NASA - National Aeronautics and Space Administration

Researchers from NASA, the National Snow and Ice Data Center and others using satellite data have detected a significant loss in Arctic sea ice this year.

On Sept. 21, 2005, sea ice extent dropped to 2.05 million sq. miles, the lowest extent yet recorded in the satellite record. Incorporating the 2005 minimum, with a projection for ice growth in the last few days of this September, brings the estimated decline in Arctic sea ice to 8.5 percent per decade.


Right animation: The minimum concentration of Arctic sea ice in 2005 occurred on September 21, 2005, when the sea ice extent dropped to 2.05 million sq. miles, the lowest extent yet recorded in the satellite record. The yellow line represents the average location of the ice edge of the perennial sea ice cover for the years 1979 through 2004. Click on image to view animation.
Credit: NASA

Sea Ice Minimum Calculated Using a Three-Year Moving Average:
+ Click to view animaton
+ High resolution image: Sea Ice Minimum 1979-1981
+ High resolution image: Sea Ice Minimum 2003-2005


Scientists involved in this research are from NASA's Goddard Space Flight Center (GSFC), Greenbelt, Md., NASA's Jet Propulsion Laboratory, Pasadena, Calif., NSIDC at the University of Colorado, Boulder, and the University of Washington, Seattle.

Satellites have made continual observations of Arctic sea ice extent since 1978, recording a general decline throughout that period. Since 2002, satellite records have revealed unusually early onsets of springtime melting in the areas north of Alaska and Siberia. In addition, the 2004-2005 winter season showed a smaller recovery of sea ice extent than any previous winter in the satellite record, and the earliest onset of melt throughout the Arctic.


Click on images for high resolution

With the exception of May 2005, every month since December 2004 has seen the lowest monthly average since the satellite record began. Although sea ice records prior to late 1978 are comparatively sparse, they imply that the recent decline exceeds previous sea ice lows. Current levels of Arctic sea ice are likely the lowest they have been for the past few centuries.

Arctic sea ice typically reaches its minimum in September, at the end of the summer melt season. As of September 2001, the trend of Arctic sea ice decline documented in the satellite record was just over 6.5 percent per decade. After the September 2004 minimum, the trend changed to 7.7 percent. The last four Septembers (2002-2005) have seen sea ice extents 20 percent below the mean September sea ice extent for 1979-2000.

The perennial ice cover is that which survives the summer melt and consists mainly of thick multiyear ice floes that are the mainstay of the Arctic sea ice cover. "Since 1979, by using passive microwave satellite data, we've seen that Arctic perennial sea ice cover has been declining at 9.6 percent per decade," said Joey Comiso, senior scientist at GSFC.



Left animation: Arctic sea ice typically reaches its minimum in September, at the end of the summer melt season, and then recover over the winter. The 2004-2005 winter-season showed a smaller recovery of sea ice extent than any previous winter in the satellite record, and the earliest onset of melt throughout the Arctic. This visualization shows seasonal fluctuations in Arctic sea ice derived from the new high resolution AMSR-E instrument on NASA's Aqua satellite. Click on image to view animation.
Credit: NASA


+ Click here for full resolution image

For the perennial ice to recover, sustained cooling is needed, especially during the summer period. This has not been the case over the last 20 years, as the satellite data show a warming trend in the Arctic, and it is not likely to be the case in the future, as climate models predict continued Arctic warming.

"Even if sea ice retreated a lot one summer, it would make a comeback the following winter, since temperatures below freezing generally cause at least a thin layer of ice to form," explains Florence Fetterer, National Oceanic and Atmospheric Administration Program Manager at NSIDC. "But in the winter of 2004-2005, sea ice didn't approach the previous wintertime level."

Patterns of natural variability play a part in Arctic sea ice decline. Scientists believe that the Arctic Oscillation (AO), a major atmospheric circulation pattern that can push sea ice out of the Arctic may have contributed to the reduction of sea ice in the mid-1990s by making the sea ice more vulnerable to summertime melt.

Sea ice decline is likely to affect future temperatures in the region. Because of its light appearance, sea ice reflects much of the sun's radiation back into space whereas dark ocean water absorbs more of the sun's energy. As sea ice melts, more exposed ocean water changes the Earth's albedo, or fraction of energy reflected away from the planet. "Feedbacks in the system are starting to take hold," says NSIDC's lead scientist Ted Scambos.



Right animation: Sea ice decline is likely to affect future temperatures in the region. Because of its light appearance, ice reflects much of the sun's radiation back into space whereas dark ocean water absorbs more of the sun's energy. As ice melts, more exposed ocean water changes the Earth's albedo, or fraction of energy reflected away from the planet. This leads to increased absorption of energy that further warms the planet in what is called ice-albedo feedback. Click on image to view animation.
Credit: NASA




However, "the system does have negative feedbacks as well," cautions Claire Parkinson, senior scientist at GSFC. "For instance, the reduced sea ice coverage will lead to more wintertime heat loss from the ocean to the atmosphere and perhaps therefore to colder water temperatures and further ice growth."

Five-Year Averages, 2002 and 2005

a) Daily ice extent

b) Daily ice area
Animation above: Five-year averages of (a) daily ice extent and (b) daily ice area from August 1 to October 15 (summer through mid-autumn). The different lines represent those from 1980 to 1984 (purple), 1985 to 1989 (blue), 1990 to 1994 (green), 1995 to 1999 (gold), and 2000 to 2004 (red). Note the progression in the reduction of ice extent and ice area from the 1980s through the 1990s and to the 2000s. A shift in the occurrence of the end of the melt period (or beginning of freeze-up) towards the later part of autumn is also apparent. For comparison, the corresponding plots for individual years in 2002 (black dotted line) and 2005 (black dash line in bold) are also shown. The lowest minimum ice cover on record occurred this year (2005) while the second lowest occurred in 2002.

+ Click here for a still image of the five-year averages

There are many factors driving changes in the Arctic, and a longer record of data will help scientists better understand the remarkable changes they are now seeing.

Arctic sea ice extend studies are funded by NASA and NOAA. In assessing Arctic sea ice extent, researchers used data from NASA, NOAA, U.S. Department of Defense, and Canadian satellites and weather observations.

+ Click here for more information and images

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Contact information for media:
Sarah Dewitt: Tel: (301) 286 0535, E-mail: Sarah.L.Dewitt@nasa.gov
Rob Gutro: Tel: (301) 286-4044. E-mail: Robert.J.Gutro@nasa.gov
Stephanie Renfrow: Tel: (303) 492-1497 E-mail: srenfrow@nsidc.org

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Related links:
+ Greenland's Ice Melt in 2005: CIRES/University of Colorado at Boulder