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Deep snow

2018-03-17 01.32.25

Fat-tired cyclists at the Knik Glacier which once stretched to near Anchorage but now lives deep in the Chugach Mountains/Craig Medred photo

 

As yet another warm Gulf of Alaska storm slammed into the 49th state’s urban underbelly on Tuesday, pushing temperatures to near 40 degrees on the slopes of the Chugach Mountains above Anchorage,  the shrinking, growing, shrinking glaciers of the north were once again in the news.

“Scientists stunned by massive snowfall increases among Alaska’s highest peaks,” read the headline above a Washington Post story reporting what most Alaska mountaineers have known for a long time now:

Warm, moisture-laden storms that come roaring north across the Pacific Ocean from down near Hawaii to dump rain on Anchorage and the surrounding area in any month from October through July can generate big snows as they push deeper into the state and higher into the Alaska Range mountains.

What Dartmouth College scientists added to the discussion on Tuesday were numbers and a twist.

Annual snowfall on a major summit in North America’s highest mountain range has more than doubled since the beginning of the Industrial Age, said a press release coming out of the East Coast school. It summarized data from ice cores researchers from Dartmouth, the  University of Maine and the University of New Hampshire collected near 13,000 feet on Mount Hunter.

They tied it to a strengthing “Aleutian low” driven by “warmer tropical sea-surface temperatures, particularly in the western tropical Pacific and Indian Oceans.” They claim to have found a clear correlation between warming seas and deepening snow.

The correlation could have broad implications for Alaska.

“Climate change can impact specific regions in much more extreme ways than global averages indicate because of unexpected responses from features like the Aleutian Low,” said Erich Osterberg, who headed the latest research effort. “The Mount Hunter (snow) record captures the dramatic changes that can occur when you get a double whammy from climate change – warming air combined with more storms from warming ocean temperatures.”

The Hunter data would indicate Alaska could witness a future getting ever snowier, at least at high elevations, as it gets ever warmer and rainier at low elevations. What all of this means in the global context of melting glaciers and rising seas is harder to say.

The balance between glacier melt due to warming at low elevations in Alaska and glacier growth due to increasing snows at higher elevations has been the subject of considerable discussion among scientists for years.

Mass balance

A few Alaska glaciers have grown in recent times, but most are shrinking as the unstoppable force of gravity drags them down out of  the cold mountains into the warmer lowlands.

Shad O’Neal, a U.S. Geological Survey (USGS) glaciologist at the USGS Alaska Science Center in Anchorage, said it is interesting that East Coast scientists managed to find a spot amidst the state’s ever-moving, ever-melting glaciers that enabled them to obtain ice cores that track annual snowfalls back 1,000 years.

But what those scientists discovered about recent snow wasn’t all that surprising. Weather patterns over the last 40 years have increasingly brought warm, moist air into Southcentral Alaska. Such air would be expected to dump a lot of snow as its move north through coastal areas into the higher, colder Alaska Range.

And though the Dartmouth study documented huge volumes of snow falling on the upper reaches of the glaciers there, the overall effect on the glaciers appears to have been minimal.

“None of the glaciers in the Alaska Range are growing,” O’Neal said, meaning that no matter how much snow is falling at higher elevations, the accumulation is being more than offset by melting at lower elevations.

So there is, at this time, no need to fear all that snow falling at 13,000 feet in the area around North America’s tallest peak is going to spark another Ice Age. In fact, just the opposite is expected.

“Glaciers have retreated dramatically during the last century in southeast Alaska, in
the Alaska Range, and along the south central coast,” the Environmental Protection Agency (EPA) noted in its 2017 year-end report. “In Glacier Bay National Park, for example, Muir Glacier has retreated more than 31 miles since it was first observed in the late 19th century.”

The retreat is expected to continue. There are lengthy, geologic processes at play. A graph with the Dartmouth study shows snowfalls starting to increase along about the time the U.S. became a nation, and then increasing dramatically sometime in the mid-1800s.

“….Wintertime snowfall has increased 117 percent since the mid-19th century in southcentral Alaska in the United States,” the press release said. ” Summer snows also showed a significant increase of 49 percent in the short period ranging less than two hundred years.”

Those summer increases and growing winter accumulation would be in the mountainous parts of Southcentral Alaska. With the exception of the winter of 2011-2012, which set an all time snow record in Anchorage, the lowland, urban heart of the region has been generally getting less snow than normal for a most of a decade.

The winter of 2014-15 set a record for the lowest amount of snow in Anchorage. Just a shade over 25 inches fell, less than a fifth the amount of three years earlier. The following winter, 2015-16, ended with only half the normal snow accumulation.

Last year started with a snow drought,but ended with a little more snow than normal after an unusually snowy January and February. That bucked what has become a trend. Four of the five least snowiest winters in Anchorage since 1999-2000 have come in the past seven snow seasons.

This year is looking like another replay.  The Anchorage Hillside is at 30 percent of normal, according to the Department of Agriculture’s Natural Resources Conservation Service. Alyeska, a ski resort in Girdwood east of the state’s largest city, is at 46 percent of normal.

