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The Great Lakes have been warmer than usual, according to National Oceanic and Atmospheric Administration readings, and while that may be welcome news for swimmers, it could help proliferate the Lakes’ invasive species.
NOAA data shows that recent surface water temperatures in each of the Great Lakes, plus Lake St. Clair, have been up to 4 degrees warmer than their daily average over the past month.
“They’re not all-time highs, but they’re above-normal to well-above-normal,” said Kevin Kacan, a forecaster at the National Weather Service office in White Lake Township.
At their most recent peaks in mid-August, each lake was several degrees above its daily average, with Superior topping out around 64 degrees (compared to an average of about 61), Michigan around 73.5 degrees (70.5), Huron around 73 degrees (69), Ontario around 76.5 degrees (72.5) and Erie around 78.5 degrees (75), according to NOAA.
That extra heat could have a few long-term effects, including aiding in “recruitment,” or growth and maturity, of native fish species, said Randy Claramunt, chief of fisheries for the Michigan Department of Natural Resources.
“Unfortunately, that also means new recruitment of non-native or invasive species,” Claramunt said.
He said DNR crews are working to monitor the Great Lakes, especially Lakes Huron, Michigan and Erie, for unwanted fish like round gobies and alewives.
According to the U.S. Environmental Protection Agency, warmer surface water also is linked to other invasive species like the zebra mussel and some types of bacteria.
According to the DNR Weekly Fishing Report, warm temperatures in Lake Erie have been affecting anglers. The warm water was keeping yellow perch in deeper waters and closer to the Ohio coast, where waters are cooler. Warm water in Lake Michigan also was troubling pier fishers in St. Joseph, the DNR reported.
The current high temps also could mean more snow in the region during the late fall and early winter, until ice cover on the Lakes reduces the chance for lake-effect snow, scientists said.
“Generally speaking, warmer water heading into the cold season provides more instability over the Lakes, which could lead to higher lake-effect snowfall,” Kacan said.
Experts said the recent high readings aren’t totally unexpected since August tends to be the most volatile time of year for the Lakes’ temperature. James Kessler, a NOAA scientist with the Great Lakes Environmental Research Laboratory, noted that surface temps still have been below average some days this summer.
Warmer surface water temperatures sometimes mean lower water levels due to increased rates of evaporation and causing ice to form later than usual, the EPA has found. That can adversely affect business because lower levels can force companies to reduce cargo, leading to higher shipping costs. It can also affect municipal water supplies and shoreline ecosystems, according to the EPA.
According to the Army Corps of Engineers’ most recent weekly update, Lakes St. Clair and Erie are above their long-term average levels for August by 3 inches; Lake Superior is 2 inches below average Lakes Michigan and Huron (which are measured together) are 5 inches below their monthly average. Lake Ontario is about an inch below its August average level.
Why so hot?
Surface water temperature is impacted by many factors, but is most directly affected by air temperature. And while recent highs have been somewhat mild, it’s been a hot summer overall, experts said.
“This summer has been hotter than normal, and it’s definitely been more humid than normal,” Kacan said. “That plays at least some role in temperatures across the Great Lakes this year.”
Kessler said other aspects that can impact surface water temperatures include solar radiation and wind, which can churn the waters.
“Obviously the Great Lakes are quite deep,” he said. “A lot of the heat content is from below,” in the subsurface waters, which are more difficult to measure and, as a result, harder to predict.
According to the EPA, water temperature, in conjunction with water level, is a key indicator of climate change in the Great Lakes.
Since NOAA’s surface water temperature data only dates to 1995, it’s difficult to chart exactly how climate change may have affected the Lakes over the long term, Kessler said.
“It’s too hard to make informed guesses about what (temperatures were like) 100 years ago,” he said.
This is the second consecutive year of notably higher-than-average temperatures in the Lakes. According to NOAA data, last year’s daily average for the entire year was the highest on record for four of the five Great Lakes. In the fifth, Lake Superior, the daily average was the second highest on record.
mreinhart@detroitnews.com
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