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Historical Variability of Sea Ice


Prior to 1950, the reconstruction of the historical record for sea ice suffered from lack of data and incomplete coverage. Since then, however, most circumpolar countries have kept regular comprehensive sea ice extent and concentration charts for waters in their jurisdiction. In order to obtain a consistent homogeneous picture of sea ice, these various ice charts have been combined with satellite observations (starting from 1972) to produce a comprehensive over 50 year record for the northern hemisphere.
monthly_ice
Figure 1: Monthly variability of sea ice extent over the Northern Hemisphere since 1954.

The monthly variability in this historic record of sea ice extent over the Northern Hemisphere is shown in Figure 1 above. The annual cycle varies from a maximum of about 15 million square kilometers in March to a minimum of about 7 million square kilometres in September. Superimposed on this are changes from year to year. The early part of this record (1951 to 1972) uses regional ice charts compiled by Professor John Walsh of the University of Alaska. Starting from 1972, the record is extracted from hemispheric analysis carried out by the US National Ice Centre. The use of satellite data in the last half of the record generally improves the coverage and reliability of sea ice information. However, it also introduced a satellite technology bias in the series. Although this bias introduces a note of caution in estimating trends in the data, there is a clear suggestion that sea ice extent has been decreasing over the last 20 years.

ice_anomaly
Figure 2: Monthly change in sea ice extent from 1979-1996 as compared to normal for the same period.

Figure 2 above shows sea ice extent by season. The trend to less sea ice is apparent especially in the summer when sea ice cover is at a minimum and the sea ice–temperature–albedo feedback is strongest. Most global climate models suggest that summer sea ice will disappear in the latter half of this century.


Regional Variability of Sea Ice Extent

Move your mouse over the image on the right to view the five main sea ice producing regions surrounding Canada. Click on each region to view a graph showing the change in extent of sea ice in that area for each year from 1978 to present. You will also see a second graph showing the relative anomaly in sea ice for each particular year since 1978. Alternatively, follow the links below to each image. Each image file is between 60 and 100kB in size (approximately).



AREA: [The Arctic Ocean] [The Arctic Islands] [Baffin Bay/Davis Strait] [Hudson Bay] [Gulf of St. Lawrence]
ANOMALY: [The Arctic Ocean] [The Arctic Islands] [Baffin Bay/Davis Strait] [Hudson Bay] [Gulf of St. Lawrence]


195 Years of Sea Ice Off Newfoundland

Figure 3 shows the record of sea ice cover off Newfoundland during the winter season (February and March). The record has been reconstruction back to 1810 by Brian Hill (Hill, 1999; Hill and Jones, 1990). The year-to-year variability is high and has been smoothed using a 9-point Gaussian smoother (heavy line). The graph also shows a longer term trend to less ice between the mid-1920s to 1970, then a recovery from 1971 to the early 1990s and then another decrease from the mid-1990s to the present. The year-to-year variability is caused by several factors. First the sea ice is transported from locations further north in the cold Labrador Current and so ocean properties of surrounding waters such as sea surface temperatures (Prinsenberg et al., 1991; Prinsenberg et al., 1997; Fang and Wallace, 1993) and low surface salinity (Mysak et al, 1990) are important. Second, the area off Newfoundland is also sensitive to monthly changes in large scale atmospheric circulation which influence regional winds and air temperatures. The region is on the western edge of the Icelandic Low (northern component of the North Atlantic Oscillation) and so the location and strength of the Icelandic Low influence sea ice cover in this region (Agnew, 1993; Rogers and van Loon, 1979; Deser and Timlin, 1997). The cause of the longer period downward trend to less sea ice in the middle of this century and over the last 10 years are the result of changes in longer term regional climate. Again longer term changes in ocean temperatures and large scale atmospheric circulation are a factor (Deser et al., 2000; Deser et al., 2002) and perhaps climate warming for the most recent trend to less sea ice.

185 years of seaice variation off Newfoundland
Figure 3: The Sea Ice record of Newfoundland from 1810. A reconstruction of the historical record of sea ice cover off Newfoundland has been carried out by Hill and Jones (1990), and more recently work by Hill (1999) who has extended the record back to 1810.

References
  • Agnew, T., 1993. Simultaneous Winter Sea-ice and Atmospheric Circulation Anomaly Patterns, Atmosph.Ocean, 31(2),259-280.
  • Deser ,C. and M. S. Timlin, 1997. Atmosphere–Ocean Interaction on Weekly Timescales in the North Atlantic and Pacific, Journal of Climate: Vol. 10, No. 3, pp. 393–408.
  • Deser,C., M. Holland, G. Reverdin, and M. Timlin, 2002. Decadal variations in Labrador Sea ice cover and North Atlantic sea surface temperatures, JGR, 107,C5, 2000JC000683.
  • Deser, C., J. Walsh, and M. Timlin, 2000. Arctic sea ice variability in the context of recent atmospheric circulation trends, J of Cl.,13,617-13,632.
  • Fang, Z. and J. Wallace, 1993. The relationship between the wintertime blocking over Greenland and the sea ice distribution over N. Atlantic, Adv. in Atmospheric Sciences, 10, 4, 453-464.
  • Prinsenberg, S., I. Petersen, Fowler, 1991. Estimates of ice-edge melt rates off Labrador and eastern Newfoundland, Canada Annal of Glaciology, 15, 163-170.
  • Prinsenberg, S. , I.K. Peterson, S. Narayanan, and J.U. Umoh, 1997. Interaction between atmosphere, ice cover, and ocean off Labrador and Newfoundland from 1962 to 1992 Can. J. Fish. And Aquat. Sci., 54(Suppl. 1), 30-39.
  • Hill, B.T. and S. J. Jones, 1990. The Newfoundland Ice Extent and the Solar Cycle from 1860 to 1988 JGR,95(C4),5385-5394.
  • Hill, B., 1999. Historical Record of sea ice and iceberg distribution around Nfld and Labrador, 1810-1958 WCRP No. 108 or WMO/TD No. 949, April/99, ACSYS, Proc. of the Workshop on Sea Ice Charts of the Arctic, Seattle, WA AU 5-7, 1998.
  • Mysak,L.A.,D. K. Manak,and R. F. Marsden, 1990. Sea-ice anomalies observed in the Greenland and Labrador Seas during 1901-1984 and their relation to an interdecadal Arctic climate cycle in Climate Dynamics, 5, 111-133.
  • Rogers,J.C., H.van Loon, 1979. The See saw in winter temperatures between Greenland and northern europe. Part II Some Oceanic and Atmospheric Effects in middle and high latitudes, MWR, 107, pp 509-519.

For historical information on sea ice conditions in northern Canadian waters, please see the Sea Ice Climatic Atlas, 1971-2000 from the Canadian Ice Service.