The Susitna Valley High School in the Matanuska-Susitna Borough north of Anchorage is at 34 percent of normal. Exit Glacier south of Anchorage on the Kenai Peninsula is at 31 percent of normal.

Exit Glacier was one of President Barack Obama’s first stops on his global-warming tour of Alaska in 2015.

It’s complicated

With more snow falling high in Alaska’s mountains and more rain and warmth at low elevations, the big, lingering climate question these days is whether the pattern seen in the past few years – the one that brings that “double whammy” to which Osterberg referred – is an anomaly or a new norm.

The urban core of Alaska, the region home to more than half the state’s population, will be a different place if it is the latter. When what climatologist Daniel Swain has described as a “ridiculously resilient ridge” of high pressure air forms over the U.S. West Coast, it serves to push tropical weather systems north across the Pacific Ocean right into Prince William Sound and then north into Anchorage and the MatSu valley.

A number of climatologists are now theorizing that rising sea surface temperatures in the tropics, which look to continue, and disappearing sea ice in the Arctic, which looks to continue, might be responsible.

These two events far from Southcentral Alaska may “have an effect in amplifying the atmospheric anomalies,” as Ming-Ying Lee of the Taiwan Center Weather Bureau wrote, that create an impenetrable wall of high-pressure air over the West Coast that blocks east-bound weather systems and sends them spinning north toward Alaska.

An intensifying Aleutian Low in the western Pacific and a ridiculously reselient ridge along the North American West Coast are almost made for that double whammy. They would sync almost perfectly to push a lot of warm, moist air north into Alaska’s midsection.

These are the sort of low-pressure weather systems that bring warm weather and rain or snow to Alaska’s urban core, and snow to the mountains to the north of where most Alaskan live.

This weather pattern has been hard to miss in Anchorage in recent years, but the Dartmouth snow data would indicate it might have been going on at some level longer than most Alaskans ever thought.

 

 

 

 

 

 

 

 

 

“The general long-term trend for glaciers in Alaska is one of sustained mass loss,” said Shad O’Neal, A USGS glaciologist who also studies Icy Bay glaciers and is based at the USGS Alaska Science Center in Anchorage. “While we have seen short term fluctuations like a heavy snow year and seasonal advance-retreat cycles, only a few tidewater glaciers are gaining mass over longer time scales, and these are exceptions, not the norm.”

 

 

 

 

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7 replies »

  1. The key factor in the accumulation is the water content of the snow. The water content of one foot of wet snow might equate to 8 feet of dry and fluffy snow. And in time, both wet and dry snow (in this example) will settle to the same thickness, the same water content. So when one says the amount of snowfall has increased, one has to ask – how is it measured? If they have a remote weather station that measures inches of snowfall, but not water content … then the results could be misleading. The best way to measure snow in the accumulation zone is to go the same location on a glacier the same time each year, say early August, and do a core sample to see what the net change was since the prior year.

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  2. “I was taught that glaciation is driven by precipitation more than temperature.”
    Care to explain your comment, here. As it stands, it doesn’t make sense IMO. Glaciation happens when the amount of precipitation is greater than the amount of ice that is lost in the Summer melt. How is one more than the other???

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    • I’ll try to find my old textbook from 1975. My professor was one of the top glaciologists (as they were called) in the discipline Consider my example that the high-precipitation regions have significantly more glaciation than say the Brooks Range where temperatures are colder. You rightly point out that precipitation and ablation are weighed against each other to conclude whether a glacier is growing or receding. A glacier can build up decades or centuries of snowpack at the upper end and not see the tongue move significantly forward. And in other cases the weight of the upper snowpack can suddenly cause the tongue to move rapidly. In conclusion, if warming causes increased precipitation, the resulting buildup of snow can be greater than the increased melting due to higher temperatures.

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  3. It doesn’t make sense that doubled snowfall amounts on Alaska Range glaciers will result in receding glaciers. Coastal glaciers are perhaps another matter. Ultimately it is a mass balance equation between the accumulation zone and the ablation zone. Also, it is worth noting that our largest ice fields are located in coastal and near-coastal environments. I was taught that glaciation is driven by precipitation more than temperature.

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    • i think most everyone thought the same, Chris, but it doesn’t appear to be working out that way. it would appear as though the Interior glaciers, though they now get a lot more snow, are not getting as much snow as the coastal glaciers, some of which get insane amounts of snow, and in the accumulation v. melt equation, the melt is winning in the Interior.
      but if one looks at the graph of accumulating snow attached to the study, you do have to wonder if at some point Alaska’s Interior glaciers couldn’t go coastal, s to speak.

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      • It gets a bit confusing what parameters are being measured. So if we are talking about “mass loss”, glaciers have been losing mass for 40,000 years for one thing. Interior (Alaska Range) glaciers are a different animal than coastal ice fields and elevation come into play too. If accumulation has doubled, then melting has more than doubled? The glaciers were obviously shrinking before the increased snowfall.

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