Guest “because climate change” by David Middleton
From the October 1, 2020 issue of Physics Today… Well, physics the day after tomorrow (good movie title)…
1 OCTOBER 2020 • page 26
The Great Lakes are filled to their brims, with no signs of receding
Experts see the fingerprints of climate change on the lakes’ record high water levels.
Physics Today 73, 10, 26 (2020); https://doi.org/10.1063/PT.3.4589
Seven years ago, Ron Wilson’s son was married on the beach in front of his cottage on the eastern shore of Lake Michigan. Were the couple to renew their vows today in the same spot, they’d be standing in nearly two meters of water. The 18-meter-wide beach has vanished, and the lake is now lapping at a steel seawall Wilson erected last winter to keep storms away from his foundation.
Water levels have always fluctuated on the Great Lakes, but the recent extreme seesawing, particularly on the upper lakes—Superior, Michigan, and Huron—is unprecedented in the century that records have been kept (see charts). Michigan and Huron, which are linked and share the same level, stood at record highs in August, 84 cm above their historic average. The two lakes bottomed out at record lows in 2013. Although a relatively modest 25 cm above average, Superior in 2020 was just 5 cm below its record peak for August set a year ago.
Signs of climate changeThe past 10 years have been the wettest on record for the Great Lakes watershed. Andrew Gronewold, associate professor for environment and sustainability at the University of Michigan, says the rainy years began well before the 2013 ebb in the upper lakes. An extended period of excess evaporation that started in 1998 more than offset the added precipitation until the polar vortex event in early 2014 caused most of the lakes to freeze over. Since then, water supply has exceeded evaporation, partly because of several especially cold winters, Gronewold says. He adds that the 2014–17 period saw the fastest three-year increase in water levels since record-keeping began.
Donald Wuebbles, professor of atmospheric science at the University of Illinois at Urbana-Champaign, says precipitation over the watershed has risen 10% over the past century and is expected to grow another 10% over the next. Precipitation in the Great Lakes region is increasingly occurring in larger events, researchers say. As a result, more rainfall runs off into streams and rivers feeding the lakes instead of being absorbed in soils. The lakes themselves make up a major portion of the watershed.
“The rate at which precipitation has changed over the past decade simply cannot be explained by historical variability alone,” says Gronewold. “The best explanation is a warming atmosphere and warming global temperature.”
The article provides this USACE chart of historical lake levels…
The caption in the article must be a typo…
Water levels on the Great Lakes have fluctuated irregularly over the past century. The peaks and troughs on Lakes Michigan and Huron have been especially pronounced. From a record low in 2013, they have surged to record highs this year. (US Army Corps of Engineers.)
Michigan-Huron appears to have been just as low as 2013 in 1965-1966 and within 1 foot of that low in the mid-1920’s and mid-1930’s. The “record highs this year” don’t look any higher than 1987 and the mid-1970’s, mid-1950’s and 1930 appear to have been within 1 foot of those record highs. I
2. Unprecedented? Not!
What does the US Army Corps of Engineers (USACE) data show?
3. No Lake Michigan for you! 2019 and 2013 are highlighted.
The peaks and troughs on Lakes Michigan and Huron have been especially pronounced. From a record low in 2013, they have surged to record highs this year.
This year isn’t over. The most recent full year of USACE records is 2019. Lakes Michigan-Huron set no monthly record highs in 2019 and only one record monthly low in 2013. 11 monthly record highs were set in 1986 and 1 in 1987. Most of the Great Lakes monthly record highs were set in the mid-1980’s. 10 of the monthly record lows for Michigan-Huron were set in 1964. The vast majority of record monthly lows for the other lakes were set in the 1920’s and 1930’s.
4. Surface elevation of Lakes Michigan-Huron in feet above International Great Lakes Datum of 1985 (IGLD 85). Green is the monthly average, red is the trailing 12-month average. The pre-1980 average, plus/minus 2 standard deviations are denoted by horizontal black lines. (USACE)
What’s really funny? They tell us that climate change caused these record highs and lows and will make the seesawing worse… But…
Longer term, it’s anyone’s guess where lake levels are headed. The range of possibilities in the six-month forecasts by the US Army Corps of Engineers is so broad in the latter months as to be of little use, researchers say.