Global Snow & Ice - July 2012
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 July 2012 was 7.94 million square km (3.07 million square miles), 21.35 percent below average. This ranked as the second smallest July sea ice extent on record for the Northern Hemisphere in the 1979-2012 period of record. The July 2012 Arctic sea ice extent was 20,000 square km (7,700 square miles) larger than the record small July extent, which occurred in 2011. During the month, the Arctic lost a total of 2.97 million square km (1.15 million square miles) of ice, with the daily sea ice extent reaching record lows briefly during the middle and end of July. July 2012 marks the 16th consecutive July and the 134th consecutive month with below-average Arctic sea ice extent. July Northern Hemisphere sea ice extent has decreased at an average rate of 7.1 percent per decade.
According to analysis by the NSIDC, Arctic sea ice continued to decline rapidly through July, much like it had in June. Sea ice coverage was below average across much of the Atlantic side of the Arctic, including the Kara, Laptev, East Siberian, and Beaufort seas. Near average sea ice coverage was observed in the Chukchi Sea. Sea ice was still blocking both the Northern Sea Route and the Northwest Passage at the end of July.
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 July 2012, at 8,300 km3 (1,990 miles3), about 700 km3 (170 miles3) less than the previous record low July volume which occurred in 2011. The July 2012 Arctic sea ice volume was also 65 percent lower than the maximum value in 1979, 55 percent below the mean value, and 2.2 standard deviations below the trend.
The July 2012 Southern Hemisphere sea ice extent was 16.7 million square km (6.4 million square miles), 2.21 percent above average and the 9th largest (26th smallest) July sea ice extent in the 1979-2012 period of record. Antarctic sea ice extent during July has increased at an average rate of 0.9 percent per decade, with substantial interannual variability.
According to NASA researchers, for several days during early July, nearly the entire Greenland ice sheet experienced a brief period of surface melting, including the summit of the ice sheet. During any given summer, about half of the ice sheet experiences some degree of melting, with most of the ice melt occurring at lower elevations. The melting was associated with a strong high pressure system bringing warmer-than-average conditions to Greenland. This phenomenon has not been observed on the Greenland ice sheet since satellite records began 34 years ago. However, ice core data indicates that such an event occurs about once every 150 years. The melting at the lower elevations in Greenland impacted population centers and infrastructure. The runoff flooded rivers, taking out structures and roads in and around Kangerlussuaq, a key transportation hub.
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite observed a large calving event on Greenland’s Petermann Glacier along the northwestern coast on July 16th and 17th. The separated iceberg was about 32.2 square km (12.5 square miles), only half the size of the ice sheet calved in 2010, but marks the second large calving of the glacier in two years. This calving marks a retreat of the glacier, with the calving front occuring father upstream than previous events.
For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page.