Global Snow and Ice - Annual 2011
Beginning in November 2017, NCEI will use version 3 of the National Snow and Ice Data Center's (NSIDC) monthly sea ice extent index. All historical monthly sea ice extent values will be updated to version 3, but historical reports will not be updated. For additional information on the methodology changes and comparisons to version 2, please visit the National Snow and Ice Data Center.
Issued: 19 January 2012
NH Snow Cover Extent
Snow Extent data were provided by the Global Snow Laboratory, Rutgers University. Period of record is 1966-2011 (46 years).
The time series to the right shows the mean Northern Hemisphere snow cover extent for winter (December-February) from 1967 through 2011. During the three month season in 2010-2011, the Northern Hemisphere experienced its third largest snow cover extent on record at 1.98 million square km (0.76 million square miles) above the average of 45.2 million square km (17.5 million square miles). Only the winter seasons of 1977-1978 and 2009-2010 had larger snow cover extents. By the spring season (March-May), the Northern Hemisphere snow cover extent shrank to a below-average extent for the time of year. The seasonal snow cover extent was 648,000 square km (250,194 square miles) below the long-term average, and ranked as the 19th smallest (27th largest) extent on record. More information on individual global snow and ice events during 2011 can be found in the Global Hazards report.
Across North America during the 2010-2011 winter (December-February) snowfall was widespread, and the seasonal snowfall extent was the third largest on record for the continent at 0.88 million square km (340,000 square miles) above the average of 17.2 million square km (6.6 million square miles). The winter seasons of 1978-1979 and 2009-2010 both had larger snow cover extents. The above average snow cover extent for North America continued into spring (March-May), and the seasonal snow cover extent was 449,000 square km (173,300 square miles) above the long-term average and ranked as the 12th largest (34th smallest) on record. For more on information on U.S. snow/ice during 2011, please see the U.S. Snow and Ice report.
In Eurasia, snow cover extent during the 2010-2011 winter was above average. The seasonal snow cover extent anomaly of 1.1 million square km (425,000 square miles) ranks as the fourth largest on record, behind the winters of 1977-1978, 2002-2003, and 1971-1972. In contrast, the seasonal snow cover extent by spring was below average. The March-May average snow cover extent for Eurasia was 1.10 million square km (425,000 square miles) below average and ranked as the 10th smallest (36th largest) on record.
Sea Ice Extent
Daily Arctic Sea ice extent trough March, with daily
ice extents for previous low-ice-extent years.
Arctic sea ice, which is measured from passive microwave instruments onboard NOAA satellites, usually expands during the cold season to a March maximum, then contracts during the warm season to a September minimum. According to the NOAA-supported National Snow and Ice Data Center (NSIDC), the maximum Arctic sea ice extent during 2011 occurred on March 7, 2011 which is near the median date of the historical annual maximum extents. The annual maximum extent of 15.86 million square km (6.1 million square miles) was within 1 percent of the smallest annual maximum on record, which occurred in 2006. On March 7 below-average ice extent was oserved across the East Greenland Sea and Sea of Okhotsk. The March 2011 monthly average Arctic ice extent was 15.80 million km (6.1 million square miles), and ranked as the second lowest March Arctic sea ice extent in the satellite record.
Arctic Sea Ice Extent on 9 September
According to the NSIDC, the minimum Arctic ice extent during 2011 occurred on September 9th, and was the second smallest on record at 4.33 million square km. The smallest ice extents on record have occurred during the past five years (2007-2011), with the smallest extent on record occurring in 2007. The average September sea ice extent was also the second smallest on record — 34.5 percent below the 1979-2000 average. During September, both the Northern Sea Route and the Northwest Passage were ice free for only the second time in recorded history; the other occurrence was in 2010. September Arctic sea ice extent has decreased at a rate of 12 percent per decade. Individually, the months of January and July set new monthly records for the smallest average sea ice extent on record. No month saw average Arctic sea ice extent above the long-term average, and the last month with above-average ice extent was May 2001.
Sea Ice Volume Anomaly
Source: UW's Polar Ice Center
According to the Polar Science Center at the University of Washington, the second smallest extent in September was accompanied by record small sea ice volume across the Arctic. Sea ice volume takes into account both the sea ice extent and ice thickness. On September 10th the sea ice volume dropped to 4,000 cubic km (960 cubic miles), the smallest single day Arctic sea ice volume in its record. Also, the monthly averaged ice volume for September 2011 was record low at 4,200 cubic km (1,007 cubic miles) — 66 percent lower than the mean over this period and 75 percent lower than the maximum value set in 1979. The loss of multi-year ice, which tends to be thicker than newly formed sea ice is likely a contributing factor to the low sea ice volume during September 2011.
For further information on the Northern and Southern Hemisphere snow and ice conditions, please visit the NSIDC News page.