Great Lakes Ice Cover

Cryosphere
This indicator measures the area and duration of ice cover in the Great Lakes.

Figures

Figure 1. Maximum Ice-Covered Area in the Great Lakes, 1973–2020

Data source: NOAA, 20215
Web update: April 2021

Figure data (CSV) EPA source data (CSV)

These graphs show the percentage of surface area in each of the Great Lakes that froze on the maximum day (the “most frozen” day) of each year since 1973. The graph at the lower right is an area-weighted average of all five lakes.

Show the data behind this figure
Year Lake Erie Lake Huron Lake Michigan Lake Ontario Lake Superior All Lakes
1973 95.7 66.70 33.0 62.6 69.8 60.6
1974 88.5 61.40 39.4 24.5 73.8 58.7
1975 80.1 55.10 28.1 14.9 64.9 50.2
1976 95.4 52.50 29.5 15.2 49.9 39.9
1977 99.8 95.00 93.1 46.7 96.0 89.9
1978 100.0 95.80 66.6 57.7 92.5 83.0
1979 100.0 96.40 92.3 86.2 97.1 94.7
1980 93.4 70.30 38.6 30.6 77.2 62.8
1981 96.0 93.80 53.8 47.6 84.7 71.3
1982 99.1 93.30 60.2 50.7 85.3 74.8
1983 40.8 31.80 23.6 12.5 20.2 22.1
1984 95.7 77.60 43.3 40.7 88.2 65.2
1985 96.0 87.40 41.3 38.2 81.9 69.8
1986 95.5 73.50 66.8 43.7 90.7 76.4
1987 88.0 43.50 20.0 8.4 14.5 27.3
1988 91.5 60.10 32.7 21.1 67.3 53.6
1989 91.6 76.30 30.9 15.5 82.3 59.2
1990 72.8 73.80 32.4 29.5 78.1 59.7
1991 35.1 43.80 21.5 11.6 89.6 44.3
1992 89.8 69.90 32.8 17.5 73.3 45.5
1993 94.3 78.30 32.2 29.0 77.2 64.4
1994 96.7 96.90 82.7 55.7 96.1 89.0
1995 94.0 41.70 21.6 18.8 28.8 32.0
1996 100.0 98.20 75.0 45.1 100.0 81.7
1997 99.6 65.30 37.8 25.6 89.0 58.4
1998 5.4 28.60 15.1 6.2 11.1 14.0
1999 74.8 36.00 23.0 17.9 18.3 26.6
2000 90.7 41.90 27.2 22.3 33.5 34.8
2001 94.0 45.70 29.5 17.9 46.7 34.4
2002 14.4 26.10 12.4 4.0 10.3 11.8
2003 95.7 96.20 48.0 49.6 95.5 80.2
2004 95.4 64.50 36.4 38.5 52.2 51.9
2005 93.0 58.90 29.4 37.8 54.5 44.2
2006 21.9 32.17 16.2 14.3 16.7 20.4
2007 95.8 71.39 37.2 23.8 51.8 55.2
2008 93.4 59.51 33.5 14.0 62.7 53.7
2009 95.6 85.11 52.3 25.9 93.6 73.9
2010 93.1 36.95 23.5 13.1 27.3 27.5
2011 95.9 63.79 29.4 31.1 33.6 40.1
2012 13.9 23.06 16.7 1.9 8.2 12.9
2013 83.7 47.75 24.4 15.6 38.6 38.4
2014 96.1 96.10 93.1 60.8 95.8 92.3
2015 98.1 96.40 72.9 82.4 95.7 88.8
2016 78.7 47.98 26.8 23.5 22.7 33.8
2017 35.5 35.35 18.2 5.8 18.7 19.4
2018 95.1 81.39 51.3 24.7 77.2 69.0
2019 94.3 95.70 55.8 39.8 94.9 80.9
2020 15.9 32.10 17.2 10.7 22.6 19.5

Figure 2. Duration of Ice Cover in the Great Lakes, 1973–2020

Data source: NOAA, 20216
Web update: April 2021

Figure data (CSV) EPA source data (CSV)

These graphs show the number of frozen days per year in each of the Great Lakes since 1973. A frozen day is defined here as a day when at least 5 percent of the lake’s surface area was covered with ice.

