Story URL: http://news.medill.northwestern.edu/chicago/news.aspx?id=215297
Story Retrieval Date: 6/19/2013 4:37:55 AM CST
Courtesy of the NOAA Great Lakes Atlas
An image of Lake Michigan on Jan. 24. Ice cover is visible in Green Bay and the straits to the north
Ice on Lake Michigan shrinks by 71 percent, fed researchers report
Ice coverage on Lake Michigan is down. Way down.
Researchers from the National Oceanic and Atmospheric Administration reported recently in the Journal of Climate that ice cover on the lake has declined 71 percent since 1973.
"There was a significant downward trend in oce coverage from 1973 to the present for all of the lakes. The total loss for overall Great Lakes ice coverage is 71 percent," said researcher Jia Wang.
George Leshkevich is a physical scientist at the Great Lakes Environmental Research Laboratory in Ann Arbor, Mich. He has been using satellites to take images of ice on the great lakes for nearly 40 years.
“If you plotted the maximum amount of ice cover on each lake for the last 40 years, it’s going to fluctuate,” Leshkevich said. “But if you plot a trend line through those points, it’s downwards. The trend is downwards.”
He remembers going out onto Lake Michigan in the 1980s and seeing large amounts of ice cover.“Michigan was quite well covered,” Leshkevich said. “You could see ice on all of the lake. For the past few years I haven’t seen that on Lake Michigan.”
Lake Michigan is currently about 20 percent covered with ice, as compared with about 55 percent in February of 2008, according to a satellite map on his website.
“Now you only see ice in Green Bay, the straits area in the northern part of the lake and some shore ice in the southern parts of the lake and around Chicago,” Leshkevich said. “There has been nothing in the midsection of the lake.
"It’s just not as constant as it was in past years.”
Leshkevich blamed the reduction of ice on both natural variation and anthropogenic, or man-made, effects.
David Kristovich, an atmospheric scientist at the Illinois State Water Survey, said warmer temperatures were a primary reason for the decrease in ice.
“A number of studies have indicated that the overall air temperatures are increasing on average throughout the year,” Kristovich said. “Through the Great Lakes areas there has been a long-term increase in winter temperatures. So there is this large-scale warming going on that you would expect to result in less ice on the lake.”
He said ice cover “plays a measurably role” in water levels for Lake Michigan, which are currently at the lowest levels since record keeping began in 1918, according to the Great Lakes Environmental Research Laboratory.
“If you have a lot of ice on the lake you will have a lot less water vapor coming up from the lake into the air,” said Kristovich. “So ice slows down the decreasing levels of the lake.”
He also said less ice cover creates as ideal condition for lake effect snow.
“For lake effect snow,” Kristovich said, “you need a warm and wet surface with cold air moving over it. When you get ice it takes away the warm surface and makes it a cold surface and blocks the vapor that can get into the air.”
Edward Rutherford is a research fishery biologist at the Great Lakes Environmental Research Laboratory. He said reduced ice coverage affects a number of fish species like the whitefish.
“There’s a definite statistical relationship between ice coverage and productivity of lake whitefish,” Rutherford said. “Reproduction seems to be better when there is more ice coverage. There is less disturbance of eggs on the spawning ground due to wind and waves and so on.”
Kristovich said having less ice also leaves the shoreline more vulnerable to damage from waves and storms.
“If the long-term increase in area air temperature that we have been observing continues for the foreseeable future,” he said, “then you would expect this trend to continue.”