DekeArndt's Blog

As we prepare for (yet another) blast of cold air across the northern plains and into the eastern U.S., we have one more indicator that this has been an especially cold season across the north-central United States and neighboring parts of Canada.

As was forecast a month in advance, Lake Superior, especially western Lake Superior, has taken on more ice earlier in the winter than during recent years. To paraphrase the Great Ron Burgundy, this is kind of a big deal, in part because it represents one of the earliest dates in recent memory for (significant) ice to appear along the western tip of the lake.

But why just stop with one reason that this is a significant development?

Top Five Reasons Why This Is A Big Deal

1. Lake Superior is big

On the off chance that you, dear reader, are not like me, and you haven't spent your entire life preparing for a big chance on Jeopardy, I'll share the facts: Lake Superior is the largest freshwater lake on earth, in terms of surface area. It holds close to ten percent of the world's (non-frozen) fresh water. It takes quite a bit of work to freeze parts of a big lake.

The lake is hardly ever completely frozen over. However, an early start, for lack of any other information, means that the seasonal freeze has a "head start" toward larger ice cover later on.

2. Ice cover impacts navigation

Straight from the Duh Department. Large bodies of ice can restrict access to navigation ports, and an early freeze means an early end to shipping season. Likewise, a late thaw means a late start to shipping season. Times like these call for vessels like these.

3. Ice cover reduces evaporative loss

When large chunks of a Great Lake freeze over, it actually protects the lake during the year's strongest evaporation period. Yep, that's right: the Great Lakes (especially Superior) often lose more water through evaporation during winter than during summer. This seems counter-intuitive (believe me: I did a triple-take when I first learned about this), but it is true: during the winter, an exposed lake is often so much warmer than the frigid air above it that evaporation rates can exceed those in the summer.

4. Reduced evaporative loss means less "Lake Effect" Snow

Evaporation, and the energy associated with it, is the big driver of "Lake Effect" or "Lake Enhanced" snowfall events. Simply put, if the lake is frozen over and evaporation is minimized, then the massive Lake Effect snow totals are put on ice, so to speak. Believe me, the residents of Michigan's Upper Peninsula will notice the difference!

5. This is a fairly reliable climate indicator.

According to locals, significant ice this early is rare, especially in comparison to a recent spate of warm winters.

Of course, the date of a lake's freeze or thaw (often called "ice out") can be traced over the years to provide a time-series of climate sensitive data. The nice thing about lake-freeze information is that it isn't as sensitive to external factors (such as disease for bloom dates, or hardware changes for the instrumental record). Instead, it's pretty much sensitive to the weather and climate itself. For that reason, there are large databases of this phenological information available, including this nice collection from the Minnesota State Climatology Office.

Lake Superior has also been considered something of a canary in a coal mine when it comes to climate change. Formal studies of the Lake's "Ice Climatology" are numerous (and long!). Recent studies have indicated that the Lake has seemed to warm more quickly than the surrounding region over the last few decades.

Of course, one cold winter (or one warm winter, for that matter) says nothing about long-term climate change. While climate-change skeptics may point to this as evidence against climate change, most climate scientists would point out that any climate ... warming or not ... will produce its share of colder-than-normal seasons.

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