LONGYEARBYEN, NORWAY—Thick sheets of ice coating roads, homes, and pastures. Dead reindeer, no radio transmissions, and flights canceled for days. When ice came to this Arctic mining outpost on the Svalbard archipelago two winters ago, it crippled the community for weeks and devastated wildlife for months. Now, scientists are saying such weather extremes in the Arctic—known as rain-on-snow events—may become more frequent in the future.

“It’s hard to study extreme weather events, which by definition are rare,” says ecologist Brage Hansen of the Norwegian University of Science and Technology in Trondheim. “So we took the opportunity in 2012.”

Brage and his co-authors focused on the rainy warm spell that brought record-high temperatures and prolonged rain to Svalbard over 2 weeks in January and February 2012. Temperatures during that period were routinely 20°C higher than normal, and on one day, the study notes, a Svalbard weather station recorded a daily average temperature of 4°C, which was “higher than at any weather station in mainland Norway on that day.” Another Svalbard station recorded 272 mm of rain during the 2 weeks; that station’s average for the whole year is 385 mm.

The water created thick pools of slush and melted snow, kept cold by the frozen ground, known as permafrost. Then temperatures dropped and everything froze, leaving Svalbard’s fjords and towns coated in thick ice, terrorizing its roughly 2000 inhabitants and decimating the most abundant animals on the archipelago—wild reindeer. Scientists measured ground ice between 10 and 20 cm thick in 200 test sites, and more than half of the ground area they monitored was still covered in the ice 5 months later.

The ice forced road closures in Longyearbyen, Svalbard’s largest settlement, and caused a so-called slush avalanche—consisting of snow, ice, and slush—that destroyed a pedestrian bridge. The town’s central antenna was disabled, halting radio transmissions, and an icy runway meant that flights to and from the archipelago were canceled for days. “Furthermore, snow-mobile driving, dog-sledding and hiking were nearly impossible during the weather event” and for months after, notes the paper, published today in Environmental Research Letters.

The impact on Svalbard’s reindeer was severe, as ice prevented the animals from digging through the snow to eat plants. In the summer of 2012, scientists found high numbers of carcasses in all seven of Svalbard’s monitored populations, and a record number in one of them.

This is “a huge difference from the historical norm,” Hansen says. “It’s important because this is the type of event we can assume will be more frequent in the future.” That’s a big problem, because the indigenous people of the Arctic depend on snowy tundra ecosystems and their wildlife. Plus, ice storms could wreak havoc on shipping, mining, and fossil fuel industries as they develop in the high latitudes.

A series of climate models the scientists used to predict local warming in the high Arctic estimated that warming temperatures will continue for years. Hansen says if those predictions bear out, some winters by 2050 could have periods with a mean temperature above freezing. More ice would then follow, which could mean “a completely different” climate on Svalbard, Hansen says, with the 2012 event an icy preview.

Geologist Jaakko Putkonen of the University of North Dakota in Grand Forks applauds the paper’s analysis of the 2012 Svalbard incident, “the best documented” of known rain-on-snow events. Reindeer and their cousins, muskoxen, “are facing an unsolvable dilemma,” he says. “As the environment in their current ranges is becoming less suitable for them … they have no land area to retreat to farther north. They will be pushed into the Arctic Ocean, metaphorically speaking.”

But winter rain in the Arctic may alter marine ecosystems as well as terrestrial ones, says Cecilia Bitz, an atmospheric scientist at the University of Washington, Seattle. The sea ice is where ringed seals live. Rain on snow “can collapse their snow caves where they raise their young,” she says. Along with the declining amount of floating ice, she adds, rain on snow is a reason the animals have been listed as threatened.

One question the study leaves unanswered is how icy spells may affect local vegetation in the tundra. So on a windy, sunny day in July, Hansen and an assistant visited experimental plots they had established in a high Arctic valley on the Advent fjord outside Longyearbyen. During the dead-of-winter months before, the scientists poured gallons of water onto the snow on several half-meter-wide squares denoted by green markers. Now, to measure how the ice might have an impact, they’re comparing plant growth in the plots with growth in other plots that remained snowy, not icy. “There might be a delayed effect on growth, or an effect on flowering—we don’t know,” Hansen said, examining one of the plants. The scientists are now analyzing their samples from this experiment, and Longyearbyen is girding for what it hopes will be a snowy, not icy, future.