An acquaintance—a figure absent from this locale for a few years—reappeared in Fairbanks last week.
The phenomenon of ice fog.
Ice fog, a surface cloud formed from the water we release into the atmosphere regularly, only becomes visible when the intense cold sets in and lingers for a while.
During the past week, with temperatures in Fairbanks dropping to as low as minus 50 F in certain areas, the ice fog was prevalent enough for Rick Thoman to represent it on a bar graph. Thoman, associated with the Alaska Center for Climate Assessment and Policy at the University of Alaska Fairbanks, observed ice fog on his graph for the first time in approximately a decade due to the prolonged cold spell.
From the late 1960s to the early 1990s, a glaciologist named Carl Benson extensively studied this occurrence in Fairbanks, becoming intimately familiar with it.
Back then, he authored several seminal papers, including one where he calculated the collective water vapor exhaled by all the sled dogs in Fairbanks on a typical winter day. (In total, the 2,000 sled dogs emitted half a ton of water vapor into the air.)
Benson, now a professor emeritus at the Geophysical Institute, delved into the enigma of ice fog in a story he penned in 1969 for his peers at the California Institute of Technology, his alma mater.
Ice fog has a critical threshold—minus 30 F. It does not materialize until the air reaches that extreme cold, and it disperses once the temperature climbs above that mark.
“Ice fog is generated when the water vapor released from urban areas encounters an air mass too frigid to absorb it, causing the condensed vapor to crystallize into minuscule ice particles,” Benson explained to the likely puzzled audience in urban California.
These ice particles descend to the ground, adhering to air pollution particles along the way.
Benson also elucidated an intriguing chemical anomaly occurring while we drive. When our vehicles burn gasoline, “the actual amount of water expelled as vapor from the exhaust is 1.3 times greater than the mass of gasoline burned.”
While the sight of cars trailing their own ethereal clouds is visually striking and a primary factor in reduced driving visibility, Benson discovered that a significant source of water vapor in the late 1960s was the liquid cooling water used in power plants. Presently, a notable contributor is an exposed section of the Chena River warmed by power plant cooling water.
In a study published in the autumn of 2023, Lea Hartl from the Alaska Climate Research Center noted that from 1950 to 1980, Fairbanks averaged over two weeks of ice fog days annually.
However, in the 30-year period from 1990 to 2020, ice fog occurred only about six days per year on average.
Why the decline? Hartl attributed it mainly to the fact that, despite sporadic occurrences of ice fog, Fairbanks experiences far fewer days with temperatures below the critical minus 30 F threshold.
As temperatures rose sufficiently in mid-February to render our water vapor invisible once more, a robin was spotted on the UAF campus. While robins typically winter along Alaska’s southern coast and on Kodiak Island, they usually migrate south from Interior Alaska in the autumn.
This particular bird, likely the same one documented on the eBird citizen-science platform in January and earlier in February, likely sustained itself on the frozen fruits of chokecherry trees, like the one it perched on when observed. Whatever sustenance the robin found, it managed to endure through weeks of ice fog-inducing temperatures. Bravo!