Would Great Lakes' levels rise or fall with global warming? Answer: Fall!

"Most climate models suggest that we may see declines in lake levels over the next 100 years; one suggests that we may see declines of up to 2.5 meters (8.2 feet)," according to Columbia University's Earth Institute.

International concern over sea level rise and other effects of climate change throughout the world were the topic of Climate Talks in Copenhagen, Denmark in 2009.  

Water levels in the Great Lakes have been decreasing since a record high was reached in 1980.  Research has found that lake levels are rising and falling a month earlier than during the 19th century.  Don't underestimate the role evaporation plays in lake levels as well as snow, ice cover, water withdrawal, the Soo and St. Lawrence locks, etc.

But the story is complex when it comes to the Great Lakes.

Earth Watch Research found:  "Global concern with climate change is primarily focused on the amount of greenhouse gases in the atmosphere.  Greenhouse gases, such as carbon dioxide, water vapor, and methane, among others, are an essential part of our atmosphere, and they serve a vital role in making our planet warm enough for life.  Greenhouse gases trap energy (in the form of longwave radiation) that is being emitted by the Earth, reflecting it back into the atmosphere to warm the planet.  As the amount of carbon dioxide in the atmosphere has increased or decreased over time, the planet’s temperature has changed in roughly the same proportion.  Scientists have determined this relationship from studying ice cores taken from Antarctica which include ice which fell as snow from over 400,000 years ago."

"Right now there is more carbon dioxide in the atmosphere than at any time measured in the ice core.  Scientists expect that this will lead to a gradual warming of the planet in most areas.  But what does this specifically mean for the Great Lakes region?  There are four aspects of the climate in the Great Lakes region where we can expect to see some changes: ice cover, evaporation levels, precipitation, and lake levels."

"Researchers have attempted to determine trends for total ice cover on the Great Lakes since 1963, unfortunately with little success.  Ice cover has varied greatly from year to year. While it has dropped significantly over the last decade, the results are not conclusive enough to suggest that this is a trend.  However, ice cover trends on smaller lakes in the 

Great Lakes region do show trends of freezing later and thawing earlier."

"Rates of evaporation and precipitation on the Great Lakes are difficult to project, and vary across the region. The Western region of the Lakes tends to be drier, while the Southeast area tends to have far more precipitation (“lake-effect” snow and rain).  Climate change models suggest that temperatures will increase over the next century over the Great Lakes.  Higher temperatures suggest an increase in evaporation, which should then lead to an increase in precipitation.  This means that current trends will likely be accentuated, with the Western Region of the Lakes being slightly drier, while the Southeast will be slightly wetter.  Warmer temperatures mean that less of this precipitation will fall as snow on average, although annual amounts will likely vary considerably.  One key question scientists are trying to answer is whether the increase in evaporation will be greater than the increase in precipitation.  Currently, scientists project that rates of evaporation will, on average, outpace rates of precipitation, although the degree of difference is still a subject of debate."

"But what does all of this mean for water levels in the Great Lakes?  This is an important question; after all, our current infrastructure around the Lakes, from ports and canals to beaches and boardwalks, were designed and built based on the water levels experienced throughout the Twentieth Century.  This is a far more complicated question than the one facing coastal cities along the oceans that are contending with sea level rise due to glacial melt and thermal expansion of water.  Water levels in the Great Lakes will be determined almost entirely by levels of precipitation and evaporation, as well as by the quantities of water removed from the watershed through consumption or diversion.  A further consideration is that water levels are controlled at two points; at the outflow from Lake Superior, and at the outflow from Lake Ontario, as regulated by the International Joint Commission.  This suggests that the Lake Superior, as the upstream lake, will serve as the bellwether for the rest of the lakes."

"Reports on this subject indicate that most climate models see declines in lake levels over the next 100 years; one suggests that we may see declines of up to 2.5 meters (8.2 feet).  Granted, this is hardly conclusive; another model that suggests a “wetter” future climate over the Great Lakes projects a small increase in lake levels.  The truth is likely somewhere in between, with water levels falling between 0.23 meters and 2.5 meters.  What is certain is that more research is needed to improve modeling of the climate in the Great Lakes region."

References: Union of Concerned Scientists Great Lakes Report; data from the Vostok Ice Core: Carbon Dioxide Information Analysis Center.  Resource on climate change: Chapter 11 of the Intergovernmental Panel on Climate Change’s (IPCC) Working Group 1 contribution to the Fourth Assessment Report; the section on North America starts on page 887; published in 2007.  “Evaluation of Potential Impacts on Great Lakes Water Resources Based on Climate Scenarios of Two GCMs,” published in the Journal of Great Lakes Research (Lofgren, B. M., F. H. Quinn, A. H. Clites, R. A. Assel, A. J. Eberhardt, and C. L. Luukkonen, 2002).  Great Lakes Environmental Research Lab (GLERL), part of the National Oceanic and Atmospheric Administration.  Great Lakes Coastal Resilience.