April 16, 2024

This story was originally published by Yale Environment 360 and is reproduced here as part of the Climate desk cooperation.

In August 2021, rain fell on top of the 10,551-foot summit of the Greenland Ice Sheet, causing an epic collapse and a more than 2,000-foot retreat of the snowline. The unprecedented event reminded Joel Harper, a glaciologist at the University of Montana who works on the Greenland ice sheet, of a strange anomaly in his data, one that suggests it might have rained much later in the season in 2008 — in the autumn, when the region is typically in deep freeze and dark for almost 24 hours a day.

When Harper and his colleagues scrutinized the measurements they collected from sensors on the ice sheet many years ago, they were amazed. Not only did it rain, but it rained for four days as the air temperature rose 30 degrees C (54 degrees F), near and above freezing. It warmed the summit’s solid layer — snow that is turning to ice — by between 11 and 42 degrees F (6 and 23 degrees C). The rainwater and surface melt that followed penetrated the firn by as much as 20 feet before it refroze, creating a barrier that would alter the flow of meltwater the following year.

All that rain is significant because the melting of the Greenland ice sheet – like the melting of other glaciers around the world – is one of the main drivers of sea level rise. Every time a rain-on-snow event occurs, Harper says, the structure of the firn layer is changed, and it becomes a little more susceptible to impacts from the next melting event. “This suggests that only a small increase in frequency and intensity of similar rain-on-snow events will have a large impact in the future,” he says.

Rain used to be rare in most parts of the Arctic: the polar regions were, and still are, usually too cold and dry for clouds to form and absorb moisture. When precipitation did occur, it mostly came as snow.

Twenty years ago, annual precipitation in the Arctic changed from about 10 inches in southern areas to as little as 2 inches or less in the far north. But as Arctic temperatures continue to warm three times faster than the planet as a whole, melting sea ice and more open water, according to a recent studybringing up to 60 percent more precipitation in the coming decades, with more rain falling than snow in many places.


Such changes would have a profound impact on sea ice, glaciers and the Greenland ice sheet — which is already melting at record rates, according to Mark Serreze, director of the National Snow and Ice Data Center at the University of Colorado. The precipitation will cause more flooding; an acceleration in permafrost thawing; profound changes to water quality; more landslides and avalanches; more misery for Arctic animals, many of which are already rapidly declining due to the changing climate; and serious challenges for the indigenous peoples who depend on those animals.

Changes can already be seen. Thunderstorms are spawn now in places where they were historically rare. In 2022 the longest thunderstorm in the history of Arctic observation was recorded in Siberia. The storm lasted nearly an hour, twice as long as typical southern thunderstorms. Just a few days earlier, a series of three thunderstorms passed through a part of Alaska that rarely experiences this.

Surface cracking, which allows water to enter the interior of the ice cap, is accelerate, thanks to rapid melting. And slush avalanches, which mobilize large volumes of water-saturated snow, are becoming common: In 2016, a rain-on-snow event Caused 800 avalanches in West Greenland.

Rick Thoman, a climate scientist based at the University of Alaska Fairbanks, says that rainfall has increased at any time of the year 17 percent in the state over the past half century, causing flooding that closed roads and landslides that one casesent 180 million tons of rock into a narrow fjord, generating a tsunami that reached 633 feet in height—one of the tallest tsunamis ever recorded worldwide.

But winter rain events are also on the rise. Where Fairbanks used to see rain on snow about two or three times a decade, Thoman says, it now occurs at least once most winters. This is a problem for local drivers because with little solar heating, ice that forms on roads from November rains usually stays until spring.

Two caribou walk down a grass slope to a sandy beach next to a block of solid ice.
Caribou walk in the foreground of a glacier on July 12, 2013 in Kangerlussuaq, Greenland.
Joe Raedle/Getty Images

The science of both rain and rain-on-snow events in the Arctic is in its infancy, and is complicated by the fact that satellites and automated weather stations have a hard time distinguishing between snow and rain, and because there is no enough scientists on the ground to evaluate firsthand what happens when rain falls on snow, says Serreze.

It was hunters who first reported in 2003 that an estimated 20,000 muskox starved to death on Banks Island, in Canada’s High Arctic, after an October rain-on-snow event. It happened again in the winters of 2013-2014 and in 2020-2021, when tens of thousands of reindeer died on Siberia’s Yamal Peninsula.

In both places the rain hardened the snow and in some places produced ice, making it almost impossible for the animals to dig down and get to the lichen, sedges and other plants they need to survive the long winter. survive.

