JPL Study - Lake Constance Water Temps Up 0.3C Per Decade For Past 50 Years

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PARIS, Dec 15, 2010 (IPS) - At first glance, Lake Constance, trapped between Germany, Switzerland, and Austria, looks as peaceful as ever. But under the lake's apparently placid waters, a dramatic change is taking place - one that threatens to obliterate much of local biodiversity. The temperature of the lake’s waters is rising at an alarming pace.

According to records from the Agency for Environmental Protection of Baden Wuerttemberg, the German federal state in which Lake Constance is situated, the lake’s water temperatures have been rising by 0.3 degrees Celsius per decade over the past 50 years. This rising of water temperatures is a global phenomenon caused by climate change. A recent study, carried out by the Jet Propulsion Laboratory (JPL) at the U.S. National Aeronautics Administration, confirmed the causal link. The JPL study, released in August, analyzed surface temperatures extracted from nighttime thermal infrared imagery for 167 large lakes distributed worldwide. The data was collected from 1985 to 2009 for the months July through September and January through March.

The authors of the study, Philipp Schneider and Simon Hook, found that nighttime surface water temperatures have been rapidly warming for the 24- year period by an average of 0.5 degrees Celsius per decade. In some lakes, temperatures rose by as much as 1.3 degrees Celsius in 10 years. This warming process slows the cyclical exchange of water layers in the lakes. Because warm water is lighter, it tends to remain on the surface of the lake, with cooler, heavier water remaining on the bottom. But during the period of the year when surface temperatures fall, the water layers rotate and mix in a cycle that transports oxygen and other nourishing elements throughout the lakes.

Depending on the size of the lake, the exchange cycle takes place once or twice a year. "But when the surface waters are warmer and remain so longer during the year, the cyclical exchange of waters slows down or does not occur at all," Karsten Rinke, director of the department of lakes at the German Helmholtz Centre for Environmental Research, told IPS. For biodiversity living at the bottom of the lakes, slowing down the exchange of waters can be fatal. "After a while, there is no more oxygen on the bottom, leading to the death of fish and other species," Rinke said.

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