Background
Changnon begins his study of Great Lakes water levels by noting that "recent shifts in lake levels [have] led to a major disaster-oriented assessment of the 'record' declines in recent years," stating that certain people have "attributed these to climate change from global warming."  In this regard, he makes particular mention of the National Geographic Society, which in 2002 ran an article entitled "Down the Drain?  The Incredible Shrinking Great Lakes" in their flagship publication National Geographic.

What was done
The author analyzed "monthly measures of lake levels for Lakes Superior, Erie, and Michigan-Huron [that] were available from the U.S. Army Corps of Engineers for 1861-2001," which data he converted to annual mean levels that he then used to calculate 5-, 15- and 25-year moving averages and associated standard deviations.

What was learned
Changnon reports that "the 141-year average lake level distributions for 5-year and longer periods show a U-shaped temporal distribution for Lake Michigan, being highest early (19th Century)," while "the distribution for Lake Erie was also U-shaped but the highest values came in recent years (1970-2001)."  Lake Superior, on the other hand, was found to have exhibited "a gradual increase over time from 1861 until about 1950 and a flat trend thereafter."  Considered together, the four lakes reached their lowest levels in the 1930s and their highest levels in the period 1982-1987, while lake level variability was highest for all lakes during the period 1923-1938.

What it means
While transiting from the cold of the Little Ice Age to the heat of the Modern Warm Period, the water levels of the U.S. Great Lakes have defied the claims of the world's climate alarmists, i.e., they have not dropped and become more erratic.  If anything, they have risen and become less erratic.