Sea Ice Extent
According to the National Snow and Ice Data Center (NSIDC), the Northern Hemisphere sea ice extent — which is measured from passive microwave instruments onboard NOAA satellites — averaged for August 2012 was 4.72 million square km (1.82 million square miles) 38.46 percent below average. This ranked as the smallest August sea ice extent in the 1979-2012 period of record. The previous smallest August Arctic sea ice extent occurred in 2007, at 5.36 million square km (2.07 million square miles). The difference in sea ice extent from this year and the previous record is nearly equivalent the land area of Texas. During August, the Arctic lost an average of 91,700 square km (35,400 square miles) of ice per day, the fastest observed loss for the month of August on record. August 2012 marks the 16th consecutive August and the 135th consecutive month with below-average Arctic sea ice extent. August Northern Hemisphere sea ice extent has decreased at an average rate of 10.2 percent per decade.
According to analysis by the NSIDC, during August, sea ice was below average across all regions of the Arctic, except the East Greenland Sea, where the ice extent was near average. The rapid ice loss for the month was dominated by large ice losses across the East Siberian and the Chukchi Seas, partially due to a large and strong cyclone which impacted the region early in August. The storm broke up a large portion of the ice sheet causing it to melt faster. The Northern Sea Route opened up by the middle of August, but the Northwest Passage remained closed at the end of the month.
On August 26th, the Arctic sea ice extent dropped to 4.10 million square km (1.58 million square miles), breaking the previous record low extent for the Arctic which occurred on September 18, 2007 at 4.17 million square km (1.61 million square miles). The combination of above-average temperatures for much of the Arctic and the large, cyclone which broke up large areas of the ice sheet, contributed to the new record low extent. By August 31st, the Arctic sea ice had dropped to 3.69 million square km (1.4 million square miles), with several weeks of melting still likely during the 2012 melt season. August 2012 marks the first time in the 1979-present period of record that Arctic sea ice has dropped below 4.0 million square km (1.54 million square miles).
Sea Ice Volume Anomlay
Source: UW's Polar Ice Center
When using Arctic sea ice extent to monitor the state of sea ice conditions across the Arctic, no information is available on the thickness of the ice. To compensate for this, the Polar Science Center at the University of Washington developed a modeled dataset to measure the volume of Arctic sea ice using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS). According to the product’s documentation, sea ice volume is an important climate indicator. It depends on both ice thickness and extent and therefore more directly tied to climate forcing than extent alone. According to this dataset, Arctic sea ice volume reached a monthly low value during August 2012, at 4,400 km3, about 700 km3 below the previous record low for August which occurred in 2011. The August sea ice volume was 76 percent below the maximum value in 1979, 67 percent below average and 2.1 standard deviations below the trend. The August 2012 value was 200 km3 above the smallest Arctic sea ice volume for any month, which occurred in September 2011.
The August 2012 Southern Hemisphere sea ice extent was 18.36 million square km (7.09 million square miles), 1.57 percent above average and the fourth largest (30th smallest) August sea ice extent in the 1979-2012 period of record. Antarctic sea ice extent during August has increased at an average rate of 0.6 percent per decade, with substantial interannual variability. Antarctic sea ice will continue to expand during its annual growth cycle which typically ends in late September or early October.
For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page.