Show the data behind this figure
Year Lake Erie Lake Huron Lake Michigan Lake Ontario Lake Superior
1973 67 108 85 67 97
1974 76 120 106 76 119
1975 65 105 97 32 95
1976 91 119 108 74 108
1977 117 136 124 118 133
1978 124 130 113 106 123
1979 96 120 117 71 137
1980 98 106 90 60 91
1981 108 113 104 67 110
1982 105 129 105 86 121
1983 47 85 64 34 86
1984 123 128 113 94 128
1985 101 116 94 85 107
1986 118 125 114 89 115
1987 56 82 72 19 48
1988 102 105 89 81 93
1989 77 124 107 43 120
1990 96 126 108 95 117
1991 64 102 81 56 93
1992 64 121 81 68 127
1993 83 121 89 62 99
1994 113 123 107 99 125
1995 80 93 61 39 79
1996 132 146 123 80 134
1997 85 128 113 75 122
1998 1 86 56 10 34
1999 80 103 80 49 54
2000 69 88 65 43 50
2001 123 130 111 80 105
2002 20 102 59 0 33
2003 105 119 102 81 103
2004 91 106 89 68 86
2005 103 123 104 70 86
2006 55 120 68 18 31
2007 70 88 69 51 67
2008 88 122 92 45 69
2009 106 132 106 65 109
2010 86 86 78 23 45
2011 113 124 102 54 84
2012 12 75 52 0 13
2013 56 105 84 25 75
2014 134 153 145 98 153
2015 104 126 109 90 126
2016 40 72 62 17 43
2017 42 101 80 4 51
2018 104 143 99 61 124
2019 87 120 93 73 97
2020 6 88 72 7 54

Figure 3. Change in Ice Cover Duration in the Great Lakes, 1973–2019

Data source: NOAA, 20197
Web update: April 2021

This map shows the average annual rate of change in the duration of ice cover in the Great Lakes from 1973 to 2019. Duration is measured as the number of days in which each pixel on the map was at least 10 percent covered by ice. Gray areas are labeled “no trend” because the change over time is not statistically significant (using a 90-percent confidence level).

EPA’s page offers no data download for this map, so it is not reproduced on this page and there is no data table for it.

Key Points

  • Since 1973, the maximum area covered in ice on the Great Lakes has varied considerably from year to year. Adding the five Great Lakes together, maximum frozen area has ranged from less than 20 percent in some years to more than 90 percent in others (see Figure 1). All five lakes have experienced some degree of long-term decrease, but the decrease is only statistically significant in one lake (Superior). Years with much-lower-than-normal ice cover appear to have become more frequent during the past two decades, especially in lakes like Erie and Superior that have a history of freezing almost completely.
  • Since 1973, the number of frozen days (duration) on all five Great Lakes has declined. Ice duration on these lakes has decreased at rates ranging from approximately one-fifth of a day per year in Lake Huron to almost a full day per year in Lakes Ontario and Superior (see Figure 2). Overall, this means the Great Lakes are frozen for eight to 46 fewer days now than they were in the early 1970s. The decreases in Lakes Ontario and Superior are statistically significant.
  • A detailed map (see Figure 3) shows that many areas of the Great Lakes have experienced significant decreases in ice cover duration, but other parts of the lakes have not changed significantly. Duration has decreased the most in areas near the shore.

Background

The Great Lakes—Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario—form the largest group of freshwater lakes on Earth. These lakes support a variety of ecosystems and play a vital role in the economy of the eight neighboring states and the Canadian province of Ontario, providing drinking water, shipping lanes, fisheries, recreational opportunities, and more.

Parts of the Great Lakes typically freeze every winter. As the Earth’s climate changes, though, rising air temperatures (see the U.S. and Global Temperature indicator) and water temperatures (see the Great Lakes Water Levels and Temperatures indicator) have led to less ice cover on many lakes in North America, including the Great Lakes.1 Ice cover is expected to decline further as the climate continues to warm.2

The area that freezes and the length of time that the lakes remain frozen can have a wide range of effects on people and ecosystems. As with other lakes (see the Lake Ice indicator), ice cover on the Great Lakes can affect aquatic ecosystems, as well as recreational opportunities such as ice fishing. Due to the size of the Great Lakes, ice cover also plays an important role in regional weather patterns and the shipping industry. While reduced ice cover could lengthen the shipping season, it also allows more water to evaporate from the lakes, which can lead to lower water levels (see the Great Lakes Water Levels and Temperatures indicator) and restrict shipping channels.3 More evaporation can also lead to an increase in precipitation over nearby land, especially “lake effect” snow (see the Snowfall indicator).4

About the Indicator

This indicator presents two related ways of measuring ice cover in the Great Lakes: area (the percentage of the lake surface area that is frozen) and duration (the length of time the lakes stay frozen). Both parts of this indicator are based on daily and weekly charts and maps created by the Canadian Ice Service and the U.S. National Ice Center, which are derived from a long-running collection of observations from ships, shore, aircraft, and satellites. Complete data are available back to 1973 for each lake.

Figure 1 shows the maximum portion of each lake’s surface area that was frozen in each year. Figure 2 tracks duration by showing the total number of days per year in which at least 5 percent of the lake surface was frozen. In each case, the period analyzed runs from December through May, with this entire “season” considered part of the same year. For example, “2020” represents conditions from December 2019 through May 2020.

