Jim Belshaw sends along a Felicity Barranger story on the dwindling of the Great Lakes. Per usual, climate change is blamed, though other hypotheses are also on the table:
Although the drop in levels in all three lakes is variously ascribed to climate change or new rainfall patterns, evidence is growing that people caused some losses in Lakes Huron and Michigan.
Gravel mining early in the 20th century by private companies and dredging by the Army Corps of Engineers, particularly in the mid-1960s, may have widened and deepened the St. Clair River, through which those two lakes drain into Lake Erie.
The flow may be eroding the riverbed. The erosion may in turn result in increased outflow, more than can be replenished by rain or snowmelt, according to a study by a group of Canadian coastal engineers.
…aren’t new rainfall patterns a kind of climate change?
I lived in Chicago in the late 80’s, and all the fear, then, was about the relentless increase in the depth of Lake Michigan. Fortunately, its cycle reversed before we lost too many buildings. I have one friend on the East side of the lake who has had to rebuild his lakefront cottage twice, because of coastal erosion. The first one had stood in the same spot for 80 years.
The great lakes have always cycled. You can go to the Indiana Dunes park to see where the waterline was much, much higher 400 years ago.
That makes it hard to tell how seriously one needs to take this study.
Also, the Chicago River used to flow into Lake Michigan. It was reversed to flow out, and into the Mississippi, in order to carry pollution away from the city. If you do the arithmetic, though, it is hard to imagine how its meager flow rate could cause any measureable change in the depth of Lake Michigan.