ability to resist both.
Earlier snowmelt means that rivers and streams will run out of water sooner in the summer and impact aquatic life as waterways diminish and sometimes dry up in summer. The areas most affected by this projected reduction of snow, a studyfound, include California’s Central Valley, the Rio Grande Valley, parts of North Africa and Southern Europe, the Mediterranean, and the Middle East. And of course human communities will be greatly impacted as well.
“People in urban areas don’t think about the fact that water could come from a thousand miles away, from a Rocky Mountain snowpack that is affected by dust, affected by climate change, affected by increase tree growth that uses more of the available water,” said Fagre of the USGS. “The fundamentals are clear – we depend on snow, period.
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