Background
With respect to the Great Lakes Basin, the authors write that "studies conducted by Cohen (1986, 1990), Sanderson (1987), and Croley (1990, 2004) have found that evaporation would be significantly increased under [IPCC-predicted] climate change scenarios," and that under such circumstances Sanderson and Smith (1990) and Smith and McBean (1993) "predicted twenty to thirty percent increases in potential evaporation and approximately a 15% increase in actual evaporation to occur." As a result of these and other related studies, many researchers have worried, in the words of Larson and Schaetzl (2001), that "increased evaporation under a possible greenhouse-enhanced climate, coupled with even more consumptive use of the Great Lakes waters, could lead to lower lake levels in the near future," which is one of the negative-trend gloom-and-doom predictions periodically dusted off and paraded before the world by the planet's climate alarmists, such as when National Geographic published an article in 2002 entitled "Down the Drain? The Incredible Shrinking Great Lakes."

What was done
McBean and Motiee used mean monthly and mean annual data series for over-lake air temperature and over-lake precipitation data for the individual Great Lakes and flow data for their connecting channels (St. Mary's River, St. Clair River, Niagara River, and St. Lawrence River) to determine long-term (1930-2000) trends in temperature, precipitation and streamflow, using regression analyses and Mann-Kendall statistics.

What was learned
The researchers report that for each of the five Great Lakes, "the best fit line shows a gentle increasing slope" with "an average increase of 0.63°C in the basin," which they say is "less in magnitude than the global climate model predictions." With respect to precipitation and streamflow, they also say they find increasing trends "in all series," with some of them being statistically significant at the 95% level. Last of all, they calculate that if the trends they found for the 1930-2000 time period continue, streamflow at the outlets of Lakes Superior, Huron, Erie and Ontario in the year 2050 will be 7%, 17%, 25% and 25% greater, respectively, than they were in the year 2000.

What it means
In spite of the climate-alarmist claim that 20th-century warming was "unprecedented" over the past one to two millennia, and that such warming in the Great Lakes region of the Northern Hemisphere should be leading to the massive lakes going "down the drain," real-world data provide no support for this contention, or anything even close to it. In fact, they tend to suggest just the opposite.

References
Cohen, S. 1986. Impacts of CO2-induced climatic change on water resources in the Great Lakes Basin. Climatic Change 8: 135-153.

Cohen, S. 1990. Methodological issues in regional impacts research. Proceedings of Conference on Climate Change: Implications for Water and Ecological Resources, Department of Geography, Occasional Paper No. 11., University of Waterloo, Canada.

Croley, T.E. 1990. Laurentian Great Lakes double-CO2 climate change hydrological impacts. Climatic Change 17: 27-47.

Croley, T.E., Hunter, T.S. and Martin, S.L. 2004. Great Lakes monthly hydrologic data. Internal Report 13, NOAA, Great Lakes Environmental Research Laboratory, Michigan, USA.

Larson, G. and Schaetzl, R. 2001. Origin and evolution of the Great Lakes. Journal of Great Lakes Research 27: 518-546.

Sanderson, M. 1987. Implications of climatic change for navigation and power generation in the Great Lakes. Climate Change Digest 87-3, Environment Canada.

Sanderson, M. and Smith, J. 1990. Climate change and water in the Grand River Basin, Ontario. Proceedings of the 43rd Conference Canadian Water Resources Association, Penticton, Canada, p. 243-261.

Smith, J.V. and McBean, E. 1993. The impact of climate change on surface water resources. In: Sanderson, M. (Ed.), Department of Geography Publication Series No. 40. Department of Geography, University of Waterloo, Waterloo, Canada, p. 25-52.