Great Lakes Ice Season Decreasing Significantly Despite Claims by Skeptics

By February 15, 2010 February 24th, 2013 Impacts

Every year or two, one or more of the Great Lakes will freeze over and ignite a winter storm of fury about how the Algorians (Al-Gore-ians)are wrong again. The Great Lakes are freezing over so the climatemongers must be wrong.  The reality of course is that our planet is warming and it is warming faster today that it was a decade or three ago.  When I saw the skeptics alarm about Lake Erie freezing over I instinctively started Googling "Great Lakes freeze up history". This time I ran across an apparent indicator of total Great Lake ice season length, or so this is what the author says. I will just reprint the entire abstract here, it is quite a telling piece of work.  Apparently the ice season on the Lakes is 45 days shorter today than it was 150 years ago and the rate of decrease of ice coverage has been greatest in the last couple of decades.

"This research documents a 150-year record pertaining to the duration of closed navigation for Bayfield harbor. Data were gathered recording the opening and closing of navigation in Bayfield, Wisconsin from 1857–2007. Data were primarily collected from the Madeline Island Ferry Line and microfilmed copies of the Bayfield County Press. Analysis of the data indicates that the duration of ice cover on Lake Superior at Bayfield, Wisconsin has decreased over the past 150 years at the rate of approximately 3 days/decade or 45 days over the course of the study. During the past 150 years, the date that the last boat is able to navigate in the Bayfield harbor indicates the onset of ice cover. This date has occurred an average of 1.6 days later every decade. Conversely, the date that the first boat is able to navigate in Bayfield harbor marking the break up of ice cover has come to an average of 1.7 days earlier every decade. Although this represents the overall trend for the past century and a half, the most dramatic changes have occurred since 1975. During this period the ice season has begun an average of 11.7 days later and ended 3.0 days earlier every decade. Bayfield’s ice season was compared to the lake’s annual maximum ice concentration (AMIC) as compiled in a study by [Assel, R.A., Cronk, K., and Norton, D. 2003. Recent trends in Laurentian Great Lakes ice cover, Climatic Change 57: 185–204, 2003.] The fraction of the potential closed navigation season that the Bayfield harbor is ice covered decreased at a rate of 0.77% a year while the AMIC decreased at a rate of 0.39% / year during the period from 1964–2001. In general, the decline in the ice cover at Bayfield mirrors the pattern shown by the AMIC, suggesting that Bayfield’s ice season could be used as a nonspecific indicator of overall lake trends."

Howk, Changes in Lake Superior Ice Cover at Bayfield, Wisconsin, Journal of Great Lakes Research, September 2008.