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28 September 2005
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Sea Ice Decline Intensifies

Figure 2: Five-day running mean—summer extent anomaly graph 2002-2005

Figure 2: Five-day running mean—summer concentration anomaly graph 2002-2005

This graph shows the daily ice extent in the summers of 2002-2005. The lines dip to a show a minimum extent each September; the lines bend upward as melting slows and fall begins.

All four years are well below the long-term 1979-2000 climatology, which is shown in black (daily climatology values interpolated from monthly means). From July through the beginning of August, the 2005 extent was consistently 1 million square kilometers (360,000 miles) below the long-term mean, and 500,000 square kilometers below the previous three low years. By September 2005, the trend slowed to just below the previous low year in 2002. However, after mid-September, the ice began to melt again, only stopping on September 21. This means that the 2005 minimum came later than any year in the satellite record.

The daily arctic total ice extents are calculated from a five-day running mean to eliminate daily variability and provide a clear trend line.
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Figure 3: Five-day running mean—September minimum concentration anomaly maps, 2002-2005

Figure 3: Five-day running mean—September minimum concentration anomaly maps, 2002-2005

These maps show the difference between “normal” sea ice extent (long-term mean), and the year indicated. The long-term average minimum extent contour (1979-2000) is in magenta. The ice extent for each year is shown by the edge of the colored region; within that extent, color bands show differing levels of sea ice concentration. Blue indicates areas where concentration is more than the long-term mean; red shows areas where concentration is less than the long-term mean. The 2005 map shows a marked reduction in extent over the past four years, all of which were also below average.

In 2002 and 2003, the ice pack also experienced much lower concentrations during the minimum, especially true north of Alaska. However, the ice cover has been much more compact during the minimums of 2004 and 2005, yielding small negative or even positive ice concentration anomalies within the ice pack.

Sea Ice extent is a measure of the area that contains at least 15 percent ice. Ice concentration is the fraction of the actual area covered by ice compared to the total area, measured in terms of percentage ice cover. The satellite does not pass directly over the North Pole; this lack of data is indicated by the gray circle in each image.
Access 1980 and 2005 images for print and online use.
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