EarthLabs > Climate and the Cryosphere > Lab 5: Evidence of Recent Change > 5B: Shrinking Sea Ice

Evidence of Recent Change

Part B: Shrinking Sea Ice

Sea Ice Extent Revisited

In August and September 2012, sea ice covered less of the Arctic Ocean than at any other time since at least 1979, when the first reliable satellite measurements began. The National Snow and Ice Data Center (NSIDC) and NASA announced in mid-September that the extent of Arctic sea ice had dropped to 3.41 million square kilometers (1.32 million square miles)—well below the previous record of 4.17 million square kilometers (1.61 million square miles) set in 2007. Loss of polar bear habitat, altered shipping routes, and shifts in global weather patterns are just a few of the side effects that may result from dwindling Arctic sea ice.

  1. Watch this video from NASA showing minimum Arctic sea ice area and trends from 1979-2011. NOTE: Pause the video around 37 seconds to keep the full graph in view. Click on the icon at the bottom right corner of the video player to view the video in full screen mode.

  2. loading the player

    Checking In

    1. How would you describe the graph of Arctic sea ice area?
      [INCORRECT] Not quite. Take another look.
      [INCORRECT] Try again.
      [INCORRECT] Oops!
      [CORRECT] You got it!
  3. Scientists at the National Snow and Ice Data Center (NSIDC) keep a constant watch over sea ice. Go to their Sea Ice Index page to explore the most current monthly sea ice extent data available. How does the data for this month compare to the 1979-2000 mean?

Sea Ice Volume

Although sea ice extent is the most widely used sea ice measure to study climate and climate change, it is not the only measure scientists use. Sea ice doesn't melt (or grow) in just two dimensions. As you saw in Lab 2B, sea ice thickness is also an important parameter. By combining information about sea ice extent (area) and sea ice thickness, scientists can determine sea ice volume, which is a better indicator of climate than sea ice extent alone. This measure is used less frequently than sea ice extent because it is much harder to determine. Currently, there is no method for getting continuous observations of Arctic sea ice volume. Observations from satellites, Navy submarines, moorings, and field measurements all have limitations in coverage over space and time. However, observations can be used in conjunction with computer models to provide estimates of sea ice volume changes on a continuous basis. One such model is the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS), which was developed at the University of Washington's Polar Science Center).

  1. Watch this video showing average monthly sea ice volume from 1979-2013, as determined by PIOMAS. NOTE: The video is large and may take several minutes to load. If you have trouble viewing the video here, click on this link to view it in another browser window.

    loading the player
    ©Andy Lee Robinson. Used with permission.


  2. Checking In

    1. You may recall from Lab 2 that Arctic sea ice goes through a yearly cycle of growth and melt, with the extent typically reaching its maximum in March and its minimum in September. From 1979-2013, during what month was Arctic sea ice volume typically at its maximum?
      [INCORRECT]
      [CORRECT]
      [INCORRECT]
      [INCORRECT]
    2. During what month was Arctic sea ice volume typically at its minimum?
      [CORRECT]
      [INCORRECT]
      [INCORRECT]
      [INCORRECT]
    3. What was the average sea ice volume for November, 2007?
      [INCORRECT]
      [INCORRECT]
      [CORRECT]
      [INCORRECT]
    4. What was the average sea ice volume for June, 1996?
      [INCORRECT]
      [CORRECT]
      [INCORRECT]
      [INCORRECT]

    Stop and Think

    1: What is the overall average trend for monthly sea ice volume between 1979 and 2013? Explain.


  3. Watch this video showing Arctic sea ice annual minimum volume from 1979-2012, as determined by the PIOMAS model. NOTE: Pause the video around 28 seconds to keep the full graph in view. Click on the icon at the bottom right corner of the video player to view the video in full screen mode.

    loading the player
    ©Andy Lee Robinson. Used with permission.

  4. Stop and Think


    2: Compare how Arctic sea ice area and volume have changed since 1979:

    1. In 1979, the minimum Arctic sea ice area was approximately 6.4 million km2. In 2011, it was 3.6 million km2. Calculate the percent change in sea ice area for this time interval. HINT: % change = 100 x (new value - old value)/old value; If the result is positive, it is a percentage increase. If the result is negative, it is a percentage decrease.
    2. Arctic sea ice volume was 16,855 km3 in 1979 and 3,261 km3 in 2013. Calculate the percent change in sea ice volume for this time interval.
    3. Based on your answers to a) and b), which has seen a more dramatic change since 1979minimum Arctic sea ice area or Arctic sea ice volume? Explain what you think this means about the current state of Arctic sea ice and climate.


Albedo Revisited

Recall from Lab 1 that albedo is a non-dimensional, unitless quantity that indicates how well a surface reflects solar energy. Albedo (α) varies between 0 and 1. Something with an albedo of 0 absorbs all incoming energy, which can be used to heat the surface or, when sea ice is present, melt the surface. A value of 1 means the surface reflects 100% of incoming energy.

Sea ice has a much higher albedo than most other surfaces on Earth, including the surrounding ocean. A typical ocean albedo is approximately 0.06, while sea ice albedo varies from approximately 0.5 to 0.7 for bare ice and up to 0.9 for sea ice covered with snow. This means that the ocean reflects only 6 percent of the incoming solar radiation and absorbs the rest, while sea ice reflects as much as 90 percent of the incoming energy. The sea ice absorbs less solar energy and keeps the surface cooler.

As you saw in Lab 2B, snow also helps insulate the sea ice, maintaining cold temperatures and delaying ice melt in the summer. After the snow does begin to melt, albedo drops to about 0.75 because of darker shallow melt ponds that form on the surface. As melt ponds grow and deepen, the surface albedo can drop down to about 0.15. As a result, melt ponds instigate more rapid ice melt.

Checking In

  1. Which of the following has the highest albedo?
    [INCORRECT]
    [CORRECT]
    [INCORRECT]
  2. What percent of incoming solar radiation is absorbed by open ocean?
    [INCORRECT] Oops! Remember, the question asked about absorbed radiation.
    [INCORRECT] Try again.
    [INCORRECT] Not quite.
    [INCORRECT] Close, but no.
    [CORRECT] You got it!

Stop and Think

3: Describe the effect declining ice coverage has on Earth's surface albedo as a function of time.



Optional Extension: Impacts of Declining Sea Ice

Want to learn more about the impacts declining sea ice extent has on life around the globe? Check out these resources:


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