The map in Figure 3 shows how the length of time the Great Lakes stay frozen has changed over time, and how these changes vary by location. Data for this part of the indicator were available through 2019. Figure 3 only shows a rate of change for pixels where the trend is statistically significant.

About the Data

Indicator Notes

Temperature trends influence ice-covered area and duration, but natural year-to-year variations and decadal climate cycles may play a bigger role.8,9 With more than four decades of data, though, this indicator clearly shows meaningful long-term trends and variations that relate to the regional climate of the Great Lakes, which is linked to broader global weather and climate patterns.10,11

Data Sources

Ice cover area and duration data were provided by the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory at: www.glerl.noaa.gov/data/ice/#historical. Similar data can be downloaded from the Great Lakes Aquatic Habitat Framework website at: www.glahf.org/data.

Technical Documentation

References

  1. Angel, J., C. Swanston, B.M. Boustead, K.C. Conlon, K.R. Hall, J.L. Jorns, K.E. Kunkel, M.C. Lemos, B. Lofgren, T.A. Ontl, J. Posey, K. Stone, G. Takle, and D. Todey. 2018. Midwest. In: USGCRP (U.S. Global Change Research Program). 2018. Impacts, risks, and adaptation in the United States: Fourth National Climate Assessment, volume II. Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.). https://nca2018.globalchange.gov. doi:10.7930/NCA4.2018.
  2. USGCRP (U.S. Global Change Research Program). 2018. Impacts, risks, and adaptation in the United States: Fourth National Climate Assessment, volume II. Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.). https://nca2018.globalchange.gov. doi:10.7930/NCA4.2018
  3. Angel, J., C. Swanston, B.M. Boustead, K.C. Conlon, K.R. Hall, J.L. Jorns, K.E. Kunkel, M.C. Lemos, B. Lofgren, T.A. Ontl, J. Posey, K. Stone, G. Takle, and D. Todey. 2018. Midwest. In: USGCRP (U.S. Global Change Research Program). 2018. Impacts, risks, and adaptation in the United States: Fourth National Climate Assessment, volume II. Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.). https://nca2018.globalchange.gov. doi:10.7930/NCA4.2018
  4. Burnett, A.W., M.E. Kirby, H.T. Mullins, and W.P. Patterson. 2003. Increasing Great Lake-effect snowfall during the twentieth century: A regional response to global warming? J. Climate 16:3535–3542
  5. NOAA (National Oceanic and Atmospheric Administration). 2021. Great Lakes Environmental Research Laboratory: Historical ice cover. Accessed March 2021. www.glerl.noaa.gov/data/ice/#historical.
  6. NOAA (National Oceanic and Atmospheric Administration). 2021. Great Lakes Environmental Research Laboratory: Historical ice cover. Accessed March 2021. www.glerl.noaa.gov/data/ice/#historical.
  7. NOAA (National Oceanic and Atmospheric Administration). 2019. Great Lakes Environmental Research Laboratory: Historical ice cover. Accessed December 2019. www.glerl.noaa.gov/data/ice/#historical.
  8. Wang, J., X. Bai, H. Hu, A. Clites, M. Colton, and B. Lofgren. 2012b. Temporal and spatial variability of Great Lakes ice cover, 1973–2010. J. Climate 25(4):1318–1329. https://journals.ametsoc.org/view/journals/clim/25/4/2011jcli4066.1.xml. doi:10.1175/2011JCL14066.1.
  9. Wang, J., R.A. Assel, S. Walterscheid, A.H. Clites, and X. Bai. 2012a. Great Lakes ice cover climatology update: Winters 2006–2011 description of the digital ice cover data set. NOAA Technical Memorandum GLERL-155. www.glerl.noaa.gov/pubs/tech_reports/glerl-155/tm-155.pdf.
  10. Bai, X., J. Wang, C. Sellinger, A. Clites, and R. Assel. 2012. Interannual variability of Great Lakes ice cover and its relationship to NAO and ENSO. J. Geophys. Res. 117:C03002. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010JC006932. doi:10.1029/2010JC006932.
  11. Wang, J., R.A. Assel, S. Walterscheid, A.H. Clites, and X. Bai. 2012. Great Lakes ice cover climatology update: Winters 2006–2011 description of the digital ice cover data set. NOAA Technical Memorandum GLERL-155. www.glerl.noaa.gov/pubs/tech_reports/glerl-155/tm-155.pdf.

Text on this page is EPA’s own published wording (a U.S. Government work, not subject to domestic copyright), extracted from EPA’s published indicator page and verified paragraph by paragraph against the archived HTML. Data, chart code, and the full extraction pipeline are maintained in the great-lakes-ice-cover repository, which this page reads its data from directly.

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