Kyle Joly, a wildlife biologist with the US National Park Service, sees an increase in rain-on-snow events as another serious challenge for the world’s 2.4 million caribou, which in rapid deterioration virtually everywhere over the past three generations. The ebb numbers are a major concern for northern indigenous people who rely on caribou for food. Public health experts fear that indigenous health will be dire compromised if the animals can no longer be hunted.

Alaska’s western Arctic herd, once the largest in North America, had 490,000 animals in 2003, but only 152,000 in 2023. But at least that herd can still be hunted. In Canada’s central Arctic, the Bathurst herd dropped from around 470,000 animals in the 1980s to just 6,240 animals today; hunting those caribou in the Northwest Territories is currently prohibited.

Caribou are highly adaptable to extreme environmental variability, and their numbers can rise and fall for a variety of reasons, according to Joly. The spread of biting flies in a warm climate can suppress their energy, as well as migration detours forced by the spread of roads and industrial development, and an increase in landfills of deep, soft snow, which with the loss of sea- ice is connected. (An ice-free ocean surface increases humidity near the surface, leading to more moisture in the atmosphere.)

Sharp ice and crusty snow can also lacerate caribou’s legs, and rain on snow has occasionally affected some of Alaska’s 32 caribou herds. For example, the day after Christmas in 2021, temperatures soared to more than 60 degrees F (15 degrees C) during a storm that dropped an inch of rain across much of the state. Alaska’s Fish and Game Department estimated it 40 percent of the moose, caribou and sheep in the interior of the state perished that winter because they could not dig through the hard snow and ice.

It is not only caribou and mouse dogs that are threatened. It is growing proof that rain that falls in parts of the arctic where precipitation usually comes as snow is killing peregrine falcon chicks, which only have downy feathers to protect them from the cold. As soon as water soaks them, the chicks succumb to hypothermia.

Few scientists have evaluated the hydrological and geochemical impacts of rain-on-snow events in polar desert regions, which are underlain by permafrost and receive very little snow in winter. Recent studies published by Queen’s University scientist Melissa Lafrenière and colleagues from several universities in Canada and the United States point to an alarming picture unfolding at the Cape Bounty Arctic Watershed Observatory on Melville Island, in Canada’s High Arctic, which since 2003 is in effect.

A shift of runoff dominated by spring and summer snowmelt following both rain and snowmelt accelerates thawing of permafrost and subsidence, filling fish-bearing lakes with sediments. One study found a fifty-fold increase in turbidity in one lake that led to an increase in mercury and a decrease in the health of Arctic char, a fish relied on by the Inuit of the Arctic.

Lafrenière says with only 20 years of measurement it is difficult to definitively point to a trend. “But we’ve seen more rain fall in bigger events, especially in late summer. In 2022, we had exceptionally heavy rains that dropped an average summer’s rain in less than 48 hours.”

To help scientists and decision makers better understand the impact of what’s happening, Serreze and his colleagues created a database of all known rain-on-snow events across the Arctic. And increasingly, scientists like Robert Way of Queen’s University in Canada are working with the Inuit and other northern indigenous peoples to establish the truth of what they think the satellites and automated weather stations are telling them and to share the data they collect and evaluate.

Way, who is of Inuit descent, was a young man when he saw parts of the George River herd, one of the world’s largest caribou herds, migrating across the ice in central Labrador. “There were thousands and thousands and thousands of them,” he recalls with wonder. The herd contained 750,000 animals in the 1980s; today it has no more than 20,000. The animals face the same climate change challenges that caribou face everywhere.

Way is working with Labrador’s Inuit to better understand how these weather events will affect caribou and food security, as well as their own journey on snow and ice. But, he says, “It’s getting harder and harder to do this research in Canada because half the weather stations are closed” because of federal budget cuts. Most of the manually operated stations, Way adds, “are being replaced by automated stations that produce data that makes it difficult for scientists to determine whether it’s raining or snowing when temperatures hover around freezing.”

To better understand how rain-on-snow events affect the Arctic, Serreze says, researchers need to better understand how often and where these events occur, and what impact they have on the land and seascape. “Satellite data and weather models can reveal some of these events, but these tools are imperfect,” he says. “Confirming what is happening on the surface and the impact of these events on reindeer, caribou and muskox requires people on the ground. And we don’t have enough people on the ground.” Researchers need to work with indigenous people “who are directly dealing with the effects of rain on snow,” he noted.

In 2007, Serreze said in a University of Colorado Boulder study that the Arctic climate may have reached a climate change. turning point which can cause a cascade of events. More rain than snow falling in the Arctic is one such event, and he expects more surprises to come. “We try to keep up with what’s going on,” he says, “but we keep getting surprised.”

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