On Lake Superior, we haven’t seen the likes of such frozen tundra in more than 30 years. In fact, at one point during this winter of 2013–2014, Lake Superior was 91 percent covered by ice—the most since 1994. Talk about a misery index. In that regard, chalk this winter up as off of the charts. However, for the health and well-being of the Lake, the punishing cold and ice was nothing but positive. With climate change and global warming top of everyone’s mind these days, a nauseating repetition of one polar vortex after another this winter was warmly welcomed.
According to the National Oceanic and Atmospheric Administration (NOAA), increased ice cover has many benefits for the environment. First, a thick ice cover with minimal snow cover allows sunlight to penetrate farther into the water column, which in turn stimulates the growth of algae during the winter that feeds other living organisms. Second, a thick ice cover shields fish eggs (particularly whitefish) from harsh winds in shallow water.
And probably the best benefit of all: The Lake will have a higher water level this year. That’s extremely good news, given that the ice cover on the Great Lakes has declined by 71 percent in the past 40 years (on average), which has led to unhealthy low lake levels. Water temperature in the summer and annual evaporation are also on the rise—again, all thanks to what scientists attribute to climate change. So, this winter and the thick ice cover will reverse this trend, say the experts.
How so, you ask? Evaporation is really what it’s all about. In an article titled “Ice Cover Affects Lake Levels in Surprising Ways,” by Lisa Borre in the January 27 issue of Water Currents, there is mention of the under-appreciation and misconception about evaporation.
The article explains that the majority of people think that most evaporation occurs during the summer when the water is warmer than the winter. The supposed logic is that the summer months are when the water is completely free of ice, and therefore the Lake has its entire surface area exposed to evaporation. However, evaporation occurs when there is a significant difference in temperature between the water and the air. Obviously, this disparity is more common in the fall, winter and spring than during the summer.
In a “typical” winter, then, of the past five to 10 years, the water has been cooling as it naturally does in the fall, but not freezing nearly as much as it has this year during the winter. With the Lake having much more exposed water in years past, evaporation has gone relatively unimpeded. This year (with nearly complete ice cover), there has been very little surface area exposed to evaporation. In addition, with the extremely thick ice cover, it is going to take much longer for it to melt during the spring. In other words, the cold water will linger longer into the summer—causing less temperature variation between the water and the land throughout the summer, and thus, less evaporation.
There also are two more factors that cause higher evaporation: low relative humidity and high wind speed. If these two ingredients are present, mixed with higher water temperature, then evaporation is greatest. Despite this perfect storm scenario, this winter of 2013–2014 will mean much less evaporation simply on the basis of much colder water temperatures throughout the summer due to thick ice cover this winter. And, if the same weather pattern continues this summer, then the air temperature will remain cooler—leaving less variation between water temperature and air temperature.
Higher water level this summer is a blessing to everyone who associates with the Lake for their livelihood or otherwise. Primarily, it’s a huge relief to the commercial shipping industry that relies on shipping lanes and channels that are deep enough for passage. For the recreationalist, boaters can ease into their docks or slips with much less worry about running aground. Environmentally, a colder lake stifles nutrients and leads to less algae bloom, which can be toxic to the aquatic food web and, in rare cases, to humans.
More personally though, a colder lake this summer might mean more dipping-of-toes than full submersions. It also might mean more mid-summer campfires, and crispy clear starlit nights. All in all, the polar vortex may have gotten a bad rap. If a little nip in the air is the only price we pay this summer, then let mother nature lay it on thick for years to come.