As the globe continues to warm at an astonishing rate due to climate change, winter is shrinking at depths we’ve never known before, including the Great Lakes.
A study conducted by scientists at the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory (GLERL) used a 30-year data set to investigate how climate change is impacting the deepest parts of Lake Michigan, the world’s fourth-largest freshwater lake.
“We found that this long-term data set not only confirms that Lake Michigan’s deep waters are warming, but also shows that winter is vanishing from them,” said Eric Anderson, the study’s lead author.
This could have a profound impact on everything from the region’s weather to its food supply.
Scientists used a long string of high-tech thermometers, which float vertically in the water and record temperatures at different depths in the lake. This instrument has been recording water temperatures every hour, almost continuously, for the past three decades.
This allowed scientists to examine the lake’s year-round temperature changes throughout the entire water column, rather than just lake surface temperatures in the summer.
The surface temperatures were relatively easy to study with buoys and satellite. Studying the depths of the world’s deep lakes has been much more difficult.
“Those surface measurements don’t tell the whole story of what’s going on,” according to the study.
Instead of just monitoring the surface, they studied how Lake Michigan’s seasonal mixing patterns – or how water at the surface mixes with deeper water – are being influenced by climate change.
Vanishing cold in Lake Michigan
Scientists found the rapid “warming that’s happening on the lake’s surface during the summer is actually impacting the lake’s deep waters during the winter,” according to the study.
What happens on the surface of the lakes, as well as hundreds of feet down, helps scientists gauge what potential impacts could be felt for the rest of the world’s deepwater lakes when facing climate change. Incredibly, more than 80% of the Earth’s non-frozen surface freshwater is found in 10 of the world’s biggest lakes.
Several of the largest lakes are warming at a faster rate than the oceans, as well as the global air temperature.
According to the study, “subsurface waters in deep lakes can provide an important signal because they integrate conditions across years, providing a climate memory, and can help identify the potential for ecological and thermal shifts.”
“Just as in the deep ocean, there has been a scarcity of data from deep in the Great Lakes, says Dr. Ellen Prager, a marine scientist and author of “Dangerous Earth: What We Wish We Knew About Volcanoes, Hurricanes, Climate Change, Earthquakes, and More.”
“By revealing the unseen, scientists are now identifying the true extent of the impacts of climate change and for the Great Lakes this could mean region disruptions to seasonal patterns, ecological shifts and changes as of yet unidentified, the unknown unknowns,” Prager says.
The great warming trend
This winter, the Great Lakes were way below normal for ice cover in January, with only 3% of the lakes frozen. Cities around the Great Lakes were several feet below normal for snowfall. With warmer than normal temperatures, this has been a trend during the past three decades, with a decreasing long-term trend in ice cover and several low-ice or nearly ice-free years since 1990.
Now we know, from this study, that the deep waters of Lake Michigan also reflect this. This could have dramatic impacts on the fisheries, recreation and the day-to-day weather in the Great Lakes region.
Lake Michigan was 10 degrees above normal during the summer of 2020. When you are that much above normal, it takes even more energy to cool the lake to where it needs to be in the winter months. This has a huge impact on lake effect snow as well.
“When the lakes are completely ice-covered, that moisture isn’t available and it effectively shuts down the development of snow,” says CNN meteorologist Dave Hennen. With a warmer lake, the lake effect snow will continue longer than it normally would.
Disruption of the entire food web
The region is home to more than 30 million people, many of whom rely on the lakes for income. The Great Lakes are the most extensive surface freshwater system globally and are warming faster than the world’s oceans.
The study suggests that with the dramatic changes to the water’s seasonal mixing patterns, this “would inevitably disrupt the structure of its entire food web, a change that could have negative impacts on fisheries and recreation.”
The Great Lakes support a combined $7 billion recreational, commercial and tribal fisheries, so a disruption in the food web could mean a tremendous hit to the region’s economy.
“Lake whitefish spawn and deposit their eggs on the bottom in shallow nearshore waters, so in years of extensive ice cover their eggs will be protected from waves and storm surge, says GLERL fishery biologist Ed Rutherford.
“Short, warm winters also are known to negatively affect yellow perch egg development, spawning and early life survival. After short winters, female yellow perch will spawn at warmer temperatures and produce smaller eggs that both hatch at lower rates and produce smaller larvae, which lowers their probability of survival,” Rutherford says.
The scientists have seen a decline in the reproductive success of both lake whitefish and yellow perch since the increase in lake temperatures in 1998.
As water temperatures warm from the surface to deep within the water column, the deeper water will experience an extended summer, or warmer period, and a shorter winter, or cooler period. With warmer water in the depths of the lake, you will begin to see harmful, non-native invasive species begin to show up in the lake.
There will also be less cycling of nutrients from the shallow to deeper depths, which will “lead to lower lake productivity and lower food for plankton eating fish,” says Rutherford.
“The consequences of changes in subsurface water temperatures will result in a profound shift in lake ecology. Without high-frequency, long-term monitoring of subsurface waters, we will be blind to the impacts of climate change on most of Earth’s fresh surface water,” the study claims.
We are already seeing evidence of a shift with land-based food supply.
Apple farmers are struggling with their harvest, due to a shift in the predictability of season. They are experiencing a later start to winter, and more frequent cold snaps later in the spring, which is taking a toll on generations old apple farming. The stress that the changing climate is putting on agriculture and the farmers is forcing come out of business, as well as a regional shift in where these foods are grown.
The climate is changing the structure of land-based food, as well as the water-based food. And now we know those impacts are reaching the depths of Lake Michigan hundreds of feet underwater.
“In all, the consequences of changes in subsurface water temperatures will result in a profound shift in lake ecology. Without high-frequency long-term monitoring of subsurface waters, we will be blind to the impacts of climate change on most of Earth’s fresh surface water,” the study claims.