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									 Arctic Sea Ice Cover: What We Have Learned
from Satellite Passive-Microwave Observations

               Claire L. Parkinson
          NASA Goddard Space Flight Center

 Presentation at the Polar Gateways Arctic Circle Sunrise 2008
       Conference in Barrow, Alaska, January 25, 2008
Global Surface Temperatures over the Last 150 Years

                                       (Courtesy Jim Hansen)
Animation of 2003 Arctic
Sea Ice Coverage, from
satellite data

                                               QuickTime™ an d a
                                               GIF decompressor
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White: Highly compact ice.

Shades of light blue: Ice of lesser

                        (Daily images)
          Selected Impacts of Sea Ice

   Insulation             Reflection of solar radiation

Hindrance to ships         Many impacts on polar life
  A Key Positive Feedback Involving Sea Ice

  Warming                      Sea ice retreat

Increased absorption       Reduced surface albedo
of solar radiation
          Sea Ice from Satellite Visible Imagery
                    and Its Limitations

Landsat image of sea ice in    Landsat image of sea ice
the Weddell Sea, November      and clouds in the Arctic,
17, 1973.                      September 5, 1972.
Satellite Detection of Sea Ice Using Microwave
   Radiation: Ice/Water Emissivity Contrast
Sample Satellite
Brightness Temper-
ature Images for
March 1, 1999, from
data from the Special
Sensor Microwave
Imager (SSMI)
Arctic Sea Ice Concentrations, March 1, 1999
  Derived from Satellite Passive-Microwave Data

  The values mapped are sea ice concentrations (percent areal coverages of ice).
          Key Satellite Passive-Microwave Instruments
•   NASA Nimbus 5 Electrically Scanning
    Microwave Radiometer (EMSR), launched
    December 1972.
•   NASA Nimbus 7 Scanning Multichannel
    Microwave Radiometer (SMMR), launched
    October 1978.
•   DMSP Special Sensor Microwave Imager
    (SSMI), first launched June 1987.
•   Japan Aerospace Exploration Agency
    (JAXA) Advanced Microwave Scanning
    Radiometer for the Earth Observing
    System (AMSR-E) on NASA’s Aqua
    spacecraft, launched May 2002.

       (Arctic sea ice, March 1, 2003, from Aqua
       AMSR-E data; image from T. Markus)
Winter and Summer Arctic Sea Ice Coverages
  Derived from Satellite Passive-Microwave Data

  The values mapped are sea ice concentrations (percent areal coverages of ice).
Monthly Arctic Sea Ice Extents
November 1978 – December 2006

                     (from Parkinson and Cavalieri, 2008)
Monthly Arctic Sea Ice Extent Deviations
     November 1978 – December 2005

    (extended from Parkinson, Cavalieri, Gloersen, Zwally, and Comiso, 1999)
Arctic September
Sea Ice Concentra-
tions, 1979-2003,
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       (from SMMR and
       SSMI data)
Length of the Northern Hemisphere
      Sea Ice Season, 2004

                                (updated from
                                Parkinson 2000a)
Trends in the Length of the Sea Ice Season
                1979 - 1986

                              (recolored from Parkinson 1992)
September 14, 2007 Arctic Sea Ice Distribution vs.
 Minima in 2005 and Averaged over 1979-2006

       (from Comiso, Parkinson, Gersten, and Stock, 2008)
(from Comiso, Parkinson,
Gersten, and Stock, 2008)
(from Comiso, Parkinson,
Gersten, and Stock, 2008)
 Satellite-Derived Reduction in Arctic Sea Ice
        Coverage since November 1978

• Decreases in the areal coverage of the
  – Marked decreases in all seasons
  – Marked decreases in most regions (with
    none of the regions having overall
• Decreases in the length of the sea ice
        Sample Consequence: Polar Bear Impact

                                                                                                             (Robert Taylor)
               in Western Hudson Bay

Sea ice coverage on April 29, 2006 (left) and November 14, 2005 (right), from Aqua’s AMSR-E satellite data

                                                           •    Earlier ice breakup, forcing earlier
                                                                polar bear retreat to land.
                                                           •    Average weight of adult female polar
                                                                bears in Western Hudson Bay: 295
                                                                kg in 1980, 230 kg in 2004.
                                                           •    Western Hudson Bay polar bear
                                                                population: about 1,200 in 1989,
                                                                about 950 in 2004.
Date when ice concentration in western Hudson Bay first
  reaches ≤ 50%, from Stirling and Parkinson (2006).
              Thinning of the Arctic Sea Ice Cover
as determined by Rothrock, Yu, and Maykut from submarine data

                                                        Mean ice draft:
                                                         1958-1976 – 3.1 m
                                                         1993-1997 – 1.8 m
                                                           Thinning: 1.3 m,
                                                           or 40% (later
                                                           adjusted down).
 Small dots are the original data points; triangles
 and squares have been seasonally adjusted to
 September 15.
                                                      (from Rothrock et al. 1999)
Laser Altimetry from the Ice, Cloud, and
   Land Elevation Satellite (ICESat)

                    (schematic from the ICESat Science Team)
                            Broader Context
• Impacts of the Ice Decreases
   – Helpful to shipping and to some marine life
   – Harmful to polar bears, some seal species,
     walruses, Arctic foxes, and other wildlife
     dependent on the ice
   – Enhances warming, through feedbacks
• Other Arctic Changes                                                  July 24, 1909
   –   Rising temperatures
   –   Declining snow cover
   –   Thawing permafrost
   –   Diminishing lake and river ice
   –   Melting glaciers
   –   Melting Greenland Ice Sheet                                    August 13, 2004
• Antarctic Sea Ice Changes
   – Major decreases in the 1970s
   – Increases overall since 1978
   – Good regional ice/temperature
                                              Retreat of Alaska’s Holgate Glacier
                                                           (photos courtesy Jim Tucker)
Southern Ocean Sea Ice Decreases in the 1970s
  Area (106 km2)

                   1973   1974   1975   1976   1977   1978   1979

 12-month running mean of sea ice area (bottom curve) and of
 ocean area with ice concentrations exceeding 1 octa (top curve)
 and 4 octas (middle curve). (Figure from Kukla and Gavin 1981.)
30-Year Record of Southern Ocean Sea Ice
           Extents, 1973-2002

      (from Cavalieri, Parkinson, and Vinnikov 2003)
• Arctic sea ice over the past 3 decades: clear overall
  decreases in every month, although with considerable
  interannual and regional variability.
• Multiple impacts of the ice decreases: climate
  feedbacks, impacts on wildlife and human activities.
• Contrast with Antarctic sea ice, which has increased
  overall since 1978.
• Likely future: continued ice decreases in the Arctic,
  eventual ice decreases in the Antarctic.
• Uncertainties: scientists do
                                             Seas of Okhotsk and Japan
  not fully understand the
  observed changes, making
  future surprises likely.

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