Alaska Climate Research Center

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Home > Blog > New research paper: Ice fog in Fairbanks is becoming less frequent

New research paper: Ice fog in Fairbanks is becoming less frequent

Have you ever wondered what it feels like to be inside an ice cloud? Visit Fairbanks in winter and you may find out! Ice fog is a kind of fog that consists only of ice particles and occurs at very low temperatures. The glossary of the American Meteorological Society states: 

“It occurs at very low temperatures, and usually in clear, calm weather in high latitudes. The sun is usually visible and may cause halo phenomena. Ice fog is rare at temperatures warmer than -30°C, and increases in frequency with decreasing temperature until it is almost always present at air temperatures of -45°C in the vicinity of a source of water vapor. Such sources are the open water of fast-flowing streams or of the sea, herds of animals, volcanoes, and especially products of combustion for heating or propulsion.”


In addition to temperatures cold enough for ice fog to form, Fairbanks also has sources of water vapor such as open leads in the Chena River, plumes from the power plants as well as emissions from traffic, heating and industrial processes. Early work on ice fog in Fairbanks even accounted for canine residents of Fairbanks adding water vapor to the air by breathing! UAF Professor Emeritus Carl Benson wrote in 1969


“There are 30,000 people and about 2,000 dogs in the Fairbanks-Ft. Wainwright area. The air that they exhale is saturated with water vapor at a temperature of 35 degrees. The dogs breathe at an average rate of 5.2 liters per minute even when they are resting; this provides 7.5 cubic meters of air per dog, per day, with a moisture content of 40 grams of water per cubic meter. So the total moisture put into the air by 2,000 Canis familiaris is at least 0.6 tons per day. This is a conservative estimate, because all of the dogs don’t rest all of the time”

Fairbanks winter: cold, dark and sometimes foggy! Photo: Carl Schmitt

How has ice fog occurrence changed over time?

As part of an ERDC funded project on microphysical properties of ice fog (more on that coming soon), the ACRC team recently analyzed whether ice fog is occurring less often now than it has in the past. Since there are no long term, continuous, direct observations of ice fog for the area, we used weather observations from Fairbanks airport and Eielson Airforce base to find out how often the following criteria were met: 

  • temperatures low enough for ice fog  
  • strongly reduced visibility.

We found a substantial reduction in the number of ice fog days and hours per winter season at both airports since the start of the time series in 1948. On average, ice fog occurrence has decreased by 60-70% over the study period, although there is large year-to-year variability. During the climate normal period 1950/51-1979/80, the median number of ice fog days at Fairbanks Airport was 16.5 – over two weeks of ice fog! During the period 1990/91-2019/20, ice fog typically occurred on only 6 days per season (median over the 30 year period). The average length of ice fog events and of the ice fog season have also decreased. 


Climatological trends are not necessarily linear and rates of change can vary over time. For example, changes in the mode of the Pacific Decadal Oscillation (PDO) can affect Alaska’s climate and many Alaskan climate time series show a “step” around the 1976 PDO shift from negative to positive mode. Fitting a linear trend to time series can obscure such features. We use a statistical technique called empirical mode decomposition to account for non-linearity in trends of ice fog occurrence. 

(top) Ice fog hours and cold hours per winter season with EMD trend residuals and (bottom) rates of change (derivatives of the trend residual) at (left) PAFA and (right) PAEI. For PAEI, the incomplete water years (1971–73) were removed before trend computation.

This shows that the greatest reduction in ice fog occurred during the 1970s and ‘80s and that trends in decreasing ice fog hours roughly track decreasing trends in hours with cold temperatures. I.e., cold temperatures occur less often so ice fog also occurs less often. However, we also find that in recent decades cold temperatures – when they do occur – are accompanied by ice fog less often than in the past. Early in the time series, very low temperatures almost always coincided with ice fog. This appears to have changed. The most likely explanation is that the amount of air pollution or near surface moisture has changed. Fairbanks dogs probably still have steamy breath but stricter standards for emissions from vehicular traffic may well have had a significant impact on the composition of the near surface atmosphere.


In summary: Ice fog in Fairbanks is on the decline. There is large interannual variability but the trends are very robust. Fewer days with temperatures cold enough for ice fog lead to less ice fog. In addition to rising temperatures due to climate change, changes in near ground moisture and/or pollution are also important for the frequency of ice fog occurrence. The observed trends are likely the result of a combination of factors: fewer occurrences of very cold temperatures due to rapid climate warming and changes in moisture or pollution. Further research is needed to more clearly separate the different driving factors.

Find the paper at: L. Hartl, C. Schmitt, T. Wong, D. A. Vas, L. Enterkin, M. Stuefer (2023). Long-Term Trends in Ice Fog Occurrence in the Fairbanks, Alaska, Region Based on Airport Observations. Journal of Applied Meteorology and Climatology, 62(9), 1263–1278.