Rivers that connect the Great Lakes have dried up completely because of climate changes in the fairly recent past, according to scientists who warn a similar situation could occur by the end of this century.
A warm period about 7,900 years ago caused lake levels to fall by about 20 meters (65 feet) below the bottoms of rivers like the Niagara and the St. Clair that drain the Great Lakes, leaving the now-crucial economic arteries for Canada and the United States high and dry.
Niagara Falls stopped, shorelines changed and forests grew on former lake beds, leaving fossil stumps far offshore today.
"People used to think the Great Lakes weren't very sensitive to changes in climate, but nature has already run the experiment and shown that under some conditions they're extremely sensitive," said John King, a geological oceanographer at the University of Rhode Island who published a study in the journal Eos. "We've demonstrated that at least once in the last 10,000 years, climate drove the lake levels down pretty substantially."
The lake levels dropped when water evaporated faster than it was replaced during a warm period that lasted for several centuries beginning about 7,900 years ago. An average temperature increase of about 5 degrees Celsius (9 degrees Fahrenheit) occurred, probably spurred by a shift in weather patterns, bringing more dry air from the north and west and less moist Gulf of Mexico air.
A 5-degree-Celsius temperature rise is at the high end of what scientists have predicted could occur by the end of this century as a result of human-induced global warming (Tom Spears, Canwest News Service, Jan. 16). -- KJH