Climate Change and Lake Superior
With field data in hand and computers crunching numbers, it's becoming obvious that Lake Superior is responding to global climate shifts as clearly as anywhere on Earth.
- Lake Superior's surface water temperature in summer has warmed twice as much as the air above it since 1980.
- Per decade since 1980, surface water temperature in summer has increased about 2 °F (1 °C), while regional air temperature has increased 1 °F (0.5 °C).1,2
- Lake Superior's ice cover is diminishing.
- The area covered by ice each winter is decreasing by about 0.5% per year.1 Ice cover in Lake Superior has decreased from 23% to 12% over the last century.2
- Wind speeds over Lake Superior are increasing.
- Since 1985, wind speeds have increased by nearly 5% per decade, exceeding trends over land. Scientists believe the faster winds could accelerate the speed of Lake Superior’s water currents, which in turn could affect the aquatic food web.3
- Lake Superior's summer stratification season is longer.
- Spring turnover has become earlier by about 1/2 day per year, leading to earlier summer stratification. The sun-warmed upper layer extends farther into the water column, making fall mixing later.1 The length of the positively stratified season has increased from 145 to 170 days over the last century.2
Although the details of regional climate predictions are still crude and model-dependent, it seems likely that around Lake Superior people should expect:
- More frequent and intense storms.4
- Increased climate variability and extremes.4
- Warmer annual temperatures.5
- Drier summers (reduction in soil moisture).5
- Warmer nights. (Minimum or 'overnight low' temperatures have been rising faster than the maximum temperature.)6
- Warmer winters. (Winter temperatures have been rising about twice as fast as annual average temperatures.)6
- Similar winter precipitation. (But more will fall as rain.)4,5
- Lower water levels in Lake Superior. (Even for scenarios that forecast increases in precipitation, most climate models predict lower water levels for Lake Superior because of increased evaporation.)3
- Changes in the species composition of both terrestrial and aquatic ecosystems.5
- Longer growing seasons.5
Proxy records of past climate variability in the Great Lakes region have been developed from tree rings, dune soils, and the sediments of small lakes and wetlands. These proxy records suggest that severe droughts, larger than any observed in the past century, occurred several times in the last few thousand years and had large and long-lasting ecological effects.7 Similarly, prolonged high water levels in the Great Lakes (highstands) have been linked to climate variability. In its geologically short life (less than 10,000 years), Lake Superior has been about 450 feet (137.16 m) higher than it is today.8 Around 1300 years ago, it seems Lake Superior completely separated from Lakes Michigan and Huron.7 As shown on the graph below, over the last 100 years, Lake Superior has fluctuated about 2.5 feet (0.8 m). The high water level in October of 1985 was 3.9 feet (1.19 m) above a low in March of 1926.9
The data in this graph originated from the U.S. Army Corps of Engineers-Detroit District.
1Austin, J.A. and S.M. Colman. 2007. Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback, Geophys. Res. Lett., 34, L06604, doi:10.1029/2006GL029021. www.agu.org/pubs/crossref/2007/2006GL029021.shtml
2Austin, J.A. and S.M. Colman. 2008. A century of temperature variability in Lake Superior. Limnol. Oceanogr. 53, 2724–2730. www.aslo.org/lo/pdf/vol_53/issue_6/2724.pdf
3Desai, A.R., J.A. Austin, V. Bennington, and G.A. McKinley. 2009. Stronger winds over a large lake in response to weakening air-to-lake temperature gradient. Nature Geosci. 2: 855–858. www.nature.com/ngeo/journal/v2/n12/abs/ngeo693.html
4Field, C.B., L.D. Mortsch, M. Brklacich, D.L. Forbes, P. Kovacs, J.A. Patz, S.W. Running, and M.J. Scott. 2007. North America. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds.) Cambridge University Press, Cambridge, UK, 617-652. www.ipcc.ch/publications_and_data/ar4/wg2/en/ch14.html
5Galatowitsch, S., L. Frelich, and L. Phillips-Mao. 2009. Regional climate change adaptation strategies for biodiversity conservation in a midcontinental region of North America. Biological Conservation 142: 2012–2022. http://www.sciencedirect.com
6Zandlo, J., modified 3/13/08. Climate Change and the Minnesota State Climatology Office: Observing the climate. Accessed 2/8/10. http://climate.umn.edu/climatechange/climatechangeobservedNu.htm
7Wilcox, D.A, T.A. Thompson, R.K. Booth, and J.R. Nicholas. 2007. Lake-level variability and water availability in the Great Lakes: U.S. Geological Survey Circular 1311, 25 p. http://pubs.usgs.gov/circ/2007/1311/pdf/circ1311_web.pdf
8Farrand, W.R. 1969. The Quaternary history of Lake Superior. Internat Assoc. Great Lakes Research.. 12th Conf., Ann Arber. Proc., p. 181-197.
9U.S. Army Corps of Engineers - Detroit District. Web page accessed 8/10. www.lre.usace.army.mil/greatlakes/hh/greatlakeswaterlevels/historicdata/longtermaveragemin-maxwaterlevels