rjzimmerman:

Excerpt from this story from the Washington Post:

Since October, the water temperatures on all five of the Great Lakes have hovered at record-high autumn levels, about five to six degrees above average. This comes after abnormally large spikes in temperature over the summer, as well.

The record-warm water temperatures over the Great Lakes fit into a pattern of warming lakes all over the planet, forced upward as human-caused climate change pushes air temperatures to record highs.

“I’m not surprised at all that the water temperatures are so warm,” said Sapna Sharma, an associate professor at York University who has studied ice for more than a decade. “Lakes are experiencing more extreme warm years.”

Sharma and her colleagues analyzed 60 lakes in the Northern Hemisphere in a September study and found a pronounced warming trend over the past 100 to 200 years. The lakes have warmed six times as fast in the past 25 years compared with any other period in the past century. Previous work shows lake warming trends extend to the Southern Hemisphere.

The warmer water temperatures are pushing the onset of ice to later in the year, as well as ending the ice season earlier. The study found that on average, lakes are losing about 17 days of ice cover per century. The lakes were freezing about 11 days later and thawing about seven days earlier.

Sharma says the cause is a sharp increase in abnormally warm weather. Since 1995, several lakes have begun to experience winters with minimal or no ice cover.

“If we continue at this same rate, over the next 75 years we’ll lose 106 more days of ice cover on average across our lakes,” said co-author Dave Richardson, a professor at the State University of New York at New Paltz. “That is losing the entire ice period for many of these lakes over the next hundred years.”

Today, researchers study ice cover to help track the health of the ecosystem. Less ice cover means more lake water can evaporate, reducing the amount of freshwater available to aquatic organisms and people. Less ice also allows the surface of the lake to warm earlier and more intensely, resulting in more algal blooms that can sometimes contaminate the water for humans. Changes in ice cover also have an economic effect on those who use the lake for fishing, sports and transportation for goods.