Duluth News Tribune: The trend for nearly 30 years has been less ice cover on the big lake, with water temperatures rising. A UMD study found the lake’s temperature has risen 4.9 degrees since 1979, about twice as fast as the rise in air temperatures in our area. The Lake Superior water-temperature increase has been cited as one of the most pronounced examples of global warming anywhere on the planet. Another study of ice-cover data for Lake Superior between Bayfield and Madeline Island by …