Study Says Climate Change Impacting US Midwest
Great Lakes Water Levels Could Drop Two Feet in 21st century
Jul 1, 2009
An interagency US government report has outlined region-by-region challenges from global climate change, and the Great Lakes region faces an especially complex array of challenges. Home to 20 percent of the world’s fresh water supply, the Great Lakes – Superior, Huron, Michigan, Erie, Ontario – could see their levels drop by as much as two feet during the 21st century.
The government report, “Global Climate Change Impacts in the United States,” was commissioned in 2007 during the Bush Administration and was released on June 16, 2009. Produced by the U.S. Global Change Research Program, which was led by the National Oceanic and Atmospheric Administration, the report is the most comprehensive report to date on climate change impacts in the US, with the latest information on rising temperatures, heavy downpours, extreme weather, sea level changes and other results of climate change.
In its sections on the US Midwest region, the report concluded that lower Great Lakes water levels would affect beaches, coastal ecosystems, fish populations, dredging requirements and shipping.
Temperatures Rising In Midwest USA
Dr. Don Wuebbles, the Harry E. Preble Professor of Atmospheric Sciences at the University of Illinois at Urbana-Champaign, served as a key researcher in the report. He said average temperatures in the US Midwest have risen in the Midwest in recent decades, especially in winter. The growing season has been extended by one week. Heavy downpours are now twice as frequent as they were a century ago, and the Midwest has experienced two record-breaking floods in the past 15 years.
Wuebbles said average annual temperatures are expected to increase by about 2 degrees Fahrenheit over the next few decades, and by as much as 7 to 10 degrees by the end of the century, he said, with more warming projected for summer than winter. Precipitation is expected to increase in the winter and spring, while summer precipitation will likely decline.
Wuebbles explained the probable decline in Great Lakes water levels would result from the effects of evaporation being dominant over effects of precipitation and runoff into the lakes.
Evaporation Lowers Lake Levels
“Under the larger climate change scenarios,” Wuebbles said, “evaporation clearly dominates and the lake levels decrease. We used the best model of the Great Lakes watersheds in doing our analyses along with three of the best climate models. We have also done it with 16 different climate models and get the same result. This is the best analysis to date. Previous analyses suggested much larger decreases than we found.”
As an internal water system, Wuebbles explained, the Great Lakes are not affected significantly by rises in sea levels. The melting of Arctic ice, which is floating, does not produce rises in sea levels. However, the melting of ice sheets in Greenland and the melting of glaciers are adding to the sea level rise, Wuebbles said.
Albedo Effect Accelerates Warming
In addition, a phenomenon called the albedo effect plays a major role in ice melt. Ice reflects heat from the sun back up into the atmosphere. When the ice is melted, there is less surface area to reflect the heat upward, and more heat is absorbed by the surrounded surface. Albedo is an accelerating effect: more melting ice means faster absorption in surrounding areas, leading to higher temperatures and more and faster ice melt.
“The albedo effect is also an important factor and is considered in our analysis,” Wuebbles said.
LaNina Spreads Cold
Weather snapshots are often misleading, Wuebbles added. Weeks and months are short-term trends compared to centuries. A few seasons of colder weather and unusual occurrences such as recent snow and hailstorms on the East Coast of the US are not necessarily contradictions of global climate change. They’re more likely related to the La Nina current which spreads cold water throughout the Pacific Ocean.
“We can't take particular weather events and say they are directly related to climate change,” Wuebbles said. “Colder temperatures the last few years are likely more related to the La Nina event, but we generally expect more of the precipitation to be in heavier downpours because of climate change. And that has been happening, especially in the [US] Northeast and the Midwest.”
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