D. Perovich1, W. Meier2, M. Tschudi3, S. Farrell4, S. Hendricks5, S. Gerland6, C. Haas5, T. Krumpen5, C. Polashenski1,7, R. Ricker5, M. Webster8
1Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
2National Snow and Ice Data Center, Boulder, CO, USA
3Aerospace Engineering Sciences, University of Colorado, Boulder, CO, USA
4NOAA Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA
5Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
6Norwegian Polar Institute, Fram Centre, Tromsø, Norway
7ERDC - CRREL, 72 Lyme Road, Hanover, NH, USA
8NASA Goddard Space Flight Center, Greenbelt, MD, USA
- The lowest winter maximum ice extent in the satellite record (1979-2017) occurred on 7 March 2017. The extent was 14.42 million km2, 8% below the 1981-2010 average. This was the third straight year of a record low winter maximum.
- The September 2017 Arctic sea ice minimum extent was 4.64 million km2, 25% lower than the 1981-2010 average minimum ice extent and the eighth lowest value in the satellite record (1979-2017). The ten lowest September extents have occurred in the last 11 years.
- In March 2017, multiyear ice (more than 1 year old) and first-year ice were 21% and 79% of the ice cover, respectively, compared to 45% and 55% in 1985 (start of record).
- CryoSat-2 results showed the third lowest central Arctic Ocean sea ice volume in April 2017 of the satellite's data record (2011-2017), after April 2012 and April 2013.
- There has been an overall decrease in end of winter snow depth on the sea ice cover in the western Arctic in the past decade.
Sea Ice Extent
The Arctic sea ice cover varies substantially over the year, with end-of-winter ice cover generally two to three times as large as at the end of summer. Sea ice is an important element of the climate system: (1) acting as a barrier between the underlying ocean and the atmosphere, (2) limiting the amount of absorbed solar energy due to its high albedo, (3) providing a habitat for biological activity, and (4) limiting human access to the Arctic Ocean. Sea ice extent (designated by a 15% sea ice concentration threshold) has been monitored using passive microwave instruments on satellite platforms since 1979. The months of September and March are of particular interest because they are the months when the Arctic sea ice typically reaches its minimum and maximum extents, respectively. Figure 1 shows maps of monthly average ice extents in March 2017 and September 2017.
Average monthly sea ice extent in March 2017 (left) and September 2017 (right) illustrate the respective winter maximum and summer minimum extents. The magenta line indicates the median ice extents in March and September, respectively, during the period 1981-2010. Maps are from NSIDC at nsidc.org/data/seaice_index
(Fetterer et al., 2002).
Based on estimates produced by the National Snow and Ice Data Center (NSIDC) Sea Ice Index (Fetterer et al., 2002), the sea ice cover reached a maximum extent of 14.42 million km2 on March 7, 2017. This was 8% below the 1981-2010 average. For the third straight year, the Arctic sea ice has experienced a new record lowest maximum value in the satellite record. The maximum extent occurred 5 days earlier than the 1981-2010 average (12 March).
On September 13, 2017, the sea ice cover reached a summer minimum value of 4.64 million km2. This was the eighth lowest extent of the satellite record. While it represents a modest increase from the 2016 minimum, it was 25% less than the 1981-2010 median minimum ice extent. The ten lowest September extents have occurred in the last 11 years (Parkinson and DiGirolamo, 2016). The September ice extent has not returned to pre-2007 levels.
Sea ice extent has decreasing trends in all months and virtually all regions except for the Bering Sea during winter (Meier et al., 2014). The September monthly average trend for the entire Arctic Ocean is now -13.2% per decade relative to the 1981-2010 average (Fig. 2). Trends are smaller during March (-2.7% per decade), 