Jul 27, 2012

Great Lakes Water Temperatures At Record Levels


A comparison between Lake Superior's average water temperature this year so far and the longer-term average. Click on the image for a larger version. Credit: GLERL.

...OK, so the lake’s average water temperature is still a bracing 68 degrees, but it's considered downright tropical for the region. As the above chart shows, based on the 30-year average, the lake’s average water temperature should be in the mid-50s. But thanks to scant lake ice cover this past winter, along with a rare March heat wave and warmer-than-average weather since then, the lake began warming earlier than normal, and that warming has kept right on going. Wintertime ice cover on the Great Lakes was the lowest observed since such records began in 1980.

“It’s pretty safe to say that what we’re seeing here is the warmest that we’ve seen in Lake Superior in a century,” said Jay Austin, a professor at the University of Minnesota at Duluth, who has researched the lake’s water temperatures back to the beginning of the 20th century.

The lake's record temperatures are yet another consequence of the record heat so far in 2012. The contiguous U.S. had its warmest January-to-June period since records began in the late 19th century. Manmade global warming will likely result in more years with very warm water temperatures, which could have significant adverse consequences for marine life. In a rare benefit from the ongoing drought, this summer has been so dry that the warm water temperatures are not resulting in major harmful algal blooms, such as one that occurred on Lake Erie last year. 

Instrument data from three buoys in Lake Superior provide a reliable record of water temperatures since about 1980, and the information also shows that, with water temperatures running in the mid-to-upper 60s (and even warmer closer to shore), “we are at record temperatures for this time of year,” according to Austin.

Austin said that water temperatures at the westernmost edge of Lake Superior are running in the mid-70s, and it was due in part to the runoff from flooding rains that struck Duluth, Minn., in late June.

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