Great Lakes Ice Cover at Highest Levels in 20 Years

This week's intense Arctic cold blast has brought the highest ice coverage on the Great Lakes in twenty years, according to data from the Canadian Ice Service. Ice coverage over Lakes Superior, Michigan, Huron, Erie, and Ontario increased from 12% to 26% over the past week, reaching levels not seen at this time of year since the last Great Lakes cold blast of this intensity, in January 1994. Most notably, Lake Erie is now more than 90% frozen over. This will spell a temproary end to intense lake effect snowstorms for areas downwind of the lake like Buffalo, New York, since Arctic winds blowing over the lake will no longer be able to pull moisture from open water to fuel heavy snows. Buffalo received more than a foot of snow from Tuesday and Wednesday's lake effect blizzard, which tapered off because the lake froze up so significantly. With Saturday temperatures over southern Great Lakes expected to warm to the mid-40s, accompanied by rain, ice formation on the Great Lakes will slow down this weekend, but ice coverage should still be above normal for the remainder of January.


Figure 1. Great Lakes ice cover on January 9, 2014. Image credit: NOAA Great Lakes Environmental Research Lab.


Figure 2. Average ice concentration in the Great Lakes during the week of January 8 - 14, for the years 1973 - 2002. Ice coverage in 2014 (Figure 1) was about double the average. Image credit: NOAA Great Lakes Environmental Research Lab.


Figure 3. Ice coverage on the Great Lakes for the week of January 8 for the period 1980 - 2014. The ice coverage this year is the highest since 1994. Canadian Ice Service
.

Increased ice cover will keep Great Lakes water levels higher
The increased ice coverage on the Great Lakes this winter is good news for water levels on the lakes, which are still struggling to recover from some record lows recorded at this time last year. During January 2013, water levels on Lake Michigan and Lake Huron fell to their all-time lowest values since record keeping began in 1918, 29 inches below the long-term average. While the water levels recovered substantially during 2013, which was one of the wettest years in Michigan's history, water levels were still a foot below average at the beginning of 2014. The above average ice cover this winter will reduce evaporation from the Great Lakes, keeping water loss lower than in recent winters. Ice cover on the Great Lakes has declined 71% since 1973, according to a 2012 study published in the Journal of Climate by researchers at NOAA's Great Lakes Environmental Research Laboratory. The loss of ice is due to warming of the lake waters, which could be due to a combination of global warming and natural cycles, the researchers said. Winter air temperatures over the lower Great Lakes increased by about 2.7°F (1.5°C) from 1973 - 2010, and by 4 - 5°F (2.3 - 2.7°C) over the northern Lakes, including Lake Superior. Lake Superior's summer surface water temperature warmed 4.5°F (2.5°C) over the period 1979 - 2006 (Austin and Colman 2007). During the same period, Lake Michigan warmed by about 3.3°F (1.7°C), Lake Huron by 4.3°F (2.4°C), and Lake Erie (which is shallow and loses and gains heat relatively quickly) showed almost no warming.

The long-term future of Great Lakes water levels is cloudy, since climate change is expected to bring competing effects. A 2011 paper by scientists at NOAA Great Lakes Environmental Research Laboratory found that lake levels could rise or fall, depending upon the climate change scenario used. On the one hand, precipitation has increased by 12% over Michigan during the past century, and is expected to increase even more in the coming decades. This would tend to increase lake levels. However, lake water temperatures are predicted to increase and ice cover decrease, which would heighten evaporation rates. This would tend to lower lake levels. The Army Corps of Engineers is considering adding speed bumps to the bottom of the St. Clair River to slow down drainage of Lake Huron, which would act to increase water levels in Lake Huron and Lake Michigan.


Figure 4. The water level on Lake Huron and Lake Michigan measured during 2012 - 2013 (red line) hit an all-time low during January 2013, beating the previous record set in March 1964. Water levels recovered some during 2013, but were still a foot below normal at the beginning of 2014. Image credit: Army Corps of Engineers.

References
Austin, J. A., and S. Colman, 2007, "Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback," Geophys. Res. Lett., 34, L06604, doi:10.1029/2006GL029021.

Wang, J., X. Bai, H. Hu, A.H. Clites, M.C. Colton, and B.M. Lofgren, 2012, "Temporal and spatial variability of Great Lakes ice cover, 1973-2010," Journal of Climate 25(4):1318-1329 (DOI:10.1175/2011JCLI4066.1)

Jeff Masters