Great Lakes Water Levels and Climate Change: Going Up or Going Down?
Ann Arbor, MI — The Great Lakes’ bottom line just got higher. Using a new method, NOAA scientists predict higher future water levels than previous models of enhanced greenhouse gas concentrations - either a smaller drop in Great Lakes water levels or actually higher levels.
Researchers from the NOAA Great Lakes Environmental Research Laboratory report on a new method for estimating evapotranspiration (loss of water from the land portion of the system as vapor) and call into question previously published climate change lake level scenarios for the Great Lakes. Evapotranspiration is a key term in the water budget of the Great Lakes - significant volumes of water are constantly being lost from the system due to this process.
Scientists used to think of air temperature as a reliable indicator of energy input. It turns out that the air temperature we feel is not only influenced by energy input from the sun, but also by greenhouse gases which bump up the mercury by slowing down heat’s escape from the earth and atmosphere. The new method takes into account both incoming and outgoing energy and yields surprisingly different results. The equations get complicated but the concept can be thought of like a trip to your local supermarket.
Think of the number of people standing in line at the checkout as the temperature. The number of people waiting to checkout might be a good indicator of how many people have been entering the store (the heat energy coming from the sun) as long as you don’t change the number of checkout lanes that are open (the heat energy escaping from the earth and atmosphere). But greenhouse gases effectively close the checkout lanes—there might not be more people coming in the store (energy input), but the number waiting to leave (temperature) increases anyway.
Evapotranspiration is dependent on energy input, not directly on the temperature. Using the old methods, temperature was used to estimate energy, which in turn was used to calculate evapotranspiration. The new method accounts for the energy more directly, resulting predictions of lesser increase in evapotranspiration. Lower losses of water to vapor mean more water is staying in the Great Lakes basin. These predictions are valid when averaged over a few decades in the mid- to late 21st century. Natural variability (ups and downs with seasons and particular weather patterns, etc) still occurs on top of this.
Original Publication Information
Results of this study, "Effects of Using Air Temperature As a Proxy for Potential Evapotranspiration in Climate Change Scenarios of Great Lakes Basin Hydrology," are reported by Brent Lofgren, Tim Hunter and Jessica Wilbarger in Volume 37, No. 4, of the Journal of Great Lakes Research, published by Elsevier, 2011.
Contacts
For more information about the study, contact Brent Lofgren, NOAA Great Lakes Environmental Research Laboratory, 4840 S. State Rd., Ann Arbor, MI 48404; brent.lofgren@noaa.gov, (734) 741-2383.
For information about the Journal of Great Lakes Research, contact Marlene Evans, Editor, National Water Research Institute, Environment Canada, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada; jglr@ec.gc.ca; (306) 975-5310.
Since 1967, IAGLR has served as the focal point for compiling and disseminating multidisciplinary knowledge on North America's Laurentian Great Lakes and other large lakes of the world and their watersheds. In part, IAGLR communicates this knowledge through publication of the Journal of Great Lakes Research, available to members in print and electronic form. A searchable archive of the journal is available online and includes the abstracts of articles from the journal's inception in 1975 through the most recent issue. In addition, complete articles are available to members who have signed up for an electronic subscription.