Two years ago, after the polar vortex set the Upper Midwest into a deep freeze for a second straight winter, scientists thought the weather phenomenon could reverse a 15-year stretch of diminished lake levels and reduced ice cover in Lake Michigan.
At first, they appeared to be right. Ice coverage across the Great Lakes reached 92.5 percent in 2014, the highest on record since 1979. With the widespread ice coverage acting as a capstone for evaporation, Lake Michigan water levels rebounded 3 feet between 2013 and 2015, an unprecedented surge from record low lake levels in 2013.
But two consecutive mild winters marked by light ice coverage and retreating lake levels are giving researchers pause. Though Lake Michigan water levels are expected to stay above the historic average through the next six months, some experts say the significant abnormalities dating back to 1997-98 — when one of the strongest El Ninos ever was recorded — may indeed be the new normal.
An El Nino is an irregular climate pattern characterized by warming ocean and atmospheric temperature, and typically generates unseasonably warm conditions during the winter months across the U.S. The 1997-98 El Nino brought widespread drought to parts of North and Central America and record-breaking rainfall and flooding to places like the West Coast. Most recently, another strong El Nino was in effect in 2015-16.
Researchers can point to noticeable changes that occurred after the 1997-98 El Nino, but it remains unclear whether that climate occurrence was a tipping point or catalyst for change.
“I’m not able to say what the cause of the recent ice and temperature conditions might be, but it is worth noting that the 1997-98 El Nino coincided with a shift in conditions in Lake Michigan,” said Eric Anderson, a physical scientist with the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory.
Since then, the concentration of Great Lakes ice has remained below its yearly peak ice cover average for 14 of the past 19 years.
Heading into March this year, when about 43 percent of the Great Lakes is frozen on average, there was only about 4.5 percent ice coverage, according to NOAA. A mid-March cold snap eventually brought this year’s maximum ice coverage to nearly 20 percent, which remains a far cry from the long-term maximum annual coverage of 55 percent.
The meager amount of ice on the lakes is a detriment to some marine life, such as whitefish, which rely on ice cover to protect their eggs from strong wind and wave action.
Winter-dependent recreation also took a blow in the past two years. This winter, Norge Ski Club in Fox River Grove postponed its annual ski jump competition for the first time in its 112-year history.
State geologist Ethan Theuerkauf said mild winters could negatively impact spring pastimes as well. During typical years, ice coverage close to the shoreline protects beaches and shoreline habitat. Without the ice acting as an insulator from waves, the coastline is more vulnerable.
“During milder winters, such as the past two winters here in Chicagoland, shore ice is either not present or only intermittently present,” Theuerkauf said. “This combined with high lake levels has resulted in increased beach erosion due to winter storm waves. The absence of ice allows these storm waves to impact further up the beach profile and results in erosion of beach and dune sand.”
But the warmer winter was a relief for some.
The Great Lakes shipping industry has been able to regain some momentum after the polar vortex winters. According to the Lake Carriers’ Association, massive ice formations during those winters cost the U.S. more than $1 billion in economic activity. Ice-related repairs to vessels also totaled more than $6 million, the association said.
Despite two years of gentler weather, the association has called on the federal government to fund a second heavy icebreaker for the Great Lakes should those icy conditions return.
Though the winter of 2016-17 began with near-normal temperatures and a daily record of 6.4 inches of snow Dec. 5 in Chicago, a frosty first half eventually gave way to unseasonably warm temperatures and unusually long stretches without snow. This winter, meteorologists saw six record-shattering daily high temperatures in Chicago between Feb. 17 and Feb. 22. And for the first time in 146 years, the National Weather Service documented no snow on the ground in Chicago in January and February.
According to the Midwestern Regional Climate Center, five states, including Illinois, saw the warmest February since record-keeping started in 1895. State climatologist Jim Angel said the temperate conditions this winter were largely driven by warm air from the Gulf of Mexico.
While climatologists contend there’s been a gradual warming in the Midwest for the past several decades, not all of them say that’s a bad thing.
“We’ve looked at this in the past and the benefits outweigh costs,” Angel said. “Homeowners come out well with lower heating and less home damage. There are fewer car accidents, fewer repairs on the road and less expense on salting.”
Scientists are concerned about the effects underwater, however.
Studies by NOAA’s research laboratory suggest that lake temperatures rose significantly around 1997-98 and have maintained those levels. Temperature monitoring equipment in Lake Michigan has shown not only an uptick in surface temperature, but also in deeper waters, indicating a long-term shift.
Over the past several decades, biologists have seen a migration of marine life in Lake Michigan.
“Fish are very temperature-sensitive,” said Philip Willink, a senior research biologist for the Shedd Aquarium. “Over the years and decades, we’re seeing a lot of cool-water fish moving north as cooler water temperatures become less common.”
The increased water temperature also means fishermen will have to go farther offshore to catch cool water fish, such as salmon. If the warming trend continues, it could present a problem for these species down the road.
“In general the lakes warm up quicker without ice,” Anderson said. “You don’t have solar radiation from sun working on melting ice. Instead, all of that energy is going into the water, warming the lake. Biology in the lake responds to that.”
Although researchers like Anderson call the trends “a jarring disturbance” over the past 20 years, it will require more research to determine the role of the El Nino.
“There’s lot variability that we are still trying to tease apart,” Anderson said.
Twitter @_tonybriscoe
Photos courtesy Space Science and Engineering Center, University of Wisconsin-Madison and NASA
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