Three weird winters have people wondering if this is new normal. Should Anchorage get used to daffodils in February and bringing in trainloads of snow from Fairbanks for the sled dog races?
The answer is no. According to climate models, a winter like this one or last year's in Southcentral Alaska shouldn't be average for a century.
"Don't get rid of your skis. This is not the end of snowy winters," said Nancy Fresco, a research professor at University of Alaska Fairbanks.
Fresco oversees a network of researchers that uses global computer models of the climate to project what will happen at particular places in Alaska, a program called SNAP, for Scenarios Network for Alaska and Arctic Planning. According to their scenario for Anchorage, the average temperature in January of this year, at 27.2 degrees Fahrenheit, was 2.4 degrees higher than the models predict for January in 2099.
That doesn't mean the models are wrong — although they might be. And it doesn't mean climate change is irrelevant. Having three failed winters was a coincidence. Climate change made that coincidence more likely.
"These three non-winters in a row for Anchorage are somewhat indicative of a trend," Fresco said. "Having three such winters in a row was more likely in this decade certainly than it would have been 50 or 100 years ago. What was an unthinkable coincidence back then is something that could and did happen now."
Mark Serreze, director of the National Snow and Ice Data Center and a professor at the University of Colorado, said the Arctic was "crazy" this year. The North Pole had close to thawing temperatures in late December.
"You've got a very, very unusual kind of weather pattern that has set up that is making it very, very warm," he said. "So this winter is really not the new Arctic."
But it will be, he said. Extremely unlikely events are becoming more likely.
One way of understanding climate is to think of it in terms of latitude. It seems impossible now for Anchorage to have an 80-degree day in January, but in Honolulu that happens all the time. If you move Anchorage gradually closer to Honolulu, the probability of having 80 degrees in January slowly grows more likely — although you would never know exactly when that warm day might come.
By changing the Earth's atmosphere, we've moved Anchorage far enough south that the impossible has become possible. But the details of our low-snow winters are more complicated.
"Each of the three winters have been similar but different," said Gene Petrescu, regional scientist for the National Oceanic and Atmospheric Administration.
Their similarity is the influence of a vast pool of warm water in the tropical Pacific Ocean. It produced fields of thunderstorms as large as Alaska. Those storm systems powered and redirected the flow of weather.
During the winter of 2013-14, the warm water pool was in the far western Pacific, Petrescu said. It sent strong flows of wet, tropical air north and east to Alaska.
The next winter, 2014-15, the area of tropical warm water had moved east. Now the flow of warm air curled over North America, diverting toward us when it hit the mountains. That made the warm air we received drier and drove the snow line far up the mountains.
This winter, tropical warm water has moved far enough east to spawn an El Niño weather pattern, which combined with the bizarrely warm Arctic — doubly unusual, because the weather on each side of us doesn't usually coordinate that way. We've had record low snow with stable warm temperatures, but the air has been cool enough to allow snow to it to stick at higher elevations.
Warm weather in early winter is a big deal for Anchorage because most of our precipitation falls in the first half of winter. If it comes as rain, we often have a long wait for snow.
For next year, Petrescu is expecting a La Niña pattern, which usually produces colder, more changeable winters in Alaska. Less chance of getting skunked for snow. Or maybe we'll have a record snow, as we did in the winter of 2011-12.
So if a big area of warm water in the topics is messing up our snowmachining, dog sledding and skiing, why is that water so warm? Is that warmth partly driven by climate change?
Maybe. There's no evidence for it, but it makes sense.
Climate is like a hall of mirrors. Every time you ask for the why of any particular event, the answer has another why as its cause. You never get back to the start. But climate is also predictable. If you turn up the lights in the hall of mirrors, it gets brighter everywhere.
We're turning up the climate on Earth with the carbon dioxide we're pumping into the atmosphere from fossil fuels. Carbon is like a blanket that captures more heat from the sun. It doesn't take much additional heat in the tropical ocean to create banks of thunderstorms that mess up Fur Rendezvous in Anchorage.
Given this complexity in the climate, the models could be wrong. But the graphs they produce have error bars, which show the span of uncertainty and of natural variation above and below the exact temperature predictions. The models accurately predicted the Anchorage climate we are seeing now, because even these extremely warm winter temperatures are within the error bars, said John Walsh, chief scientist at the International Arctic Research Center and the University of Alaska Fairbanks.
The models seem to be working, and none predicts a crazy shift to a new normal, Walsh said. Extreme precipitation events seem to be increasing with the warming climate, but winter temperatures in Alaska have always been highly variable. We'll continue to have big ups and downs, with the peaks and troughs slowly getting higher.
The most unpredictable element in predicting the future is not computer modeling but human behavior. Will we reduce carbon emissions fast enough?
If we don't, winters like this one will become frequent much sooner.
Nancy Fresco's scenarios — which you can play with at snap.uaf.edu — take into account three different future paths for reducing carbon emissions. You can zoom in on thousands of places in Alaska and Canada to see the likely future for each path. The upper scenario makes snowless Anchorage winters routine within the lifetimes of today's children.
So this rotten winter isn't the new normal yet. But we could make it that way.
Charles Wohlforth's column appears three times weekly. His book on Arctic climate change is "The Whale and the Supercomputer."
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