Researchers from NASA, the National Snow and Ice Data Centerand others using satellite data have detected a significant loss inArctic sea ice this year.
On Sept. 21, 2005, sea ice extentdropped to 2.05 million sq. miles, the lowest extent yet recorded inthe satellite record. Incorporating the 2005 minimum using satellitedata going back to 1978, with a projection for ice growth in the lastfew days of this September, brings the estimated decline in Arctic seaice to 8.5 percent per decade over the 27 year satellite record.
Scientistsinvolved in this research are from NASA's Goddard Space Flight Center,Greenbelt, Md., NASA's Jet Propulsion Laboratory, Pasadena, Calif., theNational Snow and Ice Data Center at the University of Colorado,Boulder, and the University of Washington, Seattle.
Satelliteshave made continual observations of Arctic sea ice extent since 1978,recording a general decline throughout that period. Since 2002,satellite records have revealed early onsets of springtime melting inthe areas north of Alaska and Siberia. In addition, the 2004-2005winter season showed a smaller recovery of sea ice extent than anyprevious winter in the satellite record and the earliest onset of meltthroughout the Arctic.
Arctic sea ice typically reaches itsminimum in September, at the end of the summer melt season. The lastfour Septembers (2002-2005) have seen sea ice extents 20 percent belowthe mean September sea ice extent for 1979-2000.
Perennial icecover is ice that survives the summer melt, consisting mainly of thickmultiyear ice floes that are the mainstay of the Arctic sea ice cover."Since 1979, by using passive microwave satellite data, we've seen thatthe area of Arctic perennial sea ice cover has been declining at 9.8percent per decade," said Joey Comiso, senior scientist at Goddard.
Forthe perennial ice to recover, sustained cooling is needed, especiallyduring the summer period. This has not been the case over the past 20years, as the satellite data show a warming trend in the Arctic, and itis not expected to be the case in the future, as climate models projectcontinued Arctic warming. If ice were to grow back in these areas, thenew ice would likely be thinner and more susceptible to future meltthan the thick perennial ice that it replaces.
Scientists areworking to understand the extent to which these decreases in sea iceare due to naturally occurring climate variability or longer-term humaninfluenced climate changes.
Scientists believe that the ArcticOscillation, a major atmospheric circulation pattern that can push seaice out of the Arctic, may have contributed to the reduction of sea icein the mid-1990s by making the sea ice more vulnerable to summertimemelt.
Sea ice decline could also affect future temperatures inthe region. Ice reflects much of the sun's radiation back into space.As sea ice melts, more exposed ocean water reduces the amount of energyreflected away from the Earth. "Feedbacks in the system are starting totake hold," says the National Snow and Ice Data Center's lead scientistTed Scambos.
Claire Parkinson, senior scientist at Goddard,cautions against thinking that Arctic sea ice is gone for good,especially with such limited data. "The reduced sea ice coverage willlead to more wintertime heat loss from the ocean to the atmosphere andperhaps therefore to colder water temperatures and further ice growth,"said Parkinson.
There are many factors beyond warmer temperaturesthat drive changes in the Arctic. A longer data record, combined withobservations from additional environmental parameters now availablefrom NASA satellites, will help scientists better understand thechanges they are now seeing.
The study used data from the DefenseMeteorological Satellite Program Special Sensor/ Microwave Imager anddata from NASA's Scanning Multi-channel Microwave Radiometer (SMMR) onthe NIMBUS-7 satellite.
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