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Sea ice data updated daily, with one-day lag. Orange line in extent image (left) and gray line in time series (right) show 1979 to 2000 average extent for the day shown. Click for high-resolution image. Learn about update delays
, which occasionally occur in near-real-time data. Read about the data
.—Credit: National Snow
and Ice Data Center
Note: The daily image update now uses data from the Special Sensor Microwave/Imager (SSM/I) sensor on the Defense Meteorological Satellite Program F13 satellite. For more information on the data, see the February 26 post to
Arctic Sea Ice News & Analysis.
Arctic sea ice reflects sunlight, keeping the polar regions cool and moderating global climate. According to scientific measurements, Arctic sea ice has declined dramatically over at least the past thirty years, with the most extreme decline seen in the summer melt season.
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April 6, 2009
Arctic sea ice younger, thinner as melt season begins
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Arctic sea ice extent has begun its seasonal decline towards the September minimum. Ice extent through the winter was similar to that of recent years, but lower than the 1979 to 2000 average. More importantly, the melt season has begun with a substantial amount of thin first-year ice, which is vulnerable to summer melt.
Figure 1. Arctic sea ice extent for March, 2009, was 15.16 million square kilometers (5.85 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data.
—Credit: National Snow and Ice Data Center
Overview of conditions
Sea ice extent averaged over the month of March 2009 was 15.16 million square kilometers (5.85 million square miles). This was 730,000 square kilometers (282,000 square miles) above the record low of 2006, but 590,000 square kilometers (228,000 square miles) below the 1979 to 2000 average.
Figure 2. The graph above shows daily sea ice extent. The solid blue line indicates 2008 to 2009; the dashed green line shows 2006 to 2007 (the record-low summer minimum occurred in 2007); and the solid gray line indicates average extent from 1979 to 2000. Sea Ice Index data.
—Credit: National Snow and Ice Data
Conditions in context
At the end of last summer's melt season, extensive areas of open
water froze up quickly, once air temperatures cooled in
the fall. By February 28, ice extent had reached its annual maximum.
Although the maximum ice extent occurred slightly earlier than usual, ice extent remained close to the maximum level through much
Figure 3. Monthly March ice extent for 1979 to 2009 shows a decline of 2.7% per decade.
—Credit: National Snow and Ice Data Center
March 2009 compared to past Marches
Including March 2009, the past six years have all had ice extent substantially lower than normal. The linear trend indicates that for the month of March, ice extent is declining by 2.7% per decade, an average of 43,000 square kilometers (16,000 square miles) of ice per year.
Figure 4. The map of air temperature anomalies for winter 2008 to 2009 at the 925 millibar level (roughly 1,000 meters [3,000 feet] above the surface) shows warmer-than-usual conditions over much of the Arctic Ocean. Areas in orange and red correspond to strong positive (warm) anomalies. Areas in blue correspond to negative (cool) anomalies.
—Credit: National Snow and Ice Data Center courtesy NOAA/ESRL Physical Sciences Laboratory
Arctic winter warmer than average
Overall, it was a fairly warm winter in the Arctic. Air temperatures over the Arctic Ocean were an average of 1 to 2 degrees Celsius (1.8 to 3.6 degrees Fahrenheit) above normal, with notable regional variations. The Barents Sea region was over 4 degrees Celsius (7.2 degrees Fahrenheit) warmer than average this winter. This warmth probably stemmed from unusually low sea ice extent in the region throughout much of the winter, which allowed the ocean to pump heat into the atmosphere. The Bering Sea, in contrast, experienced a cool winter, with temperatures 1 to 2 degrees Celsius (1.8 to 3.6 degrees Fahrenheit) below average. The cooler conditions were consistent with the above-average sea ice extent in the Bering Sea through much of the winter.
5. These images show declining sea ice age, which indicates a thinning Arctic sea ice cover more vulnerable to melting in summer. Ice older than two years now accounts for less than 10% of the ice cover.
—Credit: From the National Snow and Ice Data Center, courtesy J. Maslanik and C. Fowler, University of Colorado
Sea ice young and thin as melt season begins
How vulnerable is the ice cover as we go into the summer melt season?
To answer this question, scientists also need information about ice thickness. Indications of winter
ice thickness, commonly derived from ice age estimates,
reveal that the
ice is thinner than average, suggesting that it is more
susceptible to melting away during the coming summer.
As the melt season begins, the Arctic
Ocean is covered mostly by first-year ice, which formed this winter, and second-year ice, which formed during the winter of 2007 to 2008.
First-year ice in particular is thinner and more prone to
melting away than thicker, older, multi-year ice. This year, ice older
than two years accounted for less than 10% of the ice cover
at the end of February. From 1981 through 2000, such older
ice made up an average of 30% of the total sea ice cover
at this time of the year.
While ice older than two years reached record lows, the fraction of second-year sea
ice increased compared to last winter. Some of this second-year ice will survive the summer melt season to replenish the Arctic's store of older ice; however, in recent years less young ice has made it through the summer. To restore the
amount of older ice to pre-2000 levels, large amounts of this
young ice would need to endure through summer for several
years in a row.
But conditions may not always favor the survival of second-year and older ice. Each winter, winds
and ocean currents move some sea ice out of the Arctic ocean.
This winter, some second-year ice survived the 2008 melt
season only to be pushed out of the Arctic by strong winter
winds. Based on sea ice age data from Jim
Maslanik and Chuck Fowler at the University of Colorado, since the end of September 2008, 390,000 square kilometers
(150,000 square miles) of second-year ice and 190,000 square
kilometers (73,000 square miles) of older (more than two years
old) ice moved out of the Arctic.
Maslanik J. A., C. Fowler, J. Stroeve, S. Drobot, J. Zwally, D. Yi, W. Emery. 2007. A younger, thinner Arctic ice cover: Increased potential for rapid, extensive sea-ice loss. Geophysical Research Letters, 34, L24501, doi:10.1029/2007GL032043.
Fowler, C., W. J. Emery, and J. Maslanik. 2004. Satellite-derived evolution of Arctic sea ice age: October 1978 to March 2003. IEEE Geosci. Remote Sensing Letters, 1(2), 71–74, doi:10.1109/LGRS.2004.824741.
scientists provide Arctic Sea Ice News & Analysis,
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