When wildlife biologists visited a remote spot in Canada called Banks Island in the spring of 2004, they discovered thousands upon thousands of dead musk oxen. It took years to determine the cause. They called it "rain-on-snow" — the worst case of it ever documented.
"Long story short, about 20,000 musk oxen starved to death because of this event," says geologist Jaakko Putkonen. It was a "humongous event" that took place in the fall of 2003.
Putkonen, who is a professor at the University of North Dakota, has since discovered a few anecdotal accounts of big rain-on-snow events that killed reindeer in the Arctic and in Scandinavia.
What happens is this: Unusually warm weather drops rain on top of snowpack. The rain either pools at the surface or trickles down to the soil below the snowpack, then freezes into a sheet of ice. Musk oxen, which are shaggy, cow-sized animals that weigh hundreds of pounds, can't break through the ice to browse on plants underneath the snow. Sooner or later, they starve.
Putkonen says it's hard to know where and how often this is happening. The Arctic is vast and remote, and one never knows where or when a rain-on-snow event will happen. Even if you put down instruments to record one, they freeze up or get snowed under.
Now, this may be bad news for musk oxen or reindeer or caribou, but is it really a big deal? Putkonen and his fellow rain-on-snow experts — there aren't many in this specialty yet — think it is. They suspect that a warming climate may increase the number and geographic reach of these events.
"If the climate warms up, it doesn't just grow palm trees in sunny Fairbanks, Alaska," says Tom Grenfell, an atmospheric scientist at the University of Washington. "It creates more storms and mixes the atmosphere up a lot more." That could mean more rain-on-snow events, he says.
Grenfell says rain-on-snow events could also affect people who live in the high northern latitudes. "There are other places around the Arctic that have these things," he says, "like Finland and Russia, where people herd reindeer or caribou and depend for their livelihood on these things."
But so far no one knows whether these events are increasing — no one has ever checked. That's what Putkonen and Grenfell are planning to do next. They've figured out what rain-on-snow looks like on a satellite image.
Now, they have 30 years of images of the Arctic to look through.
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