Global Warming Effects Around the World

Rogers City, MI, USA

Top Impact

People (Costs)

Other Impacts

People (Water use)

Ecosystems (Lakes and rivers)

Lake Huron shipping port of Rogers City, Michigan

Global warming is increasing evaporation of the Great Lakes, which could have a profound impact on transportation, industry, agriculture, and recreation in the Midwest. The port of Rogers City, MI, faces a projected drop of more than one foot (0.41 meters) in the water level of Lake Huron by the end of this century, if our heat-trapping emissions continue unabated.1

Key Facts

The Great Lakes connect the world's largest limestone quarry at Rogers City, MI,5 on Lake Huron, with the steel mills and construction sites it supplies. As the Great Lakes warm, evaporation is increasing more than the rain and snowmelt supplying streams flowing into the Great Lakes. Water levels are therefore likely to drop.2

  • Temperatures in the Great Lakes region have risen in recent decades.2
  • Rising temperatures can cause both evaporation and precipitation to increase, so climate projections are complicated. However, scientists think that if our heat-trapping emissions continue to rise at today's rates,10 the water level of Lake Huron is likely to drop approximately 1.3 feet (0.41 meter) by the end of the century.9
  • Falling water levels reduce the capacity of ships to carry freight safely, and therefore increase shipping costs.2,11


The Great Lakes—which contain about 20 percent of the surface freshwater on Earth2—are a vital transport route for agricultural, mining, and industrial commodities as well as other goods. Shipping on the Great Lakes is an efficient, relatively cheap way to move heavy cargoes around the U.S. Midwest, between the United States and Canada, and to and from trading partners across the Atlantic and beyond.3

Since the opening of the St. Lawrence Seaway in 1959, the United States and Canada have shipped more than $300 billion' worth of cargo through the 2,000-mile waterway from the Gulf of St. Lawrence to Lake Superior.4 Agricultural products such as grain and corn account for 40 percent of this trade, while mining products such as iron ore, coal, stone, and salt comprise another 40 percent.3

Rogers City, MI—on the northwest shore of Lake Huron—is an important link in the chain of Great Lakes commerce and industry. Rogers City, a port, is also the site of the world's largest limestone quarry.5 Used in making steel and cement, limestone from Rogers City is transported to steel mills and construction sites around the Great Lakes.6

Temperatures in the Great Lakes region have risen measurably in recent decades. The largest increases have occurred in winter. In fact, the ice season has been starting later and ending earlier since the 1850s.7 Ice coverage on the Great Lakes has declined as the climate has warmed, shrinking an average of 8.4 percent per decade from 1973 to 2008. This roughly 30 percent decrease—which exposes larger areas of the lakes' surface to the air—means more evaporation in winter.2,8

What the Future Holds

Declining water levels in the Great Lakes could have a profound impact on Rogers City, other ports, and the entire Midwest.

Scientists expect water levels in the Great Lakes to drop in both summer and winter, with the greatest declines occurring in Lakes Huron and Michigan.9,10 Though the relationship is not straightforward, the likelihood that lake levels drop increases as temperatures rise.2

The combination of warming lake water, rising air temperatures, and diminishing ice cover leads to more evaporation of lake water. While precipitation in this region also tends to increase with warmer temperatures, lower water levels are likely if evaporation outpaces any gains through rainfall, snowfall, and runoff flowing into the lakes.2

If our heat-trapping emissions continue to rise at current rates, Lake Huron is projected to drop approximately 1.3 feet (0.41 meters) by the end of the century.9 In lower scenarios of future emissions,10 the drop could be less than 1 foot. Projections are difficult because scientists must take into account both warming-induced evaporation and warming-induced precipitation.9

Low lake levels reduce "draft"—the distance between the waterline and the bottom of a ship—which cuts freight capacity and raises costs. A large Great Lakes cargo ship can lose as much as 240 tons of capacity for each inch of draft lost.2 When the St. Lawrence Seaway fell to its lowest level in 35 years in 2000-2001, vessel carrying capacity dropped 10 percent.11

A recent study estimated that the projected drop in Great Lakes water levels are likely to increase Canadian commercial shipping costs 13-29 percent by 2050.11 Freight movements in the region could be seriously impaired, and extensive dredging may be required. A longer shipping season could offset some of those negative economic effects.11

However, falling lake levels have other economic, aesthetic, recreational, and environmental effects. These include lengthening distances from docked ships to the lakeshore, harming beach and coastal ecosystems, exposing toxic contaminants, and impairing recreational boating.9



  1. Photograph courtesy of the Michigan Travel Bureau.
  2. U.S. Global Change Research Program. 2009. Global climate change impacts in the United States. Edited by T.R. Karl, J.M. Melillo, and T.C. Peterson. Cambridge University Press.
  3. Great Lakes Information Network, TEACH Great Lakes. Great Lakes ports and shipping. Online at teach/ business/ ship/. Accessed April 9, 2010.
  4. Great Lakes St. Lawrence Seaway System. Seaway System—Business and Industry. Online at en/ business-and-industry/ index.html. Accessed March 30, 2010.
  5. Brennan, J. No date. The Michigan historical marker website. Online at startup.asp? startpage=S0214.htm. Accessed April 9, 2010.
  6. American Steamship Co. 2008. Great Lakes trade patterns. Online at great-lakes-trade-patterns.php. Accessed April 9, 2010.
  7. Assel, R.A., and D.M. Robertson. 1995. Changes in winter air temperatures near Lake Michigan, 1851-1993, as determined from regional lake-ice records. Limnology and Oceanography 40:165-176.
  8. Assel, R.A. 2003. An electronic atlas of Great Lakes ice cover, winters, 1973-2002. Ann Arbor, MI: Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration. Online at data/ ice/ atlas.
  9. Angel, J.R., and K.E. Kunkel. 2010. The response of the Great Lakes water levels to future climate scenarios with an emphasis on Lake Michigan-Huron. Journal of Great Lakes Research, doi:10.1016/j.jglr.2009.09.006. In press. Corrected proof accessed online April 28, 2010.
  10. Union of Concerned Scientists. 2009. Confronting climate change in the U.S. Midwest: Michigan. Cambridge, MA.
  11. National Research Council. 2008. Potential impacts of climate change on U.S. transportation. Special report 290. Washington, DC: Transportation Research Board. Online at onlinepubs/ sr/ sr290.pdf.
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