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GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L06604, doi:10.1029/2006GL029021, 2007

Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback

Jay A. Austin

Large Lakes Observatory and Department of Physics, University of Minnesota, Duluth, Minnesota, USA


Steven M. Colman

Large Lakes Observatory and Department of Geological Sciences, University of Minnesota, Duluth, Minnesota, USA


Abstract

Lake Superior summer (July–September) surface water temperatures have increased approximately 2.5°C over the interval 1979–2006, equivalent to a rate of (11 ± 6) × 10−2°C yr−1, significantly in excess of regional atmospheric warming. This discrepancy is caused by declining winter ice cover, which is causing the onset of the positively stratified season to occur earlier at a rate of roughly a half day per year. An earlier start of the stratified season significantly increases the period over which the lake warms during the summer months, leading to a stronger trend in mean summer temperatures than would be expected from changes in summer air temperature alone.

Received 7 December 2006; accepted 7 February 2007; published 23 March 2007.

Keywords: Lake Superior; climate change; ice.

Index Terms: 0746 Cryosphere: Lakes (9345); 1630 Global Change: Impacts of global change (1225); 1637 Global Change: Regional climate change; 1845 Hydrology: Limnology (0458, 4239, 4942); 4239 Oceanography: General: Limnology (0458, 1845, 4942).

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Citation: Austin, 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.