Friday, February 19, 2010

Sea Ice, No See Ice

   We're on thin ice around the arctic, and the most well-respected mathematical models have underestimated the loss of sea ice shown by current measurements.   In particular, the photo above shows the loss of "multi-year" ice from March 2004 to March 2008.  Many people may wonder about whether we have reached a "tipping point" or point at which the loss in sea ice has passed the point of no return.  As Donald Perovich, a researcher with a US Army Laboratory, said during his presentation: "It's really a question of whether we will fall off the edge of the stage or fall down the stairs, bumping along the way"
    What's the difference between sea ice and the ice from your fridge?  The tiny channels of brine which carry algae and make modeling sea ice considerably different from modeling a liquid.  In addition to being different on the microscopic scale, sea ice covers vast expanses of water and melts because of effects from underneath (the ocean currents), above (the sun, snow, and atmosphere), and within (topography, permeability).  The "albedo" that I talked about in the last post is a ratio of reflected to incident sunlight, and the average albedo of the sea ice changes as the mosaic of ponds and ice evolves through the seasons.  First-year ice has a lower albedo and therefore absorbs more heat and melts quite differently from multi-year ice.   This creates a feedback loop that causes more ice to melt and lowers the albedo more....   Many of the presentations focused on finding better ways to model the albedo by better understanding pond-formation.
   But the view from the picture above is only one slice of the story.  I'll say more about ice volume and flesh out more of the picture about Sea Ice later tonight!

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