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Alaska weather's new warmer, wetter 'normals'

Doug O'Harra
Winter solstice sun in Healy, Alaska on Dec. 21, 2011. Bob Lype photo

Think Alaska has been warmer than normal? You just might be right.

But whether that wee simmer offers regional evidence for global warming is a complicated issue, hinging on semantics, starting dates and one somewhat inconvenient question: Warmer than what? 

First, a quick primer: The "normal temperature" or precipitation for a given weather station isn't based on some tobacco-spat hunch by a grizzled meteorologist in Carhartts. Whether measured in degrees of heat or inches of snow, "normal" derives from scientifically rigorous data recorded over a specific 30-year period. 

Until last summer, the official "normals" for Alaska were the averages seen between 1971 and 2000. But every decade or so, we jump to an updated set of 30-year "normals." On July 1, the National Climatic Data Center recalibrated new normals for the United States and Alaska based on the temperature, precipitation and other natural events recorded at some 8,000 stations between 1981 and 2010. 

In other words, weather patterns during the 1970s no longer apply, with the first decade of the 21st century taking its place. (For more information on the process, check out this slide show webcast put out by the NCDC in June.) 

Among other things, the NCDC reported that the new normals were warmer in every one of the lower 48 states. Alaska followed the same trend. 

"Overall, the updated normals in Alaska are somewhat warmer," explained Corey Bogel and Rick Thoman of the National Weather Service in Fairbanks in the winter edition of the Alaska Climate Dispatch, a quarterly publication by the Alaska Center for Climate Assessment & Policy at the University of Alaska Fairbanks.

"By far the greatest absolute warming is in the winter, while most locations show no significant change in mid and late summer."

At seven major stations -- Anchorage, Fairbanks, Juneau, Kodiak, Bethel, Nome and Barrow -- June warmed between 0.5 to 1.1 degrees Fahrenheit, while winter increases were higher, as much as 2 to 3 degrees. The increase in overall average annual temperatures for the new normal period ranged from a tiny .3 degree increase at Nome to 1.3 degrees at Barrow. Anchorage simmered in the middle with a .8 degree rise.

The meteorologists found the summer rise more intriguing. "Because the potential range of temperatures is so much smaller in June than in the winter, the warming in June is, at most locations, the most statistically significant change of any month," the report explained.

Precipitation also increased at these seven major stations, ranging from 2 percent more inches of rain and snow at Nome to 15 percent more at Bethel. Anchorage's new 30-year average for 1981 to 2010 clocked in at 16.58 inches of precipitation, an increase of about 3 percent over the rain and snow seen during the 30 years between 1971 and 2000.

So what explains the slightly wetter and barely warmer averages we experienced when we drop the 1970s and add the 2000s to our climate measuring stick? To a large extent, look no further than the North Pacific Ocean.

An Alaska climate regime change

About 1976, the North Pacific underwent a climatic regime shift from a colder phase, with chillier sea surface temperatures, morphing into a new phase with warmer waters ranging from the Bering Sea to the Gulf of Alaska. This change became the driver of profound changes in marine life, transforming a region dominated by shrimp, crab and forage fish to one flush in flatfish and Pollock. It may be one of the major causes of the crash in Steller sea lions along Alaska's coast, as well as the surge in salmon returns.

The regime shift contributed to shrinking sea ice. Changes in how storms track across Alaska. And it has also bathed the state in much warmer and wetter air. Alaska, after all, is basically an 800-mile-wide peninsula thrust between two oceans. When the ocean warms and grows wilder, so goes the land.

"It so happens that 1981-2010 normals comprise almost an entire warm phase of the Pacific Decadal Oscillation (PDO), the multi- decadal pattern of sea surface temperatures in the north Pacific in which warmer-than-normal temperatures prevail in the Gulf of Alaska," the report explained. "South of the Brooks Range, mid- winter temperatures at most locations are fairly strongly correlated with the value of the PDO Index that particular winter."

The stunning jolt that the regime shift gave to Alaska air temperatures can be seen in this chart posted by the Alaska Climate Research Center. Between 1949 and 2009, annual temperatures at 19 major weather stations across Alaska rose an average of 3 degrees Fahrenheit -- almost all of the increase occurring between 1976 and 1977. Winter increases are especially dramatic, with Anchorage up 5.8 degrees and some Interior locales warming almost 9 degrees.

And yet, what happens if we start our comparison after the regime shift began? How much did it warm in the 30 years following 1977, for instance?

Not at all.

The overall statewide average annual temperature did not rise between 1977 and 2008, according these charts posted by the climate center. In fact, the statewide average dropped by one-tenth of a degree. Driven largely by a slide in spring temperatures, Anchorage actually cooled by half a degree during the same period. Only six of Alaska's 19 major weather stations saw warmer annual air, led by Barrow, in the Arctic, with an annual rise of 4 degrees.

The "stepwise shift appearing in the temperature data in 1976" can be blamed on Pacific oscillation, the center explains here, largely because it began sending gobs of that warmer and wetter air from the ocean over the state during the winter.

Alaska's new "normals" tweak the calculation a bit because they cover the 30 years beginning in 1981 rather than 1977, and the later reference date gives different and slightly warmer results. Now some data seems to suggest that PDO has been flirting with a shift back to a colder phase -- or a move on to a completely different pattern.

What then?

Contact Doug O'Harra at doug(at)alaskadispatch.com