A recent radio story about how low Mississippi River levels and their impacts on business got me thinking. Here in Michigan, we are aware of how lake levels have dropped. As shown by this chart, levels of the Great Lakes have been lower than average for the last 12 years. Lakes Michigan and Huron are particularly low. Can we attribute this to global warming? I have no idea. In fact, the chart shows that water levels have dropped below average before – including in the mid 1960’s and during the entire 1930’s – often much lower than average compared to the last 12 years.
The lakes levels are getting some attention including multiple theories as to the reasons why including climate change, recent drought conditions, warmer water temperatures, increased evaporation, loss of ice cover, changing precipitation patterns. Studies like this one have concluded that the drops in Lakes Michigan and Huron are in part due to dredging done in 1962 in the St Clair River and subsequent erosion. Others, this one, disagree. While lake levels have fluctuated within regular ranges, one study predicted permanent drops of up to two feet in lake levels.
While the cause is unclear, the effect is not. The drop in lake levels impacts pleasure boaters and commercial shipping. The drop in lake levels is unlikely to stop commercial shipping as is feared for the Mississippi River, but as lake levels drop, ships cannot carry as much – reportedly losing between 70 and 270 tons of cargo per inch of “draft” lost, depending on the size of the ship. Less cargo means, of course, higher costs and lower profitability.