Lake system ‘highly sensitive’ to climate change

Historical fluctuations in the levels of the Great Lakes, on the US-Canada border, had previously been linked to the advance and retreat of glaciers, and it was thought the lakes had been connected since their formation 16,000 years ago during the retreat of the last ice sheet.

But scientists at the University of Rhode Island (URI), working with other scientists from the US and Canada, believe the last time lake levels fell dramatically it was the result of dry climate conditions.

Between 7,900 and 7,500 years ago, this dry period caused the lakes to become disconnected as their overflow rivers ran dry.

In an article in the journal Eos, the team said that the discovery of ancient shorelines, submerged beaches and tree stumps on the floor of some lakes shows that the water line had been as much as 20 metres below the present lake level.

URI geological oceanographer John King said the Great Lakes had been seen as too large to be sensitive to climate variations.

“Now we know that to be untrue,” he said. “We’ve demonstrated that at least once in the last 10,000 years, climate drove the lake levels down pretty substantially.”

In the last century, water levels in the lakes have varied by only about two metres, helping them to play a vital role in the region’s shipping, fishing, recreation and power generation industries.

The research has raised fears about the possible economic impact to the region if climate change lowers the water levels significantly.

“The climate interval that occurred back then is different from what we’re going through now,” Mr King said.

“It would take a pretty big change to close the basins again. But the sorts of temperatures and precipitation amounts that happened then are within the range of what is predicted for 2100.

“In the worst case scenarios, a lot of things become possible.”

Kate Martin