Lack of snow, ice partially to blame for warmer winter temperatures in Minnesota
MINNEAPOLIS — If you've ever spent a sunny day on a lake, you know how bright it can be. That's because water reflects about 10% of the sunlight that hits it back into your eyes.
An icy lake is even more reflective, bouncing 30 to 40% of those rays back.
Snow is the most reflective naturally occurring surface on earth, sending 75 to 90% of sunlight back into space. When light is reflected, heat is also reflected. That's why an enormous pile of snow dubbed "Mt. Eden Prairie" lasted so late into spring.
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If there's fresh deep snow cover on the ground, meteorologists subtract between 5-10 degrees from the high temperature forecast to account for that.
The reverse is also true — when there's no snow cover, more of the sun's energy reaches the soul to warm it. That's why, this year, parts of your lawn may be green, and why temperatures have been above average so consistently.
The last few days are a great example: with northerly and northwesterly winds, this shouldn't be a mild stretch of weather for us, yet temperatures are running 10 degrees above average due to lack of snow cover.
This same principle is super-charging the effects of global warming at the earth's poles. Arctic and Antarctic sea-ice coverage has been decreasing since records began in 1979.
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In the summer, this exposes darker surfaces that absorb more heat creating a feedback process that accelerates melting. Decades-old permafrost is also thawing, releasing even more heat-trapping greenhouse gases into the atmosphere.
The last 17 years have brought the 17 lowest amounts of sea ice on record. The ice that remains is thinner and younger, meaning it's less stable and easier to melt.
And what happens in the Arctic doesn't stay there; the warmer North Pole distorts the jet stream, allowing more extreme winter temperature swings.