The NYTimes reports:
Gist: due to a number of factors the water levels in the Great Lakes are below historic averages, which is costing shippers millions. We need to fret about this. Engineering – dredging and maybe locks and turbines – could, along with increased precipitation, solve the problems indicated. Government needs to act now.
Analysis & Questions:
– In the fifth paragraph, we are told that water levels in the Great Lakes have been below their historical averages for the past 14 years. Inquiring minds want to know, but are never told, how long a period do those averages cover? 1918 is mentioned – is that it? Less than a hundred years? The Great Lakes in their present form are only about 4,000 years old, and their geology is very complicated: rifts valleys, glacial basins, crustal rebound. They were originally filled with glacial melt water, but are now filled with rain and snow. Are the water levels of the Great Lakes fundamentally stable? Over what kind of time periods? How do we know this?
– “A measure of the drop in water levels can also be attributed to the engineering that makes Great Lakes shipping possible. The 1962 dredging of the St. Clair River may have lowered the water in Lake Huron and Lake Michigan by five inches”. So, by dredging waterways we make it easier for more water to flow out of the lakes and into the ocean. They don’t make this point in the article, but the greatest drops in water level are in the West – Lake Superior is down 22″ – but hardly evident in the East – Lake Ontario is at about its average level. Since the Great Lakes drains roughly west to east, this is not surprising.
– “Climate change is expected to reduce water levels still further in the long run.” Expected by whom? According to what logic? It seems as likely as not that warmer weather would put more water vapor into the atmosphere and increase area precipitation, for example. Further, do we really understand the long-term trends? It’s quite possible the lakes are simply doomed to dry out, as the crust rebounds and no glacial water enters them. Wouldn’t we need to know what the long term trends are first before we can say what, if any, part climate change may have?
This article strikes me as a form of subtle disinformation. Rather than ask and answer the pertinent questions about the long-term direction of water levels in the Great Lakes, we proceed directly to Climate Change and other human interference (engineering those waterways the embedded human interest stories need dredged – except that would be repeating something that allegedly contributed to the problem in the first place). Also, check this out: current levels in Lake Superior are much closer to average than they are to record lows. Oops.
Geologically, lakes don’t last long. It takes a rare set of circumstances for a lake to not fill with silt and turn into a meadow within a few thousands of years, tops. And that assumes that other factors, such as precipitation and drainage, stay favorable. Once in a while, a lake sits atop a widening chasm – Lake Baikal – or a sinking plate fragment – Clear Lake, CA – or is simply really huge, like the Great Lakes, and so survives longer.
Out here in the West, the landscape is dotted with dry lake beds, lakes that were full of water a few thousand years ago. Mirror Lake in Yosemite is now Mirror Meadow, and that has happened within living memory.
Isn’t this transient nature of lakes the real news?