Lake Michigan Broke a Few Records This Summer: Here’s Why

It’s been a record-breaking year for this great lake.

You might have noticed Lake Michigan in the news a bit more than usual this summer, first for record-breaking temperatures, then for record-breaking monthly water levels.

In early July, the lake reached 75.1 degrees — that’s almost 11 degrees above average and the warmest temperature ever recorded so early in the year. But just a few weeks later, news outlets were warning swimmers of extremely low temperatures. And every month this year, high water levels have broken the monthly record.

We checked in with a few experts from UW-Milwaukee to learn a bit more about what’s causing these changes. Are they as big a deal as they might seem?

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Harvey Bootsma, a professor at the School of Freshwater Science at UWM, emphasizes that while Lake Michigan has set some new records (and come close to others), it’s important to remember that changing water levels and temperatures on their own are frequent, normal occurrences.

“In any given year, when something odd happens, it’s always tempting to attribute it to climate change,” Bootsma says. “But it’s really hard to do that in any individual year — you really need to look at long-term data records.”

There has been a gradual warming trend in Lake Michigan, but nothing so pronounced as the spike in July. The explanation for this spike is pretty simple: Wisconsin had a relatively mild winter, and that warm weather carried over into the spring and summer months, warming the lake’s surface faster than usual.

“This year there’s been kind of a warm cell that’s been hanging out over the Great Lakes, and so air temperatures, especially in July, were well above average,” Bootsma says.

As for the water temperature drop many coastal areas experienced shortly after, Bootsma says these cold spells can be largely attributed to a common process called upwelling.

The combination of warm air and calm water caused heat to remain trapped in the surface layer of the lake, while deeper water stays pretty cold. Upwelling happens when wind blows the warm surface water away from the shore and the cold water below rises up to take its place, resulting in the cold near-shore temperatures swimmers and beachgoers might have noticed later in the summer.

Potential environmental effects of continued high temperatures include algal blooms, but Bootsma says the warm spike this summer wasn’t long enough to cause any serious damage.  

The recent high water levels, however, may be having a bit more of an impact. Due to consistently heavy rainfall, Lake Michigan water levels have been rising since reaching a record low in 2013 — this year has been no exception. Water levels broke monthly records every month of 2020 so far, though they’re expected to start dropping again for the rest of the year.

Paul Roebber, an atmospheric science researcher at UWM, says high water can cause erosion, shrinking beaches and flooding, all of which result in property damage and habitat destruction. In January, for example, a storm caused up to six feet of flooding in parts of Port of Milwaukee.

“The fact that the water levels go up and down in itself is not anything remarkable — that’s just a natural process that happens in the Great Lakes,” Roebber says. “But the climate change issue is the amplification of that process.”

The challenge comes in predicting what might happen next and adapting to water level and temperature fluctuations, which are expected to become more extreme as climate change continues.                                     

“I think it’s important for people to realize that these are very large systems and we are very limited in how we can control these systems,” Bootsma says. “We have to learn to be flexible, to be able to adapt to these fluctuations as they occur over time.”

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Elizabeth Johnson is an editorial intern at Milwaukee Magazine and a journalism major at the University of North Carolina at Chapel Hill.