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Lake Superior Feels the Heat: Climate Change Discussed at Conference

Lake Superior by Chris J. Benson

Climate models for lake Superior indicate continued warming.

Climate is what we expect, weather is what we get. - Mark Twain

"In a coldly scientific way, the changes occurring around Lake Superior are fascinating," said Jay Austin, assistant professor at the University of Minnesota Duluth's Large Lakes Observatory. Evidence, complied by Austin and others, suggests that the Great Lakes Basin is responding to global climate shifts as dramatically and clearly as anywhere on Earth. With field data in hand and computers crunching numbers, it's becoming obvious that Lake Superior is feeling the heat.

Since 1980, Lake Superior has exhibited:

  • Warming twice as fast as air. Surface water temperature in summer has increased about 2 F (1 C) per decade, regional air temperature has increased 1 F (0.5 C).
  • Diminishing ice cover. The area covered by ice is decreasing by about 0.5 percent per year.
  • Increasing wind speeds (by about 30 percent, according to buoy data).
  • An extended summer season. Spring turnover is earlier by about 1/2 day per year, leading to earlier summer stratification so the sun-warmed upper layer can extend more deeply, making fall mixing later.

Out of a dozen computer models simulating Lake Superior's climate in the next century, all indicate we should expect continued warming. More frequent and intense storms, climate variability, and extremes are predicted (see below). Although the details of regional climate predictions are tricky and model-dependent, it seems likely that:

  • Summers will be drier.
  • Winters will have about the same precipitation, with more falling as rain, and more mid-season melting.
  • By 2100
  1. summers will be like summers are now in Kansas (up to 20 F (11 C) warmer) winters will be like winters are now in Wisconsin or Illinois (up to 12 F (7 C) warmer)
  2. soil moisture could decrease by 30 percent in summer.

Even for scenarios that forecast increases in precipitation, lower water levels for Lake Superior are predicted. That's because evaporation could increase from 7 to 17 percent by 2030.

Adapting to the changing climate will involve the efforts of communities, industries, and individuals.

Coastal communities: Coastal engineers believe there is a danger of under-planning using current weather extremes to define the capacity of infrastructure such as stormwater drains and sturdiness of shoreline structures such as breakwalls. Some climatologists think global warming will speed up the water cycle so that weather moves faster. With more intense rains and higher winds, coastal communities will experience more stormwater runoff, which will worsen erosion and wastewater overflows. Stormwater systems designed for the climate of 30 years ago are undersized, perhaps by 50 percent or more. Already, 1,260 billion gallons of untreated wastewater spill into in the Great Lakes each year. Along with more flooding, communities can expect to battle more fires. The frequency of forest fires correlates closely to temperature, precipitation, and soil moisture.

Shipping: The Great Lakes fleet could have operated year-round in seven out of the last ten years. An extended shipping season would offset the lighter loads ships will be carrying if water levels drop. As fiercer storms bombard coastal streams and shorelines, erosion will contribute more sediment to nearshore areas. The current price for dredging could seem like a bargain. Physical limits (like Lake Superior's bed of hard rock) will prevent dredging in some areas if water levels fall. Knowing that new disposal strategies will be needed in less than ten years, Duluth's port authority and sanitary district are exploring ways to package and sell dredge material. New vessels could be designed with lower drafts, wider beams, and to include features such as cleaner emissions and ballast water treatment systems.

Recreation: The bad news is that revenues from current winter recreation will decline. Natural resource managers predict changes in coldwater fisheries. Shipwrecks could deteriorate more rapidly in warmer water. More dredging around public accesses and private boat landings will be required. Public health professionals anticipate higher incidences of heat-related illnesses, and diseases associated with ticks and mosquitoes. The good news is the summer season will be longer, and the milder conditions during spring and fall could extend visitor traffic and reduce heating bills. Gardeners will enjoy a zone shift that will enable them to grow a wider variety of plants. Extended warm weather promises to lure boating and camping enthusiasts out more often and farther afield. However, park and rescue workers caution that people and their boats might be woefully unprepared and ill-suited for the conditions Lake Superior can throw at them, especially with the prospect of more intense storms and winds.

Lake Superior's fisheries: With a longer growing season, fish in the salmon family (and their prey) could become bigger and more abundant. Whitefish and trout will follow their optimum temperature into deeper offshore areas. The backbone of Lake Superior's commercial fisheries whitefish experience better reproductive success when their eggs are protected by winter ice, so diminishing ice cover is concerning. Invasive species are expected to take over larger portions of changing aquatic and terrestrial habitat. Because North Shore streams will flow more erratically and carry higher sediment loads, brook trout could struggle. (Unlike streams along the South Shore, the flow of North Shore tributaries depends much more on rainfall than groundwater sources.)

"An accumulating body of research is allowing us to explore the emotionally heated topic of climate change with the cool dispassion of data, the predictions of large computers, and sharp minds," said Minnesota Sea Grant Director Steve Bortone. "It seems obvious that a shift in our climate is happening and that we should be working toward a 'no regrets' approach to adapting to the changes and reducing our contribution to greenhouse gas emissions."

This article is a synthesis of presentations delivered at the Making a Great Lake Superior Conference in October 2007 and at other venues since then. Particularly, this article references the work of University of Minnesota researchers (Jay Austin, Tom Johnson, Lucinda Johnson), University of Wisconsin researchers (John Magnuson, Richard Stewart), Environment Canada researchers (David Phillips, Linda Mortsch), the U.S Army Corps of Engineers, Detroit District, Apostle Islands National Lakeshore director Bob Krumenaker, U.S. Geological Survey's Doug Wilcox, and the U.S. EPA's Global Change Research Director Joel Scheraga.

Expect the Unexpected

Lake Superior by Chris J. Benson

Schematic showing the effect on extreme temperatures when (a) the mean temperature increases, (b) the variance increases, and (c) when both the mean and variance increase for a normal distribution of temperature. Source: Intergovernmental Panel on Climate Change, 2001 Report

Averages make communication convenient, but variability may be more important to talk about when it comes to climate. As an example, although the average air temperature on the western shores of Lake Superior was a cool 40.6 F (4.8 C) in 2007, Duluthians had to dress for a tropical 88 F (31 C) and bone-chilling -25 F (-32 C) that year.

Some climatologists suggest that wildly swinging highs and lows, and extreme precipitation and droughts will be the climate norm in the 21st Century around Lake Superior. However, linking a specific event, like Superior's low level in the summer of 2007, to the larger climate change picture is difficult without the perspective of time. An unusually dry summer was followed by the second-wettest October observed (rainfall exceeded normal by 4.34 inches (11 cm)), shocking hydrologists and the public alike by abruptly raising Superior by about 10 inches (0.25 m). To compound the uncertainty of climate patterns, in its geologically brief history, Superior has exhibited two lake level cycles, one lasting about 160 years and the other about 35. The cycles don't operate with clockwork precision and could have synchronously hit their low points in 2007.

Record water levels, torrential rain, and extreme temperatures (like the summer of 2006 when Lake Superior's surface heated to an unprecedented 20 C (68 F)) might be anomalies. But, perhaps it's wise to start expecting the

By Sharon Moen
May 2008

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