Temperatures Rising in America’s Freshwater Lakes

The waters of the Great Lakes are warmer than usual this year, prompting scientists to worry that this may not be a good thing.  All five Great Lakes have been at or near record-high temperatures compared with the 30 years when such measurements have been taken.  The bad news is that there’s still a month remaining before the lakes typically reach their warmest temperatures.  Jay Austin, a physics professor at the Large Lakes Observatory in Duluth, MN, says the water is warmer because last winter there was little or no ice cover to reflect sunlight.   Scientists are unsure if it’s a blip or the new normal.  A warmer Lake Superior might be a plus for the tourism industry, but it might be bad for fishing, wildlife habitat and water levels.

“Swimmers are enjoying it,” said Al Oleksuik, who lives near the Welland River in Chippewa.  “I notice a difference here.  (The water is 24 C). It usually doesn’t hit that until mid-August. I have a feeling we’re headed towards (26 C), which is extremely warm.”  Austin said the lake is 5 to 7 C warmer than it usually is in mid-July, while the Great Lakes in general are running 2 to 7 C warmer.  “It’s going to set records, or come close, depending on where you are,” he said.

Writing in Chimes, a publication of Grand Rapids-based Calvin College, Geneva Langeland says that “Lake Michigan is warming up?  Swimmers who brave the lake’s often frigid waters might beg to differ.  But Lake Michigan’s waves aren’t alone in their slight temperature uptick; NASA satellite data suggest that lake temperatures worldwide have risen in the last 25 years, most likely as a result of global climate change.  Phillip Schneider and Simon Hook, researchers at NASA’s Jet Propulsion Laboratory in California, departed from the typical strategy of measuring global warming trends by gauging air temperatures near Earth’s surface.  Instead, the study, published in the 2010 issue of Geophysical Research Letters, used infrared satellite imagery to track changing surface temperatures in 167 large lakes splashed across the globe — including our very own Great Lakes.  The satellite data suggest that, over the past 25 years, water temperatures in large lakes have risen between .81 and 1.8 degrees Fahrenheit per decade.  These shifting temperatures varied widely among continents and hemispheres.”

According to Langeland, “Schneider and Hook noted the greatest change in northern Europe; in general, the loftier latitudes of the Northern Hemisphere consistently reported the largest temperature upticks.  The Great Lakes land squarely in that northern region.  Huron, Superior, Michigan, Erie and Ontario together comprise the world’s largest freshwater lake system.  It should come as no surprise that the ‘Big Five’ were valuable players in this study.  In fact, the Great Lakes host nine temperature-gauging buoys that were vital in verifying NASA’s satellite temperature readings.  As Schneider said, ‘The results have implications for lake ecosystems, which can be adversely affected by even small water temperature changes.’  A degree or two might be imperceptible to us, but this tiny change can have surprising repercussions.  Every organism thrives within a particular temperature range.  Altering a habitat’s air and water temperatures even slightly will kill off some creatures while allowing others to unexpectedly thrive.”

Lakes in the American West are experiencing similarly increasing temperatures.  Warming that meets statistical significance was found in Lake Tahoe along the California-Nevada border; Pyramid Lake in Nevada; and the Great Salt Lake in Utah, which were warming at a rate of more than one degree Fahrenheit per decade.  “One of the things we want to do in the future is compare these results with what the climate models predict in the region,” Hook said.  “Measuring a model’s performance in replicating changes of the recent past gives scientists a way to test the accuracy of the models being used to project future conditions.”

“Our analysis provides a new, independent data source for assessing the impact of climate change over land around the world,” Schneider said. “The results have implications for lake ecosystems, which can be adversely affected by even small water temperature changes.”

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