For two decades, studies have said a warming climate could send water levels sharply lower by boosting evaporation and reducing rain and snowfall in the Lake Superior basin, which feeds the other lakes. But a revised computer modeling system suggests those predictions were overstated, said Brent Lofgren, a scientist at the NOAA Great Lakes Environmental Research Laboratory in Ann Arbor.
“While there are still many unknowns about how climate change will unfold in the Great Lakes region, our results indicate less loss of water than earlier studies,” Lofgren said.
Water levels in the lakes have fluctuated over time. Levels have been sharply lower on Lakes Superior, Huron and Michigan much of the past decade, forcing cargo ships to carry smaller payloads. A decline of even a few inches can make a big difference because even under normal conditions, ships nearly scrape bottom in the shallow channels linking the lakes.
Low water also can prevent marina operators from renting their slips and can hamper hydropower production.
On the other extreme, excessively high water in previous decades has caused beach erosion and damaged lakeshore homes.
Scientists have made projections about climate change’s effect on levels for the past two decades, based on models developed at the Great Lakes lab that assumed air temperatures alone would determine water evaporation rates.
In a newly published paper in the Journal of Great Lakes Research, Lofgren said he and colleagues had adjusted the models to reflect how energy from the sun and from greenhouse gases — the gases that cause global warming — affect evaporation. The revisions indicate less water will be lost than previously thought, he said.
The most extreme water level swings happen on Lakes Michigan and Huron, which have been below their historical average for most of the past decade and presently are about 15 inches down, said Keith Kompoltowicz, a scientist with the U.S. Army Corps of Engineers office in Detroit.
Under the older modeling system, some studies projected that Huron and Michigan — which are connected and have the same surface level — would decline 6 feet or more this century. Models based on the new methodology suggest levels could fall up to 3 feet or actually rise about 20 inches, he said.