Lake Superior is not only shrinking, but also getting hotter

Lake Superior, the worlds largest freshwater lake, has been shrinking for years-and now it is getting hotter, a new study by US researchers has revealed.

Washington, Aug 4 : Lake Superior, the world's largest freshwater lake, has been shrinking for years-and now it is getting hotter, a new study by US researchers has revealed.

Beachgoers at the lake, which is bounded by Wisconsin, Michigan, Minnesota, and Ontario, Canada, must now walk up to 300 feet farther to reach shorelines. Some docks have also become unusable because of low water, and once-submerged lake edges now grow tangles of tall wetland plants.

"From the late 1960s to 1999, there was a 30-year period with water levels above average. But in 1999, the upper lakes started to fall below average and have mostly stayed that way," said Scott Thieme, chief of the Great Lakes Hydraulics and Hydrology Office for the US Army Corps of Engineers in Detroit, Michigan.

"Lake Superior is in its largest stretch of below average water levels since we've been recording water levels. Scientists predict that by this fall, the lake will set a new record low-about an inch (2.5 centimetres) below the old one. Now people are saying, 'Wow, this is becoming more significant'," said Thieme.

Thieme said the shrinking and heating are related, and that that both are spurred by rising global temperatures and a sustained local drought. Both Minnesota and Wisconsin have been declared moderate to severe drought areas for the past 18 months.

Thieme also rubbished theories of lake water being secretly diverted to the West.

"That lake is much, much more driven by what's happening with precipitation and evaporation, because that's where its input is coming from," said Thieme.

Further studies by Jay Austin, assistant professor at the Large Lakes Observatory, revealed that warming of the climate over the Great Lakes region (Lakes Superior, Michigan, Huron, Erie, and Ontario) was heating up Lake Superior at nearly twice the pace.

One buoy in the lake recorded a surface temperature up to 75 degrees Fahrenheit (24 degrees Celsius) in summer, unprecedented for a lake that's notoriously cold year-round.

Rising summertime air temperatures are only part of the story, though, said Prof Austin.

"Milder winters mean less ice on the lake surface, and less ice means less sunlight is reflected-and more is absorbed. So summer on the lake, defined as the time when a cap of warm water sits on top of cooler water, comes up to 12 days earlier. That means the lake has more time to warm up in response to the warmer air," Prof Austin wrote in his study published earlier this year in the journal Geophysical Research Letters.

Noel Urban, an associate professor of environmental engineering at Michigan Technological University, who set out to research whether the lake might help absorb some carbon dioxide emissions, found that Lake Superior produced more carbon dioxide than it absorbed.

He is, however, unsure whether the increased carbon output is a result of rising temperatures or other climatic factors.

"We would expect the increasing temperature to cause the lake to be more of a carbon source than a sink. That's exactly what we aim to learn with new computer models in development," National Geographic quoted Prof. Urban as saying.

ANI