Researchers document a 71 percent decline since the 1970s
By Summit Voice
SUMMIT COUNTY — University of Michigan and NOAA researchers who scoured historic Coast Guard records, satellite data and other sources have concluded that there has been a significant downward trend in ice coverage from 1973 to the present for all of the lakes.
Overall, the total loss for Great Lakes ice coverage is 71 percent during that period. with Lake Ontario showing the largest ice loss, while Lake Erie and Lake St. Clair showed the smallest amount of ice loss, at 37 percent.
The documented loss during the period is likely due to a combination of factors, including a response to cyclical hemispheric climate patterns, like El Niño-La Niña phases, changes in the Arctic Oscillation and overall global warming. Lake ice may respond differently to climate forcing in the upper and lower Great Lakes, the researchers concluded.
The year-to-year changes driven by those cyclical patterns is overshadowed by the long-term trend of significant ice loss since the 1970s, although the researchers caution that the trends from that time period shouldn’t be extrapolated back or forward.
The study also looked air and water temperatures to identify factors that could be responsible for the declining winter ice cover, finding a consistent increase in surface air temperatures over the lakes between 1973 and 2010 and an even more marked increase in summer surface water temperatures — which climbed about 2.5 degrees Celsius between 1976 and 2006, according to a separate study.
The “excessive” warming of lake water temperature relative to the local surface air temperature is caused by a positive ice/water albedo feedback due to the declining winter ice cover, similar to trends documented in the Arctic.
Lighter-colored ice reflects incoming solar radiation back into the atmosphere, but darker-colored open water absorbs more of that energy as heat. The more the water warms in the summer, the longer it takes to cool and freeze in the winter.